Power regulation for LED strings

• US 7,843,150 B2
• Filed: 06/09/2008
• Issued: 11/30/2010
• Est. Priority Date: 05/31/2007
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Wang, Michael, Xu, Jingwei, Zeng, Xianwei
• Primary Examiner(s): Owens; Douglas W
• Assistant Examiner(s): Le; Tung X
• Application Number:
  US12/135,253
• Publication Number:
  US 20080297067A1
• Time in Patent Office: 904 Days
• Field of Search: 315/185.R, 315/186, 315/192, 315/209.R, 315/291, 315/294, 315307-308, 315/312
• US Class Current: 315/307
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/347 Dynamic headroom control [DHC]
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

One embodiment of the invention includes a power regulator system. The system comprises at least one current regulator configured to maintain a substantially constant current flow through each of at least one series connected light emitting diode (LED) string. The system also comprises a power converter configured to generate an output voltage to provide power to the at least one current regulator and the at least one series connected LED string. The system further comprises a voltage regulator configured to determine a voltage that provides power to the at least one current regulator and to adjust the output voltage based on the determined voltage to mitigate power loss due to excessive voltage provided to power the at least one current regulator.

Claims

1. A power regulator system comprising:

at least one current regulator configured to maintain a substantially constant current flow through each of at least one series connected light emitting diode (LED) string;

a power converter configured to generate an output voltage to provide power to the at least one current regulator and the at least one series connected LED string; and

a voltage regulator configured to determine a voltage that provides power to the at least one current regulator and to adjust the output voltage to maintain a substantially constant output voltage based on the determined voltage to mitigate power loss due to excessive voltage provided to power the at least one current regulator, wherein the voltage regulator comprises a voltage monitor, a digital-to-analog converter (DAC), and an error amplifier, the voltage monitor being configured to one of increase and decrease a reference voltage by a predetermined increment, the DAC being configured to convert the reference voltage to an analog reference voltage, and the error amplifier being configured to compare the analog reference voltage with the output voltage and to output a command signal, the command signal is being configured as an error voltage for adjusting the output voltage of the power converter and wherein the output voltage is one of increased by a predetermined increment if the determined voltage of each of the at least one current regulator is below a minimum threshold and decreased by a predetermined increment if each determined voltage of each of the at least one current regulator is above a maximum threshold.

2. The system of claim 1, wherein the voltage regulator is configured to compare the determined voltage with a lower first threshold voltage and a higher second threshold voltage.

3. The system of claim 2, wherein a command signal is provided by the voltage regulator that commands the power converter to increase the output voltage upon the determined voltage being less than the first threshold voltage.

4. The system of claim 2, wherein a command signal provided by the voltage regulator that commands the power converter to decrease the output voltage upon the determined voltage being greater than the second threshold voltage.

5. The system of claim 1, wherein the at least one current regulator comprises at least one respective switch responsive to an enable signal configured to control a brightness of the respective at least one series connected LED string based on a duty-cycle of the enable signal.

6. The system of claim 5, wherein the voltage regulator is configured to periodically sample the voltage that provides power to the at least one current regulator based on at least one of an on-time of the enable signal and a predetermined interval.

7. The system of claim 5, wherein the voltage regulator is configured to monitor the voltage that provides power to the at least one current regulator continuously upon the enable signal being logic high.

8. An electronic device having an LED display, the electronic device comprising the system of claim 1.

9. A method for regulating power associated with at least one light emitting diode (LED) string, the method comprising:

generating an output voltage from a power converter that provides power for illuminating the at least one LED string;

regulating a current flow through each of a respective LED string of the at least one LED string via an associated current regulator powered by the output voltage;

periodically sampling at least one voltage across each associated current regulator; and

adjusting the output voltage based on the sampled at least one voltage across each associated current regulator relative to at least one threshold voltage, wherein adjusting the output voltage comprises;

one of adding and subtracting a predetermined increment to a digital representation of the output voltage based on at least one threshold voltage to generate an adjusted output signal;

converting the adjusted output signal to analog; and

setting the output voltage substantially equal to the adjusted output signal.

10. The method of claim 9, wherein adjusting the output voltage comprises increasing the output voltage by a predetermined increment upon the at least one voltage across the respective at least one current regulator being less than a minimum threshold voltage.

11. The method of claim 9, wherein adjusting the output voltage comprises decreasing the output voltage by a predetermined increment upon each of the at least one voltage across the associated at least one current regulator being greater than a maximum threshold voltage.

12. The method of claim 9, further comprising controlling a brightness of the at least one LED string based on at least one of a duty-cycle of an enable signal and a predetermined interval.

13. The method of claim 12, wherein periodically sampling the voltage across each of the at least one current regulator comprises periodically sampling the at least one voltage across each of the respective at least one current regulator during an on time of the enable signal.

14. A power regulator system comprising:

means for generating an output voltage to provide power for illuminating at least one series connected light emitted diode (LED) string;

at least one means for regulating a substantially constant current flow through each of the respective at least one series connected LED string;

means for periodically sampling voltage associated with powering a respective at least one means for regulating the substantially constant current flow; and

means for adjusting the output voltage based on a comparison of the sampled voltages with at least one threshold voltage, wherein the means for adjusting comprises a voltage monitor means, a digital-to-analog converter means (DAC), and an error amplifier means, the means for adjusting being configured to one of increase and decrease a reference voltage by a predetermined increment, the DAC being configured to convert the reference voltage to an analog reference voltage, and the error amplifier means being configured to compare the analog reference voltage with the output voltage and to output a command signal, such that the command signal is being configured as an error voltage for adjusting the output voltage of the output voltage generating means.

15. The system of claim 14, wherein the means for adjusting comprises means for comparing each of the sampled voltages with a maximum threshold voltage and a minimum threshold voltage.

16. The system of claim 15, wherein the means for adjusting the output voltage comprises means for increasing the output voltage upon at least one of the sampled voltage being less than the minimum threshold voltage and means for decreasing the output voltage upon each of the sampled voltages being greater than the maximum threshold voltage.

17. The system of claim 14, further comprising means for controlling a brightness of the respective at least one series connected LED string based on a duty-cycle of an enable signal, and wherein the means for periodically sampling voltage samples the voltage during at least one of an on-time of the enable signal and a predetermined interval.