Short Circuit Detection for Lighting Circuits

• US 20140152180A1
• Filed: 07/16/2013
• Published: 06/05/2014
• Est. Priority Date: 11/30/2012
• Status: Active Grant

• Current Assignee: Dialog Semiconductor GmbH (Renesas Electronics Corporation)
• Original Assignee: Dialog Semiconductor GmbH (Renesas Electronics Corporation)
• Inventors: Wolf, Christian, Acquas, Andrea, Jacob, Stanly, DePaula Campos, Marcelo
• Granted Patent: US 9,084,330 B2
• Time in Patent Office: Days
• US Class Current: 315/122
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: H05B 45/52 in a parallel array of LEDs
• CPC Class Codes: H05B 47/24 Circuit arrangements for protecting against overvoltage

Abstract

This invention relates to control circuits for LED systems with a feedback loop to regulate a drive voltage. A controller for the system is proposed comprising a plurality of LED circuits and a controllable power source. The controller comprises a control unit configured to cause regulation of the drive voltage based on a determination of a plurality of feedback voltages and a fault condition detecting means. At least one of the LED circuits is determined as having a fault condition if the respective feedback voltage is below a fault threshold. In response to a detected fault condition, a test voltage is applied to a cathode of the fault circuit to confirm the presence of a fault condition.

Claims

1. A fault-tolerant controller for a lighting system comprising a plurality of LED circuits and a controllable power source providing a drive voltage to power the plurality of LED circuits, the fault-tolerant controller comprising:

a control unit configured to cause regulation of the drive voltage based on a determination of a plurality of feedback voltages, one feedback voltage for each of the plurality of LED circuits; and

a fault condition detecting means configured to identify one or more fault conditions from the plurality of feedback voltages, wherein at least one of the LED circuits is determined as a fault circuit having a fault condition for which the respective feedback voltage is below a first fault circuit condition threshold, wherein the fault condition detecting means is further configured, in response to a detected fault condition, to apply a test voltage or test current to a cathode of the fault-circuit and to determine if the feedback voltage of the fault circuit is above or below a second fault circuit condition threshold.

2. The controller of claim 1 wherein the fault circuit is determined to have a short circuit if the feedback voltage of the fault circuit is below a second fault circuit condition threshold after application of the test voltage or test current.

3. The controller of claim 1 wherein the fault circuit is determined to have an open circuit condition if the feedback voltage of the fault circuit exceeds the second fault circuit condition threshold after the test voltage has been applied to the cathode of the fault circuit.

4. The controller of claim 1 wherein the fault condition detecting means comprises a plurality of pull-up circuits, one pull-up circuit provided between ground voltage and a cathode for each LED circuit, wherein each pull-up circuit comprises a voltage source and a switch, the fault condition detecting means being configured to cause closing of the switch associated with the fault circuit upon detecting a fault condition to apply the test voltage between ground voltage and the cathode of the fault circuit.

5. The controller of claim 1 wherein the controller further comprises a plurality of comparators and a plurality of logic gates, one comparator and one logic gate for each LED circuit to detect a fault condition indication for each of the LED circuits wherein a comparator is configured to conduct a comparison between the respective feedback voltage of one of the plurality of LED circuits and the first fault circuit condition threshold and to input the comparison result into the respective logic gate.

6. The controller of claim 2, wherein the fault condition detecting means is configured to determine whether a short circuit exists in the plurality of LED circuits during a pre-start test before normal operation of the LED lighting system is started, wherein no drive voltage is supplied to the plurality of LED circuits.

7. The controller of claim 6 wherein the controller is configured to disable the drive voltage to power the plurality of LED circuits if a short circuit condition is detected during the pre start test.

8. The controller of claim 6 wherein in response to a pre-start test with no short circuit condition being detected, the controller is configured to wait for a predetermined time interval before regularly determining during an operation under a normal load condition whether a fault condition exists in one of the plurality of LED circuits.

