Drive circuit for a light-emitting diode light source
A controllable lighting device may utilize a controllable impedance circuit to conduct a load current through an LED light source. The controllable impedance circuit may be coupled in series with a first switching device, which may be rendered conductive and non-conductive via a pulse-width modulated signal to adjust an average magnitude of the load current. The controllable lighting device may further comprise a control loop circuit that includes a second switching device. The second switching device may be rendered conductive and non-conductive in coordination with the first switching device to control when a feedback signal is provided to the control loop circuit and used to control the LED light source. The control loop circuit may be characterized by a time constant that is significantly greater than an operating period of the load current.
1. A drive circuit for a light-emitting diode (LED) light source, comprising:
a controllable impedance circuit configured to conduct a load current through the LED light source;
a first switching device connected in series with the controllable impedance circuit and responsive to a pulse-width modulated (PWM) signal;
a feedback circuit configured to generate a feedback signal indicative of a magnitude of the load current conducted through the LED light source;
a control loop circuit coupled to the feedback circuit and configured to generate a drive signal for controlling the controllable impedance circuit in response to a target-current control signal and the feedback signal, the control loop circuit comprising a second switching device, the second switching device capable of being rendered conductive and non-conductive in response to a switch control signal to control when the feedback signal is used to generate the drive signal, the control loop circuit configured to adjust a peak magnitude of the load current conducted through the LED light source toward a target magnitude based on the target-current control signal;
wherein the first switching device is rendered conductive and non-conductive in response to the PWM signal and a duty cycle of the PWM signal is adjusted to adjust an average magnitude of the load current, and wherein the second switching device is rendered conductive and non-conductive in response to the switch control signal in coordination with the PWM signal.
2. The drive circuit of claim 1 , wherein the control loop circuit further comprises a filter circuit configured to filter the feedback signal and the second switching device is rendered conductive and non-conductive to control when the feedback signal is provided to the filter circuit.
3. The drive circuit of claim 2 , wherein the filter circuit comprises a resistor-capacitor (RC) filter coupled to the second switching device and configured to generate a signal representative of a peak magnitude of the feedback signal when the second switching device is rendered conductive.
4. The drive circuit of claim 1 , wherein the control loop circuit further comprises an integrator circuit, the control loop circuit configured to receive the target current control signal from the control circuit and generate the at least one drive signal by integrating the difference between the target current control signal and the feedback signal via the integrator circuit.
5. The drive circuit of claim 4 , wherein the control loop circuit is characterized by a time constant, wherein the load current conducted by the controllable impedance circuit is characterized by a load current period, and wherein the time constant of the integrator circuit is greater than the load current period.
6. The drive circuit of claim 1 , wherein the first switching device is electrically coupled between the controllable impedance circuit and a circuit common.
7. The drive circuit of claim 1 , wherein the controllable impedance circuit comprises a regulation transistor configured to operate in a linear region.
8. A method of driving a light-emitting diode (LED) light source, comprising:
receiving, by an LED dimmer control circuit, output intensity data representative of an output intensity for one or more LED light sources conductively coupled to the LED dimmer control circuit;
determining, by the LED dimmer control circuit, an ON time (T ON ) to supply voltage to the one or more LED light sources based on the received output intensity data;
starting, by the LED dimmer control circuit a timer to provide an elapsed time (T);
causing, by the LED dimmer control circuit, a controllably conductive device disposed between a power source and the one or more LED light sources to transition to a CONDUCTIVE state;
responsive to the elapsed time meeting or exceeding a first time threshold (T≥T 1 ), introducing, by the LED dimmer control circuit, a current feedback signal to the LED dimmer control circuit;
responsive to the elapsed time meeting or exceeding a second time threshold (T≥T 2 ), interrupting, by the LED dimmer control circuit, the current feedback signal to the LED dimmer control circuit; and
responsive to the elapsed time meeting or exceeding the ON time (T≥T ON ), causing, by the LED dimmer control circuit, the controllably conductive device to transition to a NON-CONDUCTIVE state.
9. The method of claim 8 , wherein causing the controllably conductive device disposed between the power source and the one or more LED light sources to transition to the CONDUCTIVE state further comprises:
causing, by the LED dimmer control circuit, at least one field-effect transistor (FET) disposed between the power source and the one or more LED light sources to transition to the CONDUCTIVE state.
10. The method of claim 9 , wherein, causing the controllably conductive device to transition to the NON-CONDUCTIVE state further comprises:
responsive to the elapsed time meeting or exceeding the ON time (T≥T ON ), causing, by the LED dimmer control circuit, the FET to transition to the NON-CONDUCTIVE state.
