CIRCUITS AND METHODS FOR DRIVING LIGHT SOURCES

• US 20130049621A1
• Filed: 10/29/2012
• Published: 02/28/2013
• Est. Priority Date: 03/04/2010
• Status: Abandoned Application

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: YAN, Tiesheng, KUO, Ching-Chuan, LIU, Xueshang
• Application Number:
  US13/663,165
• Publication Number:
  US 20130049621A1
• Time in Patent Office: Days
• US Class Current: 315/205
• CPC Class Codes: H05B 45/14 using electrical feedback from LEDs or from LED modules
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 45/385 using flyback topology

Abstract

A driving circuit includes a converter, a transformer, a first sensor and a second sensor. The converter is coupled to a switch that operates in a first state or in a second state. The converter receives an input voltage and provides a regulated voltage. The transformer transforms the regulated voltage to an output voltage to power said LED light source. Both a first current through the converter and a second current through the transformer further flow through the switch when the switch operates in the first state. The first sensor coupled between the switch and a first reference node provides a first sense signal indicating a combined current of the first current and the second current. The second sensor coupled between the first reference node and a second reference node provides a second sense signal indicating only the second current.

Claims

1. A driving circuit for powering a light-emitting diode (LED) light source, said driving circuit comprising:

a converter coupled to a switch operable in a first state and operable in a second state, and configured to receive an input voltage and provide a regulated voltage;

a transformer coupled to said converter and said switch, and configured to transform said regulated voltage to an output voltage to power said LED light source, wherein both a first current through said converter and a second current through said transformer further flow through said switch when said switch operates in said first state;

a first sensor coupled between said switch and a first reference node, and configured to provide a first sense signal indicating a combined current of said first current and said second current; and

a second sensor coupled between said first reference node and a second reference node, and configured to provide a second sense signal indicating only said second current.

2. The driving circuit as claimed in claim 1, further comprising:

a controller coupled to said switch and configured to generate a driving signal to switch said switch between said first state and said second state; and

a protection circuit coupled to a pin of said controller and configured to receive said first sense signal, compare said first sense signal to a threshold, and pull a voltage of said pin to a predetermined level according to a result of said comparison.

3. The driving circuit as claimed in claim 2, wherein said controller controls said driving signal to maintain said switch at said second state if said voltage of said pin is maintained at said predetermined level.

4. The driving circuit as claimed in claim 1, wherein when said switch operates in said first state, both said first current and said second current flow through said first sensor, and only said second current flows through said second sensor.

5. The driving circuit as claimed in claim 1, wherein said first reference node is further coupled to a current path for said first current, wherein said first current flows through said current path other than said second sensor.

6. The driving circuit as claimed in claim 1, wherein said first sense signal has a voltage equal to a sum of a voltage across said first sensor and a voltage across said second sensor, and wherein said second sense signal has a voltage equal to said voltage across said second sensor.

7. The driving circuit as claimed in claim 1, further comprising:

a rectifier that provides said input voltage; and

a controller that generates a driving signal to switch said switch between said first state and said second state, wherein said rectifier and said controller have different reference grounds, and wherein said first reference node is a reference ground of said rectifier, and wherein said second reference node is a reference ground of said controller.

8. The driving circuit as claimed in claim 1, further comprising:

a controller coupled to said switch and configured to generate a driving signal to switch said switch between said first state and said second state, said controller further comprising a pin for receiving said second sense signal; and

a clamp circuit coupled between said first reference node and said pin, and configured to clamp a voltage at said pin to a predetermined level if said voltage across said second sensor drops below a predetermined threshold.

9. The driving circuit as claimed in claim 1, further comprising:

a controller coupled to said switch, and configured to provide a square wave signal based on said second sense signal, said square wave signal having an average level proportional to an average current flowing through said LED light source, and further configured to provide a driving signal based on said square wave signal to control said switch so as to control said average current.

10. The circuit as claimed in claim 9, wherein said square wave signal has a first voltage level proportional to a peak level of said second current when said transformer operates in a predetermined state, wherein said square wave signal has a second voltage level if said transformer operates in a state other than said predetermined state.

