Fault Detection Mechanism for LED Backlighting

Abstract

A fault detection mechanism for a LED string comprising a plurality of serially connected LEDs, the fault detection mechanism comprising: a control circuitry; and a voltage measuring means, in communication with the control circuitry, arranged to measure the voltage drop across at least one LED of the LED string, the control circuitry being operable to: measure the voltage drop, via the voltage measuring means, at a plurality of times, compare at least two of the measured voltage drops, and in the event the comparison of the at least two voltage drops is indicative of one of a short circuit LED and an open circuit LED, output a fault indicator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings in which like numerals designate corresponding elements or sections throughout.

With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. In the accompanying drawings:

FIG. 1A illustrates a high level schematic diagram of a first embodiment of a passive element arranged to bypass an open LED in an LED string in accordance with a principle of the invention, in which a fault detection mechanism is provided to detect the presence of an open or shorted LED in the LED string;

FIG. 1B illustrates a high level schematic diagram of a second embodiment of a passive element arranged to bypass an open LED in an LED string in accordance with a principle of the invention, in which a fault detection mechanism is provided to detect the presence of an open or shorted LED in the LED string;

FIG. 1C illustrates a high level schematic diagram of a third embodiment of a passive element arranged to bypass an open LED in an LED string in accordance with a principle of the invention, in which a fault detection mechanism is provided to detect the presence of an open or shorted LED in the LED string;

FIG. 2A illustrates a high level schematic diagram of a first embodiment of a passive element arranged to bypass an open LED in an LED string in accordance with a principle of the invention, in which a fault detection and identification mechanism is provided to detect the presence and identity of an open or shorted LED in the LED string;

FIG. 2B illustrates a high level schematic diagram of a second embodiment of a passive element arranged to bypass an open LED in an LED string in accordance with a principle of the invention, in which a fault detection and identification mechanism is provided to detect the presence and identity of an open or shorted LED in the LED string;

FIG. 2C illustrates a high level schematic diagram of a third embodiment of a passive element arranged to bypass an open LED in an LED string in accordance with a principle of the invention, in which a fault detection and identification mechanism is provided to detect the presence and identity of an open or shorted LED in the LED string;

FIG. 3 illustrates a high level schematic diagram of an embodiment in accordance with a principle of the invention in which for each LED in the LED string an electronically controlled switch is provided arranged to bypass a LED in the event that the LED exhibits an open condition, and in which a fault detection and identification mechanism is provided to detect the presence and identity of an open or shorted LED in the LED string;

FIG. 4A illustrates a high level flow chart of a calibration routine to determine the appropriate LCD chromatic control compensation for each failed LED in accordance with a principle of the invention;

FIG. 4B illustrates a high level flow chart of the operation of a chromatic control compensation function associated with a transmissive portion of an LCD monitor to compensate for an identified open or shorted LED in accordance with a principle of the invention;

FIG. 5A illustrates a high level block diagram of an LCD monitor exhibiting colored LEDs and a single color sensor arranged to provide a feedback of required color correction in accordance with a principle of the invention;

FIG. 5B illustrates a high level block diagram of an LCD monitor exhibiting colored LEDs and a plurality of regional sensors arranged to provide a feedback of required color correction in accordance with a principle of the invention;

FIG. 6A illustrate a high level block diagram of a fault detection mechanism in accordance with a principle of the current invention;

FIG. 6B illustrate a high level block diagram of a fault detection and control mechanism in accordance with a principle of the current invention;

FIG. 7A illustrate a high level flow chart of the operation of the fault detection mechanism of FIG. 6A to detect one of a short circuit LED and an open circuit LED in accordance with a principle of the current invention; and

FIG. 7B illustrates a high level flow chart of the operation of the fault detection and control mechanism of FIG. 6B to detect and identify one of a short circuit LED and an open circuit LED in accordance with a principle of the current invention.

Claims

1. A fault detection mechanism for a light emitting diode (LED) string comprising a plurality of serially connected LEDs, the fault detection mechanism comprising: a control circuitry; anda voltage measuring means in communication with said control circuitry, arranged to measure the voltage drop across at least one LED of the LED string;said control circuitry being operable to: measure said voltage drop, via said voltage measuring means, at a plurality of times;compare at least two of said measured voltage drops; andin the event said comparison of said at least two voltage drops is indicative of one of a short circuit LED and an open circuit LED, output a fault indicator.

2. A fault detection mechanism according to claim 1, wherein said at least two measured voltage drops are consecutive measured voltage drops.

3. A fault detection mechanism according to claim 1, wherein each of said plurality of LEDs is arranged with one of a serially connected diode string, a Zener diode and a voltage source connected in parallel thereto, each of said serially connected diode string, Zener diode and voltage source being configured to conduct at a voltage higher than the nominal operating voltage drop of the LED to which it is connected in parallel.

4. A fault detection mechanism according to claim 3, wherein the difference between said voltage higher than said nominal operating voltage and said nominal operating voltage presents a voltage differential indicative of an open LED.

