Battery backup power supply

• US 6,359,794 B1
• Filed: 07/19/2000
• Issued: 03/19/2002
• Est. Priority Date: 12/01/1999
• Status: Expired due to Fees

• Current Assignee: Tracewell Electronics, Inc.
• Original Assignee: Acme Electric Corp. (Hubbell, Inc.)
• Inventors: Real, Richmond Andrew
• Primary Examiner(s): Patel, Rajnikant B.
• Application Number:
  US09/619,747
• Time in Patent Office: 608 Days
• Field of Search: 363/17, 363/20, 363/141, 363/143, 363/144, 307/64, 307/65, 307/66
• US Class Current: 363/17
• CPC Class Codes: H02J 9/062 for AC powered loads

Abstract

An uninterruptible power supply includes an inverter provided with power from a utility and a battery. The battery is connected through a FET so that battery power is instantly supplied to the inverter through the intrinsic FET diode when the utility power fails. The battery discharge FET is operated by an oscillator driven control circuit. The inverter includes an amplitude circuit and a polarity circuit. The inverter amplitude circuit includes FET operated by driver circuits that ensure efficient switching. The phase shifted full bridge pulse width modulated amplitude circuit converts the input power to a pulse width modulated output representing the amplitude of the power supply voltage, which is switched by the polarity circuit and to obtain the desired output voltage polarity. A falling edge bleeder ensures that a decreasing output voltage magnitude follows the desired waveform.

Claims

1. A power supply comprising:

an inverter having a DC input and an AC output;

a first DC voltage source connected to the DC input;

a second DC voltage source connected to the DC input;

a rectifier and a switch connected in parallel, wherein the rectifier and the switch are connected between the second voltage source and the DC input and wherein the switch has a control input;

a capacitor having a first terminal connected to the switch control input and a second terminal connected to the second voltage source;

a voltage applied to the first capacitor terminal;

a second controlled switch connected between the second capacitor terminal and ground; and

an oscillator connected to operate the second controlled switch when the first controlled switch is to closed.

2. The power supply according to claim 1 wherein the inverter includes an amplitude circuit connected to control amplitude of the voltage at the AC output and further comprising a controller connected to operate the amplitude circuit and the polarity circuit so as to obtain a desired waveform at the AC output.

3. A power supply comprising:

an inverter having a DC input and an AC output, wherein the inverter includes an amplitude circuit connected to control amplitude of the voltage at the AC output and a polarity circuit connected to control polarity of the voltage at the AC output; and

a controller connected to operate the amplitude circuit and the polarity circuit so as to obtain a desired waveform at the AC output.

4. The power supply according to claim 3 wherein the amplitude circuit includes controlled switches connected and operable to generate a pulse width modulated signal.

5. The power supply according to claim 4 wherein the polarity circuit is connected to receive the pulse width modulated signal and control the polarity of the AC output.

6. The power supply according to claim 5 further comprising a transformer connected to transfer energy from the amplitude circuit to the polarity circuit.

7. The power supply according to claim 3 further comprising:

a first DC voltage source connected to the DC input;

a second DC voltage source connected to the DC input; and

a rectifier and a switch connected in parallel, wherein the rectifier and the switch are connected between the second voltage source and the DC input.

8. The power supply according to claim 7 wherein the switch is controlled so as to close when the second DC voltage source supplies power to the inverter and to open when the first DC voltage source supplies power to the inverter.

9. The power supply according to claim 7 wherein the switch has a control input and further comprising a switch control circuit including:

a capacitor having a first terminal connected to the switch control input and a second terminal connected to the second voltage source;

a voltage applied to the first capacitor terminal;

a second controlled switch connected between the second capacitor terminal and ground; and

an oscillator connected to operate the second controlled switch when the first controlled switch is to be closed.

10. The power supply according to claim 7 wherein the switch is a FET and the rectifier is a body diode of the FET.

11. The power supply according to claim 10 wherein the first DC voltage source is a full bridge DC-DC converter and the second DC voltage source is a battery.

12. The power supply according to claim 11 wherein the battery is charged by the first DC voltage source.

13. The power supply according to claim 5 wherein the amplitude circuit provides a voltage across first and second amplitude circuit terminals and the polarity circuit includes a first pair of rectifiers connected in parallel and in opposition between the first amplitude circuit terminal and the power supply output, a second pair of rectifiers connected in parallel and in opposition between the second amplitude circuit terminal and the power supply output, and a respective controlled polarity switch connected in series with each of the rectifiers, the polarity switches being controlled so that only one of the polarity switches corresponding to each diode pair is closed at any time.

14. The power supply according to claim 13 wherein the polarity circuit includes a controller for operating the controlled polarity switches such that one of the polarity switches corresponding with the first pair of rectifiers is operated coincidentally with one of the polarity switches corresponding with the second pair of rectifiers.

15. The power supply according to claim 14 wherein the switches operated coincidentally correspond with rectifiers connected to permit current flow to a single node.

