Driver circuit and method for semiconductor laser

Abstract

A driver circuit (10, 100) may include a power controller (40) to convert an input power into an output voltage; a high frequency switch (42) providing a short duration pulse of the output voltage such that a pulsed load current flows through the load; a current sensor (44) generating a signal representative of the pulsed load current; a sample and hold circuit (46) that samples a signal representing the pulse load current in synchronization with the high-frequency switch and holds a sampled signal value; and a controller (20) responsive to the sampled signal value and applying a control signal to the power controller to generate a desired output voltage and to the high frequency switch and the sample and hold circuit to control the pulsed load current to a predetermined value. A corresponding method (200) and efficiency improver are disclosed. The load may include a semiconductor laser diode or a light emitting diode.

Description

[0001] This application claims the benefit of and priority to U.S. patent application No. 18 / 409,324, filed on January 10, 2024, entitled “DRIVERCIRCUIT AND METHOD FOR ASEMICONDUCTOR LASER,” which claims the benefit of and priority to U.S. patent application No. 63 / 438,834, filed on January 13, 2023, entitled “DRIVER CIRCUIT AND METHOD FOR ASEMICONDUCTOR LASER,” the entire contents of each of which are hereby incorporated by reference herein for all purposes.

[0002] The present invention relates to a driver circuit, and in particular to a driver circuit for a load or a semiconductor laser and a method thereof.

[0003] Semiconductor lasers are widely used in a variety of electronic devices, including, for example, flashlights, gun sights, laser pointers, industrial tools, and the like. For each device, the output power (both peak and average) of the laser must be limited for safety reasons, such as eye safety and / or to avoid burns. Typically, light-emitting semiconductor diodes are operated at high currents, where they exhibit high efficiency for short periods of time, so a low duty cycle (the ratio of the on-time to the total duration of the drive signal (e.g., current) cycle) reduces the average output power level to within applicable safety limits.

[0004] Conventional semiconductor laser driver circuits typically operate in a relatively low pulse frequency range, such as from continuous wave (CW) up to a few kHz, where conventional driver circuits are able to provide sufficiently controllable pulse drive current within applicable safe power levels. These driver circuits are unable to operate at higher pulse frequencies (e.g., at or above approximately 55 kHz), in which case they are unable to adequately control peak and average current levels to maintain peak and average laser output powers within safe limits.

[0005] The U.S. Food and Drug Administration (FDA) has established rules governing the operation of laser diodes to keep their output power within safe limits to protect people who might be exposed to the laser light. Of interest are devices that output a laser beam into a space where it could expose people, such as laser pointers, certain industrial tools, and gun aiming lights. The FDA classifies these devices based on their output power; within this FDA class structure, Class IIIa allows a maximum average output power of 5 milliwatts (mW) when the pulse train has a period of 18 microseconds or less, such as at a frequency of 55 kHz or greater. See ANSI Z136.1-2007, "American National Standard for Safe Use of Lasers."

[0006] Applicants believe that there is a need for a semiconductor laser driver circuit that is capable of operating at high frequencies (e.g., at or above 55 kHz) and that is capable of operating with higher efficiency, thereby extending battery run time or enabling the use of batteries with smaller ampere-hour capacities. Applicants also believe that there may be a need, additionally or alternatively, for a driver circuit that operates to provide pulsed power to a load at a relatively high frequency or pulse rate, wherein the duration of the power pulses is of very short duration.

[0007] Therefore, a driver circuit may include: a power controller that converts input power into an output voltage; a high-frequency switch that provides a short-duration pulse of the output voltage to a load so that a pulsed load current flows therethrough; a current sensor that generates a signal representing the pulsed load current; a sample and hold circuit that samples the signal representing the pulsed load current in synchronization with the high-frequency switch and holds the sampled signal value; and a controller that responds to the sampled signal value and a reference value and applies a control signal to the power controller to generate a desired output voltage and to the high-frequency switch and the sample and hold circuit to control the pulsed load current to a predetermined value. The load may include: a light-emitting semiconductor device, a semiconductor laser diode; a green semiconductor laser diode; or a blue semiconductor laser diode; or a light-emitting diode.

[0008] A method for providing an electric power pulse to a load may include: converting input power into an output voltage; providing or applying a high-frequency, short-duration pulse of the output voltage to the load so that a pulsed load current of the same duration flows therethrough; sensing the flow of the pulsed load current to generate a signal representing the pulsed load current; sampling the signal representing the pulsed load current synchronously with the high-frequency, short-duration pulse and holding the sampled signal value; and receiving the sampled signal value and a reference value, and applying a control signal in response to the sampled signal value and the reference value to generate a desired output voltage, and controlling the high-frequency, short-duration pulse and the sampling and holding to control the electric power pulse to a predetermined value. The load may include: a light-emitting semiconductor device, a semiconductor laser diode; a green semiconductor laser diode; or a blue semiconductor laser diode; or a light-emitting diode.

[0009] In summarizing the arrangements described and / or claimed herein, selections of concepts and / or elements and / or steps described in the detailed description herein may be made or simplified. Any summary is not intended to identify key features, elements and / or steps, or essential features, elements and / or steps related to the claimed subject matter, and therefore is not intended to be limiting, and should not be interpreted as limiting or defining the scope and breadth of the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The detailed description of the preferred embodiment(s) will be more readily and better understood when read in conjunction with the accompanying drawings, which include:

[0011] Figure 1 is a schematic block diagram of an example embodiment of a lamp including a semiconductor laser and a driver circuit;

[0012] Figure 2 is a schematic circuit diagram of an example embodiment of an example embodiment of a driver circuit for a semiconductor laser;

[0013] Figure 3 is a graphical representation showing certain parameters associated with an example semiconductor laser;

[0014] Figure 4 is a graphical representation of the optical power output versus forward current for an example semiconductor laser;

[0015] Figure 5 is a graphical representation of input power and forward voltage for an example semiconductor laser at various temperatures; and

[0016] Figure 6 is a schematic diagram of a process for further increasing the operating efficiency of an example semiconductor laser in an example driver circuit described herein.

[0017] In the drawings, if an element or feature is shown in more than one figure, the same alphanumeric designation may be used to represent such element or feature in each figure, and if closely related or modified elements are shown in the drawings, the same alphanumeric designation may be annotated or designated "a" or "b", etc. to represent the modified element or feature. Similar elements or features may be represented by similar alphanumerics in different figures of the drawings and by similar terms in the specification. It is understood that the various features in the drawings are not drawn to scale, and the dimensions of the various features may be arbitrarily expanded or reduced for clarity, and any values described in any figure are for example only. DETAILED DESCRIPTION

[0018] Figure 1 is a schematic block diagram of an example embodiment of a lamp including a semiconductor laser and a driver circuit. Example lamp 10 includes electronic circuitry 100 for operating semiconductor laser 50 and, optionally, a light emitting diode (LED). Example lamp 10 includes LED D1 that generates visible light within the wavelength range of the visible spectrum, and semiconductor laser 50, which includes a laser diode LD that emits light of substantially a single wavelength (or a very narrow wavelength band) and a photodiode PD that responds to laser light emitted from laser diode LD. Power for lamp 10 is provided by, for example, a battery B.

[0019] LED D1 is powered via power conditioner 30, which receives electrical power from battery B and changes its voltage to a level suitable for powering LED D1. Current controller 35 receives electrical power from regulator 30 and preferably applies electrical power to LED D1 at a desired current level because the light output of LED D1 is more closely related to the current applied to it than to the voltage across its terminals, which is particularly sensitive to temperature. Typically, LED D1 may be a white LED for general lighting or may be a colored LED that produces, for example, red, green, blue, infrared (IR), or ultraviolet (UV) light, as may be desired for a particular application of lamp 10.

[0020] The microprocessor controller 20 may be referred to as a microcontroller 20, microprocessor 20, controller 20, or processor 20, and includes both digital and analog capabilities. The microprocessor controller 20 receives input from a control device of the lamp 10, typically an electrical switch SW, for controlling the operation of the lamp 10, such as turning the LED D1 on and off and / or changing its brightness level, in accordance with user commands input via the actuated switch. When commanded to operate the LED D1, the controller 20 provides control signals to the power regulator 30 and the current controller 35 and receives feedback signals from the power regulator 30 and the current controller 35 for controlling the voltage generated by the regulator 30 and the current applied by the controller 35 to energize the LED D1 to the level indicated by the command received.

