Wide dynamic range precision supply circuit

Abstract

A precision supply circuit capable of driving pulses of current, or DC current, through a load is described. The amount of current can be precisely controlled over a wide dynamic range. The circuit can be switched between and operated in current-control mode or voltage-control mode. The circuit can monitor recovery of compliance voltage, and amount of power dissipated in the load, and an amount of power dissipated in a power transistor to maintain safe operating levels.

Description

Attorney Docket No. OPTN-005W001Wide Dynamic Range Precision Supply CircuitCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the priority benefit, under 35 U.S.C. 119(e), of U.S.Application No. 63 / 721,194, titled “Light Control Methods and Apparatus,” filed November 15, 2024, and of U.S. Application No. 63 / 827,521, titled “Light Control Methods and Apparatus,” filed June 20, 2025. Both of these applications are incorporated herein by reference in their entirety for all purposes.BACKGROUND

[0002] Modern automated control systems can include a large number of controlled and / or monitored devices (e.g., sensors, cameras, artificial lighting, counters, motors) and one or more controllers (e.g., microprocessors or microcontrollers). The controller(s) can receive and process data from monitored devices and issue commands to operate controlled devices based, at least in part, on the data received. Such automated control systems often are implemented in dynamic environments (e.g., automated factory assembly lines including multiple inspection stations and utilizing machine vision techniques) where conditions in the environment change frequently, causing changes in signals provided by monitored devices and responsive changes in control signals output by the controlled s). Common components in these dynamic environments include controllable cameras and artificial lighting to facilitate effective imaging by the cameras. Conventional examples of such artificial lighting include, but are not limited to, LED-based lighting systems.SUMMARY

[0003] Described herein are circuitry, apparatus, and methods to precisely control current (over a large dynamic range) and program voltage (over a large range) delivered to a load, such as an LED lamp or other current-driven or a voltage-controlled device. LED lamps can be used to illuminate targets for machine vision applications closely synchronized with automated equipment. Such targets may range in size from small, micron or sub-micron objects viewed in microscopic systems to large objects that are viewed in automated vehicle assembly. In one example, the LED lamp(s) can be used as a strobing light source to illuminate objects during image acquisition by one or more cameras in an automated control system. The acquired images can then be processed to obtain information for the automatedAttorney Docket No. OPTN-005W001control system. In some implementations, circuitry for controlling current precisely and voltage delivered to one or more LED lamps can be included in a compact camera assembly (either as part of the camera package or as an add-on device) that together are used to image the objects illuminated by the one or more LED lamps.

[0004] The precision supply circuit can include a precision current controller and a programmable voltage supply that operate over a wide range of currents (at least one order of magnitude and even up to two orders of magnitude or greater) and a wide range of voltages (at least one order of magnitude), respectively. In some implementations, the precision supply circuits can operate in a current-control mode. The precision supply circuit is also configured to be operated in a voltage-control mode. The mode of operation can be selected by a user based on characteristics of the load (e.g., selected to provide improved system performance when electrically driving the load). Further, the precision supply circuit is adapted to program a supply voltage (sometimes referred to as a “compliance voltage”) for a load (such as an LED lamp which may require a compliance voltage within a range of voltages) to reduce or minimize wasted energy (heat) and / or stress in the load and / or the current controller. The precision supply circuit can provide the programmed compliance voltage from the wide range of supply voltages over which the circuit is capable of operating.

[0005] The precision supply circuit can provide current and voltage for a precise interval of time (referred to as a “pulse”) to precisely control an amount of current (and an amount of charge) delivered to the load. The pulse can have precisely-timed, fast rise and fall times with reduced overshoot following the on and off transitions of the pulse. Protection features to prevent overdriving the load and / or current controller can also be implemented with the precision supply circuit.

[0006] When the precision supply circuit is operated in voltage-control mode, a selected compliance voltage can also be applied to the load for a short period of time (e.g., 1 microsecond or less) or for long periods of time (e.g., up to 1 second or more). The electrical current delivered to the load can be gated on for the period of time determined by a control pulse applied to the precision supply circuit. Operation in voltage-control mode can involve bypassing feedback circuitry that is used for current-control mode, which can allow the supply circuit to operate with shorter, high-speed pulses than used in current-control mode. These pulses, with faster and more deterministic rise and fall times, can be located more precisely in time to improve synchronization with physical events occurring in a dynamic environment in which the precision supply circuit is deployed. Power dissipation in theAttorney Docket No. OPTN-005W001precision supply circuit can be significantly reduced when the supply circuit operates in voltage-control mode, allowing the supply circuit to accommodate longer pulses and / or pulses from voltages less well matched to the load’s behavior when driven.

[0007] The precision supply circuit can further include single-wire communication with the load to access data stored in memory at the load. Data stored in memory at the load can be used to determine how to improve electrical driving of the load. Data stored in memory at the load may indicate safe or preferred operating ranges for the load as well as information from on-board sensors at the load (e.g., thermal sensors, current and / or voltage sensors, c / c.).

[0008] Some implementations relate to a supply circuit comprising: a power transistor arranged to conduct current through a load and through a first sensing node and through a second sensing node; a programmable voltage source to apply a selected compliance voltage to an input of the load; a feedback circuit to apply a signal to a control terminal of the power transistor to control an amplitude of the current conducted by the power transistor through the load based upon a first voltage sensed at the first sensing node or a second voltage sensed at the second sensing node, such that the feedback circuit operates in a current-control mode; and a mode switching circuit to disable the feedback circuit such that the supply circuit operates in voltage-control mode, wherein the compliance voltage applied to the load is determined by the programmable voltage source.

[0009] Some implementations relate to methods of operating a supply circuit. Such methods can include acts of conducting, with a power transistor, current through a load and through a first sensing node and through a second sensing node of the supply circuit; applying, with a programmable voltage source, a selected compliance voltage to an input of the load; applying, with a feedback circuit, a signal to a control terminal of the power transistor; controlling, with the feedback circuit, an amplitude of the current conducted by the power transistor through the load based upon a first voltage sensed at the first sensing node or a second voltage sensed at the second sensing node, such that the feedback circuit operates in a current-control mode; and disabling, with a mode switching circuit, the feedback circuit such that the supply circuit operates in voltage-control mode, wherein the compliance voltage applied to the load is determined by the programmable voltage source.

[0010] Some implementations relate to methods of operating a supply circuit. Such methods can include acts of conducting, with a power transistor, current through a load and through a first sensing node and through a second sensing node of the supply circuit;Attorney Docket No. OPTN-005W001applying, with a programmable voltage source, a selected compliance voltage to an input of the load; applying, with an operational amplifier of a feedback circuit, a first signal to a control terminal of the power transistor; controlling, with the feedback circuit, an amplitude of the current conducted by the power transistor through the load based upon a first voltage sensed at the first sensing node or a second voltage sensed at the second sensing node, such that the feedback circuit operates in a current-control mode; and without disconnecting the operational amplifier, applying a second signal directly to the control terminal of the power transistor to operate the supply circuit in voltage-control mode, wherein the compliance voltage applied to the load is determined by the programmable voltage source.

[0011] Some implementations relate to a supply circuit comprising: a transistor arranged to conduct current through a load and a feedback circuit to apply a signal to the transistor to control an amplitude of the current conducted by the transistor. The feedback circuit can be configured to: receive a first feedback signal from a first sensing node located in a first current path through which at least a first portion of the current flows when the current flows through the load, and receive a second feedback signal from a second sensing node located in a second current path through which at least a second portion of the current flows when the current flows through the load and when an impedance between the first sensing node and the second sensing node is bypassed by the second current path.

[0012] Some implementations relate to a supply circuit comprising: a first transistor arranged to conduct current through a load; a first resistor in a first circuit path through which at least a first portion of the current flows; a second resistor connected in series with the first resistor through which at least a second portion of the current flows when connected to the load; a second transistor arranged to shunt the current around the second resistor; and a feedback circuit. The feedback circuit can be configured to receive a first feedback signal indicative of a first voltage dropped across the first resistor due to the first portion of the current when the second transistor shunts the current around the second resistor and to receive a second feedback signal indicative of a second voltage dropped across a combination of the first resistor and the second resistor due to the second portion of the current when the second transistor does not shunt the current around the second resistor.

[0013] Some implementations relate to a method of conducting a current through a load. The method can include acts of: receiving, at a control terminal of a transistor in a supply circuit, a signal that causes the transistor to conduct the current through a load; controlling, with a feedback circuit in the supply circuit and coupled to the transistor, an amplitude of theAttorney Docket No. OPTN-005W001current conducted by the transistor; receiving in the feedback circuit a first feedback signal from a first sensing node located in a first current path through which at least a first portion of the current flows; receiving in the feedback circuit a second feedback signal from a second sensing node located in a second current path through which at least a second portion of the current flows; and directing the second portion of the current around an impedance connected between the first sensing node and the second sensing node when receiving the second feedback signal.

[0014] Some implementations relate to a camera comprising: a housing; an imaging array to acquire images, the imaging array mounted in the housing; and a supply circuit mounted in the housing to conduct a pulse of current through a load that generates light so as to illuminate an object imaged by the imaging array during an image-acquisition period of the imaging array. The image-acquisition period comprises an interval of time during which one frame of image data is captured by the imaging array. The supply circuit can include a transistor arranged to conduct current through a load and a feedback circuit to apply a signal to the transistor to control an amplitude of the current conducted by the transistor. The feedback circuit can be configured to: receive a first feedback signal from a first sensing node located in a first current path through which at least a first portion of the current flows when the current flows through the load, and receive a second feedback signal from a second sensing node located in a second current path through which at least a second portion of the current flows when the current flows through the load and when an impedance between the first sensing node and the second sensing node is bypassed by the second current path.

[0015] Some implementations relate to a method of operating a camera. The method can include acts of receiving, at a control terminal of a transistor in a supply circuit, a signal that causes the transistor to conduct a pulse of current through a load; controlling, with a feedback circuit coupled to the transistor, an amplitude of the pulse of current conducted by the transistor; receiving in the feedback circuit a first feedback signal from a first sensing node located in a first current path through which at least a first portion of the pulse of current flows; receiving in the feedback circuit a second feedback signal from a second sensing node located in a second current path through which at least a second portion of the pulse of current flows; directing the second portion of the pulse of current around an impedance connected between the first sensing node and the second sensing node when receiving the second feedback signal; and acquiring a frame of image data of an object with an imaging array of the camera while the pulse of current is conducted through the load.Attorney Docket No. OPTN-005W001

[0016] It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein. It should also be appreciated that terminology explicitly employed herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The skilled artisan will understand that the drawings primarily are for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The drawings are not necessarily to scale; in some instances, various aspects of the inventive subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to facilitate an understanding of different features. In the drawings, like reference characters generally refer to like features (e.g., functionally similar and / or structurally similar elements).

[0018] FIG. 1A depicts a series of illumination pulses and indicates the timing of image acquisition.

[0019] FIG. IB depicts a series of illumination pulses and indicates the timing of image acquisition.

[0020] FIG. 2 is a circuit schematic for an example of a wide-range, precision supply circuit that can be used to precisely control current through a load with high precision.

[0021] FIG. 3 depicts an implementation of the precision supply circuit of FIG.2 in an LED lighting and image-acquisition system.

[0022] FIG. 4A depicts a front perspective view of a compact camera that can house the supply circuit of FIG. 2 and be used in the lighting and image-acquisition system of FIG. 3.

[0023] FIG. 4B depicts a rear perspective view of a compact camera that can house the supply circuit of FIG. 2 and be used in the lighting and image-acquisition system of FIG. 3.

[0024] FIG. 5A is an oscilloscope trace of a pulse output from a wide-range, precision supply circuit constructed in accordance with the circuit schematic of FIG. 2.

[0025] FIG. 5B shows repeatability of pulses from the wide-range, precision supply circuit constructed in accordance with the circuit schematic of FIG. 2.Attorney Docket No. OPTN-005W001

[0026] FIG. 6 is a circuit schematic for a second example of a precision supply circuit that can be used to precisely control current through a load.

[0027] FIG. 7 plots a measured relation between voltage and generated period of an oscillating signal output from voltage-to-frequency conversion circuitry along with a linear fit to the curve.

[0028] FIG. 8A is a circuit schematic of another example precision supply circuit that can be used to drive a load in current-control mode or voltage-control mode.

[0029] FIG. 8B is a circuit schematic of another example precision supply circuit that can be used to drive a load in current-control mode or voltage-control mode.DETAILED DESCRIPTION

[0030] The inventors have recognized and appreciated that variability in illumination of objects is undesirable in certain machine inspection systems. For example, variability in light level when imaging objects on an assembly line can lead to the rejection of manufactured articles that, under consistent lighting levels, would pass inspection. The reverse scenario could also occur where articles might pass inspection whereas under consistent lighting levels may not pass inspection. The inventors have further recognized and appreciated that an effective way to control some loads (such as an LED-based lighting system that is used to facilitate imaging by cameras) is to drive a precisely controlled current through the load. For an LED lamp, the light output is proportional to the current flowing through the semiconductor junction(s) of the LED lamp. The number of photons produced is essentially proportional to the number of charge carriers that traverse the band gap of the semiconductor multiplied by the quantum efficiency (QE) of the LED. Integrating current provided to the LED lamp over the duration of a current pulse can yield the optical energy generated during the pulse. The optical energy resulting from a pulse of current is essentially proportional to QE X Joic(t)dt where Tis the duration of the pulse and ic(t) is time-varying waveform of electrical current delivered to the LED lamp.