9. The controller of claim 3 wherein the controller further comprises a minimum voltage selector configured to exclude the one or more respective feedback voltages for each respective LED circuit associated with an open or short circuit condition.

10. The controller of claim 6 wherein a boost voltage to drive the LED circuit is temporarily disabled during a short circuit test.

11. The controller of claim 2 wherein the fault condition detecting means is configured to sample the feedback voltage of the fault circuit at least two times before determining a short circuit condition of the fault circuit.

12. A method of detecting a fault condition within a plurality of LED circuits of a lighting system comprising the steps of:

determining a feedback voltage for each of the LED circuits of the plurality of LED circuits;

causing regulation of a drive voltage to power the plurality of LED circuits based on the plurality of feedback voltages;

determining a fault circuit having a fault condition among the plurality of LED circuits for which the respective feedback voltage of the respective LED circuit is below a first fault condition threshold;

applying a test voltage to a cathode of a LED of the determined fault circuit having a fault condition; and

determining if the feedback voltage of the determined fault circuit having the fault condition remains below or exceeds a second fault circuit condition threshold after the test voltage is applied to the cathode of the determined fault circuit having a fault condition threshold.

13. The method of claim 12 further comprising the step of determining the fault circuit has a short circuit condition if the feedback voltage of the determined fault circuit remains below the second fault circuit condition threshold after the test voltage is applied to the cathode of the LED in the determined fault circuit having a fault condition threshold.

14. The method of claim 12 further comprising the step of determining the fault circuit as having an open circuit condition if the feedback voltage of the determined fault circuit exceeds the second fault circuit condition threshold after the test voltage has been applied to the cathode of the LED in the determined fault circuit having a fault condition threshold.

15. The method of claim 12 wherein the method of detecting a fault condition is conducted as part of a pre-start test of the lighting system, before the normal operation of the LED lighting system is started, wherein no drive voltage is supplied to the plurality of LED circuits during the pre-start test and disabling the lighting system in response to a detected short circuit condition during the pre-start test.

16. A method of detecting a pre start fault condition within a plurality of LED circuits of a lighting system comprising the steps of:

determining a feedback voltage for each of the LED circuits of the plurality of LED circuits;

causing regulation of a drive voltage to power the plurality of LED circuits based on the plurality of feedback voltages;

determining a fault circuit having a fault condition among the plurality of LED circuits for which the respective feedback voltage of the respective LED circuit is below a first fault condition threshold;

applying a test voltage to a cathode of a LED of the determined fault circuit having a fault condition;

determining if the feedback voltage of the determined fault circuit having the fault condition remains below or exceeds a second fault circuit condition threshold after the test voltage is applied to the cathode of the determined fault circuit having a fault condition threshold, wherein the fault circuit has a short circuit condition if the feedback voltage of the determined fault circuit remains below a second fault circuit detection threshold;

determining the fault circuit as having an open circuit condition if the feedback voltage of the fault circuit exceeds the second fault circuit condition threshold after the test voltage has been applied to the cathode of the LED in the fault circuit; and

determining the fault circuit as having a short circuit condition if the feedback voltage of the fault circuit is less than the second fault circuit condition threshold after the test voltage has been applied to the cathode of the LED in the fault circuit.

17. The method of claim 16 further comprising shutting down the LED system if a short condition has been detected during the pre-start test.

18. The method of claim 16 further comprising enabling the lighting system after no short circuit condition has been detected during the pre start test.

19. The method of claim 18 further comprising enabling the lighting system after no short circuit condition has been detected during the pre start test and periodically performing a test for a fault condition within the plurality of LED circuits of the lighting system.

20. The method of claim 17 wherein the LED system has been shut down because of a short circuit condition, further comprising the steps of repairing the identified short circuit followed by repeating the test method of claim 16 for detecting a pre-start fault condition.

21. A lighting system comprising:

a plurality of LED circuits;

a controllable power source; and

a controller wherein the controller can detect LED short circuits and/or LED open circuits.