Dimmable timer-based LED power supply
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.
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; and
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, wherein the timer-based variable pulse generator comprises a power factor correction circuit.
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 on-time of the pulses is controlled at least in part based on the current at the load output.
4. 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.
5. 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.
6. The dimmable power supply of claim 2 , further comprising an inverter connected between the 555 timer circuit and the switch.
7. 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.
8. The dimmable power supply of claim 7 , wherein the value of the external resistor is changed using a transistor.
9. The dimmable power supply of claim 8 , wherein the transistor is powered only during the on-time.
10. The dimmable power supply of claim 7 , wherein the value of the external resistor is changed by connecting a second resistor in parallel with the resistor.
11. The dimmable power supply of claim 7 , 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.
12. 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.
13. The dimmable power supply of claim 12 , 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.
14. 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.
15. 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.
16. 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%.
17. The dimmable power supply of claim 15 , 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.
18. 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; and
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, wherein the timer-based variable pulse generator comprises a 555 timer circuit.
19. 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; and
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.