[0021] Electronic circuit 100 includes a semiconductor laser driver circuit, which includes a controller 20, a power controller 40, a high-frequency switch 42, an LD current sensor 44, a sample and hold 46, and a photodiode current sensor 48 for operating a semiconductor laser 50, which includes a laser diode LD and a photodiode PD. In the exemplary embodiment, high-frequency switch 42, laser diode LD, and current sensor 44 are effectively connected in series for the purpose of simply and directly controlling and measuring the current flowing through laser diode LD. However, in any particular embodiment, the order in which these elements are connected in series may be changed when it can facilitate the operation of the rest of the electronic circuit 100.

[0022] The semiconductor laser 50 includes a semiconductor laser diode LD, which is driven via a power controller 40 that receives electric power from a battery B and changes its voltage to a level suitable for driving the laser diode LD. A high-frequency switch 42 receives the electric power from the power controller 40 and periodically operates to apply short pulses of this electric power to the laser diode LD, preferably resulting in a desired level of laser diode LD current, because the laser output of the laser diode LD is more closely related to the current applied thereto, whether applied continuously or in pulses, than to the voltage across its terminals.

[0023] A current sensor 44 provides a signal proportional to the current flowing through the laser diode LD, and the output signal from the current sensor 44 is sampled and held by a sample and hold circuit 46 which samples the output signal synchronously with the current pulses flowing through the laser diode LD, thereby providing a continuous representation of the amplitude of these current pulses.

[0024] When commanded to operate the laser diode LD, the digital controller 20 provides a control signal to the power controller 40, provides a pulse width modulated (PWM) switching signal to the high frequency switch 42 and the sample and hold circuit 46, and receives a feedback signal from the current sensor 44 via the sample and hold circuit 46, which feedback signal is indicative of the voltage and / or current thereof. The controller 20 thus controls the voltage generated by the power controller 40 and the amplitude, duration, and frequency of the current ILD pulses applied by the high frequency switch 42 to drive the laser diode LD to the current level indicated by the command received by it. In some embodiments, the controller 20 may also receive a feedback signal from the power controller 40 for directly controlling its output voltage VLD.

[0025] The output power of the laser 50 is required to be controlled within established standard safety levels to protect the user (e.g., eyes and skin) and those who may be exposed to such laser light, and the levels may be different for pulsed lasers (instantaneous, peak) and continuous or average lasers, and may also be a function of the laser pulse frequency. For example, the applicant understands that for laser devices that meet FDA Class IIIa operating requirements, when operating at or above 55 kHz, the maximum average laser power output must be limited by regulation to a level of 5 mW, however, to provide additional safety margins, a lower power level, such as 3.3 mW, may be selected.

[0026] According to the applicant's understanding, the FDA Class IIIa rule considers laser diodes operating with pulses of 18 microseconds or less to be continuous wave (CW) operation, so the average laser output power and the CW laser output power are considered to be the same. Class IIIa is sometimes referred to as Class 3a. A period of 18 microseconds or less typically corresponds to a pulse rate or frequency of 55 kHz or greater. Therefore, if the average output power of the device is less than 5 mW, controlling and measuring the average laser output power is sufficient for the device to meet Class IIIa requirements. In the definition described in ANSI Z136.1-2007, the "American National Standard for Safe Use of Lasers" is the definition of "critical frequency." The definition is: "Critical frequency. The pulse repetition frequency above which the laser output is considered continuous wave (CW). For example, for short unintentional exposures (0.25 s to 10 s) to nanosecond (or longer) pulses, the critical frequency is 55 kHz for wavelengths between 0.40 and 1.05 μm and 20 kHz for wavelengths between 1.05 and 1.40 μm. AMERICAN NATIONAL STANDARD Z136.1-2007."

[0027] Although the frequency at which laser pulses are generated affects laser safety requirements, in practice, the inability of conventional laser driver circuits to control the current and duration of the laser drive current pulses, and thereby the power level of the laser pulses, decreases as their pulse frequency increases (and the pulse duration becomes very short, e.g., microseconds).

[0028] One advantage of the semiconductor laser driver circuit 100 of the present arrangement is that it can control both instantaneous and average power levels even when the pulse width of the laser drive current, and thus the laser pulse, is very small. At 55 kHz, the period of the drive pulse train is approximately 18 microseconds (μsec), and the pulse width of each of its pulses may be only 1-3 μsec.

[0029] Because the instantaneous power level of the laser light produced by a semiconductor laser diode is proportional to the current (whether continuous or pulsed) flowing through the laser diode, the present driver circuit monitors and controls the frequency, pulse duration and level of the current (e.g., current pulses) applied to the semiconductor laser, and the average level of the laser light produced thereby, as described above.

[0030] In addition to the semiconductor laser diode LD, the semiconductor laser 50 also includes a photodiode PD. The photodiode PD is illuminated by a portion of the light generated by the laser diode LD, thereby providing a precisely calibrated signal, such as a photodiode current, with a known relationship to the actual optical laser output power. The current generated by the photodiode PD flows through a photodiode current sensor 48, which generates a feedback signal with a known relationship to the average level of the laser output power. The feedback signal is provided to the controller 20 for generating a control signal for the power controller 40 and the high-frequency switch 42, so that the laser diode LD generates a desired laser power level, for example, less than 5 mW.

[0031] The arrangement of the photodiode PD and photodiode current sensor 48, which senses an average photodiode current proportional to the actual laser diode LD output power, also serves to provide a safety override in the unlikely event of a fault in the current control circuits 40, 42, 44, 46. For example, if a fault causes the current applied to the laser diode to not be limited to a desired pulse width duration or level in such a way that the sample and hold circuit 46 sampling the laser diode LD current does not provide a feedback signal representative of the actual laser diode current, the current sensor 48 will provide an independent true average feedback signal that the controller 20 can utilize to limit the laser diode current and power output to remain within desired safety limits.

[0032] Figure 2is a schematic circuit diagram of an example embodiment of an electronic circuit 100 including an example embodiment of a driver circuit for a semiconductor laser. Figure 1 The project number is marked with Figure 1 The corresponding functions are described nearby related circuit elements.

[0033] The power controller 40 includes an integrated circuit IC1 that includes a switching transistor between the L1-D1 connection and ground, and is circuited with an inductor L1, a diode D1, and a capacitor C11 in a step-up DC converter configuration for stepping up the voltage provided by the battery B from its nominal value of approximately 3.2 VDC to a higher voltage VLD to be applied to the laser 50, for example, typically about 5.3 V at room temperature (about 4.3-5.7 V at 110 mA, depending on temperature), which corresponds to the desired current level to flow through a typical laser diode LD. The current ILD flowing through the laser diode LD, controlled by the controller 20, is at a desired value, for example, about 110 milliamperes (mA), to produce the desired laser output power. Controller 20 receives feedback signals, such as laser diode current ILD and laser output power, and responds thereto by providing a control signal to IC1 via a low-pass filter provided by resistor R12 and capacitor C12, thereby establishing the pulse width of the on-time of the transistor within IC1, which, for example, generates the desired current ILD through pulse width modulation (PWM) (also known as duty cycle modulation) in conjunction with the rest of the driver circuit 100. Power controller 40 integrated circuit IC1 also receives feedback signals, such as voltage feedback via resistors R9 and R10 (and capacitor C15), for controlling the output voltage VLD of power controller 40 to generate the desired current ILD flowing in laser diode LD.

[0034] This circuit adjusts the boosted output voltage VLD from the power controller 40 to produce the desired level of current ILD flowing in the laser diode LD. Feedback through the low-pass filter R12, C12 compensates the fed-back output voltage to adjust for the expected full voltage range required to produce the desired current through the laser diode LD, for example, from less than 4.3V to 7.5V or higher. The filter R12, C12 smoothes the PWM signal from the controller 20, U6 and applies it via the ballast resistor R4, the value of which adjusts (e.g., increases or decreases) the effect of the smoothed PWM signal on the VLD value produced by the power controller 40, the boost circuit IC1, L1, D1, C11.

[0035] Power controller 40 also includes a switching transistor Q3, which is enabled by controller 20 and U6 to conduct when current is applied to laser diode LD via high-frequency switch 42. Controller 20 and U6 provide a signal to IC1 to enable the step-up DC converter of power controller 40 to operate, and this signal drives transistor Q2 to conduct, which in turn drives power transistor Q3 to conduct as well, thereby applying the output from the step-up DC converter to high-frequency switch 42. This arrangement of transistor Q3 helps reduce standby power consumption when the laser diode is not powered.