5. A fault detection mechanism according to claim 3, wherein in the event the difference between a first of said at least two measured voltages and a second of said at least two measured voltage drops is within a range of the difference between said voltage higher than said nominal operating voltage and said nominal operating voltage, said comparison is indicative of a open circuit LED.

6. A fault detection mechanism according to claim 1, wherein in the event the difference between a first of said at least two measured voltages and a second of said at least two measured voltage drops is within a range of an operating voltage drop across a single LED of the LED string, said comparison is indicative of a short circuit LED.

7. A fault detection mechanism according to claim 1, further comprising: a multiplexer, responsive to said control circuitry, arranged to connect said voltage measuring means across each of said LEDs in the LED string in turn.

8. A fault detection mechanism according to claim 7, wherein said control circuitry is further operable to transmit an indication of the particular LED associated with said fault indicator.

9. A fault detection mechanism according to claim 8, further comprising a LCD chromatic control operable, responsive to said transmitted indication of said particular LED associated with said fault indicator, to adjust the color response of the liquid crystal display to at least partially compensate for said detected LED associated with said fault indicator.

10. A fault detection mechanism according to claim 7, further comprising a control unit responsive to said transmitted indication, said control unit being operable to adjust a PWM control thereby at least partially compensating for said particular LED associated with said fault indicator.

11. A fault detection mechanism according to claim 1, wherein said LED string is configured for use in backlighting one of a monitor and a television.

12. A fault detection mechanism according to claim 1, further comprising: a plurality of field effect transistors, one of each of said plurality of field effect transistors being connected across a unique one of the plurality of LEDs in the LED string and being responsive to an output of said control circuitry;said control circuitry being further operable, in the event said comparison is indicative of an open circuit LED, to operate the field effect transistor connected across said open circuit LED so as to conduct current.

13. A fault detection mechanism according to claim 12, further comprising: a multiplexer, responsive to said control circuitry, arranged to connect said voltage measuring means across each of said LEDs in the LED string in turn; anda control unit in communication with said fault indicator,wherein said control circuitry is further operable to transmit an indication of the particular LED associated with said fault indicator, andwherein said control unit is further operable to disable at least one LED thereby at least partially compensating for said one of a short circuit LED and an open circuit LED.

14. A method of fault detection comprising: providing an light emitting diode (LED) string comprising a plurality of LEDs;measuring a voltage drop across at least one LED of said provided LED string at a plurality of times;comparing at least two of said measured voltage drops; andoutputting, in the event said comparison of said at least two voltage drops is indicative of one of a short circuit LED and an open circuit LED, a fault indicator.

15. A method according to claim 14, wherein said at least two measured voltage drops are consecutive measured voltage drops.

16. A method according to claim 14, further comprising: providing, associated with each LED of said provided LED string one of a serially connected diode string, a Zener diode and a voltage source connected in parallel thereto; andconfiguring each of said one of a serially connected diode string, Zener diode and voltage source to conduct at a voltage higher than the nominal operating voltage drop of the LED to which it is connected in parallel.

17. A method according to claim 16, wherein the difference between said voltage higher than said nominal operating voltage and said nominal operating voltage presents a voltage differential indicative of an open LED.

18. A method according to claim 16, wherein in the event the difference between a first of said at least two measured voltages and a second of said at least two measured voltage drops is within a range of the difference between said voltage higher than said nominal operating voltage and said nominal operating voltage, said comparison is indicative of a open circuit LED.

19. A method according to claim 14, wherein in the event the difference between a first of said at least two measured voltages and a second of said at least two measured voltage drops is within a range of an operating voltage drop across a single LED of the LED string, said comparison is indicative of a short circuit LED.

20. A method according to claim 14, further comprising: determining the particular LED associated with said fault indicator; andoutputting an indication of the particular LED associated with said fault indicator.

21. A method according to claim 20, further comprising adjusting a color response of a liquid crystal display associated with said provided LED string to at least partially compensate for said particular LED associated with said fault indicator.

22. A method according to claim 20, further comprising adjusting a PWM control thereby at least partially compensating for said particular LED associated with said fault indicator.

23. A method according to claim 14, further comprising: enabling, in the event said fault indicator is indicative of an open circuit LED, a parallel conductive path around said open circuit LED.

24. A method according to claim 14, further comprising: disabling at least one LED, thereby at least partially compensating for said one of a short circuit LED and an open circuit LED.

25. A method of fault detection comprising: measuring a voltage drop across at least one LED of an LED string at a plurality of times;comparing at least two of said measured voltage drops; andoutputting, in the event said comparison of said at least two voltage drops is indicative of one of a short circuit LED and an open circuit LED, a fault indicator.

26. A method according to claim 25, wherein said at least two measured voltage drops are consecutive measured voltage drops.

27. A fault detection mechanism for a light emitting diode (LED) string comprising a plurality of serially connected LEDs, the fault detection mechanism comprising a control circuitry operable to: measure a voltage drop across at least one LED of an LED string at a plurality of times;compare at least two of said measured voltage drops; andin the event said comparison of said at least two voltage drops is indicative of one of a short circuit LED and an open circuit LED, output a fault indicator.

28. A fault detection mechanism according to claim 27, wherein said at least two measured voltage drops are consecutive measured voltage drops.