Dimmer control with soft start overcurrent protection

Abstract

Circuit including: an input configured to receive a control signal; a controller configured to modulate the pulse width of a pulse train using the control signal when the controller is turned on; an output configured to provide the pulse train to a driver; and First and second current limit detectors configured to receive load current information from the driver and abort an active pulse of the controller if a value of the load current information exceeds a threshold, wherein the first current limit detector includes a zero-crossing detector configured to detect a zero-crossing event of an AC source and to provide to the controller a discrete signal representing the zero-crossing event of the AC source.

Description

TECHNICAL FIELD

[0001] This registration relates to dimmers and in particular to dimmers with current limiting protection. BACKGROUND

[0002] Tungsten filaments can have a very high positive temperature coefficient of resistance. During startup, a high current (~10x) can flow until the temperature reaches a steady state (~3000K). Dimmer control and power circuits for controlling such filaments may require the use of large, expensive transistors to supply the inrush current.

[0003] US 2012 / 0092909 A1 describes a power conversion device that determines a peak value of the circuit current in each pulse cycle and a lower limit, which is lower than the peak value, from a corrected output voltage value obtained by subtracting a predetermined reference voltage from a detected output voltage and a detected input voltage. The pulse signal output unit outputs a pulse signal to the first switch when the polarity of the input voltage is positive and outputs a pulse signal to the second switch when the polarity of the input voltage is negative. A pulse signal is activated in response to the start of a pulse cycle and remains activated until a detected circuit current reaches a peak value.A pulse signal switches off when the current in the circuit reaches a peak value and switches back on when the current in the circuit drops to a lower limit.

[0004] US 2007 / 0188112 A1 describes a device for driving an LED. The driving device may include an LED unit with at least one LED and a current control unit for controlling the magnitude of the current flowing through the LED unit in response to a control signal. The LED driving device may include a voltage sensing unit for detecting a voltage across the LED unit and a control signal blocking unit for comparing the voltage detected by the voltage sensing unit with a reference voltage. The control signal blocking unit prevents the control signal from being applied to the current control unit when the detected voltage is lower than the reference voltage. US 7164238 B2 describes an energy-saving device for an inductive, resistive, or capacitive load, such as a fluorescent lamp with a magnetic ballast or an electronic ballast, operated with an AC voltage waveform.The energy-saving device includes a setting unit for adjusting a desired power operating level for the load. The energy-saving device also includes a processor configured to receive a signal from the setting unit indicating the desired power operating level for the load, determine a phase delay to be applied to an output AC waveform to be supplied to the load, and output a control signal as a result. The energy-saving device further includes an active element placed between a line providing the input AC waveform and the load. The active element receives the control signal and switches on and off at predetermined times in accordance with the control signal to generate the output AC waveform from the AC waveform.The processor contains a synchronization circuit that synchronizes with the Green Safety ground line.

[0005] However, one problem with the aforementioned devices is that large, expensive transistors must be used in the circuits for dimming devices. The subject matter of the independent claims aims to solve this problem by eliminating the need for such transistors. SUMMARY OF THE INVENTION

[0006] This document refers, among other things, to devices and methods for dimmer control. In a device example, a circuit may include an input configured to receive a control signal, a controller configured to modulate the pulse width of a pulse train using the control signal when the controller is active, an output configured to provide the pulse train to a driver, and a first and second current threshold detector configured to receive load current information from the driver and to abort an active pulse from the controller when a value of the load current information exceeds a threshold.

[0007] In particular, the invention disclosed herein solves the problem described above by comprising a first and a second current limiting detector configured to detect and limit the peak current, so that cost-effective, low-tolerance electronics can be used to reliably power or dim LED, CSL or incandescent lamp products or one or more other lighting or electrical products, such as solenoids or valves.