[0036] The high frequency switch 42 includes a switching transistor Q4 (e.g., a field effect transistor (FET)) connected in series with the laser diode LD and the current sensor 44, R6 by a pulse train generated by the controller 20 from the value of a feedback signal coupled thereto from the current sensor 44, R6 via a sample and hold circuit 46. The pulse width modulated signal from the controller 20 turns the switching transistor Q4 on and off at the PWM signal rate and timing (e.g., at a preferred pulse rate frequency of 55 kHz or higher), thereby applying voltage VLD pulses to the laser diode LD, causing current ILD having a desired value and pulse width to pulse through the laser diode LD.

[0037] As described above, semiconductor laser 50 includes a laser diode LD and a photodiode PD. Resistor R6 of current sensor 44 is connected in series with laser diode LD to sense current ILD flowing therethrough, and resistor R14 is connected in series with photodiode PD to sense the current generated therefrom when laser light generated by laser diode LD is irradiated thereon (e.g., at the operating frequency and pulse duration of driver circuit 100). Transistor Q4 of high-frequency switch 42 and transistor Q5 (e.g., a field-effect transistor (FET)) of sample-and-hold circuit 46, driven by the same PWM signal generated by controller 20 and U6, are turned on and off synchronously with each other at the operating frequency of driver circuit 100 (e.g., 55 kHz or higher), thereby synchronizing high-frequency switch 42 with sample-and-hold circuit 46.

[0038] The sample and hold circuit 46 includes a switching transistor Q5 connected to a current sensing resistor R6, which preferably has a low ohmic value to reduce power loss. In synchronization with Q4, the switching transistor Q5 is turned on in response to a pulse train generated by the controller 20, thereby periodically connecting the current sensing resistor R6 to the resistor R8 and the capacitor C9, thereby providing a sample and hold circuit 46. The sample and hold circuit 46 samples a signal representing the current ILD through the laser diode LD when the current is flowing, and holds the value of the signal on the capacitor C9 coupled to the controller 20 as feedback of the laser diode current ILD, for controlling the laser diode current ILD to a desired value, for example, 110 mA, during periodic energization.

[0039] Controller 20 receives the ILD feedback signal from C9 and compares it with a reference value, using the difference between them to increase or decrease the width (duration) of the PWM signal pulse. This PWM signal pulse adjusts the output voltage of booster 40 via R12 and R4. This output voltage is applied to laser diode LD via transistor Q4 of high-frequency switch 42 and sampled by transistor Q5 of sample-and-hold circuit 46. Simultaneously, controller 20 also increases or decreases the value of the reference signal it applies to boost DC converter IC1 of power controller 40 to adjust its output voltage VLD to the value required to cause laser diode LD to conduct the desired level of pulsed current ILD. Controlled by the aforementioned feedback loop is the amplitude of the laser diode current ILD pulses, and laser diode voltage VLD follows the need to maintain current pulses ILD at the value programmed to control them.

[0040] Note that the unique arrangement of the high frequency switch 42 and the sample and hold 46 enables accurate sensing of the relatively low current feedback signal voltage produced by the current sensor 44. As a result, the resistor R6 of the current sensor 44 can have a relatively low ohmic value, e.g., a resistance between 1 and 10 ohms and typically 1 ohm, thereby dissipating relatively little power in the current sensing resistor, e.g., approximately 2% or less in the depicted example, thereby increasing circuit efficiency, among other things.

[0041] The photodiode PD of the laser 50 is illuminated by the laser light generated by the laser diode LD, thereby generating a photocurrent proportional to the instantaneous output power level of the laser diode LD, which flows through the current sensor 48. The current sensor 48 includes a sensing resistor R14 to generate an instantaneous current feedback signal, which is averaged by a low-pass filter (e.g., a low-pass filter provided by resistor R11 and capacitor C14) and thereby provided to the controller 20 as an average laser output power feedback signal to provide independent limiting of the laser output power. This average feedback signal is compared with a reference level and used by the controller 20 to monitor and limit the average output power of the laser diode LD, which level is set to maintain the average power at a level less than the maximum allowable safe level (e.g., 5 mW, and in this example, 3.3 mW).

[0042] Because the calibration between the laser power output of the laser diode LD and the photodiode current generated by the photodiode PD varies significantly between units of the semiconductor laser 50, an adjustment is provided for setting a safe power output level limit. Provided in parallel with the photodiode sensing resistor R14 is a select-on-test (SOT) resistor SOT, which is selected as part of the calibration of the electronic circuit 100 and, in conjunction with the unit of laser 50 being driven, provides a signal that is a known representation of the output power of the laser diode LD. This signal is used to provide feedback of the laser output power to the controller 20, with the goal of limiting this output power to a level no higher than an allowable safety limit (e.g., 5 mW for a Class IIIa laser device). The photodiode current sensor 48 includes resistor R14 (and adjustment resistor SOT) and capacitor C14, which form a low-pass filter that averages the feedback signal output from the photodiode current sensor 48.

[0043] Electronic circuit 100 includes a predetermined, controlled startup procedure that ensures that the output power of laser diode LD does not exceed a maximum safe value during startup, which would otherwise occur. During startup, controller 20 sets a predetermined voltage on capacitor C12 to enable the output of power controller 40 (e.g., the boost circuit of IC1 thereof) at a voltage lower than that which would cause laser diode LD to lase at an excessive average output power level. Furthermore, transistor Q4 of high-frequency switch 42 is initially driven at a relatively low PWM duty cycle (relatively short pulse width), which maintains the average output power of laser diode LD below a safe limit at the target level of current ILD pulses.

[0044] At the same time, transistor Q5 of sample and hold 46 is driven synchronously with transistor Q4, so that the accumulated voltage on capacitor C9 sampled by controller 20 accurately reflects the actual laser diode current ILD. This process continues until the desired predetermined operating conditions are reached, for example, until the current through current sense resistor R6 and the corresponding voltage across capacitor C9 have increased or decreased to predetermined operating levels. Throughout the startup process and subsequent operation, controller 20, U6, drives transistors Q4 and Q5 at a frequency of 55 kHz or higher. Resistor R8 and capacitor C9 tend to reduce the effects of the switching delay between Q4 and Q5, so the voltage across capacitor C9 takes time to charge to the full voltage developed across current sense resistor R6 by laser diode current ILD. However, after several cycles of the current ILD pulse, the voltage across C9 does reach a voltage representative of the voltage across R6, and thus the laser diode current ILD.

[0045] The electronic circuit 100 may include a voltage regulator 60, which may include an integrated circuit U7, to provide a bias voltage VD from which the controller 20 and other parts of the circuit 100 operate. The voltage regulator may be a simple conventional voltage regulator or may include a DC converter.

[0046] Unless otherwise specified, the transistors shown and described in the example embodiments of the present application are field effect transistors (FETs), however, other forms of semiconductor switching devices may be employed in the drive circuit arrangements described herein. Although the example embodiments of the drive circuit arrangements described herein are in the context of a drive circuit for a semiconductor laser (e.g., a green semiconductor laser), they are suitable for driving other types and kinds of loads.

[0047] Figure 3 : is a graphical representation showing certain parameters associated with an example semiconductor laser. The horizontal axis is scaled in milliamperes (mA) of the current ILD flowing through the laser diode LD, for example, 50-300mA. The vertical axis on the left is marked for the voltage VLD (in volts) across the laser diode LD, which is represented by a rising graph line connecting the data points indicated by the triangle ▲ mark as a function of the current ILD (horizontal axis). As one would expect from a diode, the voltage VLD across it increases as the current ILD flowing through it increases. The vertical scale on the left is for VLD between 4.5V and 6.4V (an example laser diode LD begins to emit laser light, i.e., produces laser light, at a voltage of about 4.5V and a threshold current ILD of about 25-35mA).

[0048] Figure 3The vertical axis on the right side is a single scale from 0 to 190 for three different parameters indicated along the axis. The horizontal dashed line is a reference line at 100 on the scale (also representing an operating condition of 100% duty cycle) to provide a visual reference to aid in the readability of the chart. This reference line emphasizes a significant condition, namely that at an average output power level of 3.3mW, the average laser diode input power used to drive the example green laser diode is less than 100mW, which is only about 36% of the input power typically required in continuous (CW) operation. The duty cycle of this operating condition is changed by the laser driver circuit to produce a relatively low safe output power, for example, an average of 3.3mW, which is lower than the allowed average of 5mW.