[0031] An effective and safe way to deliver a consistent amount of light per event (e.g., a pulse of light) is to establish and maintain a constant current delivered to the LED lamp for a precise length of time ( / .< ., a consistent pulse of current for each illumination event). If the waveform of the applied electrical current and the pulse duration are controlled to be constant, then the light output for each pulse will be constant. This can result in consistent illumination and negligible illumination variability for each illumination event in either ofAttorney Docket No. OPTN-005W001two cases. An “illumination event” is considered to occur when an illuminator (such as an LED lamp) is turned on to illuminate an object to be imaged and the object is imaged by a camera while the object is illuminated.

[0032] In the first of the two cases of consistent illumination, illustrated in FIG. 1A, the duration of the lighting pulse T is longer than and spans the image-acquisition period Ti used by a camera to capture a frame of image data of the illuminated object. During the imageacquisition period Ti, the intensity of the illumination of the object is essentially constant. For example, the illumination light exhibits no greater than from 1% to 5% intensity variability between a first time ti when the pulse of illumination 10 reaches 95% of its peak value during the pulse and a second time L when the illumination intensity falls to 95% of its peak value at the end of the pulse of current. In this scenario, the camera can acquire an image of the object within the duration of the lighting pulse T (in the span of time occurring between ti and L where < T). Even though the timing of the image-acquisition period may move slightly with respect to the timing of the lighting pulse T, the illumination of each object remains essentially constant, provided the duration of remains essentially constant. Such an illumination method is depicted in FIG. 1A.

[0033] In the second illumination method, depicted in FIG. IB, the image-acquisition period is longer than the duration of the lighting pulse T and there is no other significant illumination on the object that would be detected by the camera. In some cases, the imageacquisition camera can have a narrow-band optical filter that passes only light within a small range of wavelengths (e.g., no larger than 20 nm bandwidth) that includes the illumination wavelength(s) to reject any ambient light that might have variable intensity. In the second illumination method, each illumination pulse delivers a constant amount of light energy to the object for each image acquisition. Even though the timing of the image-acquisition period T may move slightly with respect to the timing of the lighting pulse T, the illumination of each object remains essentially constant, provided the duration of T remains essentially constant. In some implementations, it may be easier to more precisely control T than T.

[0034] Establishing a constant amount of illumination (either in terms of intensity for the case of FIG. 1A or total energy for the case of FIG. IB) during each pulse of illumination 10 for these two cases can avoid significant variability in illumination of objects between acquired images and thereby improve consistent image acquisition and image analysis.Additionally, the electrical power used by the system can be reduced and the lifetime of theAttorney Docket No. OPTN-005W001illumination source extended compared to a case where the illumination source is continuously on (and not strobed for each image acquisition).

[0035] There are a wide variety of LED-based lighting systems available for object illumination, some of which can be employed in machine vision applications. These lighting systems may require a relatively large range of different operating currents (e.g., currents ranging from 100 milliamps (mA) in some examples to on the order of 100 amps (A) in other examples). The inventors have recognized and appreciated that there are multiple advantages in implementing an LED-based lighting system driver capable of operating over a relatively wide range of currents while maintaining fast rise and fall times. However, it is challenging to achieve precise control of currents, with rapid response, while also accommodating a wide range of reactive loads. In particular, unwanted levels of ringing and overshoot and increased circuit complexity can be a consequence when using adjustable gain in a feedback control circuit to drive large currents into highly capacitive loads through a wide range of (inductive) cabling and also to drive smaller currents with the same circuitry through less inductive wiring to loads with considerably lower capacitance.

[0036] Conventionally, most lighting vendors avoid these issues by either driving LED lamps through constant resistors from a voltage source that is either left on at all times (which wastes power and creates a proportionally large amount of heat that must be dissipated), or by switching power on and off by connecting the voltage source to the light via a two state switch (typically a FET operated alternately in saturation, or fully off). In both cases the voltage of the power supply and the values of the resistors must be matched to each particular LED lamp. Another approach is to drive FET or Bipolar switches into saturation to turn an LED lamp on and off multiple times to achieve a target amount of light over a period of time. This approach has been applied to LED lighting for human viewing but is unsuitable for most machine vision applications where a controlled amount of illumination must be applied in one short interval of time at the moment the target arrives at a precise location.

[0037] In view of the foregoing, the present invention is directed generally to circuits, systems, and methods for precisely conducting a wide range of currents through loads that may have different current and voltage requirements. In an example, a single wide-range, precision supply circuit is capable of driving a variety of different LED-based lighting systems over relatively large ranges of voltages and currents, and with precise control over the current and / or voltage (pulsed or continuous) provided to the LED-based lighting system.Attorney Docket No. OPTN-005W001The precise control of the current and / or voltage results in precise control over the illumination provided by the LED-based lighting system.

[0038] In an example implementation described in detail below, pulse-to-pulse illumination provided by an LED-based lighting system controlled pursuant to the inventive systems and methods disclosed herein is notably consistent (e.g., to about 1 part in 1000 in the amount of light generated from pulse-to-pulse). In one aspect, the current provided to reactive loads (through inductive cables to LED lamps having large capacitive loads) may be overdamped, but still relatively fast, e.g., with rise and fall times from approximately or exactly 1 microsecond (ps) to approximately or exactly 5 ps. Example supply circuit implementations of the inventive systems and methods are capable of operating LED-based lighting systems requiring compliance voltages from approximately or exactly 5 volts (V) to approximately or exactly 100 V with currents from approximately or exactly 100 mA to approximately or exactly 100 A, though other voltage ranges and current ranges are possible. The described circuit topology is readily configurable to drive high and low currents over a range of programmable voltages.

[0039] In yet another aspect, an additional feature of the inventive systems and methods is to monitor in real time the instantaneous power delivered to, and thermal energy stored by, a current controller of the precision supply circuit implementing the systems and methods disclosed herein, as well as the instantaneous power delivered to and thermal energy stored by the load (e.g., delivered to an LED-based lighting system to which the supply circuit is operably coupled), so as to maintain the LED-based lighting system within a user-specified appropriate range of operation. The user can specify integration limits, so that total power and / or energy can be tracked for specified integration intervals. According to some implementations, integration of the thermal energy stored in both the current controller and in the load are each performed repeatedly and continuously, evaluated for successive time intervals (e.g., every microsecond), and can be compared with their respective operating limits. Integration of consumed energy can provide information about the thermal loads on the current controller and load, which can be compared to user-specified thermal limits to maintain safe operation. In another aspect, the supply circuit curtails or discontinues a current pulse and / or prevents future pulses until the thermal energy within the supply circuit and / or LED-based lighting system has dissipated sufficiently to safely allow additional operation of the supply circuit and / or lighting system.

[0040] 1. Wide-Range, Precision Supply CircuitAttorney Docket No. OPTN-005W001

[0041] FIG. 2 is a circuit schematic for an example of a wide-range, precision supply circuit 100 that can be used to deliver a precise amount of current (pulsed or continuous) to a load 105, such as an LED lamp. In some implementations, a precision current pulse (e.g., a precisely timed pulse having a precise amount of current applied over a precise amount of time) can be delivered by the supply circuit 100 to the load 105. The precision supply circuit 100 can be generally divided into three functional sections indicated by the dashed boxes in FIG. 2. The first section comprises a wide dynamic range, precision current controller 110 that controls the conduction of current through a load 105, such as an LED lamp. The second section comprises a voltage monitor 140 that can monitor instantaneous voltage across the load. The third section comprises a programmable voltage source 170 (implemented as a buck converter in the illustrated example) to apply a voltage to the load at the output of the Buck converter (sometimes referred to as a “compliance voltage”).

[0042] In further detail, the current controller 110 includes a first switch 112, an operational amplifier 120, a second switch 114, a shunt voltage reference 130, three transistors T2, T3, T4 (at least some of which may be field-effect or bipolar transistors), and other circuit elements connected as shown in FIG. 2. The current controller 110 employs feedback to the op-amp 120 (in a feedback circuit 125) to control the gate (or base) of transistor T3 and conduct a precise level of current (from tens of milliamps to 50 A in this circuit example) through a load 105, when the load is connected to the precision supply circuit 100 (connected between output terminals labeled LED CATH and LED CV in FIG. 2).

[0043] The feedback circuit 125 includes the op-amp 120, transistor T2 having a control terminal connected to the output of the op-amp 120, and second switch 114. The op-amp 120 outputs a signal applied to the control terminal (gate in this example) of transistor T2, which is a bipolar junction transistor. In the example circuit, transistor T2 is configured as a voltage follower and adjusts the voltage applied to the control terminal (gate) of transistor T3 (or base if a BJT is used). Current flow controlled by transistor T3 passes through sensing resistors R16 and R18. Transistor T3 may be referred to as “power transistor T3 ” A voltage feedback signal can be obtained from one or both sensing resistors R16, R18) through which most (if the power transistor T3 has current leakage) or all of the current conducted through the load passes. The voltage feedback signal can be provided back to an input terminal of the op-amp 120 via the second switch 114. As such, the feedback circuit 125 precisely controls the amplitude of the current conducted by the power transistor T3 and which flows throughAttorney Docket No. OPTN-005W001the load 105. The programmable voltage source 170 supplies the voltage and current applied to the load 105 through the load terminal labeled LED CV in FIG. 2.

[0044] One or both of sensing resistors R16 and R18 can be implemented more generally as a circuit element having impedance (e.g., at least as one resistor, or a plurality of resistors connected in series and / or parallel) and may further include some inductance and / or capacitance. The sensing resistors R16, R18 can connect in series on a circuit path that runs between the load 105 and a reference potential. The reference potential can be a ground connection, as in the illustrated schematic, but could be a fixed voltage in some implementations.

[0045] Sinking current through the load 105 and through the sensing resistors R16, R18 for the example circuit can be initiated by applying a pulse-width-modulated (PWM) signal to pin PWMI (e.g, a high logic signal) and applying (subsequently in some cases) a signal to the pin labeled FIRE in FIG. 2. The PWM signal passes through the analog switch 112, is filtered with a low-pass RC filter 103, after pin PWMI in the drawing, providing a control voltage Vcthat is applied to the non-inverting terminal of the op-amp 120. Controlling the duty cycle of the PWM signal (which can be done easily with digital precision) controls the voltage level Vc applied to the non-inverting terminal of the op-amp 120. The op-amp 120 compares the control voltage Vc with the voltage sensed and received from sensing resistor(s) R16, R18, outputs a voltage to drive a voltage follower (implemented with transistor T2) that in turn drives the gate of transistor T3, causing it to go into conduction and provide enough current such that the voltage sensed by the sensing resistors equals the control voltage Vc. This feedback operation by the op-amp 120 controls the amount of current through the load 105 with high precision.

[0046] A logic high signal, for example, can be applied to a control input of the first switch 112, (via pin FIRE in the example circuit of FIG.2) to initiate flow of the current through the load for a short interval of time (e.g, as short as 10 ps or less in some cases). The signal applied to the pin FIRE, toggles the first switch 112 to apply the control voltage Vc to the non-inverting terminal of the op-amp 120. Any suitable pulse duration can be applied to the control input of the first switch to control the current pulse drawn through the load 105 with the precision supply circuit 100. In some cases, the supply circuit 100 can be operated to sink current continuously (e.g., in DC mode) by leaving the logic high signal applied to pin FIRE. Pulse durations can be from 50 ns, in some implementations, to a fully on signal. The amount of voltage applied to the gate (or base) of transistor T3 (and hence the amount ofAttorney Docket No. OPTN-005W001current flowing through transistor T3, when operating T3 in its linear range) can be controlled by adjusting the duty cycle of the PWM signal applied to PWMI, as described above.

[0047] Although the current controller 110 is arranged to sink current from the load 105 in the schematic of FIG. 2, in other implementations the current controller can be arranged to source current to the load. For example, the load can be placed between the transistor T3 and reference potential (ground in this example) and the sensing resistors R16, R18 can be moved to the drain side of transistor T3 (e.g., connect in series directly between the supply voltage LED CV and the drain of T3, or connected in series between T1 and T3 where the voltages across the resistors are sensed differentially). Other arrangements to sense current through the load with sensing resistors R16, R18 are possible, as could be determined by those skilled in the art in light of this description. The choice of transistor T3 ( / / -channel vs. / / -channel FET or npn vs. pnp B JT, for example) can depend upon the polarity of the voltage supply used to provide voltage to the load and whether the current controller 110 is arranged to source current to or sink current from the load 105.

[0048] Transistor T4 is arranged to provide a bypass circuit path around sensing resistor R16. Transistor T4 may be referred to as “shunt transistor T4.” In a first, low-current, operational setting (which is programmable at pin ISEL for the example circuit of FIG. 2), shunt transistor T4 is turned off and the second switch 114 is toggled to couple the inverting input of op-amp 120 to a first sensing node 126 located between the drain or collector of transistor T3 and the series-connected sensing resistor R16, R18. In this configuration, at least a first portion of the current conducted through the load by the power transistor T3 flows through both sensing resistors R16 and R18 (along a first circuit path that includes the first sensing node 126). The voltage sensed at the first sensing node 126 is determined by the sum of the two resistance values (0.18 ohm + 0.02 ohm = 0.2 ohm in this example). For this configuration and example circuit, a swing in current through the load from 10 mA to 5 A (e.g., a low-current setting for the precision supply circuit 100) will produce a range of feedback voltages from 2 mV to 1 V, which can be a same range of feedback voltages as for the circuit’s high-current setting.