[0008] This section serves to provide an overview of the subject matter of the present patent application. It is not intended to give an exclusive or exhaustive explanation of the invention. The detailed description serves to provide further information about the present patent application. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In the drawings, which are not necessarily drawn to scale, similar reference numerals may describe similar components in different views. Similar reference numerals with different appended letters may represent different embodiments of similar components. The drawings generally show, by way of example but not as limitations, various embodiments discussed in this document. Fig. 1A and Fig. 1B shows general lighting circuits, including example dimmer circuits. Fig. Figure 2 shows a general lighting circuit including a block diagram of an example dimmer control. Fig. Figure 3 shows a general example overcurrent detection circuit for a dimmer circuit. Fig. Figure 4 shows a general example dimmer control circuit. DETAILED DESCRIPTION

[0010] Current dimmers typically use TRIAC (triode for alternating currents) circuits to produce a symmetrical current function with alternating current (AC). TRIAC dimmers are leading-edge dimmers that turn off the AC when the voltage crosses zero volts (e.g., zero crossing, zero-crossing event) and turn on the AC at a programmable phase angle during the half-cycle. A TRIAC can be analogous to two controlled silicon rectifier transistors (SCR transistors), allowing AC operation in both the positive and negative half-cycles. A TRIAC may have a fast turn-on capability, which can provide a high AC voltage and, consequently, a fast, high load current. However, leading-edge dimmers generally do not allow direct current limiting or slew rate control.Furthermore, the “hold” current requirements of TRIAC dimmers, which are usually not symmetrical, can cause flickering in light-emitting diode (LED) and compact fluorescent (CSL) lighting products.

[0011] The present inventors have identified, among other things, a trailing-edge dimmer that can provide current limiting capabilities and, when used with LED, CSL, or incandescent lamp products, can reduce or eliminate minimum holding current requirements. In one example, the dimmer disclosed herein can include one or more current limit detectors configured to detect and limit the peak current, allowing cost-effective, low-tolerance electronics to be used to reliably power or dim LED, CSL, or incandescent lamp products, or one or more other lighting or electrical products, such as solenoids or valves.

[0012] Fig. 1A and Fig. Figure 1B shows a general example lighting circuit 100 comprising a control circuit, such as a dimmer controller 101. Each lighting circuit 100 can include a dimmer controller 101, a driver, such as a first and a second power transistor 102, 103 (Q1, Q2), a first and a second measuring resistor 104, 105 (R MESS1 , R MESS2 ) and a light source 106. In certain examples, a single integrated circuit chip may include the dimmer control 101. In one example, a setpoint resistor (R) soll ) set a control signal received from the dimmer control 101 or a dimmer setpoint received from the dimmer control 101. In certain examples, the setpoint resistance (R) can be soll ) be adjustable.

[0013] Fig. Figure 1A generally shows a two-wire dimmer application that can be used in situations where a switchgear enclosure does not have a neutral conductor, such as when only the AC live wire and the AC load live wire are available. The dimmer control 101 can be biased by the AC power when the first and second power transistors 102 and 103 are off. When the control voltage is high and the first and second power transistors 102 and 103 are on, the voltage across a supply capacitor (C) can be v ) supply the dimmer control bias voltage. During the "off time", the supply capacitor (C) can vThe diodes are charged during the positive and negative cycles via a first and second diode D1, D2 and a first resistor R1. Since the dimmer controller 101 is biased by the AC supply when the first and second power transistors 102, 103 are off, the maximum load cycle of two-wire dimmer applications is limited to approximately 75% in certain examples.

[0014] The first and second sense resistors 104 and 105 can provide the dimmer controller 101 with load current information from the driver, such as from the first and second power transistors 102 and 103 (Q1 and Q2). The sense resistors 104 and 105 can monitor a load current by detecting a voltage drop across the drain-source resistor (RDS). ON ) measure at the first and second power transistors 102, 103 and measure a measuring current (I MESS ) generate. The dimmer control can generate the measuring current (I MESS) compares with a threshold value, such as a reference current, and can interrupt one or more pulse widths configured to control the first and second power transistors 102, 103 when the measured current (I) MESS ) reaches a threshold value. In certain examples, the measuring current (I) MESS ) represent an actual load current supplied by the driver. In certain examples, the threshold can represent a current limit of the driver. The first and second measuring resistors 104, 105 (R MESS1 , R MESS2 ) can also be used to determine the phase of the AC supply voltage and zero crossing points or events using a zero crossing comparator.

[0015] Fig. Figure 1B shows a general three-wire dimmer application that can be used in situations where a neutral conductor is available in a switchgear enclosure. Fig. In terminal 1B, the neutral conductor is connected to the dimmer control 101, enabling a 100% load cycle. A supply capacitor (C) v ) is pre-tensioned and can be charged to a maximum voltage during the negative half-cycle. During the positive half-cycle, the supply capacitor (C) v ) supply a bias voltage for the dimmer control 101.

