Control of electroluminescent displays

• US 20050017650A1
• Filed: 08/08/2003
• Published: 01/27/2005
• Est. Priority Date: 07/24/2003
• Status: Active Grant

• Current Assignee: Pelikon Ltd. (Suzhou Dongshan Precision Manufacturing Company Limited)
• Original Assignee: Pelikon Ltd. (Suzhou Dongshan Precision Manufacturing Company Limited)
• Inventors: Ross, Stefan Michael, Fryer, Christopher James Newton
• Granted Patent: US 7,119,493 B2
• Time in Patent Office: Days
• US Class Current: 315/169.300
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 3/12 using electroluminescent elements
• CPC Class Codes: H05B 44/00 Circuit arrangements for operating electroluminescent light sources for operating light emitting diodes H05B45/00
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A controller for use with a multi-segment electroluminescent display 1. Control signals C1-CN control a plurality of half H-bridges H and Hc, the terminals of the half H-bridges being connected respectively to ground and to a high voltage DC supply 9. One of said half H-bridges provides a common output Vcommon and the remaining H-bridges provide drive voltages V1-VN for the segments of the display. The H bridges are driven by an oscillator 14 so that an AC voltage is selectively applied to the segments of the display. A power supply 24 provides a predetermined amount of power per unit area of the display. This is controlled by an area summation engine 22 having a segment data input, a segment counter and a memory containing area data corresponding to the segment(s) of the display. Based on the input from the segment data input, the area(s) of the segment(s) that are to be lit are obtained from the memory and summed to provide the total area to be lit. This is fed to the power supply 24, which then feeds the correct amount of power to display 1 via the half H-bridges.

Claims

1. A controller for an electroluminescent display, the controller being arranged to determine the amount of power required by the display for the demanded display output and to supply approximately that amount of power to the display.

2. A controller as claimed in claim 1, wherein the required power is determined based upon the number of display segment(s) that are to be illuminated.

3. A controller as claimed in claim 1, wherein the controller determines the amount of power required based upon the area of the individual segment(s) that are to be lit.

4. A controller as claimed in claim 1, wherein the controller comprises an area summation engine having a segment data input, a segment counter and a memory containing area data corresponding to the segment(s) of the display, wherein, based on the input from the segment data input, the area(s) of the segment(s) that are to be lit are obtained from the memory and summed to provide an output corresponding to the total area to be lit.

5. A controller as claimed in claim 1, the controller being arranged to vary the relative phase of signals applied to illuminated segment(s) of the display whereby the brightness of the segment(s) can be varied.

6. A controller as claimed in claim 1, wherein power supplied per unit area of the display that is illuminated is maintained during operation at a predetermined value.

7. A controller as claimed in claim 6, wherein the power supplied is maintained at the same predetermined value as the display ages so that the voltage across the segments increases as their capacitance decreases with age.

9. A controller as claimed in claim 1, wherein the controller compensates for the decrease in sensitivity of the display by providing a controlled increase in drive voltage as the display ages.

10. A controller as claimed in claim 9, wherein the controller determines the sensitivity of the display and sets the drive power accordingly to provide a desired level of display brightness.

11. A controller as claimed in claim 9, the controller being arranged to measure the voltage achieved on the load by the application of a known amount of energy, the achieved voltage, the amount of energy applied and the area being driven being used to estimate the capacitance per unit area of the display and thereby determine the sensitivity.

13. A controller as claimed in claim 1, the controller comprising a power supply having a reservoir capacitor with a capacitance which is significantly smaller than that of the load, the arrangement being such that the voltage at the output of the controller is allowed to “

collapse”

every cycle.

14. A controller as claimed in claim 1, comprising a power supply having a fly-back circuit, wherein a flow of current through an inductor is selectively interrupted in order to provide a sufficiently high voltage output to drive an electroluminescent display, the interruption of the current being controlled so as to provide a desired output power.

15. A controller as claimed in claim 14, wherein the inductor current is controlled by means of the output from a pulse width modulator.

16. A controller as claimed in claim 15, wherein the pulse width is determined from the square root of the area of the segments that are to be illuminated.

18. An electroluminescent display in combination with a controller claimed in claim 1.

19. A method of controlling an electroluminescent display comprising the use of a controller according to claim 1.

8. A controller for an electroluminescent display, wherein the controller is arranged to provide constant predetermined power per unit area of illuminated segments of the display.

21. A controller as claimed in claim 8, the controller comprising a power supply having a reservoir capacitor with a capacitance which is significantly smaller than that of the load, the arrangement being such that the voltage at the output of the controller is allowed to “

collapse”

every cycle.

23. A controller as claimed in claim 8, comprising a power supply having a fly-back circuit, wherein a flow of current through an inductor is selectively interrupted in order to provide a sufficiently high voltage output to drive an electroluminescent display, the interruption of the current being controlled so as to provide a desired output power.

25. An electroluminescent display in combination with a controller claimed in claim 8.

28. A method of controlling an electroluminescent display comprising the use of a controller according to claim 8.

12. A controller for an electroluminescent display, the controller being arranged to determine the sensitivity of the display segments and to drive the elements at a voltage that provides a desired level of output brightness such that the output brightness is maintained substantially constant throughout the useful life of the display.

22. A controller as claimed in claim 12, the controller comprising a power supply having a reservoir capacitor with a capacitance which is significantly smaller than that of the load, the arrangement being such that the voltage at the output of the controller is allowed to “

collapse”

every cycle.

24. A controller as claimed in claim 12, comprising a power supply having a fly-back circuit, wherein a flow of current through an inductor is selectively interrupted in order to provide a sufficiently high voltage output to drive an electroluminescent display, the interruption of the current being controlled so as to provide a desired output power.

26. An electroluminescent display in combination with a controller claimed in claim 12.

29. A method of controlling an electroluminescent display comprising the use of a controller according to claim 12.

17. A controller for an electroluminescent display having a plurality of elements which are subject to differential ageing, the controller being arranged to drive the elements so as to compensate for said differential ageing such that the elements are illuminated at substantially equal brightness throughout the useful lifetime of the display.

27. An electroluminescent display in combination with a controller claimed in claim 17.

30. A method of controlling an electroluminescent display comprising the use of a controller according to claim 17.

20. A method of controlling an electroluminescent display wherein the power supply is controlled so as to deliver the correct amount of power into the system for a given display output.