[0049] In a second, high-current setting, the second switch 114 is toggled to couple the inverting input of op-amp 120 to a second sensing node 124 between first resistor R16 and second resistor R18. In the second, high-current setting, shunt transistor T4 can be turned on (into conduction) so that the first sensing resistor R16 is bypassed. According to someAttorney Docket No. OPTN-005W001implementations, the second setting can be achieved by applying a logic high voltage to pin ISEL, which both toggles the second switch 114 and turns on transistor T4. In this high-current setting, current conducted through the load flows through the shunt transistor T4 (along a second circuit path) instead of flowing through R16 and then flows through the second sensing resistor R18, which has a lower resistance value (0.02 ohm in this example) than R16 (0.18 ohm) and the combined resistance of the two series-connected sensing resistors (0.20 ohm). The total sensing resistance for the high-current setting is one-tenth the total sensing resistance for the low-current setting. The second, high-current setting can be for high currents (e.g., currents greater than 5 A and up to 50 A). By sensing current flowing only through the smaller resistor R18, the feedback voltage is reduced by a factor of 10 compared to what would be sensed, at the first sensing node 126 if current were flowing through both sensing resistors R16 and R18. Thus, the range of feedback voltages for large current swings can be reduced to maintain the op-amp 120 in a linear operating region. For the high-current setting and the example circuit, a swing in current through the load from 100 mA to 50 A will produce a feedback voltage swing from 2 mV to 1 V. In some cases, the resistance of the second sensing resistor R18 can be less than one-quarter the resistance of the 1 1 1 first sensing resistor R16 (e.g., no greater than -, no greater than - no greater than -, no 4 5 8 greater than — )•

[0050] In this manner, the op-amp 120 can be kept in a linear range of operation for a wide range of driven currents through the load and through transistor T3 without changing the gain of the op-amp 120. This approach to controlling a wide range of currents also preserves the speed and slew rates of the op-amp such that on times (measured as 90% of peak current) and off times (measured as falling to 10% of peak current) for current pulses applied to the load 105 can be on the order of 5 ps or less for high and low current ranges. For example, by operating the supply circuit 100 in the first, low-current setting, a current of 500 mA or larger flowing through the load will produce a sensed voltage an sensing node 126 of 100 mV or larger, resulting in a fast slew rate of the op-amp 120 and fast turn-on and turn-off of the resulting load current through transistor T3. Similarly, when operating with the second, high-current setting at pin ISEL, a current of 5 A or larger through the load 105 produces the same sensed voltage at the sensing node 126 of 100 mV or larger and the same slew rates for the op-amp 120 in the feedback circuit 125.Attorney Docket No. OPTN-005W001

[0051] Naturally, the approach to controlling a wide range of currents can be extended further. For example, another resistor can be added in series with resistors R16 and R18. Another bypassing transistor (arranged like shunt transistor T4) can be added to shunt the third resistor. The second switch 114 can be replaced with a three-way switch, or another two-way switch can be added to the circuit. Another ISEL pin can be added to implement a third setting that would couple the inverting node of op-amp 120 to a third node at which the sensed voltage would be the sum of all three resistors.

[0052] The precision supply circuit 100 can be operated without the shunt transistor T4, the circuit path to bypass resistor R16, and without the second switch 114. In such an implementation, power would unnecessarily be dissipated in R16 when sensing is done at second sensing node 124 and the precision of current control may be diminished.

[0053] Another feature of the current controller 110 is that it can bias the transistor T3 and provide a small quiescent or standby current to the transistor T3 when the load 105 (e.g., LED lamp) is off. This allows the load 105 to be turned fully off (e.g., negligible or no current flowing through the load) while keeping the transistor T3 in a ready state with gate capacitances charged. Keeping the transistor in a ready (slightly conducting) state reduces the time to turn transistor T3 sufficiently on to conduct the commanded current through the load 105. The shunt voltage reference 130 is arranged in the current controller 110 (with transistor T1 and resistors R7 and R9) to act as a current source 133, using output from the programmable voltage source 170 (LED CV). This current source 133 can provide the small quiescent current to transistor T3 when full current through the load 105 is terminated to maintain transistor T3 in the ready state for rapid turn-on. The small amount of quiescent current can be less than 100 mA or less than one-tenth the full amount of current provided to the load 105 when the load is being fully driven.

[0054] Additionally, the first switch 112 can be toggled (via pin FIRE) to connect the noninverting input of the op-amp 120 to a fixed reference voltage Vref provided by a voltage divider 108. The value of Ere / can be selected to provide a sufficient biasing voltage to the gate (or base) of power transistor T3 such that the transistor T3 draws the desired amount of quiescent or standby current. This biasing voltage and quiescent current keep the power transistor from turning fully off and in a ready state, so that it can rapidly slew to an on state when receiving a next firing command via pin FIRE.Attorney Docket No. OPTN-005W001

[0055] For an example circuit implementation, the first switch 112 and the second switch 114 can be analog switches, such as single-pole double-throw analog switch SN74LVC1G3157DCKR available from Texas Instruments of Dallas Texas. Op-amp 120 can be precision operational amplifier OPA192 available from Texas Instruments of Dallas Texas, for example. The shunt voltage reference 130 can be integrated circuit LM4041 available from Texas Instruments of Dallas Texas, for example. The power transistor T3 can be a PowerTrench® MOSFET FDT86102LZ available from Onsemi of Phoenix, Arizona, though other types of transistors including bipolar transistors can be used. Transistor T4 can be a PSMN0R7-25-series MOSFET available from Nexperia of Nijmegen, Netherlands, for example, though other types of transistors including bipolar transistors can be used.Transistor T1 can be a BC856-series transistor available from Nexperia of Nijmegen, Netherlands, for example. Because only a small amount of current is supplied through transistor T1 during an idle state of transistor T3, the maximum current rating of transistor T1 can be a fraction (e.g., 1 / 10thto 1 / 100thof the maximum current rating of transistor T3).

[0056] The precision supply circuit 100 also includes the programmable voltage source 170. In the example implementation of FIG. 2, the programmable voltage source 170 comprises a buck converter that is based, in part, on a regulator chip 175 (model LMR16006 available from Texas Instruments of Dallas Texas, for example) and inductor LI. The buck converter steps down an input DC voltage (HVP provided to an input pin of the regulator chip) to a lower voltage that is determined by the duty cycle of a PWM signal applied to pin PWM V. The applied PWM signal controls the duty cycle of current switched through the buck converter’s inductor and therefore determines the output voltage from the programmable voltage source 170. Other types of programmable voltage sources can be used in other cases (e.g., a programmable buck-boost converter, a programmable flyback converter). The converter can be turned on and off with a signal applied to pin CV EN. The example programmable voltage source 170 is configured to output a compliance voltage from approximately or exactly 5 volts to approximately or exactly 50 volts, though other ranges of output voltages are possible. The programmable voltage source 170 also provides for adjustable current limiting via pin ILM, which controls a feedback voltage applied to the regulator chip’s feedback input.

[0057] The voltage monitor 140 of the precision supply circuit 100 can monitor the voltage at the output of the load 105 (e.g., LED lamp) at a high frequency, so that essentially the instantaneous voltage drop across the load can be tracked during circuit operation. TheAttorney Docket No. OPTN-005W001example voltage monitor 140 uses a high-speed analog-to-digital converter (ADC) 145 (model AD7274 available from Analog Devices of Wilmington, Massachusetts, for example) to sample a voltage indicative of the voltage at the output of the load (e.g., the voltage of the LED lamp’s cathode, LED CATH in the illustrated example). A voltage divider 150 can be used to scale the sampled voltage into a range that can be detected at an input to the ADC 145. The ADC can sample and transmit (via pin SDATA) detected voltage values at rates as high as 1 per microsecond. The sampling data rate can be determined by a clock signal provided to a clock input (via pin SCLK) of the ADC 145 and the data transmission rate can be determined by a signal applied to a select input (via pin CSn). The difference between the programmed compliance voltage Vcomp and the measured voltage Vm at the output of the load 105 (sensed by the ADC 145) determines the voltage drop in the load 105. The voltage drop in the load multiplied by the programmed current can be used to compute repeatedly (for a sequence of samples obtained by the ADC 145) the instantaneous power being provided to and dissipated in the load. If the current the load can pass at the programmed voltage is less than the programmed current, then the instantaneous power valued calculated as described will at least be an upper bound for the actual power dissipated in the load resulting at worst in a conservative estimation of the instantaneous power.

[0058] Because the ADC 145 monitors voltage at the output (or low-voltage side) of the load, it also directly monitors the voltage drop across the precision current controller 110 (voltage drop across transistor T3, transistor T4 when on, and the sensing resistor(s) R18 or R18+R16, depending on the current setting for the supply circuit 100). Voltage drops across currentsensing resistors R18 (when T4 is conducting) and across resistors R16 and R18 (when T4 is off) and transistor T3 multiplied by the programmed current provides the power dissipated in the precision current controller 110, since most of the power dissipated in the current controller is dissipated by these two or three components. If the load cannot pass the programmed current at the programmed voltage, then the calculated power will be at worst an upper bound on the actual power dissipated in the resistors. The on resistance of power transistor T4 can be negligible when T4 is turned fully on.

[0059] Monitoring the single voltage Vm at the output of the load 105 together with straightforward computation can provide several useful pieces of information: (1) the voltage drop across the load and power dissipated in the load, (2) the voltage drop across the power transistors T3, T4 and the current-sensing resistor(s) and power dissipated by these components, (3) an upper bound on the current flowing through the power transistors T3, T4Attorney Docket No. OPTN-005W001and the current-sensing resistor(s), (4) an upper bound on the current flowing through the load, (5) an upper bound on the power delivered to the load, and (6) an upper bound on the power delivered to the power transistor(s) T3, T4.

[0060] 2. Lighting and Image-Acquisition Systems

[0061] FIG. 3 depicts an implementation of the precision supply circuit 100 in an LED lighting and image-acquisition system 200. The image-acquisition system 200 includes the supply circuit 100 communicatively coupled to a controller 210 and arranged to pulse an LED lamp (load 105). The system further includes a camera 220 arranged to photograph an object 230, which may pass by the camera 220 on a conveyer 240. Such an LED lighting and image-acquisition system 200 may be implemented in a manufacturing facility (e.g., for part inspection) and may be part of a more complex automated control system.

[0062] The controller 210 can be implemented with at least one processor (such as a microcontroller, field-programmable gate array (FPGA), programmable logic controller (PLC), application-specific integrated circuit (ASIC) microprocessor, digital signal processor (DSP), or some combination thereof). The controller 210 can provide signals to control and program the supply circuit 100 (e.g., to program the compliance voltage Vcomp (at output pin LED CV) applied to the load, to program an amount of current drawn through the load, and to conduct or terminate conduction of current through the load as described above for the precision supply circuit of FIG. 2). The controller 210 can also receive signals from the supply circuit 100 (e.g., receive serial data signals from the ADC 145 representative of the near-instantaneous voltages Vm measured at the output of the load). The controller 210 can also provide signals to the camera 220 (e.g., to control acquisition of images) and receive image data from the camera 220. In some cases, the controller 210 can be implemented, at least in part, as a controller for managing coordinated operation of machine components in a complex dynamic environment, such as that described in U.S. Patent No. 9,459,607, titled “Methods, Apparatus, and Systems for Monitoring and / or Controlling Dynamic Environments,” issued October 4, 2016, which patent is incorporated herein by reference in its entirety. In some cases, intermediary circuitry can be used between the controller 210 and supply circuit 100, such as the flexible input-output circuitry described in U.S. Patent No. 11,182,326, titled “Input / Output Apparatus and Methods for Monitoring and / or Controlling Dynamic Environments,” issued November 23, 2021, which patent is incorporated herein by reference in its entirety. In some cases, the intermediary circuitry can also be included within the camera 220.Attorney Docket No. OPTN-005W001

[0063] The controller 210 can include a system clock and / or other circuitry that is used to synchronize operations through the lighting and image-acquisition system 200. For example, the controller 210 can control the start time and / or duration of a pulse applied to pin FIRE of the current controller 110 (to turn on an LED lamp for a short or long interval of time, for example). The start time and duration of a pulse can be based on clock cycles of the system clock, for example. The controller 210 can also control an image-acquisition time and / or exposure setting of the camera for image acquisition. The exposure setting may be set by providing programming input to the camera 220 or using a shutter control signal of the camera. The controller 210 can coordinate image acquisition (signal collection or exposure of the camera’s pixels) by the camera 220 with the firing of the LED lamp using conventional logic circuitry to trigger the image acquisition in response to firing of the LED lamp, or to fire the LED lamp in response to initiation of image acquisition. In some cases, the firing of the LED lamp and / or image acquisition can be based on an event detected in the lighting and image-acquisition system 200. For example, the triggering event could be the arrival, at a specific location, of a part or object transported on a conveyor 240, which may be detected with a proximity sensor. The sensor can output a signal to either or both of the supply circuit 100 and the camera 220 to initiate illumination and image acquisition, respectively. In some cases, only the camera 220 may receive the signal and forward the signal or send another signal to the supply circuit 100 to illuminate the object. In some cases, only the supply circuit 100 may receive the signal and forward the signal or send another signal to the camera 220 to acquire an image of the object.