[0016] Fig. Figure 2 shows a general lighting circuit 200 comprising a block diagram of an example dimmer controller 201. The lighting circuit 200 can include a dimmer controller 201, a light source 206, an adjustable dimmer resistor 207, a first and second sense resistor 204, 205, and a first and second power transistor 202, 203. The dimmer controller 201 can include a regulator 210, a current limit detector 211, a pulse width controller 212, and a gate driver 213. In certain examples, the dimmer controller 201 can modulate the pulse width of a pulse train according to a setpoint to control the illumination of the light source 206. The driver can include the first and second power transistors 202, 203 to supply power to the light source 206, such that the power delivered to the light source 206 is related to the pulse width.In certain examples, the dimmer control 201 may include an input that can terminate an active pulse of the pulse train regardless of the setpoint. In some examples, the input may prevent the dimmer control from generating a new active pulse.

[0017] The regulator 210 can convert the voltage of an AC power source 214 into one or more desired circuit supply voltages, such as DC power voltages.

[0018] The current limit detector 211 can monitor load current information from the driver and provide signals to limit the current of the lighting circuit 200, allowing the use of less expensive circuit components with the dimmer controller 201. In certain examples, the pulse width modulator 212 can receive dimmer setpoint information (PB_CONTROL) from a resistor coupled to an input of the dimmer controller. In some examples, the pulse width modulator 212 can control the first and second power transistors 202 and 203 to maintain the lighting at the dimmer setpoint. In certain examples, the current limit detector 211 can include a comparator to provide the pulse width modulator 212 with a turn-off signal when the driver is at or approaching a current limit, and with a turn-on signal when the driver is not operating near or above a current limit.The current limit detector 211 can provide a turn-off signal to interrupt the control of the first and second power transistors 202, 203 by means of the pulse width modulation (PWM) 212, in order to limit the current of the lighting circuit 200. In some examples, the current limit detector 211 can interrupt an active pulse of the PWM 212 using the turn-off signal. In certain examples, the lighting circuit 200 can include a gate driver to drive either the first or the second power transistor 202, 203, and in some examples, to buffer the dimmer control 201 from the first and second power transistors 202, 203.

[0019] Fig. Figure 3 shows a general example current limit detector 311 for a dimmer circuit. The current limit detector 311 can include a first transistor (Q0) configured to receive a signal at a measuring terminal (U). Me) to be clamped to a reference voltage of approximately 700 millivolts (mV) relative to Uss. In certain examples, the first transistor (Q0) can be coupled to a second transistor (Q1) to provide a representation of the voltage at the measurement terminal (U). Me to reflect the flowing current. The current at the measuring terminal (U Me The current flowing through the driver transistors (e.g., 202, 203) can provide a representation of the current flowing through them. As such, in some examples, the first and second transistors (Q0, Q1) can form a current mirror, with the first transistor (Q0) acting as a measuring transistor and the second transistor (Q1) acting as a mirror transistor. In one example, the mirrored current can be measured with a precision reference current (I). REF ) can be summed. In certain examples, the reference current (I) can be used. REF ) be coupled to a control node of a comparator transistor (M4).

[0020] In certain examples, at least part of the reference current (I) can be REF ) are derived as a mirror current through the second transistor (Q1). If the mirror current of the second transistor (Q1) is approximately equal to the reference current (I) REF If the impedance (I) equals or exceeds the impedance, the comparator transistor (M4) can switch from a low-impedance state (e.g., an on state) to a high-impedance state (e.g., an off state). When the comparator transistor (M4) is in a high-impedance state, the current (I) can flow through it. C A second current source charges a capacitor (C1). When the voltage across capacitor (C1) reaches a threshold, e.g., 3 volts or one or more other voltage levels, a logic signal (MESS) can be generated. N) are transmitted to switch off one or more power transistors, such as one or more external IGBT / MOSFET transistors, and thus provide a current limiting mechanism for the load current. In certain examples, the logic signal (MESS) can be N ) a discrete turn-off signal received by the pulse width control 212 to terminate an active pulse.