11. The method of claim 8 wherein introducing a current feedback signal to the LED dimmer control circuit further comprises:
responsive to the elapsed time meeting or exceeding the first time threshold (T≥T 1 ), filtering the current feedback signal through a low-pass filter and introducing the filtered current feedback signal to the LED dimmer control circuit.
12. The method of claim 8 wherein responsive to the elapsed time meeting or exceeding the second time threshold (T≥T 2 ), interrupting the current feedback signal to the LED dimmer control circuit further comprises:
responsive to the elapsed time meeting or exceeding a second time threshold (T≥T 2 ), interrupting, by the LED dimmer control circuit, the current feedback signal to the LED dimmer control circuit, wherein T 2 equals a difference between T ON and a time offset value (T 2 =T ON −T OFFSET ).
13. The method of claim 8 , further comprising, responsive to the introduction of the current feedback signal to the LED dimmer control circuit:
sampling the current feedback signal; and
determining an average current feedback signal using the sampled current feedback signals.
14. The method of claim 8 wherein introducing the current feedback signal to the LED dimmer control circuit, further comprises:
causing, by the LED dimmer control circuit, a feedback switch to transition to a CONDUCTIVE state to introduce the current feedback signal to the LED dimmer control circuit.
15. The method of claim 14 wherein interrupting the current feedback signal to the LED dimmer control circuit, further comprises:
causing, by the LED dimmer control circuit, the feedback switch to transition to a NON-CONDUCTIVE state to interrupt the current feedback signal to the LED dimmer control circuit.
16. A non-transitory, machine-readable, storage device that includes instructions that, when executed by an LED dimmer control circuit, causes the control circuit to:
receive output intensity data representative of an output intensity for one or more LED light sources conductively coupled to the LED dimmer control circuit;
determine an ON time (T ON ) to supply voltage to the one or more LED light sources based on the received output intensity data;
initiate a timer to provide an elapsed time (T);
cause a controllably conductive device disposed between a power source and the one or more LED light sources to transition to a CONDUCTIVE state;
responsive to the elapsed time meeting or exceeding a first time threshold (T≥T 1 ), introduce a current feedback signal to the LED dimmer control circuit;
responsive to the elapsed time meeting or exceeding a second time threshold (T≥T 2 ), interrupt the current feedback signal to the LED dimmer control circuit; and
responsive to the elapsed time meeting or exceeding the ON time (T≥T ON ), cause the controllably conductive device to transition to a NON-CONDUCTIVE state.
17. The non-transitory, machine-readable, storage device of claim 16 , wherein the instructions that cause the LED dimmer control circuit to cause the controllably conductive device disposed between the power source and the one or more LED light sources to transition to the CONDUCTIVE state further causes the control circuit to:
cause at least one field-effect transistor (FET) disposed between a power source and the one or more LED light sources to transition to a CONDUCTIVE state.
18. The non-transitory, machine-readable, storage device of claim 17 , wherein the instructions that cause the LED dimmer control circuit to cause the controllably conductive device to transition to the NON-CONDUCTIVE state further cause the control circuit to:
responsive to the elapsed time meeting or exceeding the ON time (T≥T ON ), cause the FET to transition to the NON-CONDUCTIVE state.
19. The non-transitory, machine-readable, storage device of claim 16 wherein the instructions that cause the LED dimmer control circuit to introduce the current feedback signal to the LED dimmer control circuit further cause the control circuit to:
responsive to the elapsed time meeting or exceeding the first time threshold (T≥T 1 ), introduce a low-pass filtered current feedback signal to the LED dimmer control circuit.
20. The non-transitory, machine-readable, storage device of claim 16 wherein the instructions that cause the LED dimmer control circuit to interrupt the current feedback signal to the LED dimmer control circuit further cause the control circuit to:
interrupt the current feedback signal to the LED dimmer control circuit responsive to the elapsed time meeting or exceeding the second time threshold (T≥T 2 ), wherein T 2 equals a difference between T ON and a time offset value (T 2 =T ON −T OFFSET ).
21. The non-transitory, machine-readable, storage device of claim 16 , wherein the instructions further cause the LED dimmer control circuit to:
sample the current feedback signal; and
determine an average current feedback signal using the sampled current feedback signals.
22. The non-transitory, machine-readable, storage device of claim 16 wherein the instructions that cause the LED dimmer control circuit to introduce the current feedback signal to the LED dimmer control circuit, further cause the control circuit to:
causing, by the LED dimmer control circuit, a feedback switch to transition to a CONDUCTIVE state to introduce the current feedback signal to the LED dimmer control circuit.
23. The non-transitory, machine-readable, storage device of claim 22 wherein the instructions that cause the LED dimmer control circuit to interrupt the current feedback signal to the LED dimmer control circuit, further cause the control circuit to:
cause the feedback switch to transition to a NON-CONDUCTIVE state to interrupt the current feedback signal to the LED dimmer control circuit.