[0064] Although the illustration of FIG. 3 depicts the precision supply circuit 100 separated from the camera 220, the invention is not so limited. In some implementations, the supply circuit 100 is contained on a printed circuit board (PCB) that can mount within a housing 221 of the camera 220 and the camera can be very compact in size (measuring no more than 50 mm x 50 mm x 50 mm, for example). Such a compact camera 220 is depicted in FIG. 4A and FIG. 4B. The housing 221 can include an imaging array 222, its associated operating and read-out electronics, and two or more precision supply circuits 100 to drive two or more loads 105 (e.g., two LED lamps). For example, the camera 220 can house the precision supply circuit 100 and have two outputs (LED CVl, LED CATH1), (LED CV2,LED CATH2) to drive two LED lamps (second output and lamp not shown in FIG. 3) that are spaced apart to provide more uniform illumination of the object 230, or are synchronized to provide differently illuminated views of the same object 230.Attorney Docket No. OPTN-005W001

[0065] Referring to the front perspective view of FIG. 4A, the camera 220 can include a housing 221 in which the imaging array 222 is mounted behind a lens mount 224 for a lens assembly 225 (depicted in FIG. 3). The housing can be made from a metal, plastic or combination thereof. The imaging array 222 can be a CCD or CMOS 2D imaging array and comprise any number of pixels (e.g., from 10,000 to 4,000,000 or more). The imaging array 222 can be mounted on a PCB that is secured within the housing 221. The imaging array and electronics on the PCB can include circuitry to deliver power to transistors that operate readout and resetting of the pixels, receive an external trigger signal, buffer pixel data, frame data for transmission, and transmit the data, among other functionalities. The lens mount can be a 25 mm, threaded CS mount, though other types of lens mounts can be used.

[0066] The rear of the camera 220, illustrated in the rear perspective view of FIG. 4B, can include one or more connectors to attach wiring and or cabling to the camera (e.g., for power, programming, and communications with the controller 210). For the illustrated example, two first connectors 227 (e.g., M8 female connectors) and one second connector 228 (e.g., RJ45 connector) are mounted on the rear side of the camera 220, though other kinds of connectors can be used. Power-over-ethernet (POE) can be provided through the second connector 228, which can also be used to communicatively couple the camera 220, the precision supply circuit 100, and the controller 210, and other device(s), or some combination thereof. At least one second connector 227 can connect via cable to a remotely located load 105 (e.g., LED lamp). The housing 221 can include mounting features (e.g., threaded holes 229) to secure the camera 220 to a fixed mount.

[0067] As may be appreciated, the precision supply circuit 100 (and each precision supply circuite described below) is well suited for closely-coordinated operation of a stand-alone illumination source (load 105) and camera 220. In some cases, the coordinated operation can be event-driven using data packets transmitted over a network that is part of a manufacturing facility or other monitoring system. For example, a data packet to trigger illumination and image acquisition can be transmitted when an item of manufacture reaches a stage or location in the manufacturing process. The controller 220, which may be independent of and located remotely away from one or both of the illumination source and camera 220 can receive the data packet and issue at least one command to the load 105 and camera 220 (e.g., to turn on and illumination the object and acquire an image of the object). The closely-coordinated operation of the illumination source and camera can allow imaging in both the implementations of FIG. 1A and FIG. IB.Attorney Docket No. OPTN-005W001

[0068] It should also be appreciated that the precision supply circuit 100 can be used in other applications for which precision in current, power, and / or energy delivered to a load is of value. Another application may involve testing solar cells. For example, the precision supply circuit 100 can be used to precisely control artificial light for testing the efficiency of solar cells during manufacture. Another application may involve photolithography used in the semiconductor industry. The precision supply circuit 100 can be used to control an exposure source that provides a dose of radiation to expose photoresist. Another application may be with medical devices, where the dose of radiation provided to a patient is tightly controlled. Another application may involve heating wherein a heating element is to be controlled precisely by the precision supply circuit.

[0069] 3. Power Limiting

[0070] The supply circuit 100 of FIG. 2 allows for circuit protection of the load and power transistors T3, T4 when implemented in a control system such as that illustrated in FIG. 3.As described in connection with FIG. 2, monitoring the voltage Vm at the output of the load 105 provides several pieces of useful information that can be used to protect the load 105 and power transistors T3, T4 from excessive power dissipation that could degrade these devices. As described above, the ADC 145 can continuously output near-instantaneous monitored voltage values Vm at the output of the load. These voltage values give near-instantaneous information about: (1) the voltage drop across the load, (2) the voltage drop across the power transistors T3, T4 and the current-sensing resistor(s) R16, R18, (3) the current flowing through the power transistors T3, T4 and current-sensing resistor(s), (4) the current flowing through the load, (5) the power delivered to the load, and (6) the power delivered to the power transistor(s).

[0071] An aspect of the current controller 110 is that the current IR flowing through the sensing resistor(s) R16, R18 is essentially programmed or set by the input applied to pin PWMI and controlled by the feedback circuit 125, as described above in connection with FIG. 2. Since the voltage at the inverting terminal of op-amp 120 is the voltage sensed and dropped across the sensing resistor(s) R16, R18, then the average voltage of the PWM signal applied to the non-inverting terminal of the op-amp essentially programs the current IR flowing through the sensing resistor(s) according to Ohm’s law. Calibration of the PWM signal applied to the PWMI input and resulting control voltage Vccan be stored in a look-up table to convert duty cycle of the PWM signal to voltage value of the control voltage Vc andAttorney Docket No. OPTN-005W001therefore voltage at the sensing node 126 or sensing node 124, depending on the setting of the second switch 114.

[0072] The near-instantaneous voltage drop VL across the load (item 1 above), can be determined from:where Vcomp is the known, programmed compliance voltage at the output of the programmable voltage source 170 (pin LED CV) and Vmis the measured voltage at the output of the load (pin LED CATH), as measured by the voltage monitor 140. This computation (and those in EQ. 2 through EQ. 3 below) can be done for every sampling period of the ADC 145 or for every N sampling periods, where Ais an integer from 1 to 1000. The feedback circuit 125, managed by op-amp 120, controls the current / ;? flowing through the load, as described above. This current also passes through one or both of the power transistors T3, T4 and one or both of the sensing resistors R16, R18.

[0073] The near-instantaneous power PL delivered to the load can then be approximated using EQ. 1.

[0074] The near-instantaneous power PT delivered to the power transistor(s) can be approximated asPT = IRVm(3) which overestimates the power delivered to the power transistor(s) by a small, negligible amount that is dissipated in the current-sensing resistor(s) R16, R18. In most cases, the on resistance of the power transistors T3, T4 is significantly larger than the resistances of the sensing resistors R16, R18.

[0075] The near-instantaneous values VL, IR, PL, and PT can be computed repeatedly by the controller 210, for example, in real time (e.g., every few microseconds) as the current is conducted through the load 105 and terminated. The controller 210 can also compute accumulated energy per pulse EPdelivered to the load and power transistor(s), which on a pulse-by-pulse basis is the product of power and duration tPof the current pulse.PpL=PL^P (4) PpT=Pr^p (3)Attorney Docket No. QPTN-005W001The pulse duration can be set by the controller 210 and therefore known. These calculations are based on the feedback signal of monitored low-side load voltage Vm received from the ADC 145 of the voltage monitor 140 of FIG. 2.

[0076] Power and / or energy limits for the power transistors T3, T4 PT3,Um, PT4,Um, Ers.Um, ET4,um) and load PL.Um, EL, Um) can be stored in memory 250 that can be accessed by the controller 210. In some cases, these limiting values can be read from a device using a singlewire read as described below in connection with FIG. 8A and FIG. 8B. These power and energy limits can be defined to allow for the cooling characteristics of the precision supply circuit 100 and its power transistors T3, T4 and cooling characteristics of the load 105. With these parameters, controller logic can be instantiated to inhibit (terminate) pulses of current to the load when the power and / or energy limits are exceeded. For example, the controller may continuously compare calculated power and / or energy delivered to each of the load and power transistor(s) with their corresponding power and / or energy limits and inhibit current output to the load 105 to prevent exceeding any power and / or energy limit.

[0077] In further detail and according to one implementation, an 18x18 binary multiplier in the controller 210 can be used to multiply the computed products in one or more of EQ. 2, EQ. 3, EQ. 4, and EQ. 5 above to essentially determine instantaneous power and energy levels delivered to the load 105 and power transistor(s) T3, T4. In some cases, the received binary value from the ADC 145 may be encoded in units of voltagex256 and the binary computed current can be encoded in units of milliamps. In such cases, the top 28 bits of the result from the 18x18 binary multiplier represent the instantaneous power or energy dissipated by the power transistor(s) or lamp (in milliwatts), depending on whether the multiplication is done for the transistor(s) or lamp. For cases where the maximum lamp supply voltage is less than 128 VDC, the largest possible value is less than 1024 watts, so only bits [27..8] of the 18x18 multiplier product may be used.

[0078] If the near-instantaneous power (PL and / or PT in milliwatts) are / is accumulated every microsecond that the supply circuit 100 is activated, the resulting sum(s) will represent accumulated energy(ies) in nanojoules (nJ). The real-time accumulated energy EL for the load 105 can be represented by the following expression:where PL,nis the nthcomputed near-instantaneous power PL delivered to the load (for the nthAttorney Docket No. OPTN-005W001microsecond in this example). A user can specify the integration interval m. Similar computations can be done for the power transistors T3, T4. So, calculating the accumulated energy delivered to the load and power transistors T3, T4 comprises adding the corresponding computed power values to corresponding accumulators every microsecond (or interval of time other than one microsecond). The invention is not limited to one microsecond accumulation intervals and accumulated values in units of nJ; other accumulation intervals and energy units are possible.

[0079] Since energy is also released thermally from the load 105 and power transistors T3, T4, the accumulated energy of EQ. 6 can be modified to account for thermal dissipation of energy by each device. Each device’s thermal power-dissipation rate will depend on several factors, such as the thermal conductivity between the device and the surrounding environment and the temperature of that environment. The thermal power-dissipation rate can be characterized as a thermal-dissipation power rating Pa for each device The thermaldissipation power rating will vary depending on how the device is physically implemented and what the anticipated maximum temperature of the environment will be. The thermaldissipation power rating can be determined empirically for each device, may be obtained theoretically, or obtained from device specifications for different device applications. In the case of one example camera 220 and housed precision supply circuit, the thermal-dissipation power rating was found to be approximately 500 mW for the power transistors T3, T4. Since the thermal cooling occurs all the time, the controller 210 can subtract accumulated, thermally-dissipated energy from the accumulated energy delivered to the device every computation interval to determine the net energy level Enat the device at any time. For the load, the computation is as follows:In practice, Pa can vary with temperature of the environment into which heat is dissipated. According to some implementations, a thermistor or other temperature sensor can be used to provide temperature feedback about the environment to the controller 210. The controller 210 can then select a value for Pa (e.g., from a look-up table) or compute a value for Pa based on the sensed temperature. At some point after which current is no longer conducted through the load, the energy accumulation in EQ. 7 will reduce to zero. Once the accumulator reaches a zero value, the controller can suspend accumulation until current is conductedAttorney Docket No. OPTN-005W001through the load again.

[0080] To protect a device, the controller 210 can compare a stored energy limit for the device with the device’s corresponding current value of net energy (e.g., EL.Um for the load 105 compared against EnL). If the current value of net energy equals and / or exceeds the device’s energy limit, then the controller can stop conducting current through the load until the current value of net energy drops below the energy limit. Since the comparison can be done every computation cycle, the controller 210 can curtail or discontinue conduction of current by transistor T3 before reaching the initially-intended duration of the current pulse.

[0081] The thermal-dissipation power rating and energy limit can be conservative values, such that the load temperature or transistor temperature will not rise to the point where the device’s lifetime would be significantly reduced. A control system incorporating the precision supply circuit and protection features described above makes it virtually impossible to damage the supply circuit 100 or the attached load 105 by overdriving the supply circuit or the load. As an example, the power transistors T3, T4 will be protected even if a mis-wired lamp cable connects the positive rail from the programmable voltage source 170 directly to the drain of the power transistor T4 and the circuit is fired to conduct current through the transistor T3.

[0082] 4. Example Circuit Performance

[0083] A precision supply circuit 100 has been constructed in accordance with the circuit schematic of FIG. 2. The circuit was arranged to sink 14 amps of current passing through an LED lamp for a pulse duration of approximately 100 microseconds applied to the gate of transistor T3. A trace 401 of the current pulse from the lamp is shown in FIG. 5A. The trace 401 was obtained by measuring the voltage across a 0.45-ohm resistor connected to the cathode of the lamp.

[0084] The trace 401 exhibits an overdamped behavior, shows little overshoot (less than 4%), and highly uniform current throughout the plateau of the pulse. The amplitude of the current along the plateau varies by less than 2% after the small overshoot, such that the current remains constant (to within 2%, peak-to-peak) for approximately 88% of the pulse duration. In some implementations, the current can remain constant (to within 5%, 2%, or 1%) for not less than 85%, 90%, or even 95% of the pulse duration, depending on the level of current switched through the load 105 and components selected for the current controller 110.