[0021] In certain examples, the capacitor (C1) can be configured to charge in approximately 40 microseconds (µsec), thereby forming a 25 kHz low-pass filter to suppress high-frequency noise spikes. In one example, the current limit detector can include 311 logic to receive a turn-on signal (AN) to enable or disable the overcurrent detection capability. In certain examples, a third transistor (M5) can be used to reset the voltage across the capacitor (C1).

[0022] In certain examples, the current limit detector 311 may include a zero-crossing detector (not shown) to provide an indication of a zero-crossing event (e.g., when the supply voltage crosses zero volts). In one example, a zero-crossing detector may measure the voltage (U MeUse a zero-crossing detector at the measurement terminal to detect at least one periodic zero-crossing event. For example, a zero-crossing detector could include an operational amplifier comparator. A first input to the comparator could be coupled to ground, and a second input could be coupled to the supply voltage or a representation of the supply voltage, such as the measurement voltage. Because the supply voltage varies beyond the ground voltage, either positive or negative, the output of the comparator can change. Each change in the comparator's output can represent a zero-crossing event.It is understood that an operational amplifier comparator is an example of a zero-crossing detector, that other circuits for detecting and reproducing a zero-crossing event are conceivable, and that such other zero-crossing detection circuits are within the scope of the present subject matter.

[0023] Fig.Figure 4 shows a general example dimmer control circuit 401 comprising first and second overcurrent detection circuits, such as current limit detectors 411a, 411b, a zero-crossing detector 420, a pulse width modulation (PWM) controller 412, and a current limit control logic 421. In certain examples, the dimmer control circuit 401 may include a regulator to provide one or more DC voltages to power the one or more components of the dimmer control circuit 401. The first and second current limit detectors 411a, 411b may limit the on-time of one or more circuit breakers (not shown) by means of the current limit control logic 421.In certain examples, the first current limit detector 411a can monitor and limit a current during a positive voltage phase of the AC power source, and the second current limit detector 411b can monitor and limit a current during a negative voltage phase of the AC power source, or vice versa. If no overcurrent conditions are detected, the pulse width modulator 412 can control the circuit breakers using a setpoint specified by a pulse width modulator input (PB_CONTROL). In certain examples, the pulse width modulator input can be coupled to an adjustable component, such as an adjustable resistor, to allow different dimmer settings.When an overcurrent condition is detected, the current limit control logic 421 can bypass the control of the dimmer control output (TRB GATE) using the pulse width control 412 to limit the current of the dimmer control circuit 401. Further comments

[0024] In Example 1, a circuit can include an input configured to receive a control signal, a controller configured to modulate a pulse width of a pulse train using the control signal when the controller is turned on, an output configured to provide the pulse train to a driver, and a first and second current threshold detector configured to receive load current information from the driver and to abort an active pulse from the controller if a value of the load current information exceeds a threshold.

[0025] In Example 2, the first current limit detector according to Example 1 optionally includes a zero-crossing detector configured to detect a zero-crossing event of an AC source and provide the controller with a discrete signal representing the zero-crossing event. In Example 3, the controller according to one or more of Examples 1 and 2 is optionally configured to receive the discrete signal representing the zero-crossing event and to generate a pulse at the zero-crossing event using the discrete signal representing the zero-crossing event of the AC source.

[0026] In Example 4, the circuit according to one or more of Examples 1 to 3 optionally includes a controller configured to receive power from the AC power source and to supply direct current (DC) power to the controller.

[0027] In Example 5, the threshold value according to one or more of Examples 1 to 4 optionally includes a reference current.

[0028] In Example 6, the load current information, according to one or more of Examples 1 to 5, optionally includes a first and second current representing a load current of the driver, where the first current represents load current during a positive voltage phase of the AC source and the second current represents load current during a negative voltage phase of the AC source.

[0029] In Example 7, each of the first and second current limit detectors according to one or more of Examples 1 to 6 optionally includes a comparator, each comparator comprising a transistor configured to compare the reference current with a substitute current of the first or second current, to provide a turn-on signal to the controller when the reference current is above the substitute current of the first or second current, and to provide a turn-off signal to the controller when the reference current is below the substitute current.

