Solid state lighting panels with variable voltage boost current sources

• US 20070115248A1
• Filed: 11/17/2006
• Published: 05/24/2007
• Est. Priority Date: 11/18/2005
• Status: Active Grant

• Current Assignee: Brightplus Ventures LLC (IPValuation Partners, LLC)
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Roberts, John, Murugesu, Muhinthan, Vadas, Keith
• Granted Patent: US 7,872,430 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/0653 Controlling or limiting the speed of brightness adjustment of the illumination source
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 3/3413 Details of control of colour illumination sources
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/22 using optical feedback
• CPC Class Codes: H05B 45/325 Pulse-width modulation [PWM]
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 45/40 Details of LED load circuits

Abstract

A lighting panel system includes a lighting panel having a string of solid state lighting devices and a current supply circuit having a voltage input terminal, a control input terminal, and first and second output terminals coupled to the string of solid state lighting devices. The current supply circuit is configured to supply an on-state drive current to the string of solid state lighting devices in response to a control signal. The current supply circuit includes a charging inductor coupled to the voltage input terminal and an output capacitor coupled to the first output terminal. The current supply circuit is configured to operate in continuous conduction mode in which current continuously flows through the charging inductor while the on-state drive current is supplied to the string of solid state light emitting devices.

Claims

1. A lighting panel system, comprising:

a lighting panel including a string of solid state lighting devices; and

a current supply circuit having a voltage input terminal, a control input terminal, and first and second output terminals coupled to the string of solid state lighting devices, wherein the current supply circuit is configured to supply an on-state drive current to the string of solid state lighting devices in response to a control signal;

wherein the current supply circuit comprises a charging inductor coupled to the voltage input terminal and an output capacitor coupled to the first output terminal; and

wherein the current supply circuit is configured to operate in continuous conduction mode in which current continuously flows through the charging inductor while the on-state drive current is supplied to the string of solid state light emitting devices.

2. The lighting panel system of claim 1, wherein the current supply circuit comprises:

a rectifier having an anode coupled to the charging inductor and a cathode coupled to the storage capacitor;

a controller having a control input and first and second control outputs;

a first control transistor coupled to the anode of the rectifier and having a control terminal coupled to the first control output of the controller;

wherein the first control transistor is configured to cause the charging inductor to be energized in response to a first control signal from the controller and to cause energy stored in the charging inductor to be discharged through the rectifier and into the output capacitor in response to the first control signal.

3. The lighting panel system of claim 2, further comprising a second control transistor coupled to the second output terminal of the current supply circuit and having an input coupled to the second control output of the controller;

wherein the second control transistor is configured to cause a voltage stored in the output capacitor to be applied to the first output terminal of the current supply circuit in response to a second control signal from the controller.

4. The lighting panel system of claim 3, wherein the current supply circuit further comprises:

a low pass filter between the second control output and the second control transistor.

5. The lighting panel system of claim 3, wherein the current supply circuit further comprises a sense resistor coupled to the second output terminal of the current supply circuit, and wherein the controller further comprises a feedback input coupled to the sense resistor;

and

wherein the controller is configured to activate the second control signal in response to a feedback signal received on the feedback input.

6. The lighting panel system of claim 5, wherein the current supply circuit further comprises a low pass filter coupled between the sense resistor and the feedback input of the controller.

7. The lighting panel system of claim 1, wherein the charging inductor has an inductance of about 50 μ

H to about 1.3 mH.

8. The lighting panel system of claim 7, wherein the charging inductor has an inductance of about 680 μ

H.

9. The lighting panel system of claim 1, wherein the current supply circuit is a variable voltage boost current supply circuit.

10. The lighting panel system of claim 1, further comprising a plurality of strings of solid state light emitting devices and a plurality of current supply circuits connected to respective ones of the strings of solid state light emitting devices and configured to operate in continuous conduction mode.

11. The lighting panel of claim 1, wherein the current supply circuit is configured to convert at least about 85% of input power into output power.

12. The lighting panel of claim 11, wherein the current supply circuit is configured to convert at least about 90% of input power into output power.

13. A method of generating an on-state drive current for driving a string of solid state light emitting devices in a lighting panel system, comprising:

energizing a charging inductor with an input voltage;

discharging energy stored in the charging inductor into an output capacitor; and

applying a voltage on the output capacitor to the string of solid state lighting devices;

wherein current continuously flows through the charging inductor while the on-state drive current is supplied to the string of solid state light emitting devices.

14. The method of claim 13, wherein discharging energy stored in the charging inductor into an output capacitor comprises discharging energy stored in the charging inductor through a rectifier.

15. The method of claim 13, wherein energizing the charging inductor with an input voltage comprises activating a first control transistor coupled to the charging inductor with a first control signal.

16. The method of claim 15, further comprising:

detecting an output current and activating the first control transistor in response to the detected output current.

17. The method of claim 13, wherein applying a voltage on the output capacitor to the string of solid state lighting devices comprises activating a second control transistor coupled to the string with a second control signal.

18. The method of claim 16, further comprising filtering the second control signal and applying the filtered second control signal to the second control transistor.

19. The method of claim 18, further comprising filtering the detected output current using a low pass filter.

20. A lighting panel system, comprising:

a lighting panel including a first string of solid state lighting devices configured to emit red light, a second string of solid state lighting devices configured to emit green light, and a third string of solid state lighting devices configured to emit blue light; and

at least three current supply circuits coupled to the first, second and third strings, respectively, wherein each of the current supply circuits comprises a variable voltage boost, constant current power supply circuit configured to operate in continuous current mode.

21. The lighting panel system of claim 20, further comprising:

a digital control system coupled to the current supply circuits and configured to generate a plurality of pulse width modulation (PWM) control signals,

wherein each of the current supply circuits is configured to supply an on-state drive current to the respective string of solid state lighting devices in response to one of the plurality of PWM control signals generated by the digital control system.

22. The lighting panel system of claim 21, wherein the digital control system comprises a closed loop digital control system that is configured to generate the PWM control signals in response to sensor output signals generated by at least one light sensor in response to light output by the lighting panel.