[0085] FIG. 5B plots two oscilloscope traces 401, 403 (overlaid) of the 14 A current pulseAttorney Docket No. OPTN-005W001taken at two different times. The same parameters (e.g., programmable voltage, pulse duration, etc.) were set to operate the supply circuit 100. The overlap shows very high precision and repeatability of the two pulses, which illustrates the consistency of current and therefore consistent light control by the precision supply circuit 100. The reference trace 401 (in blue) is overlaid on the later-acquired trace 403 (in white). The later-acquired trace 403 is almost entirely eclipsed by the reference trace 401. Only ambient noise picked up by the scope ground lead allows any of the later-acquired trace 403 to be visible. The pulse-to-pulse uniformity of the current (and of light exposure for an LED lamp driven by the current) is at least 1 part in 1000 and may be up to 1 part in 10,000 or even up to 1 part in 100,000.

[0086] 5. Alternative Implementations

[0087] There are additional ways to implement functionalities of the precision supply circuit 100 of FIG. 2. FIG. 6 is a circuit schematic for another example of a precision supply circuit 400 that continuously monitors the voltage on the low-voltage side of the load (e.g., at a cathode of an LED lamp). The supply circuit 400 contains similar sections to the section identified in the supply circuit 100 of FIG. 2, though implemented with different circuitry for some of the sections. For example, the supply circuit 400 includes a current controller 410, voltage monitor 440, and programmable voltage source 470. The programmable voltage source 470 is similar to the programmable voltage source 170 of FIG. 2 and includes a buck converter.

[0088] The current controller 410 includes a single current-sensing resistor R13 that provides feedback to the op-amp 420 to precisely control the current conducted through the load 105 (e.g., an LED lamp that can connect to the circuit via connector 478). Input to the op-amp 420 can be switched (with analog switch 412) between a first PWM input passed directly through a digital isolator 402 to control the amount of current conducted with power transistor T3 and a second programable PWM source 408 internal to the current controller 410 for a standby mode of the transistor T3. The programmable PWM source 408 comprises two dual retriggerable monostable multivibrators 416 (model 74AHC123 available from Texas Instruments of Dallas Texas, for example) a 128-tap linear taper digital potentiometer 418 (model MAX5128 available from Analog Devices, for example), and an op-amp 422.

[0089] The voltage monitor 440 employs a voltage-frequency conversion circuit 442 having a timer 445 (model LMC555 available from Texas Instruments of Dallas Texas, for example) to convert a voltage from bias circuitry 430 to a frequency of an oscillating signal outputAttorney Docket No. OPTN-005W001from the timer 445. An output from the timer 445 can be returned to a controller 210 to determine voltage at the output of the load.

[0090] In further detail, a frequency inversely proportional to the voltage LED CATH at the output of the load is imposed onto the feedback signal line 443 by circuit elements within the current controller 410 and voltage monitor 440. The voltage-to-frequency transfer function depends on the characteristics of these circuit elements, which in turn may depend on the intended application of the precision supply circuit 400. For instance, supply circuits 400 that operate across a wide range of voltages may have different component values than supply circuits 400 that operate across a much narrower range of voltages.

[0091] The precision supply circuit 400 can be used in the image-acquisition system 200 of FIG. 3. In order for the controller 210 to properly determine the voltage for any given precision supply circuit implementation, parameters representing the particular precision supply circuit 400 for a given device can be stored in non-volatile memory to be retrieved by the controller 210 on power-up so that the voltage-to-frequency conversion can be correctly calculated.

[0092] For instance, a linear approximation of the voltage of the form y = mx + b may be used to convert the feedback signal frequency to the voltage on the drain of the power transistor T3. But depending on characteristics of the devices in the circuit, the slope and offset of this linear approximation may vary.

[0093] For one example implementation, represented with the plot of FIG. 7, the voltage at the drain of the power transistor T3 has a non-linear dependence on the measured period (by timer 445) of the oscillating signal from the voltage-to-frequency conversion circuitry of the voltage monitor 440. FIG. 7 also plots a linear approximation to the curve, which yields a slope of 0.4285 and an offset of -23.406.

[0094] In an example controller 210, such as an FPGA, the period of each cycle of the oscillating voltage-to-frequency signal can be measured in units of 40 nanoseconds (ns), though measurements in other units are possible (e.g., from 10 ns to 500 ns). If an application requires a maximum lamp voltage of 48 VDC, the frequency range can fall between 125 kHz to 500 kHz, and the period can range from 2 ps to 8 ps. Hence, the maximum period in increments of 40 ns can be 200 measurement units, so the period value can be represented as an 8-bit binary value in the signal from the timer 445 and in controller logic.Attorney Docket No. OPTN-005W001

[0095] Since the voltage calculation involves multiplying the period times the slope, and since the controller can contain binary multipliers that can operate at 200 MHz frequencies embedded in the silicon fabric while floating-point multipliers use valuable logic resources and operate at much lower frequencies, it makes sense to use the binary multiplier and calculate output load voltage Vmas V*256 (rather than V) as follows:V*256 = (slope*period[7..0] + offset)*256

[0096] So, in this example case of FIG. 7, the slope value for multiplication can become 256x0.4285, or 110, and the offset value can become 256x-23.406, or -5992. The slope value can be stored in one byte of the controller’s non-volatile memory, while the offset value can be stored in one word of the controller’s non-volatile memory.

[0097] In the controller logic, the start of a new cycle of the oscillating voltage-to-frequency signal is determined by detecting the rising edge of the signal. The period is measured by incrementing a counter in the timer 445 every 40 ns. When the start of a new cycle is detected, the counter value is latched into the period register, and the counter is reset to zero. A 9x9 binary multiplier can be used to multiply the period register’s value by the slope value. Then a 16-bit adder can be used to add the offset value, resulting in a binary value that is approximately 256 times the voltage at the drain of the power transistor T3. In this manner, the voltage determination can be made using relatively few computational resources. For the voltage monitor 140 of FIG. 2, the voltage at the drain of the power transistor T3 is essentially measured directly and converted to a binary value with the ADC 145, considerably simplifying the voltage monitor circuitry.

[0098] FIG. 8A is a circuit schematic for another example of a precision supply circuit 700 that can be operated in current-control mode, as described for the supply circuit 100 of FIG.2, or in voltage-control mode described further below. The precision supply circuit 700 can be used in the image-acquisition system 200 of FIG. 3. The precision supply circuit 700 comprises subcircuits also used in the precision supply circuit 100 of FIG. 2. For example, the precision supply circuit 700 comprises a precision current controller 110, a voltage monitor 140, and a programmable voltage source 170. These subcircuits function as described in connection with the precision supply circuit 100 of FIG. 2 and need not be described again. The precision supply circuit 700 further comprises a mode-switching circuit 730, which increases the functionality of the precision supply circuit 700 of FIG. 7 beyond the precision supply circuit 100 of FIG. 2. The precision supply circuit 700 can be used inAttorney Docket No. OPTN-005W001the system of FIG. 3 in place of the precision supply circuit 100.

[0099] The mode-switching circuit 730 comprises a mode-switch transistor T10, a first switch 734, and a second switch 736. The first mode switch 734 and second mode switch 736 can be identical switch devices and the same as used for the first switch 112 and second switch 114 of the precision current controller 110, though different switches can be used in some implementations. The mode-switch transistor T10 and second mode switch 736 can be toggled by a first logic input (VMODE input 701) to the precision mode-switching circuit 730 to place the supply circuit 700 in voltage-control mode.

[0100] A first input signal can be applied to the VMODE input 701 (e.g., a low signal) for a first operational state. In this state, the mode-switch transistor T10 is placed in a nonconducting (open) state and the second mode switch 736 is configured to receive (through resistor R22) voltage at the low side of the load 105 (cathode of the LED in this example). With the VMODE input 701 in this first operational state, the precision supply circuit 700 can operate in current-control mode as described elsewhere herein.

[0101] When the FIRE input 702 is in a first state (e.g, a low logic signal), the first mode switch 734 can be toggled to a position where the compliance voltage Vcomp is monitored at the output of the programmable voltage source 170 (through resistor R28) by the ADC 145. When the FIRE input 702 is in a second state (e.g, to deliver a pulse of current to the load) the first mode switch 734 can be configured to connect to the output of the second mode switch 736, as is shown in the schematic of FIG. 8A. In this configuration of the modeswitch transistor T10, first mode switch 734, and second mode switch 736, the precision supply circuit 700 can operate in current-control mode exactly as described for the precision supply circuit 100 of FIG. 2, and the voltage at the low side of the load 105 is monitored. Resistors R22 and R26 form a voltage divider to scale the voltage at the low side of the load 105 for detection by the ADC 145.

[0102] Further, the mode-switching circuit 730 can be used to operate the precision supply circuit 700 in the second, voltage-control mode of operation. To initiate this mode of operation, a voltage-control signal can be applied to the VMODE input 701, raising the input and toggling the transistor T10 to a fully conducting state. A signal can also be applied to the FIRE input to toggle the first mode switch 734 to connect to the second mode switch 736. Placing the mode-switch transistor T10 in a fully conducting state pulls down the inverting input to the op-amp 120, disables the feedback circuit 125, drives the op-amp 120 to its railAttorney Docket No. OPTN-005W001quickly, and fully turns on transistor T3, allowing current to flow through the load 105. The current flowing through the load 105 will continue until voltage is removed from the VMODE input 701, turning off the mode-switch transistor T10 and turning off transistor T3. The voltage applied to the load in the voltage-control mode of operation is set by the valued programmed into the programmable voltage source 170.

[0103] The voltage-control signal applied to VMODE input 701 can also toggle the second mode switch 736 to connect to a sensing node 126 between transistor T3 and resistor R16 in a circuit path carrying current that has passed through the load 105. Also, the signal applied to VMODE input 701 initiates a pulse of current through the load 105. In this configuration, the voltage at the sensing node 126 can monitored by the ADC 145 during the pulse of current through the load. In some cases, the voltage at the sensing node 126 is monitored repeatedly during the pulse of current so that the amount of current flowing through the load 105 can be determined repeatedly during the pulse, limited only by the data acquisition rate of the ADC 145 and related data handling electronics (using Ohm’s law and the resistance value(s) R16, R18). Since the transistor T3 is fully on, its resistance Ros.on is essentially a fixed value for most of the duration of the pulse. The voltage drop across the combined resistors R16, R18 or the single resistor R18 (when transistor T4 is on) can be detected by the ADC 145. Since the values of resistor R16 and resistor R18 are known, the current IR passing through the load 105 and transistor(s) T3, or T3 and T4, can be determined very accurately by the controller 210 using Ohm’s law. Further, the voltage Vmat the output of the load 105 can be computed by calculating the voltage drop across the transistor T3 ('T RDS ,on) and adding it to the voltage measured at the sensing node 126 by the ADC 145. When T4 is driven fully on, then a voltage drop across its drain and source terminals can be determined readily.

[0104] With measurements of the voltage at sensing node 126 and computations to determine the voltage drop across transistors T3 and T4, power calculations can be done to keep the load 105 and transistor(s) T3, T4 operating at safe power levels and to avoid damaging these components, as described above.

[0105] Additionally, any droop in compliance voltage applied to the load 105 can be detected during application of the compliance voltage and current to the load 105. Such a droop will show up in the measurement of voltage at the sensing node 126. When the VMODE input 701 returns to its previous state and the FIRE input 702 is such that the first mode switch 734 connects to the compliance voltage output (through resistor R28), compliance voltage recovery between pulses can be monitored by the ADC 145. Resistor R28 can form a voltageAttomey Docket No. OPTN-005W001divider with resistor R26 to scale the detected compliance voltage for input to the ADC 145.

[0106] Operation of the precision supply circuit 700 in voltage-control mode can be advantageous when applying very short pulses of current (on the order of 10’ s of microseconds or less) to the load and also when applying pulses of long duration (e.g., 100’s of milliseconds or longer) to the load 105. In some implementations, pulse durations less than 10 microseconds and even less than 1 microsecond can be applied as drive pulses to the precision supply circuit 700 (e.g., at the FIRE input 702 and VMODE input 701) and the supply circuit 700 can gate pulses of current through the load 105 having durations less than 10 microseconds and even less than 1 microsecond, respectively in response to voltagecontrol signals applied to the VMODE input 701. When the supply circuit 700 is operated in voltage-control mode, the feedback circuit 125 with op-amp 120 becomes disabled, allowing a faster response time by the precision supply circuit 700 to an input pulse.

[0107] An applied pulse to the FIRE input 702 toggles two switches in the supply circuit 700: the first switch 112 and the first mode switch 734. The first switch 112 of the current controller 110 can be toggled by the FIRE input 702 from a (1) first position in which the first switch 112 receives a fixed voltage bias from the voltage divider 108 for establishing the standby current in transistor T3 to a (2) second position in which the first switch 112 receives a signal applied to the PWM I input of the supply circuit 700. In voltage-control mode, the signal applied to the PWM I input can have an average voltage greater than the reference voltage applied to the inverting terminal of the op-amp 120 by the mode-switch transistor T10 (nearly ground potential in the illustrated example, except for any small voltage drop across transistor T10). Since the inverting input of the operational amplifier 120 is pulled down (in this example) via transistor T10 when the supply circuit 700 is in voltage-control mode, the operational amplifier 120 is driven to its rail voltage by the application of PWM I to the non-inverting input of the op-amp. The speed at which the op-amp 120 goes to the rail voltage is limited only by the op-amp’s slew rate. When the op-amp reaches the rail voltage, there is no overshoot or oscillations. Because the feedback circuit 125 is disabled, there is no feedback-related delay in driving the operational amplifier 120 to its rail voltage, thus allowing shorter drive pulses and shorter pulses of current delivered to the load 105. The recovery of the operational amplifier 120 after application of the drive pulse may limit the turn-off time of the supply circuit 700, however the recovery time of the op-amp can generally be faster than the loop bandwidth of the feedback circuit 125.

