Light-emitting element driving device

Patent metadata

Field	Value
Publication number	US-9237627-B2
Application number	US-201414496213-A
Country	US
Kind code	B2
Filing date	Sep 25, 2014
Priority date	Jun 9, 2009
Publication date	Jan 12, 2016
Grant date	Jan 12, 2016

Abstract

Short circuit failures and open circuit failures of light-emitting elements used for the backlight in an LCD panel can be reliably and easily detected. The voltage at the node between each series-connected light-emitting element array and a drive circuit is detected as a monitored voltage. A maximum detector detects the highest and a minimum detector detects the lowest of these monitored voltages. Short circuit or open circuit failure of a light-emitting element is detected by comparing the voltage difference between the maximum detector output and the minimum detector output with a specific reference voltage.

First claim

The invention claimed is:

1. A light-emitting element driving device for driving a plurality of light-emitting element strings connected in parallel, the light-emitting element driving device comprising:
a failure detector that monitors voltages at the plurality of light-emitting element strings, and detects a failure of each light-emitting element string of the plurality of light-emitting element strings;
a drive current controller that generates a plurality of drive current control signals; and
a plurality of drive current generators, each drive current generator of the plurality of drive current generators supplying a drive current to a corresponding one of the plurality of light-emitting element strings based on a corresponding one of the plurality of drive current control signals; and
a minimum detector that detects a minimum voltage of the voltages at the plurality of nodes and outputs a certain voltage which represents the minimum voltage, wherein
each of the plurality of drive current generators independently adjusts a drive current of the corresponding one of the plurality of light-emitting element strings.

2. The light-emitting element driving device of claim 1 , wherein
the plurality of light-emitting element strings includes a first light-emitting element string, and
if the failure detector detects a failure of the first light-emitting element string, the light-emitting element driving device isolates the first light-emitting element string from the light-emitting element driving device.

3. The light-emitting element driving device of claim 1 , wherein each of the plurality of drive current generators changes a duty ratio of the drive current supplied to the corresponding one of the plurality of light-emitting element strings.

4. The light-emitting element driving device of claim 1 , wherein each of the plurality of drive current generators changes an effective value of the drive current supplied to the corresponding one of the plurality of light-emitting element strings.

5. The light-emitting element driving device of claim 1 , wherein the failure detector includes:
a first failure detector that generates a first monitored voltage corresponding to a highest voltage of the voltages at the plurality of nodes;
a second failure detector that generates a second monitored voltage corresponding to one of the voltages at the plurality of nodes, the second monitored voltage being smaller than the first monitored voltage;
a reference power source that generates a reference voltage, and outputs a sum voltage which represents a sum of the second monitored voltage and the reference voltage; and
a comparator that compares the first monitored voltage and the sum voltage.

6. A light-emitting element driving device for driving a plurality of light-emitting element strings connected in parallel, the light-emitting element driving device comprising:
a drive current controller that generates a plurality of drive current control signals; and
a plurality of drive current generators, each drive current generator of the plurality of drive current generators supplying a drive current to a corresponding one of the plurality of light-emitting element strings based on a corresponding one of the plurality of drive current control signals, wherein
the light-emitting element driving device monitors voltages at each of the plurality of light-emitting element strings, and detects a failure of each light-emitting element string of the plurality of light-emitting element strings,
each of the plurality of drive current generators independently adjusts a drive current of the corresponding one of the plurality of light-emitting element strings, and
the light-emitting element driving device includes a minimum detector that detects a minimum voltage of the voltages at the plurality of nodes and outputs a certain voltage which represents the minimum voltage.

7. The light-emitting element driving device of claim 6 , wherein
the plurality of light-emitting element strings includes a first light-emitting element string, and
if the light-emitting element driving device detects a failure of the first light-emitting element string, the light-emitting element driving device isolates the first light-emitting element string from the light-emitting element driving device.

8. The light-emitting element driving device of claim 6 , wherein each of the plurality of drive current generators changes a duty ratio of the drive current supplied to the corresponding one of the plurality of light-emitting element strings.

9. The light-emitting element driving device of claim 6 , wherein each of the plurality of drive current generators changes an effective value of the drive current supplied to the corresponding one of the plurality of light-emitting element strings.

10. The light-emitting element driving device of claim 6 , further comprising a failure detector that monitors the voltages at the plurality of nodes, and detects the failure of each light-emitting element string of the plurality of light-emitting element strings.

11. The light-emitting element driving device of claim 6 , wherein the voltages at the plurality of nodes are monitored when each of the plurality of drive current generators is driving the corresponding one of the plurality of light-emitting element strings.

12. The light-emitting element driving device of claim 1 , further comprising an error amplifier that receives the certain voltage output from the minimum detector.

13. The light-emitting element driving device of claim 6 ,
wherein the light-emitting element driving device includes an error amplifier that receives the certain voltage output from the minimum detector.

14. The light-emitting element driving device of claim 12 , wherein the light-emitting element driving device includes a pulse width modulation controller and a path between the error amplifier and the pulse width modulation controller.

15. The light-emitting element driving device of claim 13 , wherein the light-emitting element driving device includes a pulse width modulation controller and a path between the error amplifier and the pulse width modulation controller.

16. The light-emitting element driving device of claim 1 , wherein a voltage different from the minimum voltage is generated based on the minimum voltage.

17. The light-emitting element driving device of claim 6 , wherein a voltage different from the minimum voltage is generated based on the minimum voltage.

18. The light-emitting element driving device of claim 1 , wherein the certain voltage is the same as the minimum voltage.

19. The light-emitting element driving device of claim 6 , wherein the certain voltage is the same as the minimum voltage.

Assignees

• Panasonic Corp

Inventors

• Takata Go
• Kataoka Shinichiro
• Yamamoto Yasunori
• Kawahara Tsukasa
• Ueda Ryuji
• Itou Daisuke

Classifications

• H05B45/347

  Dynamic headroom control [DHC] · CPC title

• H05B45/48

  having LEDs organised in strings and incorporating parallel shunting devices · CPC title

• G09G3/3406

  Control of illumination source (illumination devices structurally associated with liquid crystal cells G02F1/1336) · CPC title

• H05B45/46 Primary

  having LEDs disposed in parallel lines · CPC title

• G09G2320/0233

  Improving the luminance or brightness uniformity across the screen · CPC title