Power control system for current regulated light sources

• US 7,804,256 B2
• Filed: 03/12/2008
• Issued: 09/28/2010
• Est. Priority Date: 03/12/2007
• Status: Active Grant

• Current Assignee: Signify Holding B.V. (Signify N.V.)
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Melanson, John L.
• Primary Examiner(s): VO, TUYET THI
• Application Number:
  US12/047,262
• Publication Number:
  US 20080224636A1
• Time in Patent Office: 930 Days
• Field of Search: 315/247, 315/246, 315/224, 315/225, 315/291, 315/297, 315307-311, 315/185.S, 315312-324, 315/274, 315/278, 315/279, 363/19, 363/15, 363/21.01, 363/23, 363/21.05, 363/21.09, 363/21.1, 363/21.11, 363/21.12, 363/21.13
• US Class Current: 315/291
• CPC Class Codes: H05B 45/355 Power factor correction [PFC]; Reactive power compensation
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]
• CPC Class Codes: Y10S 315/04 Dimming circuit for fluorescent lamps

Abstract

A light emitting diode (LED) lighting system includes a PFC and output voltage controller and a LED lighting power system. The controller advantageously operates from an auxiliary voltage less than a link voltage generated by the LED lighting power system. The common reference voltage allows all the components of lighting system to work together. A power factor correction switch and an LED drive current switch are coupled to the common reference node and have control node-to-common node, absolute voltage that allows the controller to control the conductivity of the switches. The LED lighting system can utilize feed forward control to concurrently modify power demand by the LED lighting power system and power demand of one or more LEDs. The LED lighting system can utilize a common current sense device to provide a common feedback signal to the controller representing current in at least two of the LEDs.

Claims

1. A light emitting diode (LED) lighting system comprising:

a power factor correction (PFC) and LED drive controller, the controller comprising;

a digital signal processor, coupled to the LED feedback node and configured to;

operate from a digital level supply voltage;

generate a PFC control signal; and

generate an LED current control signal;

a first buffer, coupled to the processor, and configured to;

operate from a medium level supply voltage, wherein the medium level supply voltage is greater than the digital level supply voltage;

receive the PFC control signal; and

convert the PFC control signal into a PFC switch control signal to control conductivity of a high voltage PFC switch; and

a second buffer, coupled to the processor, and configured to;

operate from the medium level supply voltage;

receive the LED current control signal; and

convert the LED current control signal into an LED current control switch signal to control conductivity of a high voltage LED current control switch.

2. The lighting system of claim 1 wherein the controller further comprises:

an LED feedback node to receive an LED current feedback signal representing one or more current levels in one or more switching LED systems; and

a voltage feedback node to receive an input voltage feedback signal representing an input voltage level provided to the lighting system;

wherein the processor is further configured to generate the PFC control signal in response to the input voltage level represented by the input voltage feedback signal and to generate the LED drive current control signal in response to the one or more current levels represented by the LED current feedback signal.

3. The lighting system of claim 1 wherein the digital supply voltage has an absolute value less than or equal to 8 volts, the medium level supply voltage has an absolute value less than or equal to 50 volts, and the high voltage PFC switch is coupled between voltage nodes having a voltage difference during normal operation of the lighting system of at least 100 volts, and the high voltage LED drive current switch is coupled between voltage nodes having a voltage difference during normal operation of the lighting system of at least 100 volts.

4. The lighting system of claim 1 wherein during normal operation of the lighting system, the medium level voltage is less than or equal to approximately 15% of the voltage at the first high voltage source node relative to a voltage at the common voltage reference node.

5. The lighting system of claim 1 further comprising:

a dimmer signal input to receive a dimmer signal;

wherein the controller is configured to;

control power delivered by a switching power converter to a switching LED system; and

concurrently modify power demand by the power factor correction control system and modify power supplied by the switching power converter in accordance with changes in a dimming level indicated by the dimmer signal.

6. The lighting system of claim 5 wherein the controller comprises a first control module to control power factor correction by the switching power converter and a second control module to control power delivered by the switching power converter and both the first and second control modules include inputs to receive the dimmer signal.

7. The lighting system of claim 1 further comprising:

a common voltage reference node;

a first high voltage source node to conduct a primary voltage;

a second high voltage source node to conduct a link voltage of the lighting system;

the PFC switch coupled to the common voltage reference node and the first high voltage source node; and

the LED current control switch to control current to at least one LED, wherein the LED current control switch is coupled to the common voltage reference node and the second high voltage source node;

wherein, during normal operation of the lighting system, the PFC switch and an LED current control switch of the LED lighting system have respective control node-to-common node, absolute voltages that allow the controller to control the conductivity of the switches and provide power factor correction and supply an approximately constant current to an LED switching system for each dimming level indicated by a dimmer signal.