[0108] When the operational amplifier 120 is driven to its rail voltage, the output of the op-Attorney Docket No. OPTN-005W001amp drives transistor T3 into saturation (fully on and conducting). As such, the voltage drop VDS across transistor T3 becomes small and dependent on the “on” resistance RDS, on of the transistor (which can be a few milliohms). Thus, power dissipation in the supply circuit 700 is greatly reduced in voltage-control mode compared to current-control mode. Accordingly, longer pulse durations can be handled by the supply circuit 700 in voltage mode with reduced risk of overheating the transistor T3 and transistor T4 (if activated).

[0109] Although the first switch 734 and the second switch 736 of the mode-switching circuit are tied with other components (first switch 112, T10) to the FIRE input 702 and VMODE input 701, respectively, they need not be tied to the other components. The first switch 734 and the second switch 736 can be independently controlled from FIRE input 702 and the VMODE input 701 by adding two more logic input signals to the precision supply circuit 700. Such an implementation can allow the mode-switch transistor T10 to be operated independently of the second switch 736 and the first switch 734 to be operated independently of the first switch 112 of the current controller 110. Such independent control can be used to gather more information about power dissipation and operation of the supply circuit 700. For example, independent application of logic control signals to the first switch 734 and second switch 736 can allow three different voltage measurements by the ADC 145. The first measurement can obtain the compliance voltage Vc at the output of the programmable voltage source 170 as described above, e.g., to monitor recovery voltage between pulses. A second voltage measurement can obtain the voltage Vm at the low side of the load (e.g., the cathode voltage when the load comprises an LED lamp). A third voltage measurement can obtain the voltage Vs at the sensing node 126 at the beginning of the pulse and / or during the pulse. These measurements could be made at any time during operation of the precision supply circuit 700. In some applications, substantial capacitance can be coupled to the programmable voltage source 170 and back up the compliance voltage so that Vcomp will not change by more than 5% during the pulse in some cases, not more than 3% in some cases, not more than 2% in some cases, not more than 1% in some cases, and even not more than 0.5% in some cases. In some cases, the variation in Vcomp is no greater than 100 mV, no greater than 20 mV, no greater than 5 mV, or even no greater than 1 mV during the pulse. “During the pulse” in this context means over a majority (more than 50%) of the time between a turnon of the pulse to 95% peak value (time ti in FIG. 1A) and the following turn-off of the pulse when dropping to 95% peak value (time L). In voltage-control mode, since T3 is in saturation with low on resistance Vm and Vs can exhibit negligible difference.Attorney Docket No. OPTN-005W001

[0110] Another feature of the precision supply circuit 700 of FIG. 8A is a communicative, single-wire connection 750 to the load 105 for purposes of retrieving information from the load. Some loads (such as packaged LED lamps 710) can comprise memory 715 (e.g., 1-wire memory) storing operating information about the load. In the case of an LED lamp 710, the operating information might include tables of operating parameters, e.g., maximum operating voltage, maximum amount of current for a given amount of time, maximum continuous power, maximum instantaneous power, etc. Single-wire (1-wire) communications can be used to retrieve such operating information over the single-wire connection 750. The operating information can be used by a controller 210 to monitor and maintain safe operating levels for the load 105 and power transistors T3, T4 as described above.[OHl] Data stored in memory 715 can also include identifying information for the load (such as a unique identifier or serial number). In complex systems with many loads which could have similar outward appearance but different electrical characteristics, the identifying information can be helpful to a system administrator or technician installing and / or servicing the system. The identifying information can be used to locate and keep track of each load 105 and for issuing commands by the system controller 210 to one or more targeted loads. In some cases, data can be written to the memory 715 by the controller 210.

[0112] FIG. 8B illustrates a circuit schematic for another implementation of the precision supply circuit 700b. The precision supply circuit 700b comprises subcircuits also used in the precision supply circuit 100 of FIG. 2 and the precision supply circuit 700 of FIG. 8A. For example, the precision supply circuit 700 comprises a precision current controller 110, a voltage monitor 140, and a programmable voltage source 170. The same subcircuits need not be described again. The precision supply circuit 700b can be used in the system of FIG. 3 in place of the precision supply circuit 100. The precision supply circuit 700b of FIG. 8B also includes a single-wire connection 750 to the load 105 for purposes of retrieving information from the load, as described above in connection with the precision supply circuit 700 of FIG.8A.

[0113] The mode-switching circuit 731 for the precision supply circuit 700b of FIG. 8B differs from the mode-switching circuit 730 of the precision supply circuit 700 shown in FIG. 8A. The mode-switching circuit 731 comprises a transistor pair T10, T13 connected to the voltage-control, VMODE input 701. The transistor pair comprises a field-effect transistor (FET) having a drain coupled to the base terminal of a pup bipolar junction transistor (BJT) T13. In the example circuit, a high voltage applied to the VMODE input 701 turns on theAttorney Docket No. OPTN-005W001mode-switch transistor T10 pulling down the base terminal of the pnp bipolar junction transistor T13, which turns on BJT T13. When BJT T13 turns on, a high voltage is applied directly to the gate of transistor T3, bypassing the op-amp 120 and driving T3 into saturation. In this method of switching to voltage-control mode, the op-amp 120 is not disconnected from the control terminal of transistor T3. Advantageously, the op-amp turns fully off quickly, rather than going into saturation. Recovery of the op-amp 120 from a fully off state can be appreciably faster than recovery from saturation.

[0114] Driving T3 into saturation allows current to flow through the load 105. The voltage applied to the load 105 is determined by the programmable voltage source 170. As described above, this voltage can be programmed by adjusting the duty cycle of a signal applied to the PWM V input. Removing voltage from VMODE input 701 turns off transistors T10, T13, and T3, terminating current flow through the load 105. Sensing of voltages (compliance voltage Vcomp and voltage at the sensing node 126) can be carried out as described above in connection with FIG. 8A along with operation of switch 734 and switch 736.

[0115] Using the two transistors T10, T13 can improve the speed of the precision supply circuit 700b over the precision supply circuit 700 shown in FIG. 8A. Using the two transistors T10, T13 can avoid relying on the feedback loop transition time and slew rate of the operational amplifier 120 for the implementation of FIG. 8A. Accordingly, even shorter pulses of current at a programmed voltage can be applied to the load with the precision supply circuit 700b of FIG. 8B than is possible for the circuit of FIG. 8A. For example, current pulses as short as 50 ns may be applied to the load 105 with the precision supply circuit 700b of FIG. 8B.

[0116] In some implementations, the pulse-width modulation inputs to the precision supply circuits described above can be implemented with digital-to-analog converters. Before, during, and after application of a current pulse through the load 105, the precision supply circuits of FIG. 8A and FIG. 8B can be used as described above to measure voltages across the load 105, across the sense resistors (R16 and R18, or only R18 with R16 shunted by T4), and at the output of the programmable voltage source 170 (compliance voltage Vcomp). Such measurements can be used to monitor any drop in the compliance voltage before and after the pulse to determine whether there is sufficient capacitance to maintain the compliance voltage after both current and voltage shots.Attorney Docket No. OPTN-005W001

[0117] 6. Interfacing with the Precision Supply Circuit

[0118] The precision supply circuits described above can be communicatively coupled to, and interface with, the system controller 210 and camera 220. During operation, there can be significant information exchanged between any of the precision supply circuits and a system controller 210 and / or camera 220. The information can include, but is not limited to, various parameters, data, flags, settings, etc. Some examples of device interfacing are described below.

[0119] 6.1 Configuration and Protection Information

[0120] Protection parameters for a precision supply circuit can be in memory that can be accessed by the controller 210. At least some of the parameters in Table 1 and / or other protection parameters can be stored in the non-volatile memory of the controller 210 (such as a protection parameter register indicated by Table 1, though more or less information can be included in the register than listed in the tables). These parameters can be instantiated separately for each precision supply circuit in a system, while in cameras, only the flags, Cvmin, and Cvmax parameters can be instantiated separately - the remaining parameters can be shared.Table 1: NV Protection Parameters

[0121] In example cameras, the shared protection parameters (Vslope, Voffsel, FETcooling, and FETthresh) begin at byte offset 199 of the configuration page, while the flag parameters (flags') can be stored at byte offset 206 for strobe controller 0 and byte offset 207 for strobe controller 1, and the Cvmin and Cvmax parameters can be stored at byte offset 208 and 210 for strobe controller 0 and 1, respectively.Attorney Docket No. OPTN-005W001Table 2: Protection Status Register

[0122] Table 2 depicts examples of protection status information that can be stored in memory (e.g., a protection status register). Bits 1..0 of the flags parameter indicate what protection is incorporated into the precision supply circuit channel. Bit 2 of the flags parameter indicates whether the LampCooling and LampThresh values received by the device are encoded linearly (ranging to 65.535 watts and 274.877 joules, respectively) or exponentially (ranging to 1048 watts and 4,397,777 joules, respectively). Setting bit 3 indicates that the precision supply circuit supports an adjustable compliance rail, while setting bit 4 indicates if precision supply circuit information is included in the statistics packet (for cameras only). The remaining flags bits can be reserved.

[0123] Table 3 provides an example of configuration flags which can be stored in a configuration flags register. More or fewer configuration flags can be included in the register than listed in the table.Table 3: Configuration flags

[0124] 6.2 Control

[0125] Certain device protection values can be set by the controller 210 through a write feature request to the precision supply circuit. The corresponding control parameters can beAttorney Docket No. OPTN-005W001added at word offset 10 through 12 of the write feature request payload, as exemplified in Table 4, though more or less information can be included in a register than listed in the table.Table 4: Write Feature Payload

[0126] The LampCooling and LampThresh parameters can be encoded linearly or exponentially, depending on the configuration of the precision supply circuit. In the linear configuration, the LampCooling parameter can be represented in mW (for a range of 0 to 65.535 watts) and the LampThresh parameter can be represented in increments of 4.194303 mJ (for a range of 0 to 274.87371264 joules). In the exponential configuration, the top 2 bits can indicate the power, allowing for power values of x 1, x4, x 16, and x64. For example, a power value of x64 will indicate the LampCooling parameter is represented in increments of 64 mW (for a range of 0 to 1048.512 watts) and the LampThresh parameter can be represented in increments of 268.435392 mJ (for a range of 0 to 4,397.778075648 joules).

[0127] In addition, bit 1 in the ISCmode register can be used to cause an alarm event from the precision supply circuit to be transmitted at the end of every current pulse to the load, not just when the LampThresh or FETthresh energy threshold has been exceeded. Bit 2 in the ISCmode register can be used to enable the lamp protection. Bit 3 in the ISCmode registerAttorney Docket No. OPTN-005W001can be used to activate the lamp for set-up purposes.

[0128] 6.3 Status

[0129] The protection parameters and status can be read by the host controller 210 using a read feature request. Write feature parameters will be read from the same offsets they are assigned in the write feature payload. Non-volatile configuration parameters can be read using the non-volatile memory transfer read feature request. Additional data from the control circuitry can be included in word offsets 13 through 20 of a read feature request payload as indicated in Table 5, though more or less information can be included than listed in the table.Attorney Docket No. OPTN-005W001Table 5: Data for Read Feature Payload

[0130] 6.4 Alarms

[0131] In the event that a precision supply circuit is de-activated because an energy threshold is exceeded, notification in the form of an event packet can be transmitted by the precision supply circuit to the controller 210. For cameras, the event transmit port at index 2 (previously reserved) can be used to send the alarm event for a first precision supply circuit housed in the camera 220, and the event transmit port at index 3 (also previously reserved) can be used to send the alarm event for a second precision supply circuit housed in the camera 220. For some implementations, the event transmit port at index 14 can be used to send an alarm event. The target MAC(s), event ID, etc. can be determined by settings in the Txdescriptor for the assigned port. If no target MAC address is assigned, no event packet willAttorney Docket No. OPTN-005W001be transmitted.

[0132] The alarm event payload can be defined as in Table 6, though more or less information can be included than listed in the table.Table 6: Alarm Event Payload

[0133] The calculated near-instantaneous powers at the load 105 (e.g., LED lamp) and / or power transistors T3, T4 can be represented in units of 1 mW, though other units are possible and the units for the lamp and transistors can be different. The calculated energy for the load and / or power transistors can be represented in units of 64 nJ, though other units are possible and the units for the lamp and transistors can be different.

