CIRCUITS AND METHODS FOR DRIVING LIGHT SOURCES

• US 20120126710A1
• Filed: 11/23/2010
• Published: 05/24/2012
• Est. Priority Date: 11/23/2010
• Status: Active Grant

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: LIN, Yung Lin, KUO, Ching Chuan, LEE, Sheng Tai
• Granted Patent: US 9,030,121 B2
• Time in Patent Office: Days
• US Class Current: 315/185.R
• CPC Class Codes: H05B 45/44 with an active control inside an LED matrix

Abstract

Embodiments in accordance with the present invention provide circuits and methods for driving light sources, e.g., a light-emitting diode (LED) light source. In one embodiment, a lamp includes a rectifier rectifying an AC voltage to a rectified AC voltage, an LED light source, and a switch coupled to the LED light source in series controlling a current through the LED light source according to a predetermined current reference. The LED light source and the switch coupled in series receive the rectified AC voltage while the switch is controlled linearly.

Claims

1. A lamp comprising:

a rectifier for rectifying an AC voltage to a rectified AC voltage;

a light-emitting diode (LED) light source, wherein a terminal of said LED light source receives said rectified AC voltage; and

a switch coupled to said LED light source in series and for controlling a current through said LED light source according to a predetermined current reference, wherein said switch is controlled linearly.

2. The lamp of claim 1, wherein said LED light source is powered on and regulated when a signal indicative of said rectified AC voltage is greater than a DC voltage, and wherein said LED light source is powered off when said signal indicative of said rectified AC voltage is less than said DC voltage.

3. The lamp of claim 2, wherein said DC voltage represents a forward voltage of said LED light source.

4. The lamp of claim 2, wherein said DC voltage is proportional to an average level of said rectified AC voltage.

5. The lamp of claim 1, wherein said rectified AC voltage comprises a periodic voltage signal.

6. The lamp of claim 1, wherein said rectified AC voltage comprises a half-wave sinusoidal voltage signal.

7. The lamp of claim 1, further comprising:

control circuitry coupled to said switch and for controlling said switch linearly by comparing a sensing signal indicative of said current through said LED light source to a reference signal indicative of said predetermined current reference.

8. The lamp of claim 7, further comprising:

a current sensor coupled to said LED light source in series and for providing said sensing signal.

9. The lamp of claim 7, wherein said control circuitry comprises an amplifier for comparing said sensing signal to said reference signal and for generating an error signal to control said switch linearly.

10. The lamp of claim 1, wherein a power factor PF of said lamp is obtained by:

11. The lamp of claim 1, wherein said LED light source comprises an LED string further comprising a plurality of LEDs coupled in series.

12. A controller for controlling power to a light-emitting diode (LED) light source which receives a rectified AC voltage, said controller comprising:

a switch coupled to said LED light source in series; and

control circuitry coupled to said switch and for comparing a sensing signal indicative of a current through said LED light source to a reference signal indicative of a current reference and for generating a control signal to control said switch linearly,

wherein said controller powers on said LED light source when a signal indicative of said rectified AC voltage is greater than a DC voltage, and wherein said controller powers off said LED light source when a signal indicative of said rectified AC voltage is less than said DC voltage.

13. The controller of claim 12, wherein said control circuitry comprises an amplifier for comparing said sensing signal to said reference signal and for generating an error signal to control said switch linearly.

14. The controller of claim 12, wherein said DC voltage represents a forward voltage of said LED light source.

15. The controller of claim 12, wherein said DC voltage is proportional to an average level of said rectified AC voltage.

16. The controller of claim 12, wherein said control circuitry controls said switch linearly when said signal indicative of said rectified AC voltage is greater than said DC voltage, and wherein said control circuitry turns off said switch when said signal indicative of said rectified AC voltage is less than said DC voltage.

17. The controller of claim 16, further comprising:

a switch coupled to said control circuitry; and

a comparator for comparing said signal indicative of said rectified AC voltage to said DC voltage and for generating a control signal to control said switch.

18. The controller of claim 12, wherein said rectified AC voltage comprises a periodic voltage signal.

19. The controller of claim 12, wherein said rectified AC voltage comprises a half-wave sinusoidal voltage signal.

20. The controller of claim 12, wherein said LED light source comprises an LED string further comprising a plurality of LEDs coupled in series.