LED BRIGHTNESS CONTROL

• US 20070109328A1
• Filed: 01/09/2007
• Published: 05/17/2007
• Est. Priority Date: 04/12/2000
• Status: Abandoned Application

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Lewis, Roger
• Application Number:
  US11/621,467
• Publication Number:
  US 20070109328A1
• Time in Patent Office: Days
• US Class Current: 345/691
• CPC Class Codes: G09G 2320/0606 Manual adjustment
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336

Abstract

A device for controlling the brightness of a one or more LEDs (light emitting diodes) includes a modulator having at least 11 bits of pulse width modulation resolution. A buffer receives pulses from the modulator. A driver may be coupled to receive pulses from the buffer and drive the one or more LEDs. A currently limiter may be employed to prevent damage to the one or more LEDs. An update rate may be selected to limit perceptible flicker of the one or more LEDs.

Claims

1. A device for use in controlling one or more LEDs (light emitting diodes), comprising:

a modulator having at least 11 bits of pulse width modulation resolution;

a buffer adapted to receive pulses from the modulator; and

a buffer output that provides pulses from the buffer adapted for connection to a driver.

2. The device of claim 1 wherein the driver comprises a switch adapted to turn on and off within a time frame corresponding to the pulses provided by the modulator through the buffer.

3. The device of claim 1 wherein the modulator has an update rate of at least approximately 100 Hz.

4. The device of claim 1 and further comprising a driver coupled to the buffer output and coupled to an LED backlight.

5. The device of claim 4 wherein the LED backlight is coupled to illuminate a liquid crystal display.

6. The device of claim 1 adapted to prevent a current draw of the one or more LEDs from exceeding a threshold value.

7. The device of claim 6 wherein the adapted device comprises current sensing feedback circuitry to prevent a current draw of the one or more LEDs from exceeding a threshold value.

8. The device of claim 1 wherein the modulator comprises one or more of:

firmware, hardware, and software.

9. A device comprising:

one or more LEDs (light emitting diodes);

a modulator having at least 11 bits of pulse width modulation resolution while maintaining an update rate fast enough to preclude perceptible flicker;

a buffer adapted to receive pulses from the modulator; and

a driver that receives pulses from the buffer and provides them to the one or more LEDs.

10. A device for controlling one or more LEDs (light emitting diodes), the device comprising:

a modulator having at least 11 bits of pulse width modulation resolution while maintaining an update rate fast enough to preclude perceptible flicker;

a buffer coupled to the modulator and adapted to receive pulses from the modulator; and

a driver that receives pulses from the buffer and having an output for coupling to the one or more LEDs.

11. The device of claim 10 wherein the driver is a switch adapted to turn on and off within a time frame corresponding to the pulses provided by the modulator through the buffer.

12. The device of claim 10 adapted to prevent a current draw of the one or more LEDs from exceeding a threshold value.

13. The device of claim 10 wherein the buffer has a response time at least as fast as a shortest duration pulse from the modulator.

15. A method for controlling one or more LEDs (light emitting diodes), the method comprising:

receiving a control signal having at least 11 bits of pulse width modulation resolution and an update rate that precludes flicker over a wide dimming range;

buffering the control signal using a buffer that operates with a response time at least as fast as the shortest duration pulse of said control signal to obtain a buffered control signal; and

making the buffered control signal available to a driver to drive the one or more LEDs according to said buffered control signal.

16. The method of claim 15 and further comprising limiting an amount of current supplied to the entire array while maintaining continued operation of the one or more LEDs.

17. The method of claim 15 wherein the control signal is provided by an 8 bit modulator with 8 additional timer states to form a virtual 11 bit modulator.

18. A method for controlling the brightness of a LED device, the method comprising:

receiving a pulse width modulated control signal representative of a desired LED device brightness and having at least 11 bit resolution and an update rate that prevents flicker;

supplying power to the LED device in accordance with said pulse width modulated control signal; and

preventing a magnitude of current drawn by the LED device from exceeding a predetermined threshold value while maintaining continued operation of the LED device.

19. The method of claim 18 wherein the update rate is at least approximately 100 Hz.

20. A device for use in controlling one or more LEDs (light emitting diodes), comprising:

a modulator having a dimming resolution of at least 2¹¹;

a buffer adapted to buffer pulses from the modulator; and

a buffer output adapted to provide pulses from the modulator to a driver.

21. The device of claim 20 and further comprising a current limiter.

22. The device of claim 21 wherein the current limiter comprises current sensing feedback circuitry to prevent a current draw of the one or more LEDs from exceeding a threshold value.