[0134] 6.5 Statistics

[0135] Cameras with one or more internal, precision supply circuits can be configured to include information about the operation of the circuit(s) in a camera statistics packet. The statistics packet can be transmitted at the end of each image acquisition, for example, or after a sequence of image acquisitions. The statistics packet data can include at least some alarm event payload data, for example, as well as the pulse duration tP(on-time of T3 to conduct current through the load 105). An example of statistics packet data is shown in Table 7, though more or less information can be included in the packet than listed in the table.Attorney Docket No. OPTN-005W001Table 7: Statistics Packet Data

[0136] The precision supply circuit 100, 400 and methods of operating the precision supply circuit can be implemented in various ways, some of which are listed below.(1) A supply circuit (100) comprising: a transistor (T3) arranged to conduct current through a load (105); a feedback circuit (125) to apply a signal to the transistor (T3) to control an amplitude of the current conducted by the transistor, wherein the feedback circuit is configured to: receive a first feedback signal from a first sensing node (126) located in a first current path through which at least a first portion of the current flows when the current flows through the load, or receive a second feedback signal from a second sensing node (124) located in a second current path through which at least a second portion of the current flows when the current flows through the load and when an impedance (R16) between the first sensing node and the second sensing node is bypassed by the second current path.(2) The supply circuit of configuration (1), wherein the feedback circuit comprises: an operational amplifier (120) to receive the first feedback signal and the second feedback signal; and a switch (114) to couple the first sensing node or the second sensing node to a first input terminal of the operational amplifier.(3) The supply circuit of configuration (2) wherein the switch is a first switch, the supply circuit further comprising: a second switch (112) to couple a second input terminal of the operational amplifier to a first input (PWMI) configured to receive a pulse-width-modulated signal or to a reference voltage source arranged to provide a fixed voltage.(4) The supply circuit of configuration (3), further comprising: a current source (133) coupled to the transistor, wherein the fixed voltage causes a standby current to flow through the transistor from the current source and negligible or no current to flow through the load.Attorney Docket No. OPTN-005W001(5) The supply circuit of configuration (2) or (3), wherein the impedance is a first impedance, the supply circuit further comprising: a second impedance (R18) connected in series with the first impedance and located between the second sensing node and a reference potential.(6) The supply circuit of configuration (5), wherein the second impedance is smaller than the first impedance.(7) The supply circuit of any one of configurations (1) through (6), wherein the feedback circuit controls the amplitude of the current to be constant to within 2% for not less than 85% of a pulse during which the current is conducted through the load by the transistor.(8) The supply circuit of any one of configurations (1) through (7), wherein the transistor (T3) is a first transistor, the supply circuit further comprising: a second transistor (T4) configured in the second current path and configured to bypass the second portion of the current in the second current path.(9) The supply circuit of any one of configurations (1) through (8), further comprising a programmable voltage source (170) to apply a voltage to the load.(10) The supply circuit of configuration (9), wherein the programmable voltage source comprises a buck converter.(11) The supply circuit of any one of configurations (1) through (10), further comprising a voltage monitor (140, 440) to detect a voltage at a drain or collector of the transistor.(12) The supply circuit of configuration (11), wherein the voltage monitor comprises an analog-to-digital converter (145) to sample the voltage.(13) The supply circuit of configuration (11), wherein the voltage monitor comprises voltage-to-frequency circuitry (442) and a timer (445) to detect the voltage.(14) The supply circuit of configuration (11) in combination with a controller (210), wherein the controller is configured to repeatedly, for a sequence of sampling intervals; receive a signal from the voltage monitor indicative of the voltage at the drain or collector during a measurement interval that includes at least one sampling interval of the sequence of sampling intervals; compute a power delivered to the load during the measurement interval based, atAttorney Docket No. OPTN-005W001least in part, on the received signal; and compute a power delivered to the transistor based, at least in part, on the received signal.(15) The combination of configuration (14), wherein the controller is further configured to: accumulate a plurality of the computed powers delivered to the load to determine, at least in part, a current energy level of the load; compare the current energy level of the load against an energy limit for the load; and discontinue conducting current through the load by the transistor if the current energy level of the load exceeds the energy limit for the load.(16) The combination of configuration (15), wherein determining the current energy level of the load includes accounting, by the controller, for a thermal power-dissipation rate of the load.(17) A supply circuit (100) comprising: a first transistor (T3) arranged to conduct current through a load (105); a first resistor (R18) in a first circuit path through which at least a first portion of the current flows; a second resistor (R16) connected in series with the first resistor through which at least a second portion of the current flows when connected to the load; a second transistor (T4) arranged to shunt the current around the second resistor; and a feedback circuit (125) to receive a first feedback signal indicative of a first voltage dropped across the first resistor due to the first portion of the current when the second transistor shunts the current around the second resistor and to receive a second feedback signal indicative of a second voltage dropped across a combination of the first resistor and the second resistor due to the second portion of the current when the second transistor does not shunt the current around the second resistor.(18) The supply circuit of configuration (17), wherein the feedback circuit comprises: an operational amplifier (120) to receive the first feedback signal from a first sensing node (124) at a terminal of the first resistor and the second feedback signal from a second sensing node at a terminal of the second resistor; and a switch (114) to couple the first sensing node or the second sensing node to a first input terminal of the operational amplifier.(19) The supply circuit of configuration (18) wherein the switch is a first switch, the supply circuit further comprising: a second switch (112) to couple a second input terminal of the operational amplifier to a first input (PWMI) arranged to receive a pulse-width-modulated signal or to a reference voltage source) arranged to provide a fixed voltage.Attorney Docket No. OPTN-005W001(20) The supply circuit of configuration (19), further comprising a current source (133) coupled to the transistor, wherein the fixed voltage causes a standby current to flow through the transistor from the current source and negligible or no current to flow through the load.(21) The supply circuit of any one of configurations (17) through (20), wherein the second resistor is smaller than the first resistor.(22) The supply circuit of any one of configurations (17) through (21), wherein the feedback circuit controls an amplitude of the current to be constant to within 2% for not less than 85% of a pulse during which the current is conducted through the load by the transistor.(23) The supply circuit of any one of configurations (17) through (22), wherein the transistor (T3) is a first transistor, the supply circuit further comprising: a second transistor (T4) configured in the second current path and configured to bypass the second portion of the current in the second current path.(24) The supply circuit of any one of configurations (17) through (23), further comprising a programmable voltage source (170) to apply a voltage to the load.(25) The supply circuit of any one of configurations (17) through (24), further comprising a voltage monitor (140, 440) to detect a voltage at a drain or collector of the transistor.(26) The supply circuit of any one of configurations (17) through (25) in combination with a controller (210), wherein the controller is configured to repeatedly, for a sequence of sampling intervals: receive a signal from the voltage monitor indicative of the voltage at the drain or collector during a measurement interval that includes at least one sampling interval of the sequence of sampling intervals; compute a power delivered to the load during the measurement interval based, at least in part, on the received signal; and compute a power delivered to the transistor based, at least in part, on the received signal.(27) The combination of configuration (26), wherein the controller is further configured to: accumulate a plurality of the computed powers delivered to the load to determine, at least in part, a current energy level of the load; and compare the current energy level of the load against an energy limit for the load; and discontinue conducting current through the load by the transistor if the current energy level of the load exceeds the energy limit for the load.Attorney Docket No. OPTN-005W001(28) A method of conducting a current through a load, the method comprising: receiving, at a control terminal of a transistor (T3) in a supply circuit, a signal that causes the transistor to conduct the current through a load (105); controlling, with a feedback circuit (125) in the supply circuit and coupled to the transistor (T3), an amplitude of the current conducted by the transistor; receiving in the feedback circuit a first feedback signal from a first sensing node (126) located in a first current path through which at least a first portion of the current flows; receiving in the feedback circuit a second feedback signal from a second sensing node (124) located in a second current path through which at least a second portion of the current flows; and directing the second portion of the current around an impedance (R16) connected between the first sensing node and the second sensing node when receiving the second feedback signal.(29) The method of (28), wherein the feedback circuit includes an operational amplifier (120) and a switch (114), the method further comprising: receiving the first feedback signal or the second feedback signal at a first input terminal of the operational amplifier; coupling, with the switch, the first sensing node to the first input terminal to receive the first feedback signal; and coupling, with the switch, the second sensing node to the first input terminal to receive the second feedback signal.(30) The method of (29), wherein the switch is a first switch, the method further comprising: coupling, with a second switch (112), a second input terminal of the operational amplifier to a first input (PWMI) of the supply circuit that is configured to receive a pulse-width-modulated signal; and coupling, with the second switch (112), the second input terminal of the operational amplifier to a reference voltage source arranged to provide a fixed voltage.(31) The method of (30), further comprising: delivering, with a current source (133), a standby current to flow through the transistor in response to coupling the second input terminal of the operational amplifier to the second input, such that negligible or no current flows through the load.(32) The method of any one of (28) through (31), further comprising: controlling, with the feedback circuit, the amplitude of the current to be constant to within 2% for not less than 85% of a pulse during which the current is conducted through the load by the transistor.(33) The method of any one of (28) through (32), wherein the transistor (T3) is a first transistor, the method further comprising: bypassing, with a second transistor (T4)Attorney Docket No. OPTN-005W001configured in the second current path, the second portion of the current in the second current path.(34) The method of any one of (28) through (33), further comprising: detecting, with a voltage monitor (140, 440), a voltage at a drain or collector of the transistor.(35) The method of any one of (28) through (31), further comprising: receiving, with a controller that is communicatively coupled to the supply circuit, a signal from the voltage monitor indicative of the voltage at the drain or collector during a measurement interval that includes at least one sampling interval of a sequence of sampling intervals; computing, with the controller, a power delivered to the load during the measurement interval based, at least in part, on the received signal; and computing, with the controller, a power delivered to the transistor based, at least in part, on the received signal.(36) The method of (35), further comprising: accumulating, with the controller, a plurality of the computed powers delivered to the load to determine, at least in part, a current energy level of the load; comparing, with the controller, the current energy level of the load against an energy limit for the load; and issuing a command to from the controller to the supply circuit to discontinue conduction of the current through the load by the transistor if the current energy level of the load exceeds the energy limit for the load.(37) The method of (36), further comprising: accounting, by the controller, for a thermal power-dissipation rate of the load when determining the current energy level of the load.(38) A camera (220) comprising: a housing (221); an imaging array (222) to acquire images, the imaging array mounted in the housing; a supply circuit (100, 400) mounted in the housing to conduct a pulse of current through a load (105) that generates light so as to illuminate an object (230) imaged by the imaging array during an image-acquisition period of the imaging array, the image-acquisition period comprising an interval of time during which one frame of image data is captured by the imaging array, wherein the supply circuit comprises: a transistor (T3) arranged to conduct current through a load (105); a feedback circuit (125) to apply a signal to the transistor (T3) to control an amplitude of the current conducted by the transistor, wherein the feedback circuit is configured to: receive a first feedback signal from a first sensing node (126) located in a first current path through which at least a first portion of the current flows when the current flows through the load, and receive a second feedback signal from a second sensing node (124) located in a second current path through which atAttorney Docket No. OPTN-005W001least a second portion of the current flows when the current flows through the load and when an impedance (R16) between the first sensing node and the second sensing node is bypassed by the second current path.(39) The camera of configuration (38), further comprising: a mount (224) to receive a lens assembly; a first connector (228) coupled to the housing to communicatively couple to a controller; and a second connector (227) coupled to the housing to connect to the load.(40) The camera of configuration (39), wherein the first connector receives power-over-ethernet.(41) The camera of configuration (38) or (39), wherein the housing has a maximum edge dimension no larger than 50 mm.(42) The camera of any one of configurations (38) through (41), wherein the feedback circuit comprises: an operational amplifier (120) to receive the first feedback signal and the second feedback signal; and a switch (114) to couple the first sensing node or the second sensing node to a first input terminal of the operational amplifier.(43) The camera of configuration (42) wherein the switch is a first switch, the supply circuit further comprising: a second switch (112) to couple a second input terminal of the operational amplifier to a first input (PWMI) configured to receive a pulse-width-modulated signal or a to a reference voltage source arranged to provide a fixed voltage.(44) The camera of configuration (43), further comprising: a current source (133) coupled to the transistor, wherein the fixed voltage causes a standby current to flow through the transistor from the current source and negligible or no current to flow through the load.(45) The camera of any one of configurations (38) through (44), wherein the impedance is a first impedance, the supply circuit further comprising: a second impedance (R18) connected in series with the first impedance and located between the second sensing node and a reference potential.(46) The camera of configuration (45), wherein the second impedance is smaller than the first impedance.Attorney Docket No. OPTN-005W001(47) The camera of any one of configurations (38) through (46), wherein the feedback circuit controls the amplitude of the current to be constant to within 2% for not less than 85% of a pulse during which the current is conducted through the load by the transistor.(48) The camera of any one of configurations (38) through (47), wherein the transistor (T3) is a first transistor, the supply circuit further comprising: a second transistor (T4) configured in the second current path and configured to bypass the second portion of the current in the second current path.(49) The camera of any one of configurations (38) through (48), further comprising a programmable voltage source (170) to apply a voltage to the load.(50) The camera of any one of configurations (38) through (49), further comprising a voltage monitor (140, 440) to detect a voltage at a drain or collector of the transistor.(51) The camera of configuration (50) in combination with a controller (210), wherein the controller is configured to repeatedly, for a sequence of sampling intervals: receive a signal from the voltage monitor indicative of the voltage at the drain or collector during a measurement interval that includes at least one sampling interval of the sequence of sampling intervals; compute a power delivered to the load during the measurement interval based, at least in part, on the received signal; and compute a power delivered to the transistor based, at least in part, on the received signal.(52) The combination of configuration (51), wherein the controller is further configured to: accumulate a plurality of the computed powers delivered to the load to determine, at least in part, a current energy level of the load; compare the current energy level of the load against an energy limit for the load; and discontinue conducting current through the load by the transistor if the current energy level of the load exceeds the energy limit for the load.(53) A method of operating a camera, the method comprising: receiving, at a control terminal of a transistor (T3) in a supply circuit, a signal that causes the transistor to conduct a pulse of current through a load (105); controlling, with a feedback circuit (125) coupled to the transistor (T3), an amplitude of the pulse of current conducted by the transistor; receiving in the feedback circuit a first feedback signal from a first sensing node (126) located in a first current path through which at least a first portion of the pulse of current flows; receiving in the feedback circuit a second feedback signal from a second sensing node (124) located in aAttorney Docket No. OPTN-005W001second current path through which at least a second portion of the pulse of current flows; directing the second portion of the pulse of current around an impedance (R16) connected between the first sensing node and the second sensing node when receiving the second feedback signal; and acquiring a frame of image data of an object with an imaging array of the camera while the pulse of current is conducted through the load.(54) The method of (53), further comprising: biasing the transistor in a ready state after conducting the pulse of current through the load; providing a standby current to the transistor from a current source (133) while the transistor is in the ready state, such that negligible or no current flows through the load while the transistor is in the ready state.(55) The method of (53) or (54), wherein the feedback circuit includes an operational amplifier (120) and a switch (114), the method further comprising: receiving the first feedback signal or the second feedback signal at a first input terminal of the operational amplifier; coupling, with the switch, the first sensing node to the first input terminal to receive the first feedback signal; and coupling, with the switch, the second sensing node to the first input terminal to receive the second feedback signal.(56) The method of (55), wherein the switch is a first switch, the method further comprising: coupling, with a second switch (112), a second input terminal of the operational amplifier to a first input (PWMI) of the supply circuit that is configured to receive a pulse-width-modulated signal; and coupling, with the second switch (112), the second input terminal of the operational amplifier to a reference voltage source arranged to provide a fixed voltage.(57) The method of any one of (53) through (56), further comprising: controlling, with the feedback circuit, the amplitude of the pulse of current to be constant to within 2% for not less than 85% of a pulse during which the pulse of current is conducted through the load by the transistor.(58) The method of any one of (53) through (57), wherein the transistor (T3) is a first transistor, the method further comprising: bypassing, with a second transistor (T4) configured in the second current path, the second portion of the pulse of current in the second current path.(59) The method of any one of (53) through (58), further comprising detecting, with a voltage monitor (140, 440), a voltage at a drain or collector of the transistor.Attorney Docket No. OPTN-005W001(60) The method of (59), further comprising: receiving, with a controller that is communicatively coupled to the supply circuit, a signal from the voltage monitor indicative of the voltage at the drain or collector during a measurement interval that includes at least one sampling interval of a sequence of sampling intervals; computing, with the controller, a power delivered to the load during the measurement interval based, at least in part, on the received signal; and computing, with the controller, a power delivered to the transistor based, at least in part, on the received signal.(61) The method of (60), further comprising: accumulating, with the controller, a plurality of the computed powers delivered to the load to determine, at least in part, a current energy level of the load; comparing, with the controller, the current energy level of the load against an energy limit for the load; and issuing a command to from the controller to the supply circuit to discontinue conduction of the pulse of current through the load by the transistor if the current energy level of the load exceeds the energy limit for the load.(62) The method of (61), further comprising accounting, by the controller, for a thermal power-dissipation rate of the load when determining the current energy level of the load.