[0030] In Example 8, each of the first and second current limit detectors according to one or more of Examples 1 to 7 optionally includes a current mirror configured to receive one of the first or second currents at a measuring transistor of the current mirror and to provide the substitute current at a mirror transistor of the current mirror.

[0031] In Example 9, the comparator of the first current limit detector according to one or more of Examples 1 to 8 is optionally configured to receive load current information during the positive voltage phase of the AC source, to compare the load current information with the threshold during the positive voltage phase of the AC source, and to abort the active pulse of the control if a value of the load current information exceeds a threshold during the positive voltage phase of the AC source.The comparator of the second current limit detector according to one or more of Examples 1 to 8 is optionally configured to receive load current information during the negative voltage phase of the AC source, to compare the load current information during the negative voltage phase of the AC source with a threshold value, and to abort the active pulse of the control if a value of the load current information during the negative voltage phase of the AC source exceeds a threshold value.

[0032] In Example 10, the input, control, output and the first and second current limit detectors according to one or more of Examples 1 to 9 are optionally included in a single integrated circuit chip.

[0033] In Example 11, the single integrated circuit chip according to one or more of Examples 1 to 10 optionally includes a controller configured to receive power from the AC power source and to supply DC power to the controller.

[0034] In Example 12, a method can include receiving a control signal at an input of a control circuit, modulating a pulse width of a pulse train using the control signal when a control of the control circuit is turned on, providing the pulse train to a driver using an output of the control circuit, receiving load current information from the driver at a first or second current limit detector of the control circuit, receiving a threshold value at a first or second current limit detector, and aborting an active pulse of the control when a value of the load current information exceeds a threshold value.

[0035] In Example 13, receiving load current information according to one or more of Examples 1 to 12 optionally includes receiving a first and second current, which are representative of the load current at each of the first and second current limit detectors.

[0036] In Example 14, receiving the threshold value according to one or more of Examples 1 to 13 optionally includes receiving a reference current at one of the first or second current threshold detectors.

[0037] In Example 15, the method according to one or more of Examples 1 to 14 optionally includes mirroring one of the first and second currents to provide a current that substitutes for the load current using a current mirror.

[0038] In Example 16, the procedure according to one or more of Examples 1 to 15 optionally includes comparing the substitute current with the reference current using a comparator transistor.

[0039] In Example 17, terminating an active control pulse according to one or more of Examples 1 to 16 optionally includes receiving the reference current at a control node of the comparator transistor and deriving a larger current, approximately equal to the surrogate current, from the control node of the comparator transistor when a current limit of the driver is exceeded, where the reference current is surrogate for the current limit of the driver.

[0040] In Example 18, the method according to one or more of Examples 1 to 17 optionally includes detecting a zero-crossing event of an AC source coupled to the control circuit using one of the first or second current limit detectors, and providing a discrete signal representing the zero-crossing event of the AC source to the control.

[0041] In Example 19, the method according to one or more of Examples 1 to 18 optionally includes receiving the discrete signal representing the zero-crossing event at the controller and triggering the active pulse using the discrete signal representing the zero-crossing event of the AC source.

[0042] In Example 20, a system can include an input configured to receive a control signal, a controller configured to modulate a pulse width of a pulse train using the control signal when the controller is turned on, a regulator configured to receive power from an AC source and provide DC power to the controller, an output configured to provide the pulse train to a driver, first and second current limit detectors configured to receive load current information from the driver and to abort an active pulse from the controller when a value of the load current information exceeds a threshold, the first current limit detector including a zero-crossing detector configured to detect a zero-crossing event of the AC source and provide the controller with a discrete,to provide a signal representing the zero-crossing event of the AC source; wherein the controller is configured to receive the discrete signal representing the zero-crossing event and to generate a pulse at the zero-crossing event using the discrete signal representing the zero-crossing event of the AC source, wherein the threshold includes a reference current, wherein the load current information includes a first and second current representing a load current of the driver, wherein the first current represents load current during a positive voltage phase of the AC source and the second current represents load current during a negative voltage phase of the AC source, wherein each of the first and second current threshold detectors includes a comparator, wherein each of the comparators includes a transistor configured toto compare the reference current with a substitute current of one of the first or second currents, to provide the controller with a turn-on signal when the reference current is above the substitute current of one of the first or second currents, and to provide the controller with a turn-off signal when the reference current is below the substitute current, wherein each of the first and second current limit detectors comprises a current mirror configured to receive one of the first or second currents at a sensing transistor of the current mirror and to provide the substitute current at a mirror transistor of the current mirror, wherein the comparator of the first current limit detector is configured to receive load current information during the positive voltage phase of the AC power source,to compare the load current information during the positive voltage phase of the AC source with the threshold value and to terminate the active pulse of the control if a value of the load current information during the positive voltage phase of the AC source exceeds a threshold value; wherein the comparator of the first current limit detector is configured to receive load current information during the negative voltage phase of the AC source, to compare the load current information during the negative voltage phase of the AC source with the threshold value, and to terminate the active pulse of the control if a value of the load current information during the negative voltage phase of the AC source exceeds a threshold value, wherein the input, control, output, and the first and second current limit detectors are included in a single integrated circuit chip.

