Dimmable Timer-Based LED Power Supply

• US 20120299500A1
• Filed: 11/18/2011
• Published: 11/29/2012
• Est. Priority Date: 11/22/2010
• Status: Active Grant

• Current Assignee: Innosys, Inc.
• Original Assignee: Innosys, Inc.
• Inventors: Sadwick, Laurence P., Sackett, William B., Brady, Michael D.
• Granted Patent: US 8,773,031 B2
• Time in Patent Office: Days
• US Class Current: 315/224
• CPC Class Codes: H05B 45/32 Pulse-control circuits
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/385 using flyback topology
• CPC Class Codes: H05B 45/56 involving measures to prevent abnormal temperature of the LEDs

Abstract

Various embodiments of a dimmable power supply are disclosed herein. For example, some embodiments provide a dimmable power supply including an input current path, a switch in the input current path, an energy storage device connected to the input current path, a load output connected to the energy storage device, and a timer-based variable pulse generator connected to a control input of the switch. The timer-based variable pulse generator is adapted to generate a stream of pulses having a variable on-time and off-time. The dimmable power supply is adapted to vary the on-time and off-time to control a current at the load output.

Claims

1. A dimmable power supply comprising:

an input current path;

a switch in the input current path;

an energy storage device connected to the input current path;

a load output connected to the energy storage device;

a timer-based variable pulse generator connected to a control input of the switch, the timer-based variable pulse generator being adapted to generate a stream of pulses having a variable on-time and off-time, wherein the dimmable power supply is adapted to vary the on-time and off-time to control a current at the load output.

2. The dimmable power supply of claim 1, wherein the timer-based variable pulse generator comprises a 555 timer circuit.

3. The dimmable power supply of claim 1, wherein the timer-based variable pulse generator comprises a power factor correction circuit.

4. The dimmable power supply of claim 1, wherein the on-time of the pulses is controlled at least in part based on the current at the load output.

5. The dimmable power supply of claim 1, further comprising a bias power supply, wherein the timer-based variable pulse generator is powered by the bias power supply, and wherein the on-time of the pulses is controlled at least in part based on a voltage level from the bias power supply.

6. The dimmable power supply of claim 1, wherein the on-time of the pulses is controlled based on a plurality of control signals, the plurality of control signals comprising an indication of input current level, an indication of the current at the load output, and an indication of a voltage level of a bias power supply powering the timer-based variable pulse generator.

7. The dimmable power supply of claim 2, further comprising an inverter connected between the 555 timer circuit and the switch.

8. The dimmable power supply of claim 2, wherein the on-time is controlled at least in part on a value of an external resistor connected to the 555 timer circuit.

9. The dimmable power supply of claim 8, wherein the value of the external resistor is changed using a transistor.

10. The dimmable power supply of claim 9, wherein the transistor is powered only during the on-time.

11. The dimmable power supply of claim 8, wherein the value of the external resistor is changed by connecting a second resistor in parallel with the resistor.

12. The dimmable power supply of claim 8, wherein the external resistor comprises a programmable resistor, and wherein the value of the external resistor is changed by changing a state of the programmable resistor.

13. The dimmable power supply of claim 2, further comprising a soft start circuit connected to the 555 timer, wherein the soft start circuit is adapted to reduce the on-time during a startup period of the 555 timer.

14. The dimmable power supply of claim 13, wherein the soft start circuit comprises a transistor turned on based on a voltage of a bias power supply that powers the 555 timer, wherein the transistor adjusts an external resistance to set the on-time of the 555 timer.

15. The dimmable power supply of claim 1, wherein power consumption is reduced by powering at least one active circuit element loop in a feedback loop only during the on-time.

16. The dimmable power supply of claim 1, further comprising a load current feedback circuit connected between the load output and the timer-based variable pulse generator to control the on-time, the load current feedback circuit comprising a plurality of time constants.

17. The dimmable power supply of claim 2, further comprising a diode connected between a pair of terminals on the 555 timer, thereby providing different charging and discharging paths for the 555 timer to produce a duty cycle of less than about 50%.

18. The dimmable power supply of claim 16, wherein the load current feedback circuit comprises a plurality of operational amplifiers, each connected to the load output and to a reference voltage, each having a different time constant.

19. A method of controlling a load current, the method comprising:

generating a stream of pulses in a timer-based variable pulse generator to turn on and off a switch in an input current path, creating a switched input current path;

providing a load current from the switched input current path;

measuring the load current;

reducing an on-time of a timer in the timer-based variable pulse generator if the load current exceeds a current threshold.

20. The method of claim 19, further comprising dithering a frequency of the switch.