Power supply for a load control device
View Patent ↗A load control device is adapted to be disposed in series with an AC voltage source and an electrical load and is operable to provide substantially all voltage provided by the AC voltage source to the load. The load control device comprises a controllably conductive device, a controller, a zero-crossing detector, and a power supply for generating a substantially DC voltage for powering the controller. The power supply is operable to charge an energy storage device to a predetermined amount of energy each half-cycle. The controller is operable to determine when the power supply has stopped charging from the zero-crossing detector each half-cycle, and to immediately render the controllably conductive device conductive to conduct the full load current. Before the controllably conductive device begins to conduct each half-cycle, only a minimal voltage develops across the power supply to allow the energy storage device to charge.
1. A load control device for controlling the amount of power delivered to an electrical load from an AC power source, the load control device comprising:
a controllably conductive device adapted to carry a load current from the AC power source to the load when the controllably conductive device is conductive;
a power supply comprising an energy storage device and adapted to charge the energy storage device when the controllably conductive device is non-conductive; and
a controller operable to determine when the power supply has charged the energy storage device to a predetermined amount of energy and to subsequently cause the controllably conductive device to become conductive immediately after determining that the power supply has charged the energy storage device to the predetermined amount of energy;
wherein the power supply comprises a passive charging path for the energy storage device, and an active charging path for the energy storage device, the passive charging path allowing the energy storage device to receive energy at a first rate, the active charging path allowing the energy storage device to receive energy at a second rate greater than the first rate.
2. The load control device of claim 1 , wherein the power supply only charges the energy storage device through the active charging path near the zero-crossings of the load current.
3. The load control device of claim 2 , further comprising:
a zero-crossing detector operable to provide a control signal to the controller when the power supply has stopped charging.
4. The load control device of claim 3 , wherein the controller causes the controllably conductive device to become conductive in response to the control signal provided by the zero-crossing detector.
5. The load control device of claim 4 , wherein the controller comprises a microprocessor.
6. The load control device of claim 2 , wherein the power supply comprises a cat-ear power supply.
7. The load control device of claim 1 , wherein the controller is coupled to the power supply to selectively enable and disable the active charging path.
8. The load control device of claim 7 , wherein the controller is operable to enable the active charging path when the electrical load is on.
9. The load control device of claim 7 , wherein the controller is operable to disable the active charging path when the electrical load is off.
10. The load control device of claim 1 , wherein the energy storage device comprises a storage capacitor.
11. The load control device of claim 10 , wherein the power supply comprises a rectifier coupled across the controllably conductive device for supplying a DC voltage to the storage capacitor.
12. The load control device of claim 11 , wherein the rectifier comprises a rectifier bridge.
13. The load control device of claim 1 , wherein the controllably conductive device comprises a semiconductor switch.
14. The load control device of claim 6 , wherein the semiconductor switch comprises a triac.
15. The load control device of claim 6 , wherein the semiconductor switch comprises a FET in a rectifier bridge.
16. The load control device of claim 6 , wherein the semiconductor switch comprises two FETs in anti-series connection.
17. The load control device of claim 1 , further comprising:
a communication circuit coupled to the controller and operable to transmit control information for controlling the electrical load.
18. The load control device of claim 1 , wherein the load control device operates as an electronic timer.
19. The load control device of claim 1 , wherein the power supply imposes a low voltage drop relative to the peak value of the AC voltage such that substantially all of the AC voltage is available to the load during the time when the controllably conductive device is non-conductive.
20. A method of controlling the amount of power delivered to an electrical load from an AC power source, the method comprising the steps of:
coupling a controllably conductive device in series electrical connection between the AC voltage source and the electrical load;
controlling the controllably conductive device to be conductive each half-cycle of the AC power source to turn the load on;
controlling the controllably conductive device to be non-conductive each half-cycle of the AC power source to turn the load off;
charging an energy storage device by conducting a substantially sinusoidal current having a first magnitude through the energy storage device when the load is off; and
charging the energy storage device by conducting a non-sinusoidal current having a second magnitude through the energy storage device when the load is on, the second magnitude greater than the first magnitude.
21. The method of claim 20 , further comprising the step of:
determining when the energy storage device has charged to a predetermined amount of energy.
22. The method of claim 21 , further comprising the step of:
generating a control signal representative of when the energy storage device has charged to the predetermined amount of energy;
wherein the step of rendering the controllably conductive device conductive is completed in response to the control signal.
23. The method of claim 20 , wherein the step of rendering the controllably conductive device conductive occurs immediately after the energy storage device has charged to the predetermined amount of energy.
24. The method of claim 20 , wherein a low voltage drop relative to the peak value of the AC voltage is developed across the controllably conductive device and substantially all of the AC voltage is available to the load during the time when the controllably conductive device is non-conductive.
25. A load control device for controlling the amount of power delivered to an electrical load from an AC power source, the load control device comprising:
a controllably conductive device adapted to control the amount of power delivered from the source to the load to turn the load on and off;
a power supply comprising an energy storage device, a passive charging path for charging the energy storage device, and an active charging path for charging the energy storage device, the passive charging path operable to conduct a substantially sinusoidal current having a first magnitude when the active charging path is disabled, the active charging path operable to conduct a non-sinusoidal current having a second magnitude greater than the first magnitude when the active charging path is enabled; and
a controller coupled to the power supply and operable to enable the active charging path when the load is on and to disable the active charging path when the load is off.