[0043] In Example 21, a system or apparatus may include means for performing one or more of the tasks according to Examples 1 to 20, or a machine-readable means comprising instructions which, when performed by a machine, cause the machine to perform any one or more of the tasks according to Examples 1 to 20, or may optionally be combined with any part or combination of parts of any one or more of Examples 1 to 20 to comprise such a system or apparatus.

[0044] The detailed description above includes references to the accompanying drawings, which form part of the detailed description. The drawings illustrate specific embodiments in which the invention can be carried out. These embodiments are also referred to herein as "examples." Such examples may include components beyond those shown or described. However, the present inventors are also considering examples in which only the components shown or described are provided.Furthermore, the present inventors are also considering examples that use any combination or permutation of the components shown or described (or one or more aspects thereof), either relating to a particular example (or one or more aspects thereof) or relating to other examples (or one or more aspects thereof) shown or described herein.

[0045] All publications, patents, and patent documents referenced in this document are incorporated herein by reference in their entirety, as if they were incorporated individually by reference. In the event of inconsistent usage between this document and the documents incorporated by reference, the usage in the incorporated references should be considered supplementary to that in this document; in the case of irreconcilable inconsistencies, the usage in this document shall prevail.

[0046] In this document, the terms "a" or "an" are used, as is customary in patent documents, to encompass one or more than one, irrespective of any other instances or uses of "at least one" or "one or more." In this document, the term "or" is used to refer to a non-exclusive "or," such that "A or B" encompasses "A but not B," "B but not A," and "A and B," unless otherwise specified. In this document, the terms "include" / "contain" and "in which" are used as plain language equivalents of the corresponding terms "comprise" and "whereby."Furthermore, in the following claims, the terms "include" / "contain" and "comprise" are not exhaustive; that is, a system, device, article, or method comprising components beyond those listed in a claim under such a term is still considered to fall within the scope of protection of the claim. Moreover, in the following claims, the terms "first," "second," and "third," etc., are used merely as identifiers and do not intend to impose numerical requirements on their objects.

[0047] The process examples described here may be at least partially machine- or computer-implemented. Some examples may include a computer-readable or machine-readable medium encoded with instructions that can be used to configure an electronic device to execute processes such as those described in the examples above. Execution of such processes may include code such as microcode, assembly language code, higher-level language code, or the like. Such code may include computer-readable instructions for executing various processes. The code may form parts of computer program products. Furthermore, in one example, the code may be stored tangible on one or more volatile, non-transient, or non-volatile tangible computer-readable media, such as during execution or at other times.Examples of these tangible, computer-readable media may include, but are not limited to, hard disks, removable magnetic disks, removable optical disks (e.g., Compact Disks and Digital Video Disks), magnetic cartridges, memory cards or sticks, random access memory (RAM), read-only memory (ROM), and the like.

[0048] The above description is intended for illustrative purposes and is not meant to be limiting. For example, the examples described above (or one or more aspects thereof) may be used in combination. Other embodiments may be used, for example, by a person skilled in the art after reviewing the above description. The summary allows the reader to quickly determine the nature of the technical disclosure. It is provided with the understanding that it is not intended to interpret or limit the scope or meaning of the claims. Furthermore, various features may be grouped in the above detailed description to streamline the disclosure. This should not be interpreted as meaning that an unclaimed disclosed feature is essential to any claim.Rather, an inventive subject matter may be present in fewer than all features of a particular disclosed embodiment. Therefore, the following claims, each claim standing alone as a separate embodiment, are hereby included in the detailed description, and it is intended that such embodiments may be combined with one another in various combinations and permutations. The scope of protection of the invention should be determined with reference to the pending claims, together with the scope of protection of equivalents to which such claims are entitled.