8. The lighting system of claim 7 wherein the control node-to-common node voltages of the PFC switch and the LED current control switch are less than or equal to 0.15 times a voltage at the first voltage source node relative to a voltage at the common voltage reference node.

9. The lighting system of claim 7 wherein:

the PFC switch and the LED current control switch are members of the group consisting of;

field effect transistors and insulated gate bipolar transistors;

the control nodes of the PFC switch and the LED current control switch are members of the group consisting of;

a field effect transistor gate node and an insulated gate bipolar transistor gate node; and

the common nodes of the PFC switch and the LED current control switch are members of the group consisting of;

a field effect transistor source node and an insulated gate bipolar transistor emitter.

10. The lighting system of claim 7 further comprising:

a third voltage source node to conduct a third voltage, wherein the third voltage is lower than the link voltage and the supply voltage; and

one or more transistors coupled to the third voltage source node and the common voltage reference node, wherein the one or more transistors operate from voltages at the third voltage source node and the common voltage reference node.

11. The lighting system of claim 7 further comprising:

a current sense device coupled to the LED drive current switch node and the common voltage reference node and, during normal operation of the lighting system, having a voltage across the current sense device less than or equal to 0.15 times a voltage at the first voltage source node relative to the voltage at the common voltage reference node and provides a feedback signal for controlling the LED current control switch.

12. The lighting system of claim 11 wherein the current sense device is a resistor.

13. The lighting system of claim 11 further comprising:

a plurality of LED drive current switches, wherein each LED drive current switch controls current to at least one LED and is coupled to the common voltage reference node, the first voltage source node, and the controller; and

a single current sense device coupled to the LED drive current switches, wherein, during normal operation of the lighting system, the current sense device senses current in all of the LED drive current switches and provides a feedback signal for use by the controller to control current in all of the LED current control switches.

14. The lighting system of claim 13 further comprising:

multiple LED chains comprising one or more LEDs, wherein each LED chain is coupled to one of the current sense devices.

15. A method comprising:

operating a digital signal processor of a power factor correction (PFC) and output voltage controller from a digital level supply voltage;

generating a PFC control signal; and

generating an LED current control signal;

operating a first buffer, coupled to the processor, from a medium level supply voltage, wherein the medium level supply voltage is greater than the digital level supply voltage;

receiving the PFC control signal;

converting the PFC control signal into a PFC switch control signal to control conductivity of a high voltage PFC switch; and

operating a second buffer, coupled to the processor, from the medium level supply voltage;

receiving the LED current control signal; and

converting the LED current control signal into an LED current control switch signal to control conductivity of a high voltage LED current control switch.

16. The method of claim 15 wherein the controller includes an LED feedback node to receive an LED current feedback signal representing one or more current levels in one or more switching LED systems and a voltage feedback node to receive an input voltage feedback signal representing an input voltage level provided to the lighting system, the method further comprising:

generating the PFC control signal in response to the input voltage level represented by the input voltage feedback signal; and

generating the LED drive current control signal in response to the one or more current levels represented by the LED current feedback signal.

17. The method of claim 15 wherein the digital supply voltage has an absolute value less than or equal to 8 volts, the medium level supply voltage has an absolute value less than or equal to 50 volts, and the high voltage PFC switch is coupled between voltage nodes having a voltage difference during normal operation of the lighting system of at least 100 volts, and the high voltage LED drive current switch is coupled between voltage nodes having a voltage difference during normal operation of the lighting system of at least 100 volts.

18. The method of claim 15 further comprising:

generating a first voltage, wherein the first voltage is a link voltage;

operating a switching power converter of an LED lighting power system from the first source voltage relative to a common voltage, wherein the switching power converter includes the PFC switch;

operating the PFC switch at a control node-to-common node, absolute voltage to allow the PFC and output voltage controller to control the PFC switch and provide power factor correction for the switching power converter;

operating the LED current control switch at a control node-to-common node, absolute voltage to allow the PFC and output voltage controller to control the LED current control switch to supply an approximately constant current to an LED switching system for each dimming level indicated by a dimmer signal; and

controlling conductivity of the PFC switch and the LED current control switch with the PFC and output voltage controller.

