POWER SUPPLY FOR LIGHT EMITTING DIODE ROADWAY LIGHTING FIXTURE

• US 20120001566A1
• Filed: 01/26/2010
• Published: 01/05/2012
• Est. Priority Date: 01/27/2009
• Status: Active Grant

• Current Assignee: LED Roadway Lighting Ltd.
• Original Assignee: LED Roadway Lighting Ltd.
• Inventors: Josefowicz, Jack Yitzhak, Winters, Alan Shawn, Chen, Qiuning, Neary, Mark Adam
• Granted Patent: US 8,760,072 B2
• Time in Patent Office: Days
• US Class Current: 315/291
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/12 using optical feedback
• CPC Class Codes: H05B 45/14 using electrical feedback from LEDs or from LED modules
• CPC Class Codes: H05B 45/18 using temperature feedback
• CPC Class Codes: H05B 45/355 Power factor correction [PFC]; Reactive power compensation
• CPC Class Codes: H05B 45/382 with galvanic isolation between input and output
• CPC Class Codes: H05B 45/385 using flyback topology
• CPC Class Codes: H05B 47/105 in response to determined parameters
• CPC Class Codes: H05B 47/11 by determining the brightness or colour temperature of ambient light
• CPC Class Codes: Y02B 20/40 Control techniques providing energy savings, e.g. smart controller or presence detection

Abstract

A high efficiency light emitting diode power supply for roadway lighting fixtures is provided. The power supply enables conditioning and monitoring of input power and monitors LEDs current to ensures consistent performance of the LED by changing a power correction factor. The LED output can also be adjusted based upon age or external input parameters and by modifying the power correction factor value. In addition, the LED output can be dimmed, turned down in output to a lower level at any time of night for a prescribed duration in order to further save energy. This dimming function uses a programming scheme that keeps track of the “seasons” (summer, fall, winter and spring) so that time of night is tracked accurately all year long.

Claims

1. A method of operating a power supply for light emitting diode (LED) module in a roadway fixture, the method comprising:

performing electro-magnetic interference (EMI) filtering of an incoming alternating current (AC) current;

performing AC to direct current (DC) rectification of the AC current;

stepping down the rectified DC current based upon a power correction factor (PFC) value;

providing the stepped down DC current to the LED module;

measuring a current through the LED module;

determining the PFC value based upon at least the measured current through the LED module; and

feeding-back the determined PFC to control the stepped down DC current.

2. The method of claim 1 further comprising performing secondary filtering of the stepped down DC current to reduce ripple of voltage and current.

3. The method of claim 1 wherein measuring the LED current further comprises averaging the measured current which has a high voltage ripple content to determine an average current passing through the LED module.

4. The method of claim 1 further comprising determining an output mode of the roadway fixture based upon a constant current mode to provide a constant current over the life-time of the LED module by adjusting the PFC value to maintain a constant current through the LED module.

5. The method of claim 1 further comprising a ramp-over-time current mode to provide an increasing current to the LED module to maintain illumination output over time by adjusting the PFC value.

6. The method of claim 5 further comprises determining a turn-on cycle used in determining an age of the LED module.

7. The method of claim 6 wherein the PFC value is further determined based upon a determined output mode and the determined age of the LED module.

8. The method of claim 1 wherein calculating the PFC value is further based upon an external input.

9. The method of claim 8 wherein the external input is selected from the group comprising:

a motion sensor, a wireless transmitter/receiver, a light output sensor and an ambient light sensor.

10. The method of claim 1 wherein PFC correction value is further based upon a dimming sequence retrieved from a dimming schedule defining a desired light output level of the LED module over a length of a night period.

11. The method of claim 10 further comprising determining the dimming schedule by:

determining the length of the night period from a sunset time and a sunrise time determined from a light sensor;

storing the determined length of the night period in memory;

determining if a required plurality of lengths of consecutive night periods have been stored;

averaging the required plurality of lengths of consecutive night periods; and

performing a lookup in a dimming schedule based upon the average length of the night period to determine the dimming sequence associated with the length of the night period.

12. The method of claim 11 wherein if the required plurality of lengths of consecutive night period has not been stored the desired light output level of the LED module is set to a default value.

13. The method of claim 11 further comprising clearing the stored consecutive night periods if the determined length of the night period is not within a defined tolerance range and wherein the desired light output level of the LED module is set to a default value.

14. The method of claim 11 further comprising determining that a power interruption has occurred and clearing the stored consecutive night periods and wherein the desired light output level of the LED module is set to a default value.

15. A power supply for use with a light emitting diode (LED) module in a roadway lighting fixture, the power supply comprising:

an electro-magnetic interference filter for filtering an alternating current (AC) current;

an AC rectifier for rectifying the AC current to a direct current (DC) current;

a power factor correction (PFC) circuit maintaining the DC current waveform in phase with line voltages by switching a flyback transformer based upon a received PFC value;

a secondary side filtering module for reducing voltage and current ripple in the DC current;

an LED current sensor module for detecting a current value used by the LED module in a return line from the LED module; and

a micro-controller for monitoring the LED current and processing input to determine the PFC value to be applied to the flyback transformer based upon the detected LED current value.

16. The power supply of claim 15 wherein the AC rectifier is a discrete diode bridge.

17. The power supply of claim 15 wherein the flyback transformer converts a DC voltage from 165 V to 36 V.

18. The power supply of claim 15 wherein the LED current sensor detects the current value by sampling the current in the return line of the LED module resulting in a small voltage which is directly proportional to the current flowing to the LED module.

19. The power supply of claim 15 where in micro-controller utilizes high ripple voltages representing a proportion current and is averaged and compared to a set value programmed in the micro-controller memory to determine the PFC value.

20. The power supply of claim 15 wherein the micro-controller counts each turn-on sequences and stores it into its internal memory to keep track of how many days to determine the PFC value to compensate for LED output degradation due to aging.

21. The power supply of claim 15 wherein the micro-controller receives input from a light output sensor to be used in determining the PFC value.

22. The power supply of claim 21 wherein the micro-controller further comprises a memory for storing a dimming schedule table comprising a plurality of dimming sequences each based upon a length of the average night period, the dimming sequences defining one or more associated PFC values to be applied over an illumination period.

23. The power supply of claim 22 wherein the dimming schedule is determined by the micro-processor by:

determining the length of the night period from a sunset time and a sunrise time determined from a light sensor;

storing the determined length of the night period in memory;

determining if a required plurality of lengths of consecutive night periods have been stored;

averaging the required plurality of lengths of consecutive night periods; and

performing a lookup from the dimming schedule table based upon the average length of the night period to determine the dimming sequence associated with the length of the night period.

24. The power supply of claim 23 wherein if the required plurality of lengths of consecutive night period has not been stored the desired light output level of the LED module is set to a default value.

25. The power supply of claim 23 further comprising clearing the stored consecutive night periods if the determined length of the night period is not within a defined tolerance range and wherein the desired light output level of the LED module is set to a default value for the dimming sequence.

26. The power supply of claim 25 further comprising determining that a power interruption has occurred and clearing the stored consecutive night periods and wherein the desired light output level of the LED module is set to a default value for the dimming sequence.

27. The power supply of claim 15 wherein the micro-controller receives input from a wireless transmitter/receiver to be used in determining the PFC value.

28. The power supply of claim 15 wherein the micro-controller receives input from a motion sensor to be used in determining the PFC value.