Claims

[1] Circuit comprising: an input configured to receive a control signal; a controller configured to modulate a pulse width of a pulse train using the control signal when the controller is turned on; an output configured to provide the pulse train to a driver; and first and second current limit detectors configured to receive load current information from the driver and to abort an active pulse of the controller when a value of the load current information exceeds a threshold, wherein the first current limit detector comprises a zero-crossing detector configured to detect a zero-crossing event of an AC power source and provide a discrete signal representative of the zero-crossing event of the AC power source to the controller. [2] The circuit of claim 1, wherein the controller is configured to receive the discrete signal representative of the zero-crossing event and generate a pulse at the zero-crossing event using the discrete signal representative of the zero-crossing event of the AC power source. [3] The circuit of claim 1, comprising a regulator configured to receive power from the AC power source and provide DC power to the controller. [4] A circuit according to claim 1, wherein: the threshold includes a reference current: the load current information comprises a first and second current representative of a load current of the driver, the first current representative of load current during a positive voltage phase of the AC power source and the second current representative of load current during a negative voltage phase of the AC power source; each of the first and second current limit detectors of a comparator, each of the comparators comprising a transistor configured to compare the reference current with a representative current of one of the first or second currents, provide an on signal to the controller when the reference current is above the representative current of one of the first or second currents, and provide an off signal to the controller when the reference current is below the representative current; and each of the first and second current limit detectors of a current mirror configured to receive one of the first or second current at a sense transistor of the current mirror and to provide the representative current to a mirror transistor of the current mirror. [5] The circuit of claim 4, wherein the comparator of the first current limit detector is configured to receive load current information during the positive voltage phase of the AC power source, compare the load current information during the positive voltage phase of the AC power source with the threshold, and abort the active pulse of the controller when a value of the load current information during the positive voltage phase of the AC power source exceeds the threshold;and wherein the comparator of the second current limit detector is configured to receive load current information during the negative voltage phase of the AC power source, compare the load current information during the negative voltage phase of the AC power source with the threshold, and abort the active pulse of the controller if a value of the load current information during the negative voltage phase of the AC power source exceeds the threshold.; [6] The circuit of claim 1, wherein the input, the controller, the output, and the first and second current limit detectors are included in a single integrated circuit chip, and wherein the single integrated circuit chip includes a regulator configured to receive power from the AC power source and provide DC power to the controller. [7] Procedure comprising: Receiving a control signal at an input of a control circuit; modulating a pulse width of a pulse train using the control signal when a control of the control circuit is turned on; Providing the pulse train to a driver using an output of the control circuit; Receiving load current information from the driver at one of a first or second current limit detector of the control circuit; Receiving a threshold value at one of the first or second current limit detectors; and Cancel an active pulse of the controller if a value of the load current information exceeds a threshold. [8] The method of claim 7, wherein: receiving load current information comprises receiving a first and second current representative of the load current, respectively, at each of the first and second current limit detectors; and receiving the threshold comprises receiving a reference current at one of the first or second current limit detectors. [9] A method according to claim 8, comprising: Mirroring one of the first or second currents to provide a current representative of the load current using a current mirror; and Comparing the representative current with the reference current using a comparator transistor. [10] The method of claim 9, wherein aborting an active pulse of the controller comprises receiving the reference current at a control node of the comparator transistor and deriving a larger current approximately equal to the representative current from the control node of the comparator transistor when a current limit of the driver is exceeded, the reference current being representative of the current limit of the driver. [11] A method according to claim 10, comprising: Detecting a zero-crossing event of an AC power source coupled to the control circuit using one of the first or second current limit detectors and providing a discrete signal representative of the zero-crossing event of the AC power source to the controller; and Receiving the discrete signal representing the zero-crossing event at the controller and initiating the active pulse using the discrete signal representing the zero-crossing event of the AC source.

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