[0049] The other three graph lines relative to the right vertical axis represent:

[0050] (1) Instantaneous laser output power (in mW), represented by the solid data line connecting its data points indicated by the circular ● marks;

[0051] (2) the average input power of the laser diode LD (in mW), represented by the solid data line connecting its data points indicated by the X marks; and

[0052] (3) The duty cycle (ratio of the on-time to the total period of the pulse train) or DC (average) percentage of the pulse current applied to the laser diode LD, represented by the solid line connecting the data points indicated by the diamond ◇ marks, is required to obtain an average laser output power of 3.3 mW.

[0053] As one might expect, as the voltage and current applied to the laser diode increase, the instantaneous input power to the laser diode LD increases as their product. Note that the relationship between input power and laser output power is not linear because of the threshold current of the laser diode and because the conversion efficiency of electrical energy (input power) to optical energy (output power) changes as a function of the operating conditions of the laser diode LD. At relatively low voltages and currents, the efficiency of the laser diode LD is relatively low, as is often the case when it is operated in CW, and its efficiency increases as its voltage and current increase, then decreases at relatively high voltages and currents.

[0054] Operating the laser diode at higher current levels and low duty cycles enables a significant improvement in the efficiency provided by the driver circuits described herein. This can be seen in the laser diode input data line (X data points), which reaches a minimum at intermediate levels of voltage and current.

[0055] At a constant average laser output power (e.g., 3.3 mW), optimal laser diode efficiency is seen to be achieved within a range of input current ILD, in this example, at a laser drive current ILD of 110-120 mA and around ILD≈180 mA, and an average laser diode input power of approximately 83 mW (all approximate values). When driven conventionally, the example green laser diode requires an input power of approximately 280 mW to achieve the same laser diode output power achieved in this example at approximately 83 mW, which includes the semiconductor laser driver circuit 100 as described herein—an improvement of approximately 70% in reducing input power, resulting in an approximately 3.4 times longer operating runtime.

[0056] This significantly longer runtime greatly extends battery life and / or allows the use of physically smaller or lower capacity batteries to maintain the original runtime, and is therefore a highly desirable advantage and a significant advantage to the user. In devices (e.g., lamps) where a single battery or power supply powers a laser diode and another light source (or other load), the driver circuits described herein enable more advantageous power sharing between the various loads.

[0057] Continuing with the same example, where the laser diode driver circuit 100 operates to apply current ILD pulses through the laser diode LD indicating a current pulse duty cycle of about 15% with a repetition period of about 18 microseconds or a current pulse width of about 2.7 microseconds or less, for example, at a pulse rate of about 55 kHz, such extremely short pulse widths are too short to be provided or applied by conventional laser diode driver circuits and cannot be adequately and efficiently controlled by conventional laser diode driver circuits, but can be achieved by the arrangements described herein.

[0058] Figure 4 is the optical power output (P) of an example semiconductor laser as a function of temperature opt ) relative to the forward current (I F ) is shown for continuous wave operation of an example green laser diode at temperatures of 25°C, 40°C, and 60°C. opt Relative to I F As the temperature increases from 25°C to 60°C, the current required to obtain a 5mW power output increases from about 35mA to about 45mA. For a power output of 3.3mW, the current I FThe inflection point increases from about 30 mA to about 42 mA, and the threshold current at the "knee point" in the figure increases from about 25 mA to about 32 mA. Below the inflection point current, all power applied to the laser diode generates heat, not laser light, and therefore the efficiency is zero. By pulsing the laser diode current to a much higher current level over a series of short time periods (e.g., relatively short duration pulses at a high repetition rate (e.g., 55 kHz or higher)), the power dissipated below the inflection point becomes a much less significant portion of the total power applied during each pulse, and thus significantly improves the effective efficiency of the laser diode in converting electrical energy into laser energy. As needed, the controller 20 is configured or can be configured to change the laser diode current ILD in response to changes due to temperature in order to maintain the desired average output power of the laser diode.

[0059] Figure 5 is a graphical representation of the input power and forward voltage of an example semiconductor laser at various temperatures, and Figure 6 2 is a schematic diagram of a process 200 for further increasing the operating efficiency of an example semiconductor laser in an example driver circuit as described herein. As described above, the semiconductor driver circuit enables the semiconductor laser to operate at a desired pulsed current to significantly improve the efficiency of the semiconductor laser for a predetermined operation (e.g., maximum average laser output power). Figure 5 The graphical representation shows characteristics, such as voltage VLD and input power, of the laser diode LD of the semiconductor laser device 50 when operated at various operating temperatures (e.g., at -20°F (Fahrenheit), room temperature (approximately 70°), and 140°F) to produce, for example, an average laser output power of 3.3 milliwatts.

[0060] When the input voltage VLD to the semiconductor laser diode increases monotonically with increasing input current ILD, the input power exhibits minimum values (indicated by "valleys" in the figure by dashed circles) at different levels of input current ILD at different temperatures. These minimum values or valleys represent operating conditions where the semiconductor laser diode LD has the highest efficiency at that given temperature. As a result, it would be advantageous for the semiconductor laser driver circuit 100 to also control the operating point of the semiconductor laser diode LD to be at or near its minimum input power level at the operating temperature present at any given time.

[0061] exist Figure 5In the example of FIG, electrical characteristics of an example sample of a semiconductor laser device, such as VLD and LD average input power, are shown for operating the device at three example temperatures (e.g., -20°F, room temperature (~70°F), and 140°F) and while producing an average laser output power of 3.3 mW. In the example shown, the high-efficiency operating point is approximately ILD = 180 milliamperes (mA) at room temperature, approximately 100 mA at -20°F, and approximately 190 mA at 140°F. It should be understood that the specific operating conditions of each particular unit of the semiconductor laser device will vary from unit to unit and as the electrical conditions and temperature change.

[0062] Therefore, it is expected that the described laser driver circuit will operate the semiconductor laser device at a high-efficiency current ILD related to its characteristics at its operating temperature. In this operation, the desired ILD current may be different for different semiconductor laser devices, and the high-efficiency operating point may be different at different temperatures. Therefore, the operating point is controlled by controlling the laser device operating current ILD rather than relying on its operating temperature.

[0063] exist Figure 1 and Figure 2 In an exemplary embodiment, the processor 20 or controller 20 controls the level and duty cycle of laser current pulses ILD to control the operating conditions of the laser diode LD of the semiconductor laser device 50, for example, to produce a predetermined maximum average laser output power. The calculated level of laser diode current ILD nominally associated with this output power operating condition can be referred to as a "target" laser current ILD. The processor 20 is configured to control the laser diode current ILD to become the "target" laser diode current ILD, for example, by varying the amplitude of the voltage VLD and / or the duty cycle of the pulses applied to the laser diode LD relative to an initial "target" current ILD.

[0064] Furthermore, to adapt to changes in the operating conditions of the laser diode LD in use, the processor 20 can, and preferably is, configured to change the “target” laser diode current ILD, for example, by increasing or decreasing the amplitude of the voltage VLD and / or the duty cycle of the pulses applied to the laser diode LD from the initial “target” current ILD, to obtain a larger or smaller “target” current corresponding to the laser diode current ILD that is approximately at the high-efficiency operating point of the laser diode LD under the then-current electrical and temperature conditions. Thereafter, as the then-current electrical and temperature conditions change, the processor 20 will continue to change the operating point of the laser diode LD, thereby maintaining the laser diode LD operating approximately at the high-efficiency operating point.

[0065] Figure 6An example process 200 of the aforementioned operation is shown. The process 200 begins by setting 205 an initial predetermined level (e.g., a target level) of a pulsed current ILD to be applied to the semiconductor laser diode LD to produce a desired average laser output power (e.g., 3.3 mW average), and setting 210 the duty cycle to a predetermined safe initial level of pulsed laser current (e.g., 10%) (the duty cycle is the ratio of the on-time of a pulse to the time period between the start of successive pulses of the laser current). After setting 205, 210 these initial levels, the resulting pulsed laser diode current ILD is measured 215 and compared 220 to the target level of pulsed laser diode current ILD. When the target current is on target, i.e., at the target or desired current level, the process proceeds to step 230 to measure the average optical output power produced by the semiconductor laser device 50.

[0066] However, when the target pulse current to the laser diode LD is below the target level, then the laser diode current ILD is increased 222 by a predetermined amount, for example by increasing the output voltage VLD from the power controller 40, which determines the voltage of the pulses and the laser diode current ILD they produce, and when the target current exceeds the target level, then the laser diode current ILD is decreased 224 by a predetermined amount, for example by decreasing the output voltage VLD from the power controller 40 and thus decreasing the current level of the pulses. However, when the pulse current ILD is significantly higher (“by a lot”) or significantly lower (“by a lot”), then the process 200 returns from step 222 or from step 224 to again repeatedly measure 215 and compare 220 the pulsed laser diode current ILD until ILD approaches the target level, at which point the process 200 proceeds to step 230 to measure the average optical output power produced by the semiconductor laser device 50.

