Controlling operation of a secondary power supply of an electricity meter during AC power loss

1. An alternating current (AC) line voltage detection circuit comprising:

an AC sense circuit;

a power supply control circuit; and

a power supply hold-up circuit,

wherein the AC sense circuit is configured to generate a signal to a processor and to the power supply control circuit in response to sensing an absence of AC line voltage,

wherein in response to receiving the signal from the AC sense circuit, the power supply control circuit is configured to generate a control signal to a power supply to shut down the power supply, wherein the power supply is configured to provide power to the processor,

wherein in response to receiving the signal from the AC sense circuit, the processor is configured generate a signal to the power supply hold-up circuit,

in response to receiving the signal from the processor, the power supply hold-up circuit is configured to generate a signal to the power supply control circuit to prevent shut down of the power supply, wherein the signal generated by the power supply hold-up circuit overrides the signal from the AC sense circuit, and

wherein the processor is further configured to generate a subsequent signal to the power supply hold-up circuit to permit shut down of the power supply and the processor.

2. The AC line voltage detection circuit of claim 1 , wherein the AC sense circuit is configured to sense a presence or an absence of AC line voltage and generate a signal to the processor,

wherein in response to detecting the presence of AC line voltage, the AC sense circuit is configured to generate a first signal to the processor and a second signal to the power supply control circuit, and

in response to detecting the absence of AC line voltage, the AC sense circuit is configured to generate a third signal to the processor and a fourth signal to the power supply control circuit.

3. The AC line voltage detection circuit of claim 2 , wherein the first signal and the second signal are time varying signals, and the third signal and the fourth signal are DC signals.

4. The AC line voltage detection circuit of claim 2 , wherein the power supply control circuit comprises a first circuit coupled to a resistor-capacitor (RC) circuit and a diode,

wherein in response to receiving the second signal from the AC sense circuit, the RC circuit and the diode maintain the first circuit in a first state, and

wherein the first circuit in the first state causes a signal to be transmitted to the power supply to maintain power supply operation.

5. The AC line voltage detection circuit of claim 4 , wherein in response to receiving the fourth signal from the AC sense circuit, the RC circuit and the diode maintain the first circuit in a second state, and

wherein the first circuit in the second state causes a signal to be transmitted to the power supply to shut down operation of the power supply.

6. The AC line voltage detection circuit of claim 4 , wherein the first circuit is a logic circuit or a transistor.

7. The AC line voltage detection circuit of claim 4 , wherein in response to receiving the third signal from the AC sense circuit, the processor or a delay circuit is configured to generate a signal to the power supply hold-up circuit,

wherein the signal to the power supply hold-up circuit overrides the third signal from the AC sense circuit and prevents the power supply from shutting down.

8. The AC line voltage detection circuit of claim 7 , wherein the power supply hold-up circuit comprises a second circuit,

wherein in response to receiving the signal from the processor or the delay circuit, the second circuit is configured to change from a first state to a second state, and

wherein in the second state the second circuit is configured to cause the signal to the power supply control circuit that overrides the second signal from the AC sense circuit to be generated.

9. The AC line voltage detection circuit of claim 8 , wherein the second circuit is a logic circuit or a transistor.

10. The AC line voltage detection circuit of claim 7 , wherein the processor is configured to generate the signal to the power supply hold-up circuit for a period of time for the processor to complete power-loss operations.

11. The AC line voltage detection circuit of claim 10 , wherein the power-loss operations comprise one or more of performing measurements of voltage or current or both, processing data related to a loss of AC power, or transmitting data to a radio of an electricity meter for subsequent transmission to a head end system.

12. An electricity meter, comprising:

a processor configured to control operations of portions of circuitry of the electricity meter;

a power supply configured to supply power to the processor; and

an alternating current (AC) line voltage detection circuit comprising:

an AC sense circuit;

a power supply control circuit; and

a power supply hold-up circuit,

wherein the power supply control circuit is configured to generate a signal to the power supply based on a signal received from the AC sense circuit and a signal received from the power supply hold-up circuit,

wherein the signal generated by the power supply control circuit causes the power supply to either maintain operation or shut down according to the signals received from the AC sense circuit and the power supply hold-up circuit.