19. The method of claim 18 wherein:

operating the PFC switch of the switching power converter at a control node-to-common node, absolute voltage to allow a PFC and output voltage controller to control the PFC switch and provide power factor correction for the switching power converter comprises operating the PFC switch of the LED lighting power system at a control node-to-common node, absolute voltage less than or equal to 0.15 times the first source voltage relative to the common voltage reference; and

operating the LED current control switch at a control node-to-common node, absolute voltage to allow the PFC and output voltage controller to control the LED current control switch to supply an approximately constant current to an LED switching system for each dimming level indicated by a dimmer signal comprises operating the LED current control switch at a control node-to-common node, absolute voltage less than or equal to 0.15 times the first source voltage relative to the common voltage reference.

20. The method of claim 18 wherein the PFC and LED current control switches comprise field effect transistors and controlling conductivity of the PFC switch and LED current control switch with the PFC and output voltage controller comprises providing respective duty cycle modified control signals to gates of the PFC switch and LED current control switch.

21. The method of claim 18 further comprising:

receiving a rectified primary supply voltage, wherein a root mean square (RMS) value of the primary supply voltage is greater than the medium level voltage;

boosting the primary supply voltage to the first source voltage, wherein boosting the primary supply voltage further comprises modulating the conductivity of the PFC switch to generate a power factor corrected first source voltage.

22. The method of claim 18 further comprising:

operating additional LED current control switches at respective current node voltages less than or equal to 0.15 times the first source voltage relative to the common voltage reference, wherein each LED current control switch controls current through a respective chain of LEDs and each chain of LEDs includes at least one LED;

receiving feedback signals, wherein each feedback signal represents a respective current conducted by one of the LED current control switches; and

controlling conductivity of each LED current control switch with the PFC and output voltage controller in response to the feedback signal.

23. The method of claim 18 further comprising:

receiving a dimmer signal; and

controlling conductivity of the PFC switch and the LED current control switch further comprises;

concurrently controlling the conductivity of the PFC switch and the LED current control switch to modify power demand by LED lighting power system and modify power supplied by the lighting system in accordance with changes in a dimming level indicated by the dimmer signal.

24. The method of claim 18 wherein the second source voltage is less than or equal to approximately 15% of the first source voltage.

25. The method of claim 18 further comprising:

operating one or more transistors of the PFC and output voltage controller from a third voltage source node and the common voltage reference, wherein the third voltage is lower than the link voltage and the second source voltage.

26. The method of claim 18 wherein a switching LED system includes the LED and controlling conductivity of the LED current control switch further comprises:

receiving a feedback signal from a switching LED system; and

responding to the feedback signal to maintain a predetermined current to each LED.

27. The method of claim 26 further comprising:

sensing a voltage across a resistor representing a current through each LED, wherein the voltage sensed across the resistor is the feedback signal.

28. The method of claim 18 further comprising:

operating additional LED current control switches at respective current node voltages less than or equal to 0.15 times the first source voltage relative to the common voltage reference, wherein each LED current control switch controls current through a respective chain of LEDs and each chain of LEDs includes at least one LED;

receiving a single feedback signal representing current conducted by each LED current control switch; and

controlling conductivity of each LED current control switch with the PFC and output voltage controller in response to the feedback signal.

29. The method of claim 28 wherein controlling conductivity of each LED current control switch with the PFC and output voltage controller in response to the feedback signal comprises:

determining during separate periods of time the respective currents conducted by each LED current control switch.

30. A light emitting diode (LED) lighting system comprising:

an LED lighting power system, wherein during normal operation of the LED lighting system the LED lighting power system generates a first source voltage relative to a common voltage, wherein the first source voltage is a link voltage, and the LED lighting power system includes;

a switching power supply having a power factor correction (PFC) switch, wherein during normal operation of the LED lighting system, the PFC switch of the LED lighting power system operates at a current node voltage less than or equal to 0.1 times the first source voltage relative to the common voltage reference; and

an LED current control switch, wherein during normal operation of the LED lighting system, the LED current control switch operates at a current node voltage less than or equal to 0.1 times the first source voltage relative to the common voltage reference;

a PFC and output voltage controller coupled to conductivity control nodes of the first and LED drive current switches, wherein during normal operation of the lighting control system, the controller operates from a second source voltage relative to the common voltage and controls conductivity of the PFC switch and the LED current control; and

at least one LED coupled to the LED current control switch.