[0067] Step 230 measures the average output power of the semiconductor laser diode LD using a value provided by the current of the photodiode PD in the semiconductor laser device 50. The photodiode PD is included in the semiconductor laser device 50 and is calibrated to generate a current proportional to the average output power from the laser diode LD, such as a sense current or feedback current. In addition to the natural control of the average laser output power generated by the control of the laser diode current ILD in steps 215 to 224, this step initiates independent monitoring of the average laser output power to control the average laser output power, for example, to keep the power within safe limits.

[0068] Limiting the average laser output power using the photodiode PD current begins by comparing the average laser diode output power using the feedback current measured by the current sensor 48 from step 230 with its predetermined limit value (e.g., a target value, such as 3.3 mW) 234. When the average output power is the predetermined value, then the process 200 proceeds to step 240 to calculate the laser diode LD power consumption.

[0069] When the average output power of the laser diode LD is less than (below or less than) a predetermined value, the duty cycle for applying the pulsed current ILD to the laser diode LD is increased 236, and process 200 returns to step 215 to measure the level of the pulsed laser diode current ILD again. When the average output power is greater than (exceeds or is higher than) the predetermined value, the duty cycle for applying the pulsed current ILD to the laser diode LD is decreased 238, and process 200 returns to step 215 to measure the level of the pulsed laser diode current ILD again. Steps 234-236-238, as well as the preceding steps 215 through 230, are repeated as needed to maintain the average laser diode output power at a predetermined average power level, such as a 3.3 mW safety limit or lower. When the preceding steps 215-234 result in the average laser diode output power being at its target level, i.e., output power on target (YES at 240), process 200 proceeds to step 240.

[0070] Step 240 includes calculating 240 the power consumption of the laser diode LD and / or calculating 240 the power drawn from the battery, and may include one or more of the following example methods: The laser diode LD power level may be calculated / calculated 240 by multiplying the value of the duty cycle of the pulsed laser current ILD by the value of the laser diode boost voltage VLD by the value of the laser diode pulsed current ILD. Alternatively, the battery power draw may be calculated / calculated 240 by calculating / calculating the value of the power drawn from a power source (e.g., a battery), and may include, for example, multiplying the voltage VB measured at the battery terminals by a measured or calculated value of the current flowing therefrom (e.g., its current draw). Both methods for step 140 may produce instantaneous values, or may produce a series of values that can be averaged or integrated to determine the cumulative average energy generated by the semiconductor laser diode LD and / or the cumulative energy drawn from the power source, which can be used to manage the operating conditions of the semiconductor laser device and / or lamp or other device including such a laser device.

[0071] The laser diode LD power consumption from step 240-yes is compared 245 to its predetermined minimum value. When the laser diode LD power consumption is less than (245-yes) its predetermined minimum value (e.g., a value stored in a memory of the processor 20 or controller 20), the current value of the pulsed laser diode current ILD and the current value of the laser diode LD power consumption are stored 250 (e.g., in a memory of the processor 20), and the process 200 proceeds to step 255 to adjust the level of the pulsed laser diode current ILD. When the laser diode LD power consumption is not less than (245-no) its predetermined minimum value (i.e., greater than its predetermined minimum value), the process 200 proceeds directly to step 255.

[0072] Typically, step 255 is used to increase the target value of the laser diode current ILD by 255 pulses when the power consumption of the laser diode LD is less than the stored minimum value, and to decrease the target value of the laser diode current ILD by 255 pulses when the power consumption of the laser diode LD is not less than the stored minimum value. However, there are or may be certain regions of the characteristics of the semiconductor laser diode LD in which the aforementioned situation is not the case, for example, Figure 3 For a region where ILD is in the range of approximately 100 mA to 130 mA, in which case the change to the target value of ILD by the logic of step 255 may be opposite to that earlier.

[0073] The logic of step 255 can be configured for the processor to determine whether to increase or decrease the current ILD based on the trend of its previous actions to increase or decrease the current ILD. The logic of step 255 can be alternatively and / or additionally configured to adjust the level of the pulsed laser diode current ILD in fixed increments and / or can be configured to adjust the level of the pulsed laser diode current ILD by calculating larger or smaller increments as a function of the magnitude of the difference between the stored minimum power level and the measured / calculated power level.

[0074] Step 255 increases the laser diode pulse current if increasing it reduces the calculated power calculated in step 240, or decreases the laser diode pulse current if increasing it now increases the calculated power calculated in step 240, so that the process of increasing and decreasing the output voltage 222, 224 and / or the pulse current duration 236, 238 tends to minimize the laser diode power consumption or battery power draw (as the case may be), thereby changing the operating conditions of the laser diode LD to a high efficiency condition. In a similar manner, if reducing ILD reduces the power calculated in step 240, step 255 reduces the pulse current ILD, or increases the current ILD if reducing ILD increases the power calculated in step 240.

[0075] Operating a laser diode LD under high efficiency conditions tends to minimize the power required from a battery or other power source while maintaining a desired predetermined level of average laser diode output power, and thus can be considered an "optimal" or "near-optimal" operating condition if the power consumed by the laser diode and / or drawn from a power source (e.g., a battery) is reduced, which tends to extend the operating time of the lamp or other load.

[0076] The process 200 then returns to step 215 to measure the pulsed laser diode current ILD again and repeat process steps 215 to 255 to maintain the operating conditions of the laser diode LD within predetermined values of the pulsed laser diode current ILD and the average laser diode output power when the semiconductor driver circuit 100 and the lamp 10 are operating (e.g., turned on). In this manner, the operation of the semiconductor laser device 50 and the laser diode LD therein can be maintained within desired ranges and limits, e.g., for safe operation and human safety.

[0077] It should be noted that the added functionality provided by process 200 can be employed at all times during operation of the semiconductor laser device of a light or other device, or only during certain times of operation, as may be deemed desirable. For example, a decision to employ the functionality of process 200 may be made only when the power source (e.g., a battery) of lamp 10 has discharged beyond a predetermined amount, which may be determined, for example, based on the terminal voltage of the power source or by accumulating the current or power drawn therefrom, thereby further extending the operating time of a lamp or other device employing circuit 100. The latter option may help limit the maximum current drawn from the power source (e.g., a battery) because its terminal voltage decreases as it discharges, which may protect the battery and / or extend the operating time of the lamp or device.

[0078] Consider the specific operating examples described in this and the next five sections of a typical operating scenario for process 200, keeping in mind that the conditions are examples and will vary depending on the specific characteristics of each unit of the semiconductor laser driver circuit 100, the values and tolerances of the electronic components therein, the semiconductor laser device 50, the electrical power source, and temperature and other environmental factors. Assume that the current ILD of the semiconductor laser LD is operating at an initial value of 110 mA, with a corresponding power consumption of 86 mW by the laser diode LD. The operating parameter "86 mW" at "110 mA" is then stored in memory as the assumed "minimum" power consumption, as this is the only data point to date.

[0079] Processor 20 can "test the waters" by determining the results when the laser diode target current ILD is reduced to 100 mA. A reduction may be chosen initially because, for example, it would be preferable to operate near the rated maximum current capability of the semiconductor laser LD, if it were not "required" to do so. When current ILD was set to 100 mA, it was found that the power consumption of the laser diode LD increased to approximately 89 mW, indicating that the chosen direction for changing the current level was the wrong one; however, the operating parameters of the laser diode LD were within safe limits. In response, processor 20 returns to ILD = 110 mA in step 255, and the power consumption returns to approximately 86 mW. This means that "86 mW" at "110 mA" is still the desired minimum power consumption, i.e., a more efficient condition.

[0080] Because previously reducing the laser diode current ILD to 100 mA resulted in increased power consumption, the processor 20 can "test the waters" again to determine what the result would be if the ILD target were increased to 120 mA. Then, when operating at ILD = 120 mA, the laser diode LD power consumption drops to approximately 85 mW, which determines the new minimum power operating point: "85 mW at 120 mA" is stored in memory as the new minimum power, i.e., higher efficiency, condition.

[0081] The next processor 20 step 255 "tests the waters" again to determine what the results will be if the target ILD current value is further increased to 130mA. Under this new operating condition, the power consumption is approximately 87mW, which determines that the current ILD current increase is "too much." Therefore, the processor 20 step 255 returns to ILD = 120mA, the previously determined "optimal" operating point; however, for example, assume that due to, for example, temperature changes, the power consumption at ILD = 120mA is now approximately 86mW. Therefore, "86mW" at "120mA" is now stored in memory as the minimum power consumption operating point.

