Circuits and methods for driving light sources

• US 8,698,419 B2
• Filed: 02/10/2012
• Issued: 04/15/2014
• Est. Priority Date: 03/04/2010
• Status: Expired due to Fees

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: Yan, Tiesheng, Kuo, Ching-Chuan, Lin, Feng, Xu, Jianping
• Primary Examiner(s): TRAN, ANH Q
• Application Number:
  US13/371,351
• Publication Number:
  US 20120139433A1
• Time in Patent Office: 795 Days
• Field of Search: None
• US Class Current: 315/302
• CPC Class Codes: H05B 41/2821 by means of a single-switch converter or a parallel push-pull converter in the final stage H05B41/285 takes precedence
• CPC Class Codes: H05B 41/2822 using specially adapted components in the load circuit, e.g. feed-back transformers, piezoelectric transformers; using specially adapted load circuit configurations
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 47/10 Controlling the light source

Abstract

A circuit for driving a light-emitting diode (LED) light source includes a converter, a saw-tooth signal generator, and a controller. The converter includes a switch which is controlled by a driving signal. The converter provides a sense signal indicating the current through said LED light source. The saw-tooth signal generator generates a saw-tooth signal based on the driving signal. The controller generates the driving signal based on signals including the saw-tooth signal and the first sense signal to adjust the current through the LED light source to a target level and to correct a power factor of the driving circuit by controlling an average current of the input current to be substantially in phase with said input voltage.

Claims

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

a converter operable for receiving an input voltage and an input current and powering said LED light source, that comprises a switch controlled by a driving signal, and operable for providing a first sense signal indicating a current through said LED light source;

a saw-tooth signal generator, coupled to said converter, operable for generating a saw-tooth signal based on said driving signal; and

a controller, coupled to said converter and said saw-tooth signal generator, operable for generating said driving signal based on signals comprising said saw-tooth signal and said first sense signal to adjust said current through said LED light source to a target level and to correct a power factor of said driving circuit by controlling an average current of said input current to be substantially in phase with said input voltage.

2. The circuit as claimed in claim 1, wherein said converter further comprises an energy storage element, a current of which is controlled by said switch.

3. The circuit as claimed in claim 2, wherein said controller further comprises:

an error amplifier operable for generating an error signal based on said first sense signal and a reference signal indicating said target level of said current through said LED light source; and

a comparator, coupled to said error amplifier, operable for comparing said saw-tooth signal with said error signal to control said driving signal,

wherein said driving signal has a first state and a second state, wherein said current through said energy storage element is increased when said driving signal is in said first state, and is decreased when said driving signal is in second state.

4. The circuit as claimed in claim 3, wherein said saw-tooth signal increases during said first state of said driving signal, and wherein said driving signal is switched to said second state when said saw-tooth signal reaches said error signal.

5. The circuit as claimed in claim 3, wherein a time duration for said saw-tooth signal to increase from a predetermined level to said error signal is constant if said current through said LED light source is maintained at said target level.

6. The circuit as claimed in claim 2, wherein said controller is further operable for receiving a detection signal indicating an electrical condition of said energy storage element, wherein said driving signal has a first state and a second state, wherein said current through said energy storage element is increased when said driving signal is in said first state, and is decreased when said driving signal is in said second state, wherein said driving signal is switched to said first state if said detection signal indicates that said current through said energy storage element decreases to a predetermined level.

7. The circuit as claimed in claim 2, wherein said energy storage element comprises:

a first inductor electrically coupled to said switch and said LED light source, wherein said current of said energy storage element flows through said first inductor; and

a second inductor, magnetically and electrically coupled to said first inductor, operable for generating a detection signal indicating an electrical condition of said first inductor.

8. The circuit as claimed in claim 7, wherein said first inductor and said second inductor are electrically coupled to a common node between said switch and said first inductor, wherein said common node provides a reference ground for said controller, and wherein said reference ground is different from the ground of said circuit.

9. The circuit as claimed in claim 1, wherein said saw-tooth signal generator comprises:

a diode and a first resistor coupled in parallel between a first node and a second node; and

a capacitor and a second resistor coupled in parallel between said second node and ground, wherein said first node receives said driving signal, and said second node provides said saw-tooth signal.

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

a rectifier operable for receiving an input alternating current (AC) current and an input AC voltage and providing said input current,

wherein said controller is operable for correcting said power factor such that said input AC current is substantially in phase with said input AC voltage.

11. A method for powering a light-emitting diode (LED) light source, said method comprising:

receiving an input voltage and an input current;

converting said input voltage to an output voltage to drive said LED light source;

controlling a current flowing through an energy storage element according to a driving signal so as to regulate a current flowing through said LED light source;

receiving a first sense signal indicating said current through said LED light source;

generating a saw-tooth signal based on said driving signal; and

controlling said driving signal based on signals comprising said saw-tooth signal and said first sense signal to adjust said current through said LED light source to a target level and to correct a power factor of a driving circuit by controlling an average current of said input current to be substantially in phase with said input voltage.

12. The method as claimed in claim 11, further comprising:

receiving a second sense signal indicating said current through said energy storage element; and

filtering said second sense signal to generate said first sense signal.

13. The method as claimed in claim 11, further comprising:

generating an error signal indicating a difference between said first sense signal and a reference signal indicating said target current level of said current through said LED light source;

comparing said saw-tooth signal with said error signal;

receiving a detection signal indicating an electric condition of said energy storage element;

switching said driving signal to a first state if said detection signal indicates said current through said energy storage element decreases to a predetermined level;

switching said driving signal to a second state according to a result of said comparison;

increasing said current through said energy storage element when said driving signal is in said first state; and

decreasing said current through said energy storage element when said driving signal is in said second state.

14. The method as claimed in claim 13, wherein a time duration for said saw-tooth signal to increase from a predetermined level to said error signal is constant if said current through said LED light source is maintained at said target level.