11. The circuit as claimed in claim 10, wherein said transformer comprises a primary winding and a secondary winding, wherein said second current flowing through said primary winding increases during said first state of said switch, and a third current flowing through said secondary winding decreases during said second state of said switch, and wherein said transformer operates in said predetermined state during a time period when said third current through said secondary winding decreases.

12. The circuit as claimed in claim 9, wherein said controller comprises:

a driver configured to generate said driving signal to control said switch;

a sampling circuit configured to sample a peak level of said second current according to said second sense signal and generate a peak signal having a first level proportional to said peak level; and

a multiplexer configured to transfer said peak signal to said driver if said transformer operates in said predetermined state, and otherwise transfer a predetermined signal having a second level to said driver.

13. The circuit as claimed in claim 9, wherein said controller and said transformer constitute a negative feedback loop, wherein said negative feedback loop maintains an average voltage of said square wave signal to be equal to a reference signal, so as to maintain an average current flow through said LED light source at a target level.

14. The circuit as claimed in claim 1, wherein a triode for alternating current (TRIAC) component receives an alternating current (AC) voltage, and is turned on and off during each cycle of said AC voltage to generate said input voltage, wherein said circuit further comprises:

a controller configured to receive a monitoring signal indicating said input voltage, monitor a conductance status of said TRIAC component according to said monitoring signal, and generate a driving signal according to said conductance status, said driving signal switching said switch between said first state and said second state to control dimming of said LED light source.

15. The circuit as claimed in claim 14, wherein said controller further comprises:

a signal generator configured to generate a detection signal having an average level proportional to an average current flowing through said LED light source;

a TRIAC detector configured to generate a reference signal according to said monitoring signal, said reference signal indicating a target level for said average current through said LED light source; and

a driver coupled to said signal generator and said TRIAC detector, and configured to generate said driving signal based on said detection signal and said reference signal so as to control said switch to adjust said average current to said target level.

16. The circuit as claimed in claim 15, wherein said TRIAC detector monitors a time to turn on said TRIAC component in each cycle of said AC voltage according to said monitoring signal, and generates said reference signal according to said time.

17. The circuit as claimed in claim 15, wherein said TRIAC detector generates a square wave signal according to said monitoring signal, and filters said square wave signal to generate said reference signal indicating an average level of said square wave signal.

18. A controller for controlling power to a light-emitting diode (LED) light source, said controller comprising:

an output pin configured to generate a driving signal to operate a switch, wherein a converter converts an input voltage to a regulated voltage based on operations of said switch, and wherein a transformer transforms said regulated voltage to an output voltage based on said operations to power said LED light source, wherein both a first current through said converter and a second current through said transformer further flow through said switch when said switch operates in a first state;

a protection pin coupled to a protection circuit, wherein said protection circuit senses a combined current of said first current and said second current by detecting a total voltage across a first resistor and a second resistor, wherein said first resistor is coupled between said switch and a first reference node, and said second resistor is coupled between said first reference node and a second reference node; and

a sense pin coupled to said first reference node, and configured to sense only said second current by detecting a voltage across said second resistor,

wherein said controller controls said driving signal according to signals on said sense pin and said protection pin.

19. The controller as claimed in claim 18, wherein said controller further comprises:

a feedback pin coupled to an auxiliary winding of said transformer, wherein a signal received by said feedback pin indicates whether said transformer operates in a predetermined state, and wherein said controller generates a square wave signal having an average level proportional to an average current flowing through said LED light source based on signals on said sense pin and said feedback pin.

20. The controller as claimed in claim 19, wherein said square wave signal has a first level proportional to a peak level of said second current when said transformer operates in said predetermined state, and wherein said square wave signal has a second level if said transformer operates in a state other than said predetermined state.

21. The controller as claimed in claim 19, wherein said transformer comprises a primary winding and a secondary winding, wherein said second current flowing through said primary winding increases when said switch operates in said first state, and a third current flowing through said secondary winding decreases when said switch operates in a second state, and wherein said transformer operates in said predetermined state during a time period when said third current through said secondary winding decreases.