[0137] 7. Conclusion

[0138] While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the function and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application or applications for which the inventive teachings is / are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and / or method described herein. In addition, any combination of two or more such features,Attorney Docket No. OPTN-005W001systems, articles, materials, kits, and / or methods, if such features, systems, articles, materials, kits, and / or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

[0139] Also, various inventive concepts may be embodied as one or more methods, of which an example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

[0140] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and / or ordinary meanings of the defined terms.

[0141] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

[0142] The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and / or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and / or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0143] As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when separating items in a list, “or” or “and / or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of’ or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” orAttorney Docket No. OPTN-005W001“exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[0144] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and / or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0145] In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of’ and “consisting essentially of’ shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.What is claimed is:

Claims

Attorney Docket No. OPTN-005W001CLAIMS1. A supply circuit (700, 700b) comprising:a power transistor (T3) arranged to conduct current through a load (105) and through a first sensing node (126) and through a second sensing node (124);a programmable voltage source (170) to apply a selected compliance voltage to an input of the load;a feedback circuit (125) to apply a signal to a control terminal of the power transistor to control an amplitude of the current conducted by the power transistor through the load based upon a first voltage sensed at the first sensing node or a second voltage sensed at the second sensing node, such that the feedback circuit operates in a current-control mode; and a mode switching circuit (730) to disable the feedback circuit such that the supply circuit operates in voltage-control mode, wherein the compliance voltage applied to the load is determined by the programmable voltage source.

2. The supply circuit of claim 1, further comprising:a first resistor (R16) connected between the first sensing node;a second resistor (R18) connected between the second sensing node and a reference potential; anda shunt transistor (T4) connected in parallel with the first resistor to bypass the current around the first resistor when the shunt transistor is turned on, wherein:a first amount of the current flowing through the load produces a first voltage value at the first sensing node, andbypassing the first resistor with the shunt transistor allows a larger second amount of the current to flow through the load and produce the first voltage value at the second sensing node, thereby increasing a dynamic range of the supply circuit.

3. The supply circuit of claim 2, wherein a resistance of the second resistor is less than one-quarter the resistance of the first resistor.

4. The supply circuit of any one of claims 1 through 3, further comprising:an operational amplifier (120) arranged in the feedback circuit and having an output arranged to drive the control terminal of the power transistor;a first switch (112) to couple a first input terminal of the operational amplifier to a first input (PWMI) configured to receive a pulse-width-modulated signal or to a reference voltage source arranged to provide a fixed voltage; andAttorney Docket No. OPTN-005W001a second switch (114) to couple the first sensing node or the second sensing node to a second input terminal of the operational amplifier such that the operational amplifier can receive a signal indicative of the first voltage or the second voltage to control the amplitude of the current delivered to the load.

5. The supply circuit of claim 4, further comprising:a mode-switch transistor (T10) arranged to connect the second input terminal of the operational amplifier to a reference potential and thereby cause the operational amplifier to go into saturation.

6. The supply circuit of claim 4, further comprising:a mode-switch transistor (T10) arranged to cause application of a turn-on voltage to the control terminal of the power transistor, wherein the application of the turn-on voltage bypasses the operational amplifier.

7. The supply circuit of claim 6, further comprising:a voltage monitor 140 configured to monitor at least one voltage in the supply circuit; a first mode switch (734) arranged in the mode switching circuit to couple an input to the voltage monitor to a second mode switch (736) arranged in the mode switching circuit, or to couple the input to the voltage monitor to an output of the load; anda second mode switch (736) arranged in the mode switching circuit to couple an input of the first mode switch to the first sensing node or to couple the input of the first mode switch to an output of the load.

8. The supply circuit of claim 7, wherein a single control input to the supply circuit is arranged to control activation of the mode-switch transistor and activation of the second mode switch.

9. The supply circuit of claim 7 or 8, wherein the voltage monitor comprises an analog-to-digital converter (145).

10. The supply circuit of claim 7 or 8, wherein the voltage monitor comprises a voltage-to-frequency converter.

11. The supply circuit of claim 7 or 8, in combination with a controller (210), wherein the supply circuit further comprises:Attorney Docket No. OPTN-005W001a first resistor (R16) connected between the first sensing node; anda second resistor (R18) connected between the second sensing node and a reference potential, and wherein the controller is configured to:receive measurements of an output voltage Vmat the output of the load from the voltage monitor;compute a voltage drop across the load;determine a sensed voltage Vs at the first sensing node;compute a load current delivered to the load based at least on a resistance value of the second resistor;compute a power delivered to the load current and the voltage drop across the load; andcompare the computed power delivered to the load with a power limit value for the load.

12. The supply circuit of claim 12, wherein the controller is further configured to:compute a voltage drop across the power transistor;compute a power delivered to the power transistor; andcompare the computed power delivered to the power transistor with a power limit value for the power transistor.

13. The supply circuit of claim 12, wherein the controller is further configured to:receive measurements of the compliance voltage to be applied to the input of the load prior to conducting a pulse of the current through the load; anddetermine if the compliance voltage has recovered from a previous pulse of the current applied to the load.

14. The supply circuit of claim 7 or 8, in combination with a camera, wherein the supply circuit and the camera are configured such that:the supply circuit applies a pulse of current to the load during a time when the camera acquires an image, andthe load comprises an illumination source arranged to illuminate an object imaged by the camera.

15. The supply circuit of claim 4, further comprising:a current source (133) coupled to the power transistor, wherein the fixed voltageAttorney Docket No. OPTN-005W001causes a standby current to flow through the transistor from the current source and negligible or no current to flow through the load.

16. A method of operating the supply circuit of claim 1, the method comprising:conducting, with a power transistor (T3), current through a load (105) and through a first sensing node (126) and through a second sensing node (124) of the supply circuit;applying, with a programmable voltage source (170), a selected compliance voltage to an input of the load;applying, with a feedback circuit (125), a signal to a control terminal of the power transistor;controlling, with the feedback circuit, an amplitude of the current conducted by the power transistor through the load based upon a first voltage sensed at the first sensing node or a second voltage sensed at the second sensing node, such that the feedback circuit operates in a current-control mode; anddisabling, with a mode switching circuit (730), the feedback circuit such that the supply circuit operates in voltage-control mode, wherein the compliance voltage applied to the load is determined by the programmable voltage source.

17. The method of claim 16, wherein a first resistor (R16) is connected between the first sensing node and the second sensing node, the method further comprising:bypassing, with a shunt transistor (T4), flow of the current around the first resistor such that the amplitude of the current conducted by the power transistor through the load based on the second voltage sensed at the second sensing node.

18. The method of claim 16, wherein the feedback circuit comprises an operational amplifier (120), the method further comprising:coupling, with a first switch (112), a first input terminal of the operational amplifier to a first input (PWMI) configured to receive a pulse-width-modulated signal;filtering the pulse-width-modulated signal; andcoupling, with a second switch (11 ), the first sensing node or the second sensing node to a second input terminal of the operational amplifier such that the operational amplifier can receive a signal indicative of the first voltage or the second voltage to control the amplitude of the current delivered to the load.Attorney Docket No. OPTN-005W00119. The method of claim 18, further comprising:applying, using a mode-switch transistor, a control signal directly to the control terminal of the power transistor without disconnecting the operational amplifier to disable the feedback circuit and operate the supply circuit in voltage-control mode.

20. The method of claim 19, further comprising:monitoring, with a voltage monitor (140), a voltage at the first sensing node repeatedly during a pulse of the current;computing repeatedly, with a controller, an amount of the current flowing through the load during the pulse of the current;determining repeatedly, with the controller, an amount of power delivered to the load during the pulse of current; andcomparing the amount of power delivered to the load to a power limit value for the load.

21. The method of claim 19, further comprising:monitoring, with a voltage monitor (1 0), a voltage at the first sensing node repeatedly during a pulse of the current;computing repeatedly, with a controller, an amount of the current flowing through the power transistor during the pulse of the current;determining repeatedly, with the controller, an amount of power delivered to the power transistor during the pulse of current; andcomparing the amount of power delivered to the power transistor to a power limit value for the power transistor.

22. The method of claim 19, further comprising:monitoring, with a voltage monitor (140), a voltage at an input to the load following a pulse of the current to determine if the voltage at the input of the load recovers to the selected compliance voltage prior to application of a subsequent pulse of the current to the load.

23. The method of any one of claims 16 through 22, wherein the load comprises a lightemitting diode (LED), the method further comprising, while the supply circuit is operating in current-control mode,:applying a pulse of the current to the LED to illuminate an object; andAttorney Docket No. OPTN-005W001acquiring an image of the object with a camera while the object is illuminated with the LED.

24. The method of any one of claims 16 through 22, wherein the load comprises a lightemitting diode (LED), the method further comprising, while the supply circuit is operating in voltage-control mode, :applying a pulse of the current to the LED to illuminate an object; andacquiring an image of the object with a camera while the object is illuminated with the LED.

25. A method of operating the supply circuit of claim 1, the method comprising:conducting, with a power transistor (T3), current through a load (105) and through a first sensing node (126) and through a second sensing node (124) of the supply circuit;applying, with a programmable voltage source (170), a selected compliance voltage to an input of the load;applying, with an operational amplifier (120) of a feedback circuit (125), a first signal to a control terminal of the power transistor;controlling, with the feedback circuit, an amplitude of the current conducted by the power transistor through the load based upon a first voltage sensed at the first sensing node or a second voltage sensed at the second sensing node, such that the feedback circuit operates in a current-control mode; andwithout disconnecting the operational amplifier, applying a second signal directly to the control terminal of the power transistor to operate the supply circuit in voltage-control mode, wherein the compliance voltage applied to the load is determined by the programmable voltage source.

26. A method of operating the supply circuit of claim 1, the method comprising:conducting, with a power transistor (T3), current through a load (105) and through a first sensing node (126) and through a second sensing node (124) of the supply circuit;applying, with a programmable voltage source (170), a selected compliance voltage to an input of the load;applying, with an operational amplifier (120) of a feedback circuit (125), a signal to a control terminal of the power transistor;controlling, with the feedback circuit, an amplitude of the current conducted by the power transistor through the load based upon a first voltage sensed at the first sensing node orAttorney Docket No. OPTN-005W001a second voltage sensed at the second sensing node, such that the feedback circuit operates in a current-control mode; anddriving, with a mode switching circuit (730), the operational amplifier into saturation and keeping the operational amplifier in saturation to operate the supply circuit in voltagecontrol mode, wherein the compliance voltage applied to the load is determined by the programmable voltage source.

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