DRIVING CIRCUIT OF LIGHT EMITTING DIODES HAVING AT LEAST ONE BYPASS CIRCUIT, AND DRIVING METHOD THEREOF

• US 20120262074A1
• Filed: 03/20/2012
• Published: 10/18/2012
• Est. Priority Date: 04/13/2011
• Status: Abandoned Application

• Current Assignee: Cyntec Co. Ltd. (Delta Electronics Incorporated)
• Original Assignee: Cyntec Co. Ltd. (Delta Electronics Incorporated)
• Inventors: Lu, Bau-Ru, Lu, Chun-Hsien, Li, Jeng-Jen, Wang, Wei-Cheng
• Application Number:
  US13/425,412
• Publication Number:
  US 20120262074A1
• Time in Patent Office: Days
• US Class Current: 315/186
• CPC Class Codes: H05B 45/18 using temperature feedback
• CPC Class Codes: H05B 45/48 having LEDs organised in strings and incorporating parallel shunting devices

Abstract

A driving circuit of light emitting diodes includes a power supply circuit, at least one bypass circuit, and a temperature control circuit. The power supply circuit is used for providing a driving voltage to at least one series of light emitting diodes. Each bypass circuit of the at least one bypass circuit is used for being turned on when an ambient temperature is lower than a predetermined temperature. The temperature control circuit is coupled to the at least one bypass circuit for detecting the ambient temperature, and sending a control signal to the at least one bypass circuit when the ambient temperature is lower than the predetermined temperature. Therefore, the driving voltage can still drive the at least one series of light emitting diodes when the ambient temperature is lower than the predetermined temperature.

Claims

1. A driving circuit of light emitting diodes having at least one bypass circuit, the driving circuit comprising:

a power supply circuit for providing a driving voltage to at least one series of light emitting diodes;

at least one bypass circuit, each bypass circuit of the at least one bypass circuit being used for being turned on when an ambient temperature is lower than a predetermined temperature; and

a temperature control circuit coupled to the at least one bypass circuit for detecting the ambient temperature, and sending a control signal to the at least one bypass circuit when the ambient temperature is lower than the predetermined temperature.

2. The driving circuit of claim 1, wherein the power supply circuit is a Buck converter.

3. The driving circuit of claim 1, wherein the power supply circuit is a Boost/Buck converter.

4. The driving circuit of claim 1, wherein the bypass circuit is an N-type metal-oxide-semiconductor transistor.

5. The driving circuit of claim 1, wherein the bypass circuit is a P-type metal-oxide-semiconductor transistor.

6. The driving circuit of claim 1, wherein the bypass circuit is a transmission gate.

7. The driving circuit of claim 1, wherein the temperature control circuit comprises:

a divider resistor having a first terminal for receiving a first voltage, and a second terminal;

a thermistor having a first terminal coupled to the second terminal of the divider resistor, and a second terminal coupled to ground; and

a comparator having a first input terminal coupled to the second terminal of the divider resistor, a second input terminal for receiving a reference voltage, and an output terminal for outputting the control signal, wherein the comparator outputs the control signal according to a voltage of the first input terminal of the comparator and the reference voltage.

8. The driving circuit of claim 1, wherein the temperature control circuit comprises:

a comparator for detecting a voltage drop generated by a direct current resistance of an inductor of the power supply circuit, and outputting an enable signal according to the voltage drop and a predetermined value; and

a control unit for outputting the control signal when the control unit receives the enable signal.

9. The driving circuit of claim 1, wherein the temperature control circuit comprises:

a divider resistor having a first terminal for receiving the driving voltage, and a second terminal; and

a thermistor having a first terminal coupled to the second terminal of the divider resistor, and a second terminal;

wherein the control signal is a voltage of the first terminal of the thermistor.

10. The driving circuit of claim 9, wherein the bypass circuit is a silicon-controlled rectifier (SCR), wherein the silicon-controlled rectifier has a first terminal coupled to the second terminal of the divider resistor, a second terminal coupled to the second terminal of the thermistor, and a third terminal, wherein at least one light emitting diode is coupled between the second terminal and the third terminal of the silicon-controlled rectifier.

11. The driving circuit of claim 1, wherein each series of light emitting diodes of the at least one series of light emitting diodes is coupled to at least one bypass circuit in parallel.

12. A driving method for controlling at least one bypass circuit of a driving circuit of light emitting diodes, the driving method comprising:

detecting an ambient temperature of a series of light emitting diodes;

determining whether the ambient temperature is lower than a predetermined temperature;

sending a control signal when the ambient temperature is lower than the predetermined temperature; and

turning on at least one bypass circuit to make two terminals of at least one light emitting diode of the series of light emitting diodes short-circuited according to the control signal.

13. The driving method of claim 12, further comprising:

turning off the at least one bypass circuit when the ambient temperature is higher than the predetermined temperature.

14. A driving circuit of light emitting diodes having at least one bypass circuit, the driving circuit comprising:

a power supply circuit for providing a driving voltage to at least one series of light emitting diodes;

at least one bypass circuit, each bypass circuit of the at least one bypass circuit being used for being turned off after the power supply circuit is powered on for a predetermined time; and

a timer for sending a control signal to the at least one bypass circuit to turn off the at least one bypass circuit after the power supply circuit is powered on for the predetermined time.

15. The driving circuit of claim 14, wherein each series of light emitting diodes of the at least one series of light emitting diodes is coupled to at least one bypass circuit in parallel.

16. A driving method for controlling at least one bypass circuit of a driving circuit of light emitting diodes, the driving method comprising:

providing a driving voltage to a series of light emitting diodes;

sending a control signal to at least one bypass circuit after the driving voltage is provided to the series of light emitting diodes for a predetermined time; and

turning off the at least one bypass circuit according to the control signal.