Circuit for vehicle lighting

• US 8,169,147 B2
• Filed: 09/17/2009
• Issued: 05/01/2012
• Est. Priority Date: 09/17/2009
• Status: Expired due to Fees

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: Hsu, Cheng-Wei, Liu, Da, Lee, ShengTai, Lin, Yung Lin
• Primary Examiner(s): Chang, Daniel D
• Application Number:
  US12/561,483
• Publication Number:
  US 20110062869A1
• Time in Patent Office: 957 Days
• Field of Search: 315/77, 315/82, 315/291, 315/294, 315/297, 315/301, 315/307, 315/313
• US Class Current: 315/77
• CPC Class Codes: B60Q 11/005 for lighting devices, e.g. indicating if lamps are burning or not
• CPC Class Codes: H05B 45/54 in a series array of LEDs
• CPC Class Codes: H05B 45/58 involving end of life detection of LEDs
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A circuit for driving a vehicle lamp includes a current path coupled between a power line and ground, and a monitoring unit coupled to the power line. The current path includes a dummy load. The monitoring unit can monitor a testing signal applied to the power line. The testing signal can test whether the vehicle lamp operates properly. The monitoring unit can conduct the current path to enable a current to flow through the dummy load to ground to decrease a total resistance of the circuit if the testing signal is detected.

Claims

1. A circuit for driving a vehicle lamp, comprising:

a current path coupled between a power line and ground and comprising a dummy load; and

a monitoring unit coupled to said power line and operable for monitoring a testing signal applied to said power line, wherein said testing signal is operable for testing whether said vehicle lamp operates properly, and wherein said monitoring unit is operable for conducting said current path to enable a current to flow through said dummy load to ground to decrease a total resistance of said circuit if said testing signal is detected.

2. The circuit of claim 1, further comprising:

a DC/DC converter coupled to said power line and operable for providing regulated power to said vehicle lamp;

a current sensor coupled to said vehicle lamp and operable for providing a sensing signal indicative of a current flowing through said vehicle lamp; and

a controller coupled to said current sensor and operable for controlling said DC/DC converter based on said sensing signal, and operable for determining a conductance status of said current path based on said sensing signal.

3. The circuit of claim 2, wherein said controller is operable for cutting off said current path if said vehicle lamp is in an open circuit condition.

4. The circuit of claim 2, wherein said controller is operable for cutting off said current path if said vehicle lamp is in a short circuit condition.

5. The circuit of claim 1, wherein said dummy load comprises a resistor.

6. The circuit of claim 1, wherein said monitoring unit comprises a capacitor, wherein a voltage across said capacitor increases above a threshold if said testing signal is applied to said power line, and wherein said capacitor turns on a switch in said current path if said voltage across said capacitor is above said threshold.

7. The circuit of claim 6, wherein said voltage across said capacitor is below said threshold if said testing signal is absent from said power line, and wherein said switch is turned off if said voltage across said capacitor is below said threshold.

8. The circuit of claim 1, wherein said monitoring unit comprises a first capacitor coupled to said power line and for passing through said test signal and for isolating DC power on said power line.

9. The circuit of claim 8, wherein said monitoring unit further comprises:

a first diode with a cathode coupled to said first capacitor and an anode coupled to ground; and

a second diode with an anode coupled to said first capacitor and a cathode coupled to ground through a second capacitor,

wherein said current path comprises a switch, and wherein a conductance status of said switch is determined by a voltage across said second capacitor.

10. A light assembly, comprising:

a light source; and

a circuit coupled to a power line for driving said light source, comprising;

a first capacitor coupled to said power line, wherein a voltage across said first capacitor increases above a threshold if a testing signal for testing whether said light source operates properly is applied to said power line;

a current path coupled between said power line and ground, wherein said current path is conducted to decrease a total resistance of said circuit if said voltage across said first capacitor is above said threshold.

11. The light assembly of claim 10, further comprising:

a DC/DC converter coupled to said power line and operable for providing regulated power to said light source;

a current sensor coupled to said light source and operable for providing a sensing signal indicative of a current flowing through said light source; and

a controller coupled to said current sensor and operable for controlling said DC/DC converter based on said sensing signal, and operable for determining a conductance status of said current path based on said sensing signal.

12. The light assembly of claim 11, wherein said controller is operable for cutting off said current path if said light source is in an open circuit condition.

13. The light assembly of claim 11, wherein said controller is operable for cutting off said current path if said light source is in a short circuit condition.

14. The light assembly of claim 10, wherein said current path comprises a resistor.

15. The light assembly of claim 10, wherein said light source comprises a light emitting diode (LED) string.

16. The light assembly of claim 10, wherein said circuit comprises:

a second capacitor coupled to said power line;

a first diode with a cathode coupled to said second capacitor and an anode coupled to ground; and

a second diode with an anode coupled to said second capacitor and a cathode coupled to ground through said first capacitor;

wherein said current path comprises a switch, and wherein a conductance status of said switch is determined by a voltage across said first capacitor.

17. A method for driving a vehicle lamp by a circuit, comprising:

monitoring a testing signal on a power line, wherein said testing signal tests whether said vehicle lamp operates properly;

conducting a current path between said power line and ground to decrease a total resistance of said circuit if said testing signal is detected; and

cutting off said current path if said testing signal is absent.

18. The method of claim 17, further comprising:

monitoring a current flowing through said vehicle lamp; and

cutting off said current path if said vehicle lamp is in an open circuit condition.

19. The method of claim 17, further comprising:

monitoring a current flowing through said vehicle lamp; and

cutting off said current path if said vehicle lamp is in a short circuit condition.

20. The method of claim 17, further comprising:

converting input power from said power line to regulated power by a DC/DC converter;

controlling said DC/DC converter based on a current flowing through said vehicle lamp; and

powering said vehicle lamp by said regulated power.

21. The method of claim 17, further comprising:

charging a capacitor by said testing signal; and

turning on a switch in said current path to conduct said current path if a voltage across said capacitor is greater than a threshold.