LED DRIVING CIRCUIT

• US 20100072898A1
• Filed: 10/17/2007
• Published: 03/25/2010
• Est. Priority Date: 10/18/2006
• Status: Active Grant

• Current Assignee: KOA Corporation
• Original Assignee: KOA Corporation
• Inventors: Ohashi, Mitsuo, Sagara, Iwao, Komatsu, Hideyuki
• Granted Patent: US 8,324,816 B2
• Time in Patent Office: Days
• US Class Current: 315/127
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/345 Current stabilisation; Maintaining constant current
• CPC Class Codes: H05B 45/392 wherein the LEDs are placed as freewheeling diodes at the secondary side of an isolation transformer

Abstract

An LED driving circuit is provided for making it possible to economically drive a serially connected LED circuit by means of a switching device with a relatively low withstanding voltage even if the number of serially connected LED devices increases. In an LED driving circuit provided with a serially connected LED circuit (11) in which many LED devices are serially connected and a switching device (13) serially connected with the serially connected LED circuit (11) to control that an electrical current flowing through the serially connected LED circuit (11) is turned on or off, wherein a circuit device (15), which comprises a resistor, a constant voltage diode, a constant current diode, or the like, is connected in parallel with the switching device to make a minute current flow through the serially connected LED circuit (11) to the extent that the LED devices are not turned on when the switching device is turned off.

Claims

1. An LED driving circuit comprising:

a serially connected LED circuit, in which many LED devices are serially connected; and

a switching device serially connected with the serially connected LED circuit to control that an electrical current flowing through the serially connected LED circuit is turned on or off;

wherein a circuit device is connected in parallel with the switching device to make a minute current flow through the serially connected LED circuit to the extent that the LED devices are not turned on when the switching device is turned off.

2. The LED driving circuit according to claim 1, wherein the circuit device comprises a resistor device.

3. The LED driving circuit according to claim 1, wherein the circuit device comprises a constant voltage diode device.

4. The LED driving circuit according to claim 1, wherein the circuit device comprises a constant current diode device.

5. The LED driving circuit according to claim 1, wherein the circuit device comprises a combination of a constant voltage diode device and a transistor to form a voltage limiting circuit, which has large electrical current capacity over a constant voltage.

6. An LED driving circuit comprising:

a serially connected LED circuit, in which n pieces of LED devices having forward voltage Vf respectively are serially connected; and

a switching device serially connected with the serially connected LED circuit to control that an electrical current flowing through the serially connected LED circuit is turned on or off;

wherein the LED driving circuit further comprises;

a DC power supply, in which power supply voltage Vcc is, Vcc>

Vf×

n;

a circuit device connected in parallel with the switching device to make a minute current flow through the serially connected LED circuit to the extent that the LED devices are not turned on when the switching device is turned off; and

the switching device, in which applicable maximum voltage V_CEO is, V_CEO<

Vcc.

7. An LED driving circuit comprising:

a serially connected LED circuit, in which many LED devices are serially connected;

a first switching device serially connected with the serially connected LED circuit to control an electrical current flowing through the serially connected LED circuit;

a current setting resistor circuit, which comprises a plural of resistors connected in parallel with each other between the first switching device and a ground terminal, and second switching devices, each of which is serially connected with each of the plural of resistors; and

a setting circuit for setting on or off of the second switching devices respectively.

8. The LED driving circuit according to claim 7, wherein an output of a buffer amplifier is connected with a control terminal of the first switching device, and an output of a multiplexer is connected with an input of the buffer amplifier.

9. The LED driving circuit according to claim 8, wherein an output of a D/A converter is connected with one input terminal of the multiplexer, and a ground voltage is connected with the other input terminal of the multiplexer.

10. The LED driving circuit according to claim 7, wherein a fuse device is connected with a circuit, which includes the serially connected LED circuit and the first switching device.

11. The LED driving circuit according to claim 7, wherein a diode device is connected in parallel with the serially connected LED circuit.

12. An LED driving circuit comprising:

a serially connected LED circuit, in which many LED devices are serially connected; and

a first switching device serially connected with the serially connected LED circuit to control an electrical current flowing through the serially connected LED circuit; and

a fuse device serially connected with the serially connected LED circuit and the first switching device.

13. An LED driving circuit comprising:

a serially connected LED circuit, in which many LED devices are serially connected;

a first switching device serially connected with the serially connected LED circuit to control an electrical current flowing through the serially connected LED circuit; and

a diode device connected in parallel with the serially connected LED circuit.

14. An LED driving circuit comprising:

a serially connected LED circuit, in which many LED devices are serially connected;

a first switching device serially connected with the serially connected LED circuit to control an electrical current flowing through the serially connected LED circuit;

a switching device cascade connected with the first switching device, the switching device connected between the serially connected LED circuit and the first switching device;

a current setting resistor device connected between the first switching device and a ground terminal;

a buffer amplifier connected with a base terminal of the first switching device;

a multiplexer connected with an input of the buffer amplifier to switch LED on signal and off signal; and

a lighting time control circuit to form times of the LED on signal and off signal.

15. The LED driving circuit according to claim 14, wherein a condenser device is connected in parallel with the current setting resistor device.

16. The LED driving circuit according to claim 14, wherein the lighting time control circuit comprises a circuit for setting LED on time and off time and a counter for forming a variable length pulse of the LED on time and off time, so that the multiplexer outputs LED on signal to the buffer amplifier at the LED on time, and the multiplexer outputs LED off signal to the buffer amplifier at the LED off time.

17. The LED driving circuit according to claim 14, wherein an output of the D/A converter is connected with an on-signal terminal of the multiplexer and ground voltage is connected with an off-signal terminal of the multiplexer.

18. An LED driving circuit comprising:

a serially connected LED circuit, in which many LED devices are serially connected;

a first switching device serially connected with the serially connected LED circuit to control an electrical current flowing through the serially connected LED circuit;

a current setting resistor device connected between the first switching device and a ground terminal; and

a condenser device connected in parallel with the current setting resistor device.

19. The LED driving circuit according to claim 18, wherein a diode device is connected in parallel with the serially connected LED circuit.