LIGHT EMITTING DIODE DRIVING CIRCUIT

• US 20080315773A1
• Filed: 06/18/2008
• Published: 12/25/2008
• Est. Priority Date: 06/21/2007
• Status: Active Grant

• Current Assignee: DB HiTek Co., Ltd.
• Original Assignee: Dongbu HiTek Co., Ltd.
• Inventors: Pang, Sung-Man
• Granted Patent: US 8,148,903 B2
• Time in Patent Office: Days
• US Class Current: 315/151
• CPC Class Codes: H05B 45/12 using optical feedback

Abstract

A LED driving circuit that may control current flow into an LED on a current path according to the amount of light sensed from the LED. An LED driving circuit for driving at least one LED may include at least one of: An optical sensor for receiving light emitted from the LED and generating a feedback signal having a level corresponding to an amount of the received light. A current regulator provided on a path through which current of the LED flows for regulating an amount of current flowing into the LED according to a comparison of the feedback signal with a first reference signal.

Claims

1. An apparatus comprising a light emitting diode (LED) driving circuit configured to drive at least one LED, wherein the circuit comprises:

an optical sensor configured to receive light emitted from the LED and generate a feedback signal corresponding to an amount of light received by the optical sensor; and

a current regulator configured to regulate an amount of current flowing into said at least one LED according to a comparison of the feedback signal with a first reference signal.

2. The apparatus of claim 1, wherein the current regulator is connected between a negative electrode of said at least one LED and a reference voltage source.

3. The apparatus of claim 2, wherein the reference voltage source is grounded.

4. The apparatus of claim 1, comprising:

a voltage inspector configured to inspect a voltage of said at least one LED and generate a control signal; and

a charge pump configured to supply a voltage to said at least one LED according to the control signal.

5. The apparatus of claim 4, wherein:

the charge pump is configured to supply to said at least one LED the voltage corresponding to an operation mode; and

the operation mode is determined according to the control signal designating one of a plurality of operation modes having different voltage gains.

6. The apparatus of claim 4, wherein the voltage of said at least one LED is a voltage supplied to said at least one LED.

7. The apparatus of claim 4, wherein the voltage of said at least one LED is a voltage across both electrodes of said at least one LED.

8. The apparatus of claim 1, wherein the optical sensor comprises:

a light receiving diode configure to receive light emitted from said at least one LED; and

a first load connected between the light receiving diode and a reference voltage source, wherein the feedback signal is derived from a voltage at a connection point of the light receiving diode and the first load.

9. The apparatus of claim 8, wherein the reference voltage source is grounded.

10. The apparatus of claim 8, wherein the light receiving diode comprises:

a negative electrode connected to the charge pump; and

a positive electrode connected to the first load.

12. The apparatus of claim 8, wherein:

the first load comprises a first resistor connected between a positive electrode of the light receiving diode and the reference voltage source; and

the feedback signal is a voltage across both ends of the first resistor.

13. The apparatus of claim 1, wherein the current regulator comprises:

a first comparator configured to compare a level of the feedback signal with a level of the first reference signal;

a first transistor connected between a negative electrode of said at least one LED and a reference voltage source, where the first transistor is driven in response to the comparison of the feedback signal with the first reference signal; and

a second load connected between the first transistor and the reference voltage source.

14. The apparatus of claim 13, wherein the reference voltage source is grounded.

15. The apparatus of claim 13, wherein the current regulator comprises a first reference signal generator configured to generate the first reference signal.

16. The apparatus of claim 15, wherein the first reference signal generator comprises:

a second operational amplifier comprising a positive input terminal configured to receive a second reference signal;

a second load connected between a negative input terminal of the second operational amplifier and the reference voltage source;

a third transistor configured to supply a reference current to the second load in response to an output of the second operational amplifier;

a current mirror configured to generate a mirror current of the reference current; and

a third resistor, wherein the mirror current flows into the third resistor and wherein the first reference signal corresponds to a voltage across both ends of the third resistor.

17. The apparatus of claim 1, wherein the current regulator comprises:

a second comparator configured to compare the feedback signal with the first reference signal;

a second reference signal generator configured to generate a second reference signal in response to the comparison of the feedback signal with the first reference signal;

a first operational amplifier comprising a positive input terminal connected to the second reference signal generator;

a second transistor connected between a negative electrode of said at least one LED and a reference voltage source, wherein the second transistor is driven by an output of the first operational amplifier; and

a third load connected between a negative input terminal of the first operational amplifier and the reference voltage source.

18. The apparatus of claim 17, wherein the reference voltage source is grounded.

19. The apparatus of claim 17, wherein second reference signal generator comprises:

a fourth transistor through which a reference current flows, wherein the fourth transistor is driven in response to the comparison of the feedback signal with the first reference signal;

a forth resistor connected between the fourth transistor and the reference voltage source;

a current mirror configured to generate a mirror current of the reference current; and

a fifth resistor, wherein the mirror current flows into the fifth transistor and wherein the second reference signal corresponds to a voltage across both ends of the fifth resistor.

20. The apparatus of claim 1, comprising a switch configured to selectively supply the feedback signal to the current regulator.

11. The apparatus of 8, wherein the light receiving diode comprises:

a negative electrode connected to a positive electrode of said at least one LED; and

a positive electrode connected to the first load.