22. The controller as claimed in claim 18, wherein said protection circuit pulls a voltage at said protection pin to a predetermined level if said total voltage across said first and second resistors is greater than a threshold, and wherein said controller controls said driving signal to maintain said switch in a second state if said voltage at said protection pin is pulled to said predetermined level.

23. The controller as claimed in claim 18, wherein said first reference node is a reference ground of a rectifier that generates said input voltage, and wherein said second reference node is a reference ground of said controller.

24. The controller as claimed in claim 18, wherein a triode for alternating current (TRIAC) component converts an alternating current (AC) voltage to said input voltage, wherein said controller further comprises:

a monitoring pin configured to receive a monitoring signal indicating said input voltage, wherein said controller monitors a conductance status of said TRIAC component according to said monitoring signal, and controls said driving signal according to said conductance status to control dimming of said LED light source.

25. The controller as claimed in claim 24, further comprising:

a signal generator configured to generate a detection signal having an average level proportional to an average current flowing through said LED light source;

a TRIAC detector configured to generate a reference signal according to said monitoring signal, said reference signal indicating a target level for said average current through said LED light source; and

a driver configured to generate said driving signal based on said detection signal and said reference signal so as to control said switch to adjust said average current to said target level.

26. The controller as claimed in claim 25, wherein said controller monitors a time to turn on said TRIAC component in each cycle of said AC voltage according to said monitoring signal, and generates said reference signal according to said time.

27. A method for controlling power to a light-emitting diode (LED) light source, said method comprising:

converting an input voltage to a regulated voltage by a converter;

transforming said regulated voltage to an output voltage by a transformer to power said LED light source;

operating a switch according to a driving signal, wherein both a first current through said converter and a second current through said transformer further flow through said switch when said switch operates in a first state;

receiving a first sense signal indicating a combined current of said first current and said second current by detecting a total voltage across a first sensor and a second sensor, wherein said first sensor is coupled between said switch and a first reference node, and wherein said second sensor is coupled between said first reference node and a second reference node;

receiving a second sense signal indicating only said second current by detecting a voltage across only said second sensor; and

controlling said driving signal to adjust a current flowing through said LED light source according to said first sense signal and said second sense signal.

28. The method as claimed in claim 27, further comprising:

providing a square wave signal based on said second sense signal, wherein said square wave signal has an average level proportional to an average current flowing through said LED light source; and

controlling said driving signal based on said square wave signal to adjust said average current to a target level.

29. The method as claimed in claim 28, further comprising:

adjusting said square wave signal to a first level proportional to a peak level of said second current when said transformer operates in a predetermined state; and

adjusting said square wave signal to a second constant level if said transformer operates in a state other than said predetermined state.

30. The method as claimed in claim 29, wherein said transformer includes a primary winding and a secondary winding, wherein said second current flowing through said primary winding increases during said first state of said switch, wherein a third current flowing through said secondary winding decreases until reaching a predetermined level during a second state of said switch, wherein said method further comprises:

determining that said transformer operates in said predetermined state when said third current decreases during said second state of said switch.

31. The method as claimed in claim 27, wherein said first reference node is a reference ground of a rectifier that generates said input voltage, and wherein said second reference node is a reference ground of a controller that performs the step of controlling said driving signal.

32. The method as claimed in claim 27, further comprising:

comparing said first sense signal to a threshold;

pulling a voltage on a pin of a controller to a predetermined level according to a result of said comparison; and

controlling said driving signal to maintain said switch at said second state if said voltage on said pin is pulled to said predetermined level.

33. The method as claimed in claim 27, further comprising:

converting an alternating current (AC) voltage to said input voltage by a triode for alternating current (TRIAC) component;

monitoring a conductance status of said TRIAC component according to a monitoring signal indicating said input voltage;

generating a reference signal indicating a target level for an average current through said LED light source according to said monitoring signal; and

controlling said driving signal according to said reference signal to switch said switch between said first state and said second state to control dimming of said LED light source.

34. The method as claimed in claim 33, further comprising:

monitoring a time to turn on said TRIAC component in each cycle of said AC voltage according to said monitoring signal; and

generating said reference signal according to said time.