Power supply for use in an electronic energy meter

1. A power supply for use in an electronic electricity meter operable to receive and monitor a three-phase line voltage, the power supply comprising:

a voltage rectifier positioned to receive the line voltage and generate a DC bus voltage;

a transformer having a primary winding and a secondary winding, wherein the DC bus voltage is applied to the primary winding such that current flows through the primary winding, wherein the primary winding discharges to the secondary winding to define an output voltage of the power supply;

a switch connected to the primary winding for selectively permitting and preventing the flow of current through the primary winding, wherein when the current is prevented from flowing through the primary winding, the primary winding discharges to the secondary winding;

a control circuit coupled to the switch to provide a control signal to the switch to control the operation of the switch between an on and an off position;

a voltage feedback circuit positioned to receive the output voltage from the secondary winding of the transformer and operable to compare the output voltage to a desired reference voltage, wherein the voltage feedback circuit prevents the flow of current through the primary winding when the output voltage exceeds the desired reference voltage; and

an over voltage circuit positioned to receive the DC bus voltage and coupled to the control circuit, wherein the over voltage circuit is operable to generate an over voltage signal to the control circuit to prevent the generation of the control signal by the control circuit to prevent the flow of current through the primary winding when the DC bus voltage exceeds an upper voltage limit.

2. The power supply of claim 1 further comprising a current limiting circuit operable to compare the current flowing through the primary winding to an upper current limit, wherein the current limiting circuit generates an over current signal to the control circuit to prevent generation of the control signal by the control circuit to prevent the flow of current through the primary winding when the sensed current exceeds the upper current limit.

3. The power supply of claim 2 wherein the current limiting circuit includes a timing circuit that controls the duration of the over current signal.

4. The power supply of claim 1 wherein the over voltage circuit includes hysteresis such that the over voltage circuit compares the DC bus voltage to a selected upper voltage limit and generates the over voltage signal when the DC bus voltage exceeds the upper voltage limit and terminates the over voltage signal when the DC bus voltage falls below an adjusted upper voltage limit less than the upper voltage limit.

5. The power supply of claim 1 wherein the line voltage received by the voltage rectifier is one of a wide range of service voltages supplied by an electrical service provider and wherein the output voltage of the power supply is independent of the line voltage.

6. The power supply of claim 1 wherein the primary winding includes a first coil and a second coil connected in series.

7. The power supply of claim 6 wherein the secondary winding of the transformer includes a first coil and a second coil connected in parallel.

8. The power supply of claim 1 wherein the control signal generated by the control circuit is a periodic signal having repeating pulses each separated by an off time, each pulse having an on time duration, wherein the on time duration is determined based upon the value of the DC bus voltage.

9. The power supply of claim 8 wherein the on time duration decreases as the value of the DC bus voltage increases and the on time duration increases as the DC bus voltage decreases.

10. A power supply for use in an electronic electricity meter operable to receive and monitor a three-phase line voltage, the power supply comprising:

a voltage rectifier positioned to receive the line voltage and generate a DC bus voltage;

a transformer having a primary winding and a secondary winding, wherein the DC bus voltage is applied to the primary winding such that current flows through the primary winding, wherein the primary winding discharges to the secondary winding to define an output voltage of the power supply;

a switch connected to the primary winding for selectively permitting and preventing the flow of current through the primary winding, wherein when the current is prevented from flowing through the primary winding, the primary winding discharges to the secondary winding;

a control circuit coupled to the switch to provide a control signal to the switch to control the operation of the switch between an on and an off position;

an over voltage circuit positioned to receive the DC bus voltage and coupled to the control circuit, wherein the over voltage circuit is operable to generate an over voltage signal to the control circuit to prevent the generation of the control signal by the control circuit to prevent the flow of current through the primary winding when the DC bus voltage exceeds an upper voltage limit; and

a current limiting circuit operable to compare the current flowing through the primary winding to an upper current limit, wherein the current limit circuit generates an over current signal to the control circuit to prevent the generation of the control signal by the control circuit when the sense current exceeds the upper current limit;

wherein the control signal generated by the control circuit is a periodic signal having repeating pulses each separated by an off time, each pulse having an on time duration, wherein the on time duration is determined based upon the value of the DC bus voltage.

11. The power supply of claim 10 wherein the on time duration decreases as the value of the DC bus voltage increases and the on time duration increases as the DC bus voltage decreases.

12. The power supply of claim 10 wherein the current limiting circuit includes a timing circuit that controls the duration of the over current signal.

13. The power supply of claim 10 wherein the over voltage circuit includes hysteresis such that the over voltage circuit compares the DC bus voltage to the upper voltage limit and generates the over voltage signal when the DC bus voltage exceeds the upper voltage limit and terminates the over voltage signal when the DC bus voltage falls below an adjusted upper voltage limit less than the upper voltage limit.

14. The method for supplying power to the operating components of an electronic electricity meter that meters electrical energy, the energy having a variable line voltage, the method comprising the steps of:

rectifying the line voltage to generate a DC bus voltage;

providing a transformer having a primary winding and a secondary winding;

providing the DC bus voltage to the primary winding of the transformer;

providing a switch that selectively permits and prevents a flow of current through the primary winding, wherein the primary winding discharges to the secondary winding upon the prevention of current flow through the primary winding;

providing a control circuit that controls the operation of the switch;

comparing the value of the DC bus voltage to an upper voltage limit and generating an over voltage signal to the control circuit when the DC bus voltage exceeds the upper voltage limit;

comparing the current flowing through the primary winding of the transformer to an upper current limit;

generating an over current signal to the control unit when the current flowing through the primary winding exceeds the upper current limit; and

operating the control circuit to prevent the flow of current through the primary winding upon receipt of the over voltage signal or the over current signal at the control circuit.

15. The method of claim 14 wherein the control circuit prevents the discharge of the primary winding upon receipt of the over current signal.