13. The electricity meter of claim 12 , wherein the AC sense circuit is configured to generate a first signal to the processor and the power supply control circuit when AC line voltage is sensed and to generate a second signal to the processor and the power supply control circuit when AC line voltage is not sensed.

14. The electricity meter of claim 13 , wherein the first signal is a time varying signal, and the second signal is a direct current (DC) signal.

15. The electricity meter of claim 13 , wherein the power supply control circuit comprises a first circuit coupled to a resistor-capacitor (RC) circuit and a diode,

wherein the RC circuit and the diode are configured to maintain the first circuit in a first state upon receipt of the first signal from the AC sense circuit, and

wherein the first circuit in the first state is configured to cause a signal to be transmitted to the power supply to maintain power supply operation.

16. The electricity meter of claim 15 , wherein the RC circuit and the diode are configured to maintain the first circuit in a second state upon receipt of the second signal from the AC sense circuit, and

wherein the first circuit in the second state causes a signal to be transmitted to the power supply to shut down operation of the power supply.

17. The electricity meter of claim 15 , wherein the first circuit is a logic circuit or a transistor.

18. The electricity meter of claim 13 , wherein in response to receiving the second signal from the AC sense circuit, the processor or a delay circuit is configured to generate a signal to the power supply hold-up circuit,

wherein the signal to the power supply hold-up circuit is configured to override the second signal from the AC sense circuit and prevent the power supply from shutting down.

19. The electricity meter of claim 18 , wherein the power supply hold-up circuit comprises a second circuit,

wherein in response to receiving the signal from the processor, the second circuit is configured to change from a first state to a second state, and

wherein in the second state the second circuit is configured to cause the signal to the power supply control circuit that overrides the second signal from the AC sense circuit to be generated.

20. The electricity meter of claim 19 , wherein the second circuit is a logic circuit or a transistor.

21. The electricity meter of claim 18 , wherein the processor or the delay circuit is configured to generate the signal to the power supply hold-up circuit for a period of time for the processor to complete power-loss operations.

22. The electricity meter of claim 21 , wherein the power-loss operations comprise one or more of performing measurements of voltage or current or both, processing data related to a loss of AC power, or transmitting data to a radio of the electricity meter for subsequent transmission to a head end system.

23. A method for operating an electricity meter during a loss of alternating current (AC) power, the method comprising:

sensing, by an AC sense circuit, an absence of AC line voltage;

generating, by the AC sense circuit, a first signal to a processor and to a power supply control circuit indicating a sensed loss of AC line voltage;

generating, by the power supply control circuit, a second signal configured to cause a power supply to shut down, wherein the second signal is generated after a delay time, and wherein the power supply is configured to supply power to the processor;

in response to receiving the first signal, generating, by the processor, a third signal to a hold-up circuit to prevent shut down of the power supply;

in response to receiving the third signal, generating, by the hold-up circuit, a fourth signal to the power supply control circuit prior to an end of the delay time;

in response to receiving the fourth signal, generating, by the power supply control circuit, a fifth signal to the power supply, wherein the fifth signal is configured to maintain operation of the power supply and permit the processor to complete power-loss operations, wherein the fourth signal overrides the second signal during the loss of AC line voltage;

generating, by the processor, upon completion of the power loss operations, a sixth signal to the hold-up circuit indicating that the processor has completed the power-loss operations;

in response to receiving the sixth signal, generating, by the hold-up circuit, a seventh signal to the power supply control circuit, wherein the seventh signal causes the power supply control circuit to be controlled by the first signal; and

in response to receiving the seventh signal, generating, by the power supply control circuit, an eighth signal to the power supply, wherein the eighth signal causes the power supply to shut down,

wherein shutting down the power supply shuts down the processor and other circuitry powered by the power supply.

24. The method of claim 23 , wherein the power loss operations comprise one or more of performing measurements of voltage or current or both, processing data related to a loss of AC power, or transmitting data to a radio of the electricity meter for subsequent transmission to a head end system.