Power supply for a load control

1. A power supply adapted to be coupled in series electrical connection between an AC voltage source and an electrical load for generating a DC voltage, the power supply comprising:

an energy storage capacitor, the DC voltage produced across the capacitor;

a charging circuit adapted to be coupled in series electrical connection between the source and the load and to conduct a load current from the source to the load, the charging circuit coupled to the energy storage capacitor for charging the energy storage capacitor;

a controllably conductive device coupled in parallel electrical connection with the charging circuit and having a control input for rendering the controllably conductive device conductive, the controllably conductive device adapted to carry the load current from the source to the load when the controllably conductive device is conductive; and

a triggering circuit coupled to the control input of the controllably conductive device for causing the controllably conductive device to become conductive when the energy storage capacitor has charged to a desired maximum value;

wherein the charging circuit is adapted to conduct the load current from the source to the load when the controllably conductive device is non-conductive, the charging circuit imposing a low voltage drop relative to the peak value of an AC voltage of the AC voltage source, such that substantially all of the AC voltage is available to the load during the time when the controllably conductive device is non-conductive.

2. The power supply of claim 1 , wherein the controllably conductive device comprises a bidirectional semiconductor switch.

3. The power supply of claim 2 , wherein the bidirectional semiconductor switch comprises a triac.

4. The power supply of claim 1 , wherein the desired maximum value of the DC voltage is approximately 5.1 volts.

5. The power supply of claim 4 , wherein a break-over voltage of the triggering circuit is approximately 6.3 V.

6. The power supply of claim 1 , wherein the low voltage drop of the charging circuit is approximately 6.3 volts or less.

7. The power supply of claim 1 , wherein the charging circuit comprises a rectifier bridge coupled in parallel electrical connection with the controllably conductive device, the rectifier having DC terminals coupled to the energy storage capacitor such that the DC voltage is produced across the capacitor, the rectifier bridge and the energy storage capacitor adapted to conduct the load current when the controllably conductive device is non-conductive.

8. A power supply disposed in series with an AC load for charging an energy storage device from an AC voltage of an AC supply, the power supply comprising:

a controllably conductive device adapted to carry a load current from the AC supply to the load when the controllably conductive device is conductive;

a triggering circuit for causing the controllably conductive device to become conductive; and

a charging circuit for charging the energy storage device when the controllably conductive device is non-conductive, a voltage of approximately 6.3 V or less generated across the charging circuit when the controllably conductive device is non-conductive;

wherein the triggering circuit is operable to cause the controllably conductive device to become conductive when the energy storage device has charged to a predetermined amount of energy.

9. The power supply of claim 8 , wherein the energy storage device comprises a storage capacitor and a DC voltage is generated across the energy storage capacitor.

10. The power supply of claim 9 , wherein the DC voltage has a maximum value of approximately 5.1 volts.

11. The power supply of claim 8 , wherein a break-over voltage of the triggering circuit is approximately 6.3V.

12. A power supply adapted to be disposed in series electrical connection between an AC voltage source and an electrical load for generating a DC voltage, the power supply comprising:

a triac adapted to be coupled in series electrical connection between the source and the load and having a gate for rendering the triac conductive, the triac adapted to carry a load current from the source to the load when the triac is conductive;

a triggering circuit coupled to the gate of the triac for causing the triac to become conductive;

a rectifier bridge coupled in parallel electrical connection with the triac and having DC terminals, the rectifier bridge adapted to conduct the load current when the triac is non-conductive; and

an energy storage capacitor coupled to the DC terminals of the rectifier bridge, such that the DC voltage is generated across the energy storage capacitor, the energy storage capacitor adapted to conduct the load current through the rectifier bridge when the controllably conductive device is non-conductive;

wherein the triggering circuit causes the triac to become conductive when the energy storage capacitor has charged to a desired maximum voltage.

13. The power supply of claim 12 , further comprising:

a limiting resistor coupled in series with the rectifier bridge, the series-combination of the rectifier bridge and the limiting resistor adapted to be coupled in series between the source and the load, the limiting resistor adapted to limit the magnitude of the load current through the rectifier bridge.

14. A power supply adapted to be disposed in series electrical connection between an AC voltage source and an electrical load for generating a DC voltage, the power supply comprising:

a triac adapted to be coupled in series electrical connection between the source and the load and having a gate for rendering the triac conductive, the triac adapted to carry a load current from the source to the load when the triac is conductive;

a triggering circuit coupled to the gate of the triac for causing the triac to become conductive;

a rectifier bridge coupled in parallel electrical connection with the triac and having DC terminals, the rectifier bridge adapted to conduct the load current when the triac is non-conductive; and

an energy storage capacitor coupled to the DC terminals of the rectifier bridge, such that the DC voltage is generated across the energy storage capacitor, the energy storage capacitor adapted to conduct the load current through the rectifier bridge when the controllably conductive device is non-conductive;

wherein the triggering circuit causes the triac to become conductive when the energy storage capacitor has charged to a desired maximum voltage

further comprising;

a limiting resistor coupled in series with the rectifier bridge, the series-combination of the rectifier bridge and the limiting resistor adapted to be coupled in series between the source and the load, the limiting resistor adapted to limit the magnitude of the load current through the rectifier bridge,

further comprising:

a firing capacitor coupled to the junction of the limiting resistor and the rectifier bridge, such that the series-combination of the limiting resistor and the firing capacitor are coupled in parallel with the triac;

wherein the triggering circuit is coupled between the control input of the triac and the junction of the limiting resistor and the firing capacitor, the triggering circuit operable to conduct current to and from the gate of the triac when a voltage across the firing capacitor exceeds a break-over voltage of the triggering circuit.

15. The power supply of claim 14 , wherein the rectifier bridge is coupled in parallel with the firing capacitor, such that the limiting capacitor, the rectifier bridge, and the energy storage capacitor conduct the load current when the triac is non-conductive.

16. The power supply of claim 12 , wherein the triggering circuit comprises a semiconductor triggering device.

17. The power supply of claim 16 , wherein the semiconductor triggering device comprises a diac coupled in series with the gate of the triac.

18. The power supply of claim 16 , wherein the triggering circuit comprises a zener diode and two semiconductor switches coupled such that a pulse of current is conducted through the gate of the triac when the voltage across the zener diode exceeds a break-over voltage of the zener diode.