[0082] For example, after some predetermined time, processor 20 step 255 may try to "test the water" again by gradually reducing, i.e., lowering, the target level of pulsed current ILD. If the reduction in ILD results in reduced (or the same) power consumption, the changed operating conditions will become the new "optimal" operating point, and the processor will then try to reduce ILD by one more level to determine whether lower power consumption will occur.

[0083] Otherwise, processor 20 will return to the previously determined "optimal" level for the current ILD and subsequently attempt a gradual increase, i.e., increase, of target current ILD. If this ILD current level results in a decrease in power consumption (or remains unchanged), this operating condition will become the new "optimal" operating point, and processor 20 will attempt another step increase, i.e., increase, of current ILD in step 255. If the recent increase in current ILD results in an increase in power consumption, processor 20 will return to the previously determined "optimal" level for the current ILD at some predetermined time until it ventures out again and "tests the waters" again. This concludes the six-part example.

[0084] In typical embodiments, and in some cases of preferred embodiments, the described arrangement operates efficiently with a semiconductor laser diode LD that produces green laser light, for example, light of approximately 510-530 nm, and more generally produces light in the visible range of approximately 400-700 nm. The present driver circuit is also advantageous for driving other devices that exhibit threshold input levels and / or higher efficiency at higher currents and shorter pulse widths, for example, a blue laser diode is just one example of such a device. Note that driver circuit efficiencies approximately 2-3 times greater than conventional laser diode driver circuits have been achieved using the described driver circuit 100.

[0085] A driver circuit for providing electric power pulses to a load may include: a power controller that receives input power and converts the input power into an output voltage; a high-frequency switch configured to provide or apply short-duration pulses of the output voltage to the load, causing a pulsed load current of the same duration to flow therethrough; a current sensor through which the pulsed load current flows, for generating a signal representing the pulsed load current; a sample-and-hold circuit configured to sample the signal representing the pulsed load current synchronously with the high-frequency switch and hold the sampled signal value; and a controller that receives the sampled signal value and, in response to the sampled signal value and a reference value, is configured to apply a control signal to the power controller to generate a desired output voltage and to the high-frequency switch and the sample-and-hold circuit to control the pulsed load current to a predetermined value. The pulsed load current has a repetition rate of at least 55 kHz and a duration of less than 9 microseconds. The load may include: a semiconductor laser diode; a green semiconductor laser diode; a blue semiconductor laser diode; or a light-emitting diode. In this driver circuit, the controller: compares the measured value of the pulsed load current with its target value, and increases the output voltage and / or the duration of the pulsed load current pulse when the measured value of the pulsed load current is less than its target value, and reduces the output voltage and / or the duration of the pulsed load current pulse when the measured value of the pulsed load current is greater than its target value. In this driver circuit, the controller: compares the measured value of the output of the load with its target value, and increases the duration of the pulsed load current pulse when the measured value of the output of the load is less than its target value, and reduces the duration of the pulsed load current pulse when the measured or calculated value of the output of the load is greater than its target value. In this driver circuit, the controller: determines the power consumption by calculating the power consumption of the load or calculating the power drawn from the power supply; stores the power consumption when its most recently determined value is less than its previously stored value; and changes the duration of the pulsed load current pulse in a direction that further reduces the determined power consumption.

[0086] A driver circuit for providing electric power pulses to a light-emitting semiconductor device may include: a power controller including a DC converter that receives input power and converts the input power into an output voltage; a high-frequency switching transistor configured to provide or apply short-duration pulses of the output voltage to the light-emitting semiconductor device so that a pulsed load current of the same duration flows therethrough; a current sensing resistor through which the pulsed load current flows and for generating a signal representing the pulsed load current; a sample and hold circuit including a switching transistor configured to sample the signal representing the pulsed load current synchronously with the high-frequency switching transistor and hold the sampled signal value; and a controller that receives the sampled signal value and, in response to the sampled signal value and a reference value, is configured to apply a control signal to the power controller to generate a desired output voltage and a pulse-width modulated drive signal to the high-frequency switching transistor and the sample and hold circuit switching transistor to control the pulsed load current to a predetermined value. The repetition rate of the pulsed current in the light-emitting semiconductor device is at least 55 kHz, and its short duration is less than 9 microseconds. The light-emitting semiconductor device may include: a semiconductor laser diode; a green semiconductor laser diode; a blue semiconductor laser diode; or a light-emitting diode. In the driver circuit, a controller compares a measured value of a pulsed light-emitting semiconductor device current with a target value, and increases an output voltage and / or a duration of a pulse of the pulsed light-emitting semiconductor device current when the measured value of the pulsed light-emitting semiconductor device current is less than the target value, and decreases the output voltage and / or the duration of a pulse of the pulsed light-emitting semiconductor device current when the measured value of the pulsed light-emitting semiconductor device current is greater than the target value. In the driver circuit, a controller compares a measured value of an output of the light-emitting semiconductor device with a target value, and increases a duration of a pulse of the pulsed light-emitting semiconductor device current when the measured value of the output of the light-emitting semiconductor device is less than the target value, and decreases the duration of a pulse of the pulsed light-emitting semiconductor device current when the measured value or calculated value of the output of the light-emitting semiconductor device is greater than the target value. In the driver circuit, the controller determines power consumption by calculating the power consumption of the light-emitting semiconductor device or calculating the power drawn from a power supply; stores the power consumption when its most recently determined value is less than its previously stored value; and changes the duration of the pulse of the pulsed light-emitting semiconductor device current in a direction that further reduces the determined power consumption.

[0087] A method for providing electric power pulses to a load may include: converting input power into an output voltage; providing or applying high-frequency, short-duration pulses of the output voltage to the load so that a pulsed load current of the same duration flows therethrough; sensing the flow of the pulsed load current to generate a signal representing the pulsed load current; sampling the signal representing the pulsed load current synchronously with the high-frequency, short-duration pulses and holding the sampled signal value; and receiving the sampled signal value and a reference value and applying a control signal in response to the sampled signal value and the reference value to generate a desired output voltage and control the high-frequency, short-duration pulses and the sampling and holding to control the electric power pulses to a predetermined value. In this method, the high-frequency repetition rate of the pulsed load current is at least 55 kHz and its short duration is less than 9 microseconds. The method may also include: establishing a target value as a reference value for the pulsed load current; measuring the value of the pulsed load current; comparing the measured value of the pulsed load current with the target value, increasing the output voltage and / or the duration of the pulsed load current pulses when the measured value of the pulsed load current is less than the target value, and decreasing the output voltage and / or the duration of the pulsed load current pulses when the measured value of the pulsed load current is greater than the target value; and repeating the preceding steps. The method may further include: establishing a target value for the output of the load; measuring the value of the output of the load; comparing the measured value of the output of the load with its target value, increasing the duration of the pulsed load current pulse when the measured value of the output of the load is less than its target value, and decreasing the duration of the pulsed load current pulse when the measured value or calculated value of the output of the load is greater than its target value; and repeating the previous steps. The method may further include: determining the power consumption by calculating the power consumption of the load or calculating the power drawn from the power supply; storing the power consumption when its most recently determined value is less than its previously stored value; and changing the duration of the pulsed load current pulse in a direction that further reduces the determined power consumption. In this method, the load includes: a semiconductor laser diode; or a green semiconductor laser diode; or a blue semiconductor laser diode; or a light emitting diode.

[0088] A method for providing electrical power pulses to a laser diode may include: converting input power into an output voltage; providing or applying high-frequency, short-duration pulses of the output voltage to the laser diode so that a pulsed laser diode current of the same duration flows therethrough; sensing the flow of the pulsed laser diode current to generate a signal representing the pulsed laser diode current; sampling the signal representing the pulsed laser diode current synchronously with the high-frequency, short-duration pulses and holding the sampled signal value; and receiving the sampled signal value and a reference value and applying a control signal in response to the sampled signal value and the reference value to generate a desired output voltage and control the high-frequency, short-duration pulses and the sampling and holding to control the electrical power pulses to a predetermined value. In this method, the high-frequency repetition rate of the pulsed laser diode current is at least 55 kHz and its short duration is less than 9 microseconds. The method may further include: (a) establishing a target value as a reference value for the pulsed laser diode current; (b) measuring the value of the pulsed laser diode current; comparing the measured value of the pulsed laser diode current with the target value, increasing the output voltage and / or the duration of the pulsed laser diode current pulse when the measured value of the pulsed laser diode current is less than the target value, and decreasing the output voltage and / or the duration of the pulsed laser diode current pulse when the measured value of the pulsed laser diode current is greater than the target value; and repeating the above steps. The method may further include: establishing a target value for the output of the laser diode; measuring the value of the output of the laser diode; comparing the measured value of the output of the laser diode with the target value, increasing the duration of the pulsed laser diode current pulse when the measured value of the output of the laser diode is less than the target value, and decreasing the duration of the pulsed laser diode current pulse when the measured value or calculated value of the output of the laser diode is greater than the target value; and repeating the above steps. The method may further include: determining the power consumption by calculating the power consumption of the laser diode or calculating the power drawn from the power supply; storing the power consumption when its most recently determined value is less than its previously stored value; and changing the duration of the pulsed laser diode current pulses in a direction that further reduces the determined power consumption. The laser diode may include: a semiconductor laser diode; or a green semiconductor laser diode; or a blue semiconductor laser diode; or a light emitting diode.

