Series connected power supply for semiconductor-based vehicle lighting systems

• US 20070108843A1
• Filed: 11/17/2005
• Published: 05/17/2007
• Est. Priority Date: 11/17/2005
• Status: Active Grant

• Current Assignee: Magna International Incorporated
• Original Assignee: Magna International Incorporated
• Inventors: Preston, Nigel, MacDonald, Jamie
• Granted Patent: US 7,710,050 B2
• Time in Patent Office: Days
• US Class Current: 307/112
• 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
• CPC Class Codes: H05B 45/54 in a series array of LEDs

Abstract

A novel and advantageous power supply is disclosed for lighting systems employing semiconductor light sources where the semiconductor light sources are connected in series. The power supply includes a constant current source to supply current to the semiconductor light sources and a bypass switch is provided around each semiconductor light source, or each sub-string of series connected semiconductor light sources. By opening or closing respective bypass switches, individual semiconductor light sources or sub-strings of semiconductor light sources can be illuminated or extinguished as desired. If the bypass switches are electrically controllable, such as semiconductor switches or relays, failures of one or more semiconductor light sources can be determined by the power supply and failed light sources can be bypassed and/or redundant semiconductor elements illuminated to replace failed light sources. Further, if the bypass switches are semiconductor switches, the power supply can employ pulse width modulation techniques to dim one or more semiconductor light sources as desired.

Claims

1. A power supply for series-connected semiconductor light sources, comprising:

a constant current source to supply a pre-selected level of electrical current to the series connected semiconductor light sources; and

a bypass switch across each respective one of the semiconductor light sources, each bypass switch operating when closed to provide a current path around a respective semiconductor light source.

2. A power supply according to claim 1 wherein the constant current source is a buck boost converter.

3. A power supply according to claim 1 wherein the constant current source is a Single Element Primary Inductor Circuit (SEPIC).

4. A power supply according to claim 1 wherein the bypass switches are relays.

5. A power supply according to claim 4 wherein the relays are electromechanical relays.

6. A power supply according to claim 1 wherein the bypass switches are semiconductor switches.

7. A power supply according to claim 1 further comprising a controller to operate the bypass switches.

8. A power supply according to claim 7 wherein the bypass switches are semiconductor switches.

9. A power supply according to claim 8 wherein the controller is operable to open and close each respective bypass switch and is further operable to pulse width modulate the operation of at least one bypass switch to dim the corresponding semiconductor light source.

10. A power supply according to claim 7 wherein the controller is further operable to detect failures of semiconductor light sources.

11. A power supply according to claim 10 wherein the controller detects closed circuit failures of semiconductor light sources by measuring the change in voltage across the constant current source while opening and closing respective bypass switches.

12. A power supply according to claim 10 wherein the controller detects open circuit failures of semiconductor light sources by measuring the current provided by the power supply.

13. A power supply according to claim 10 wherein the controller detects open circuit failures of semiconductor light sources by measuring the voltage provided by the power supply.

14. A power supply according to claim 10 wherein at least one series connected semiconductor light source is redundant and its respective bypass switch is opened by the controller upon determination by the controller of a failure of another semiconductor light source.

15. A power supply according to claim 10 wherein the controller further generates an output signal indicating the detection of a failure of a semiconductor light source.

16. A power supply according to claim 15 wherein the output signal indicates which semiconductor light source has failed.

17. A power supply according to claim 1 further comprising two or more series connected semiconductor light sources arranged as a sub-string of semiconductor light sources, the sub-string having a corresponding bypass switch across it.

18. A power supply according to claim 7 further comprising at least one temperature sensor providing a signal to the controller to indicate a measured temperature, the controller being responsive to the measured signal to alter the current supplied to at least one semiconductor light source.

19. A power supply according to claim 18 wherein the controller is operable to alter the current by pulse width modulating the operation of at least one bypass switch.

20. A power supply according to claim 18 comprising at least two temperature sensors, each respective temperature sensor providing a respective signal to the controller to indicate a respective measured temperature, the controller being responsive to each respective measured signal to alter the current supplied to each respective semiconductor light source.