Driving circuit with continuous dimming function for driving light sources

• US 8,076,867 B2
• Filed: 03/31/2009
• Issued: 12/13/2011
• Est. Priority Date: 12/12/2008
• Status: Active Grant

• Current Assignee: Feit Electric Company Incorporated
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: Kuo, Ching-Chuan, Lin, Yung-Lin
• Primary Examiner(s): Choi, Jacob Y
• Assistant Examiner(s): VU, JIMMY T
• Application Number:
  US12/415,028
• Publication Number:
  US 20100148681A1
• Time in Patent Office: 987 Days
• Field of Search: 315/185.R, 315/224, 315/225, 315/244, 315/245, 315/287, 315/291, 315/307, 315/312, 315/314
• US Class Current: 315/291
• CPC Class Codes: H05B 31/50 specially adapted for ac
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/392 wherein the LEDs are placed as freewheeling diodes at the secondary side of an isolation transformer
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A driving circuit for controlling power of a light source includes a power converter coupled to a power source and the light source, and a dimming controller coupled to the power converter. The power converter can receive power from the power source and provide a regulated power to the light source. The power converter includes a control switch coupled in series with the light source. The dimming controller can monitor a power switch coupled between the power source and the driving circuit, and receive a dimming request signal and a dimming termination signal. The dimming request signal can indicate a first set of operations of the power switch. The dimming termination signal can indicate a second set of operations of the power switch. The dimming controller can continuously adjust the regulated power from the power converter by controlling the control switch if the dimming request signal is received, and can stop adjusting the regulated power from the power converter if the dimming termination signal is received.

Claims

1. A dimming controller for controlling dimming of a light emitting diode (LED) light source, said dimming controller comprising:

a terminal for receiving a dimming request signal indicative of a first plurality of operations of a power switch, and for receiving a dimming termination signal indicative of a second plurality of operations of said power switch, wherein said power switch transfers power from an AC power source to a bridge rectifier when said power switch is on, and wherein a power converter receives input power from said bridge rectifier and provides output power to said LED light source,

wherein said dimming controller adjusts said output power by controlling a control switch in series with said LED light source if said dimming request signal is received and until said dimming termination signal is received, and wherein said first plurality of operations of said power switch comprises a first turn-off operation followed by a first turn-on operation, and wherein said second plurality of operations of said power switch comprises a second turn-off operation followed by a second turn-on operation.

2. The dimming controller of claim 1, further comprising:

a trigger monitoring unit for receiving said dimming request signal and said dimming termination signal; and

a dimmer coupled to said trigger monitoring unit and for generating a dimming signal to adjust a target power level of said power converter coupled to said dimming controller.

3. The dimming controller of claim 2, wherein said dimmer comprises:

a clock generator for generating a clock signal;

a counter coupled to said clock generator and driven by said clock signal; and

a digital-to-analog converter coupled to said counter and for generating said dimming signal based on a counter value of said counter,

wherein said trigger monitoring unit enables said clock generator to drive said counter when said dimming request signal is received by said trigger monitoring unit, and disables said clock generator from driving said counter when said dimming termination signal is received by said trigger monitoring unit.

4. The dimming controller of claim 2, wherein said dimming controller operates in a burst dimming mode in which a pulse width modulation signal is generated based on said dimming signal, wherein a duty cycle of said pulse width modulation signal is determined by said dimming signal, and wherein said pulse width modulation signal controls said control switch.

5. The dimming controller of claim 2, wherein said dimming controller operates in an analog dimming mode in which a comparator compares said dimming signal with a current monitoring signal indicating an LED current flowing through said LED light source and generates a control signal to control said control switch.

6. A system comprising:

a power converter coupled to a power source and a light emitting diode (LED) light source and for receiving power from said power source, and for providing output power to said LED light source; and

a dimming controller coupled to said power converter and for monitoring a power switch coupled to said power source, and for continuously adjusting said power from said power converter upon detection of a first plurality of operations of said power switch until a second plurality of operations of said power switch are detected, said dimming controller comprising;

a clock generator for generating a clock signal upon detection of said first plurality of operations of said power switch; and

a counter driven by said clock signal for providing a counter value to adjust said output power from said power converter.

7. The system of claim 6, wherein said power converter comprises:

a control switch coupled in series with said LED light source,

wherein said dimming controller is coupled to said control switch and adjusts said output power from said power converter by controlling said control switch.

8. The system of claim 6, further comprising:

an AC/DC converter for converting an AC power from said power source to a DC power,

wherein said power switch is coupled between said power source and said AC/DC converter.

9. The system of claim 6, wherein said first plurality of operations of said power switch comprises a first turn-off operation followed by a first turn-on operation, and wherein said second plurality of operations of said power switch comprises a second turn-off operation followed by a second turn-on operation.

10. The system of claim 6, wherein said power converter comprises an inductor coupled in series with said LED light source.

11. The system of claim 6, further comprising:

an energy storage unit coupled to said dimming controller and for powering said dimming controller when said power switch is turned off.

12. The system of claim 6, wherein said dimming controller comprises:

a trigger monitoring unit for detecting said first plurality of operations of said power switch and said second plurality of operations of said power switch; and

a dimmer coupled to said trigger monitoring unit and for generating a dimming signal to adjust a target power level of said power converter based on said counter value.

13. The system of claim 12, wherein said dimmer comprises:

a digital-to-analog converter coupled to said counter and for generating said dimming signal based on said counter value.

14. The system of claim 12, wherein said dimming controller operates in a burst dimming mode in which a pulse width modulation signal is generated based on said dimming signal, wherein a duty cycle of said pulse width modulation signal is determined by said dimming signal, and wherein said pulse width modulation signal controls a control switch coupled in series with said LED light source.

15. The system of claim 12, wherein said dimming controller operates in an analog dimming mode in which a comparator compares said dimming signal with a current monitoring signal indicating an LED current flowing through said light source and generates a control signal to control a control switch coupled in series with said LED light source.

16. A method for controlling dimming of a light emitting diode (LED) light source, said method comprising:

powering said LED light source based on output power from a power converter;

receiving a dimming request signal indicative of a first plurality of operations of a power switch coupled between a power source and said power converter; and

adjusting said output power from said power converter in response to said dimming request signal until a dimming termination signal indicative of a second plurality of operations of said power switch is received,

wherein adjusting said output power further comprises;

driving a counter based on a clock signal;

generating a dimming signal based on a counter value of said counter; and

controlling a control switch coupled in series with said LED light source based on said dimming signal to adjust said output power.

17. The method of claim 16, wherein said first plurality of operations of said power switch comprises a first turn-off operation followed by a first turn-on operation, and wherein said second plurality of operations of said power switch comprises a second turn-off operation followed by a second turn-on operation.

18. The method of claim 16, further comprising:

disabling said clock signal if said dimming termination signal is received.