[0089] As used herein, the terms "approximately," "approximately," and / or "about" mean that dimensions, sizes, formulations, parameters, shapes, and other quantities and characteristics are not and need not be exact, but may be approximate and / or larger or smaller as necessary, thereby reflecting tolerances, conversion factors, rounding, measurement errors, etc., judgment, and other factors known to those of ordinary skill in the art. In general, dimensions, sizes, formulations, parameters, shapes, or other quantities or characteristics are "approximately" or "substantially" or "substantially" whether or not expressly stated. Note that embodiments of widely varying sizes, shapes, and dimensions may employ the described arrangements.

[0090] As used herein, the term "and / or" includes both conjunctive and disjunctive cases, thus, a phrase in the form "A and / or B" includes "A" or "B" or "A and B." Similarly, phrases in the form "A, B, and / or C" or phrases in the form "A and / or B and / or C" include "A," "B," "C," "A and B," "A and C," "B and C," and "A and B and C." Furthermore, the term "at least one of" one or more elements is intended to include one of any one element, more than one of any one element, and two or more elements, up to and including all elements, thus, for example, a phrase in the form "at least one of A, B, and C" includes "A," "B," "C," "A and B," "A and C," "B and C," and "A and B and C."

[0091] As used herein with respect to the power applied to a semiconductor laser diode, the term "short" means that the duration of the electrical power pulses applied to the semiconductor laser diode is equal to or less than the duration necessary for the laser diode to operate in FDA Class IIIa, which duration allows a maximum average output power of 5 milliwatts (mW) when the period of the pulse train is 18 microseconds or less, such as at a frequency of 55 kHz or greater. See ANSI Z136.1-2007, "American National Standard for Safe Use of Lasers."

[0092] As used herein, the term "predetermined" means predetermined or determined in advance with respect to whatever the term refers to. The term can apply to physical objects or things and / or intangible things, such as signals or data. Examples include fixed values, positions, conditions, and / or restrictions, however, predetermined is not limited to fixed values, positions, conditions, and / or restrictions. Predetermined values, positions, conditions, and / or restrictions can change or otherwise vary over time, over a sequence, and / or over a random series of values, positions, conditions, and / or restrictions.

[0093] As used herein, the terms "substantial" and "essentially" mean that the things referred to as "substantial" or "essentially" are sufficiently similar in form and / or function to be used in the present invention in a manner included or suggested by the description and / or claims herein and / or their equivalents. The terms "substantial" and "essentially" may include and / or be meanings other than the terms "approximately," "approximately," and / or "about" herein.

[0094] As used herein, the terms "connected" and "coupled," and variations thereof, may or may not be exact synonyms, but may also include some similarities and some differences, and the terms are used interchangeably herein. While the term "connected," as indicated by its context, may be used generally to refer to elements that are in direct electrical and / or physical contact with each other, the term "coupled," as indicated by its context, may be used generally to refer to elements that are in indirect electrical and / or physical contact with each other, e.g., via one or more intermediate elements, so as to cooperate and / or interact with each other, and may also include elements that are in direct contact.

[0095] The term "battery" may be used herein to refer generally to sources of electrical power and electrochemical devices including one or more electrochemical cells and / or fuel cells, and thus a battery may include a single cell or multiple cells, whether as individual units or as packaged units. A battery is one example of a type of electrical power source suitable for use in portable or other devices. Such devices may employ power sources including, but not limited to, fuel cells, supercapacitors, solar cells, and the like, as well as electrochemical cells. Any of the foregoing may be disposable or rechargeable, or both, and / or multiples thereof may be combined into a battery pack or battery assembly or other such assembly or package, and any, some, or all of these may be referred to herein under the general term "battery."

[0096] Various embodiments of the battery may have one or more battery cells, for example, one, two, three, four, or five or more battery cells, as may be considered appropriate for any particular device. The battery may employ various types and varieties of battery chemistries, for example, carbon-zinc, alkaline, lead-acid, nickel-cadmium (Ni-Cd), nickel-metal-hydride (NiMH), or lithium-ion (Li-Ion) or lithium-ion-phosphate battery types, having an appropriate number of cells and battery capacity to provide the desired operating time and / or life for a particular device, and may be single-use or rechargeable, or both. Examples may include a three-cell Ni-Cd or NiMH battery typically producing approximately 3.6V, a lithium-ion battery typically producing approximately 3.5-3.7V, it being noted that the resulting voltage will be higher near full charge and lower during discharge, particularly when higher currents are supplied and when a low charge level is reached, such as when becoming discharged.

[0097] The power controller 40 and / or the power regulator 30 and / or the regulator 60 can be, for example, a DC converter. The term DC converter as used herein refers to any electronic circuit that receives electrical power at one voltage and current level at an input and provides DC electrical power at a different voltage and / or current level at an output. Examples may include a DC-DC converter, an AC-DC converter, a boost converter, a buck converter, a buck-boost converter, a single-ended primary inductor converter (SEPIC), a linear regulator, a series regulation element, a current level regulator, and the like. Its input and output can be DC coupled and / or AC coupled, for example, through a transformer and / or a capacitor. The DC converter may or may not include a circuit for, for example, regulating the voltage and / or current level at its output, and may have one or more outputs that provide electrical power at different voltages and / or current levels and / or in different forms (e.g., AC or DC).

[0098] Furthermore, what is referred to as “optimal” or “deemed optimal” may or may not be a truly optimal condition, but may be a condition that is considered desirable or subjectively “optimal” because it is selected based on decision rules and / or criteria defined by the designer and / or applicable control function (e.g., processor 20 or controller 20) and / or criteria of or associated with process 200.

[0099] Although the present invention has been described in terms of the foregoing exemplary embodiments, variations within the scope and spirit of the invention, as defined by the following claims, will be readily apparent to those skilled in the art. For example, the driver circuit 100 can be used to drive other devices and loads to which power pulses are applied at a relatively high frequency (e.g., a high pulse repetition rate). Examples include semiconductor laser diodes; or green semiconductor laser diodes; or blue semiconductor laser diodes; or light emitting diodes.

[0100] While the laser diode driver circuit 100 has been described as typically operating at a frequency of at least 55 kHz, this operating frequency can be higher and / or can vary within a frequency range, preferably 55 kHz or higher. As long as the frequency is 55 kHz or higher, the pulse width of the PWM current ILD applied to the laser diode LD and its frequency or repetition rate can vary within a predetermined range. The repetition rate of the pulsed load current ILD is at least 55 kHz, and the duty cycle of the PWM drive signal is relatively short, at approximately 50% or less, for example, typically less than approximately 40%, resulting in a short duration or pulse width of less than approximately 9 microseconds, for example, 7.2 microseconds.

[0101] While the preferred current flowing through the laser diode LD in the described example embodiment is, for example, 110-120 mA at room temperature, this current level may be different for different laser diodes and at different temperatures.

[0102] Each U.S. provisional application, U.S. patent application, and / or U.S. patent identified herein is hereby incorporated by reference in its entirety for any and all purposes no matter how referred to or described herein.

[0103] Finally, the numerical values described are typical values or example values, not limiting values, and do not exclude significantly larger and / or significantly smaller values. The values in any given embodiment may be much larger and / or much smaller than the examples or typical values described.

