DRIVING CIRCUIT FOR LIGHT EMITTING ELEMENT, LIGHT EMITTING DEVICE USING SAME, AND DISPLAY APPARATUS

• US 20130038819A1
• Filed: 02/24/2011
• Published: 02/14/2013
• Est. Priority Date: 02/26/2010
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Ishikawa, Hiroyuki
• Granted Patent: US 10,152,926 B2
• Time in Patent Office: Days
• US Class Current: 349/69
• 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 2330/045 Protection against panel overheating
• CPC Class Codes: G09G 3/342 using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
• CPC Class Codes: H05B 45/37 Converter circuits
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines

Abstract

LED terminals are respectively provided to light emitting units, and are each connected to the second terminal of the corresponding one of the light emitting units. Current sources are respectively provided to the LED terminals, and are respectively configured to supply adjustable driving currents to the respective light emitting units via the respective LED terminals. A reference voltage source generates a reference voltage that corresponds to the driving current. A control circuit controls a DC/DC converter such that the lowest voltage from among voltages at the LED terminals matches the reference voltage

Claims

1. A driving circuit configured to control a DC/DC converter configured to generate a driving voltage to be applied to a first terminal to which at least one light emitting units are commonly connected, and to supply a driving current to each of the at least one light emitting units, the driving circuit comprising:

at least one driving terminals respectively provided to the at least one driving terminals, each configured to be connected to a second terminal of the corresponding light emitting unit;

at least one current sources respectively provided to the at least one light emitting units, each configured to supply a adjustable driving current to the corresponding light emitting unit via the corresponding driving terminal;

a reference voltage source configured to generate a reference voltage having a voltage level that corresponds to the driving current; and

a control circuit configured to control the DC/DC converter such that a lowest voltage from among voltages at the at least one driving terminals matches the reference voltage.

2. A driving circuit according to claim 1, wherein the at least one light emitting units are each configured to generate a driving current that corresponds to a common first voltage which indicates a target value of the driving current,

and wherein the reference voltage source is configured to generate the reference voltage according to the first voltage.

3. A driving circuit according to claim 2, wherein the at least one light emitting units are each configured to generate a driving current that is proportional to the common first voltage which indicates a target value of the driving current,

and wherein the reference voltage source is configured to generate a reference voltage that is changed in a stepwise manner according to the first voltage.

4. A driving circuit according to claim 2, wherein the at least one light emitting units are each configured to generate the driving current that is proportional to the common first voltage which indicates a target value of the driving current,

and wherein the reference voltage source is configured to generate a reference voltage that is substantially proportional to the first voltage.

5. A driving circuit according to claim 1, wherein the at least one light emitting units are each configured to generate the driving current that corresponds to a common first voltage which indicates a target value of the driving current,

and wherein the reference voltage source is configured to generate the reference voltage according to one from among the driving currents generated by the at least one light emitting units.

6. A driving circuit according to claim 5, wherein the reference voltage source is configured to generate a reference voltage that changes in a stepwise manner according to the driving current generated by the light emitting unit.

7. A driving circuit according to claim 5, wherein the reference voltage source is configured to generate a reference voltage that is substantially proportional to the driving current generated by the light emitting unit.

8. A driving circuit according to claim 1, further comprising:

a thermal shutdown circuit configured to shut down the driving circuit itself when a temperature to be monitored exceeds a predetermined first threshold value; and

a terminal temperature detection circuit arranged in a vicinity of an external connecting terminal to be monitored, via which the driving current flows, and configured to generate a detection signal which indicates that the temperature of the external connecting terminal to be monitored has become abnormal when the temperature to be monitored exceeds a second threshold value that is lower than the first threshold value.

9. A driving circuit according to claim 8, wherein the external connecting terminal to be monitored is the driving terminal.

10. A driving circuit according to claim 8, wherein the second threshold value is determined according to a lowest temperature that leads to deterioration of a solder which is welded to the external connecting terminal to be monitored in a process in which the driving circuit is mounted on a printed-circuit board.

11. A driving circuit according to claim 8, wherein the first threshold value is set to 130 degrees or more,

and wherein the second threshold value is set to 100 degrees or less.

12. A driving circuit according to claim 8, wherein the terminal temperature detection circuit is provided to each of the at least one driving terminals.

18. A light emitting apparatus comprising:

at least one light emitting units;

a DC/DC converter configured to supply a driving voltage to each of the at least one light emitting units; and

a driving circuit according to claim 1, configured to supply a driving current to each of the at least one light emitting units, and to control the DC/DC converter.

19. A display apparatus comprising:

a liquid crystal panel; and

a light emitting apparatus according to claim 18, with the its light emitting unit configured as a backlight arranged on the back face of the liquid crystal panel.

13. A driving circuit configured to control a DC/DC converter configured to generate a driving voltage to be applied to a first terminal to which at least one light emitting units are commonly connected, and to supply a driving current to each of the at least one light emitting units, the driving circuit comprising:

at least one driving terminals respectively provided to the at least one light emitting units, each configured to be connected to a second terminal of the corresponding light emitting unit;

at least one current sources respectively provided to the at least one driving terminals, each configured to supply the driving current to the corresponding light emitting unit via the corresponding driving terminal;

a control circuit configured to control the DC/DC converter such that a lowest voltage from among voltages at the at least one driving terminals matches a reference voltage;

a thermal shutdown circuit configured to shut down the driving circuit itself when a temperature to be monitored exceeds a predetermined first threshold value; and

a terminal temperature detection circuit arranged in a vicinity of an external connecting terminal to be monitored, via which the driving current flows, and configured to generate a detection signal which indicates that the temperature of the external connecting terminal to be monitored has become abnormal when the temperature to be monitored exceeds a second threshold value that is lower than the first threshold value.

14. A driving circuit according to claim 13, wherein the external connecting terminal to be monitored is the driving terminal.

15. A driving circuit according to claim 13, wherein the second threshold value is determined according to a lowest temperature that leads to deterioration of a solder which is welded to the external connecting terminal to be monitored in a process in which the driving circuit is mounted on a printed-circuit board.

16. A driving circuit according to claim 13, wherein the first threshold value is set to 130 degrees or more,

and wherein the second threshold value is set to 100 degrees or less.

17. A driving circuit according to claim 13, wherein the terminal temperature detection circuit is provided to each of the at least one driving terminals.

20. A light emitting apparatus comprising:

at least one light emitting units;

a DC/DC converter configured to supply a driving voltage to each of the at least one light emitting units; and

a driving circuit according to claim 13, configured to supply a driving current to each of the at least one light emitting units, and to control the DC/DC converter.