Light-emitting element driving device
View Patent ↗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.
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 drive circuit group that includes at least two drive circuits and supplies a plurality of drive currents to drive the plurality of light-emitting element strings, respectively;
a failure detector that monitors voltages at a plurality of nodes between a ground and 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 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; and
an error amplifier that receives the certain voltage output from the minimum detector, wherein
the drive circuit group independently adjusts a brightness of each of the plurality of light-emitting element strings.
2. The light-emitting element driving device of claim 1 , wherein the failure includes a short circuit failure and an open circuit failure.
3. The light-emitting element driving device of claim 1 , wherein the voltages at the plurality of nodes are monitored when the drive circuit group is driving the plurality of light-emitting element strings.
4. The light-emitting element driving device of claim 1 , wherein the failure detector has a timer function.
5. 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.
6. The light-emitting element driving device of claim 1 , wherein the drive circuit group changes a duty ratio of each of the plurality of drive currents.
7. The light-emitting element driving device of claim 1 , wherein the drive circuit group changes an effective value of each of the plurality of drive currents.
8. The light-emitting element driving device of claim 1 , wherein the drive circuit group adjusts the brightness of each of the plurality of light-emitting element strings based on a plural-channel control signal.
9. The light-emitting element driving device of claim 6 , wherein the drive circuit group changes the duty ratio of each of the plurality of drive currents based on a plural-channel control signal.
10. The light-emitting element driving device of claim 7 , wherein the drive circuit group changes the effective value of each of the plurality of drive currents based on a plural-channel control signal.
11. The light-emitting element driving device of claim 1 , further comprising a power controller that generates a control signal to control a transistor, wherein
the transistor is connected to the plurality of light-emitting element strings.
12. The light-emitting element driving device of claim 11 , further comprising a comparator that controls the power controller.
13. The light-emitting element driving device of claim 11 , wherein the power controller is a pulse width modulation controller.
14. The light-emitting element driving device of claim 11 , wherein the light-emitting element driving device stabilizes an output voltage generated based on a switching of the transistor by feedback loop control.
15. 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.
16. 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 a plurality of nodes between a ground and 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;
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;
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; and
an error amplifier that receives the certain voltage output from the minimum detector, wherein
each of the plurality of drive current generators independently adjusts a brightness of the corresponding one of the plurality of light-emitting element strings.
17. The light-emitting element driving device of claim 16 , 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.
18. The light-emitting element driving device of claim 16 , 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.
19. The light-emitting element driving device of claim 16 , 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.
20. The light-emitting element driving device of claim 16 , 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.
21. 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 a plurality of nodes between a ground and 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 brightness 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, and an error amplifier that receives the certain voltage output from the minimum detector.
22. The light-emitting element driving device of claim 21 , 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.
23. The light-emitting element driving device of claim 21 , 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.
24. The light-emitting element driving device of claim 21 , 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.
25. The light-emitting element driving device of claim 21 , 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.
26. The light-emitting element driving device of claim 21 , 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.
27. The light-emitting element driving device of claim 1 , 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.
28. The light-emitting element driving device of claim 16 , 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.
29. The light-emitting element driving device of claim 21 , 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.
30. The light-emitting element driving device of claim 1 , wherein a voltage different from the minimum voltage is generated based on the minimum voltage.
31. The light-emitting element driving device of claim 16 , wherein a voltage different from the minimum voltage is generated based on the minimum voltage.
32. The light-emitting element driving device of claim 21 , wherein a voltage different from the minimum voltage is generated based on the minimum voltage.
33. The light-emitting element driving device of claim 1 , wherein the certain voltage is the same as the minimum voltage.
34. The light-emitting element driving device of claim 16 , wherein the certain voltage is the same as the minimum voltage.
35. The light-emitting element driving device of claim 21 , wherein the certain voltage is the same as the minimum voltage.