Claims

1. A driver circuit for providing electric power pulses to a load, comprising: a power controller that receives input power and converts the input power into an output voltage; a high frequency switch configured to provide short duration pulses of the output voltage to the load such that a pulsed load current of the same duration flows therethrough; a current sensor, through which the pulse load current flows, for generating a signal representing the pulse load current; a sample and hold circuit configured to sample a signal representing the pulsed load current in synchronization with the high-frequency switch and to hold a sampled signal value; and A controller receives the sampled signal value and is responsive to the sampled signal value and a reference value, and is configured to apply a control signal to the power controller to produce a desired output voltage, and to the high frequency switch and the sample and hold circuit to control the pulsed load current to a predetermined value.

2. The driver circuit of claim 1, wherein the pulsed load current has a repetition rate of at least 55 kHz and a short duration of less than 9 microseconds.

3. The driver circuit according to claim 1 , wherein the load comprises: semiconductor laser diodes; or Green semiconductor laser diodes; or blue semiconductor laser diodes; or Light-emitting diodes.

4. The driver circuit according to claim 1, wherein The controller: comparing the measured value of the pulsed load current with its target value, and The output voltage and / or the duration of the pulsed load current pulses are increased when the measured value of the pulsed load current is less than its target value, and the output voltage and / or the duration of the pulsed load current pulses are decreased when the measured value of the pulsed load current is greater than its target value.

5. The driver circuit according to claim 4, wherein The controller: comparing the measured value of the load's output to its target value, and The duration of the pulsed load current pulses is increased when the measured value of the output of the load is less than its target value, and is decreased when the measured or calculated value of the output of the load is greater than its target value. The driver circuit according to claim 5 , wherein: The controller: Determine power consumption by calculating the power consumption of the load or calculating the power drawn from the power supply; When its most recently determined value is less than its previously stored value, the power consumption is stored; and The duration of the pulsed load current pulses is varied in the direction of further reducing the determined power consumption.

7. A method for providing an electric power pulse to a load, comprising: Convert input power into output voltage; Provides high frequency, short duration pulses of output voltage to the load, causing pulsed load current of the same duration to flow through it; sensing the flow of a pulsed load current to generate a signal representative of the pulsed load current; sampling a signal representing the pulsed load current synchronously with the high frequency short duration pulses and holding the sampled signal value; and Receives a sampled signal value and a reference value, and applies a control signal in response to the sampled signal value and the reference value to generate a desired output voltage, and controls high frequency short duration pulses and sampling and holding to control the electric power pulse to a predetermined value.

8. The method of claim 7, wherein the high frequency repetition rate of the pulsed load current is at least 55 kHz and the short duration thereof is less than 9 microseconds.

9. The method according to claim 7, further comprising: (a) establishing a target value as a reference value of the pulse load current; (b) measuring the value of the pulse load current; (c) comparing the measured value of the pulsed load current with its target value, (d) increasing the output voltage and / or the duration of the pulsed load current pulses when the measured value of the pulsed load current is less than its target value, and decreasing the output voltage and / or the duration of the pulsed load current pulses when the measured value of the pulsed load current is greater than its target value; and (e) Repeat steps (b) to (d) of this claim.

10. The method according to claim 9, further comprising: (a) Establishing a target value for the load output; (b) measuring the output value of the load; (c) comparing the measured value of the load's output with its target value, (d) increasing the duration of the pulsed load current pulses when the measured value of the output of the load is less than its target value, and decreasing the duration of the pulsed load current pulses when the measured or calculated value of the output of the load is greater than its target value; and (e) Repeat steps (b) to (d) of this claim.

11. The method according to claim 10, further comprising: Determine power consumption by calculating the power consumption of the load or calculating the power drawn from the power supply; When its most recently determined value is less than its previously stored value, the power consumption is stored; and The duration of the pulsed load current pulses is varied in the direction of further reducing the determined power consumption.

12. The method of claim 7, wherein the load comprises: semiconductor laser diodes; or Green semiconductor laser diodes; or blue semiconductor laser diodes; or Light-emitting diodes.

13. A driver circuit for providing electric power pulses to a light emitting semiconductor device, comprising: a power controller including a DC converter that receives input power and converts the input power into an output voltage; a high frequency switching transistor configured to provide a short duration pulse of output voltage to the light emitting semiconductor device so that a pulsed light emitting semiconductor device current of the same duration flows therethrough; a current sensing resistor, through which the current of the pulse light emitting semiconductor device flows, for generating a signal representing the current of the pulse light emitting semiconductor device; a sample and hold circuit including a switching transistor configured to sample a signal representing a current of the pulsed light emitting semiconductor device in synchronization with the high frequency switching transistor and to hold a sampled signal value; and A controller receives the sampled signal value and, in response to the sampled signal value and a reference value, is configured to apply a control signal to the power controller to generate a desired output voltage, and to apply a pulse width modulated drive signal to the high frequency switching transistor and the sample and hold circuit switching transistor to control the current of the pulse light emitting semiconductor device to a predetermined value.

14. The driver circuit according to claim 13, wherein: The repetition rate of the pulse current in the light emitting semiconductor device is at least 55 kHz, and its short duration is less than 9 microseconds.

15. The driver circuit according to claim 13, wherein the light emitting semiconductor device comprises: semiconductor laser diodes; or Green semiconductor laser diodes; or blue semiconductor laser diodes; or Light-emitting diodes.

16. The driver circuit according to claim 13, wherein: The controller: comparing the measured value of the current of the pulsed light emitting semiconductor device with its target value, and When the measured value of the pulsed light-emitting semiconductor device current is less than its target value, the output voltage and / or the duration of the pulsed light-emitting semiconductor device current pulse is increased, and when the measured value of the pulsed light-emitting semiconductor device current is greater than its target value, the output voltage and / or the duration of the pulsed light-emitting semiconductor device current pulse is reduced.

17. The driver circuit according to claim 16, wherein: The controller: comparing a measured value of the output of the light emitting semiconductor device with a target value thereof, and The duration of the pulsed light emitting semiconductor device current pulse is increased when the measured value of the output of the light emitting semiconductor device is less than its target value, and the duration of the pulsed light emitting semiconductor device current pulse is decreased when the measured or calculated value of the output of the light emitting semiconductor device is greater than its target value.

18. The driver circuit according to claim 17, wherein: The controller: determining the power consumption by calculating the power consumption of the light emitting semiconductor device or calculating the power drawn from a power supply; When its most recently determined value is less than its previously stored value, the power consumption is stored; and The duration of the current pulses of the pulsed light-emitting semiconductor device is changed in the direction of further reducing the determined power consumption.

19. A method for providing electrical power pulses to a laser diode, comprising: Convert input power into output voltage; providing a high frequency, short duration pulse of output voltage to the laser diode so that a pulsed laser diode current of the same duration flows therethrough; sensing a pulsed laser diode current flow to generate a signal representative of the pulsed laser diode current; sampling a signal representing a pulsed laser diode current synchronously with the high frequency short duration pulses and holding the sampled signal value; and Receives a sampled signal value and a reference value, and applies a control signal in response to the sampled signal value and the reference value to generate a desired output voltage, and controls high-frequency short-duration pulses and sampling and holding to control the electric power pulse to a predetermined value.

20. The method of claim 19, wherein the high frequency repetition rate of the pulsed laser diode current is at least 55 KHz and its short duration is less than 9 microseconds.

21. The method of claim 19, further comprising: (a) Establishing a target value as a reference value for the pulsed laser diode current; (b) measuring the value of the pulsed laser diode current; (c) comparing the measured value of the pulsed laser diode current with its target value, (d) increasing the output voltage and / or the duration of the pulsed laser diode current pulses when the measured value of the pulsed laser diode current is less than its target value, and decreasing the output voltage and / or the duration of the pulsed laser diode current pulses when the measured value of the pulsed laser diode current is greater than its target value; and (e) Repeat steps (b) to (d) of this claim.

22. The method according to claim 21, further comprising: (a) Establishing a target value for the output of a laser diode; (b) measuring the value of the output of the laser diode; (c) comparing the measured value of the output of the laser diode with its target value, (d) increasing the duration of the pulsed laser diode current pulses when the measured value of the output of the laser diode is less than its target value, and decreasing the duration of the pulsed laser diode current pulses when the measured or calculated value of the output of the laser diode is greater than its target value; and (e) Repeat steps (b) to (d) of this claim.

23. The method according to claim 22, further comprising: Determine the power consumption by calculating the power consumption of the laser diode or calculating the power drawn from the power supply; When its most recently determined value is less than its previously stored value, the power consumption is stored; and The duration of the pulsed laser diode current pulses is varied in the direction of further reducing the determined power consumption.

24. The method of claim 19, wherein the laser diode comprises: semiconductor laser diodes; or Green semiconductor laser diodes; or blue semiconductor laser diodes; or Light-emitting diodes.

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