16. The power supply according to claim 13 wherein the polarity circuit controller includes two transformers, wherein one of the transformers is connected to control two of the polarity switches corresponding with rectifiers connected to permit current flow to a single node and the other of the transformers is connected to control two other of the polarity switches.

17. The power supply according to claim 16 wherein the polarity circuit controller includes an oscillator connected to control current through the transformer and a polarity signal connected to control current through the transformer, wherein the polarity signal is connected to ensure that only one of the two transformers is on at the same time.

18. The power supply according to claim 16 wherein the polarity circuit controller includes a respective rectifier and filter connected between each polarity switch and the corresponding transformer.

19. The power supply according to claim 16 wherein the polarity circuit controller includes a shut down circuit connected to selectively block current flow through the transformers.

20. The power supply according to claim 13 wherein the amplitude circuit includes controlled switches connected and operable to generate a pulse width modulated signal at the amplitude circuit terminals.

21. The power supply according to claim 20 wherein the polarity circuit is connected to receive the pulse width modulated signal and control the polarity of the AC output by operation of the polarity switches.

22. The power supply according to claim 13 wherein the terminals are output terminals of a transformer.

23. The power supply according to claim 22 wherein the transformer includes a center tap connected to ground.

24. The power supply according to claim 3 wherein the inverter includes an energy dissipator selectively connected across the output of the power supply.

25. The power supply according to claim 3 wherein the inverter includes a bleeder resistor selectively connected across the output of the power supply.

26. The power supply according to claim 25 further comprising a switch for selectively connecting the bleeder resistor across the output of the power supply and a bleeder control circuit for operating the switch wherein the bleeder control circuit is connected to permit current flow through the bleeder resistor when voltage at the AC output exceeds a desired amplitude.

27. The power supply according to claim 25 further comprising a switch for selectively connecting the bleeder resistor across the output of the power supply and a bleeder control circuit for operating the switch wherein the bleeder control circuit is connected to permit current flow through the bleeder resistor when voltage at the AC output is ramping toward zero volts.

28. The power supply according to claim 3 further comprising:

a resistor connected across the power supply output; and

a controlled switch connected in series with the resistor and operated responsive to a voltage across the power supply output to close the switch when the output voltage amplitude exceeds a specified value.

29. The power supply according to claim 3 further comprising:

a resistor connected across the power supply output; and

a controlled switch connected in series with the resistor and operated responsive to a voltage across the power supply output to close the switch when the output voltage amplitude is ramping toward zero volts.

30. The power supply according to claim 3 wherein the amplitude circuit includes controlled switches for controlling current determining the output of the amplitude circuit and a gate driver for each controlled switch wherein the gate driver comprises:

a controller connected to provide a voltage to a control terminal of the controlled switch; and

an energy storage device connected to apply a voltage to a control terminal of the switch when the controlled switch is to be closed and to discharge a voltage from the control terminal switch when the controlled switch is to be opened.

31. The power supply according to claim 30 further comprising a transformer connected between the controller and the controlled switch wherein the controller is a pulse width modulator.

32. The power supply according to claim 30 wherein the energy storage device comprises a first capacitor connected to apply the voltage to the control terminal of the controlled switch and a second capacitor connected to discharge the voltage from the control terminal of the controlled switch.

33. The power supply according to claim 32 wherein the controlled switch is a FET and the first capacitor is connected between a gate and a source of the FET by a second controlled switch that is closed when the controller applies a positive voltage to the gate and the second capacitor is connected between the gate and the source of the FET by a third controlled switch that is closed when the controller applies a negative voltage to the gate.

34. The power supply according to claim 3 wherein the amplitude circuit includes a FET having a gate and a source for controlling output voltage and further comprising a gate driving circuit for controlling the FET comprising:

a first capacitor connected between the gate and the source;

a first switch connected in series with the first capacitor;

a second capacitor connected between the gate and the source; and

a second switch connected in series with the second capacitor, wherein the first and second switches are turned on alternately so that when the first switch is closed, a charge on the first capacitor applies a voltage to the gate and when the second switch is closed, the second capacitor discharges a voltage from the gate.

35. A battery discharge circuit for connecting a battery to a load comprising:

a diode connected between the battery and the load;

a controlled switch connected in parallel with the diode, the switch having a control input; and

a switch control circuit comprising;

a capacitor having a first terminal connected to the switch control input and a second terminal connected to the battery;

a voltage applied to the first capacitor terminal;

a second controlled switch connected between the second capacitor terminal and ground; and

an oscillator connected to operate the second controlled switch when the first controlled switch is to be closed.

36. A gate driver comprising:

a FET having a gate and a source;

a first capacitor connected between the gate and the source;

a first switch connected in series with the first capacitor;

a second capacitor connected between the gate and the source; and

a second switch connected in series with the second capacitor, wherein the first and second switches are turned on alternately so that when the first switch is closed a charge on the first capacitor applies a voltage to the gate and when the second switch is closed the second capacitor discharges a voltage from the gate.