Regulated battery charger

• US 4,897,591 A
• Filed: 05/06/1987
• Issued: 01/30/1990
• Est. Priority Date: 05/06/1987
• Status: Expired due to Fees

• Current Assignee: ALARIS Medical Systems, Inc. (Becton, Dickinson & Co)
• Original Assignee: Fisher Scientific Group, Inc.
• Inventors: Spani, Wayne M.
• Primary Examiner(s): HICKEY, ROBERT
• Application Number:
  US07/047,413
• Time in Patent Office: 1,000 Days
• Field of Search: 320/20, 320/21, 320/22-24, 320/31, 320/32, 320/39, 320/40, 323/319
• US Class Current: 320/164
• CPC Class Codes: H02J 7/00711 with introduction of pulses during the charging process
• CPC Class Codes: H02J 7/007182 in response to battery voltage
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators

Abstract

The present invention is an electrical circuit for regulating the average current through and the voltage across a load, such as a rechargeable battery. The circuit includes at least one semiconductor switching device connected in series with the load for controlling the current through the load. A current control loop is provided in the circuit to maintain the average current through the load at a constant level despite changes in the resistance of the load. Also provided is a voltage control loop which acts to limit the voltage across the load to a value below a predetermined voltage level.

Claims

1. A circuit for regulating the average current through and the voltage applied across the first and second terminals of a load, the circuit comprising:

a transformer secondary having two end terminals and a center tap, the center tap being connected to the first terminal of the load;

a pair of individually and selectively operable switching elements, each of said switching elements being connected between the second terminal of the load and a respective one of the end terminals of the transformer secondary, each of said switching elements during the duty cycle thereof completing a closed current path in which current flows through the load in a single common current flow direction;

a sense element comprising a resistance of less than 1 ohm connected in series with the load for producing a sensed voltage proportional to the current through the load;

a current control loop connected to the sense element and the switching device, the current control loop adapted for controlling the duty cycle of the switching elements to maintain a constant average current through the load;

means for establishing a preselected threshold voltage; and

a voltage control loop having a comparator circuit for comparing the voltage present at the terminals of the load and a preselected threshold voltage for flexibly decreasing the duty cycle of the switching elements controlled by the current control loop, to maintain charging current above a trickle charge in proportion to the amount by which said load voltage exceeds said threshold voltage, and maintaining said load voltage at or below said preselected threshold voltage.

2. A circuit as defined in claim 1 wherein the load comprises a battery.

3. A circuit as defined in claim 1 wherein the switching elements comprise semiconductor switching devices.

4. A circuit as defined in claim 3 wherein the semiconductor switching elements comprise silicon controlled rectifiers.

5. A circuit as defined in claim 4 wherein the current control loop comprises:

integration means for integrating the sensed voltage produced by the sensing element and for producing therefrom an integrated signal representing the average current flow through the load; and

comparison means for comparing the integrated signal to a reference voltage and producing a corresponding control signal.

6. A circuit as defined in claim 5 wherein the integration means comprises an amplifier configured as an integrator.

7. A circuit as defined in claim 6 wherein the amplifier has a gain greater than one.

8. A circuit as defined in claim 6 wherein the integration means further comprises an RC circuit connected to the output of the amplifier.

9. A circuit as defined in claim 5 wherein the comparison means comprises a comparator and a reference voltage generator.

10. A circuit as defined in claim 5 wherein the comparison means comprises a first and a second inverting comparator, the output of the first comparator being connected to the inverting input of the second comparator.

11. A circuit as defined in claim 10 the current control loop further comprises isolation means for isolating the output of the second comparator from the switching device.

12. A circuit as defined in claim 11 wherein the isolation means comprises an opto-isolator.

13. A battery charging circuit comprising:

an alternating current power source comprising a secondary winding of a transformer, the secondary winding having first and second end terminals and a center tap, the center tap being connected to a first terminal of the battery;

a switching device connected in series with the battery for permitting current flow in a single direction therethrough, the switching device comprising first and second semiconductor switching elements each having a first and a second current carrying terminal, the first current carrying terminal of each semiconductor switching element being connected to a second terminal of the battery, the second current carrying terminal of the first semiconductor switching element being connected to the first end terminal of the secondary winding, and the second current carrying terminal of the second semiconductor switching being connected to the second end terminal of the secondary winding;

sensing means connected in series with the battery and the switching device for producing a sensed voltage proportional to the current through the battery;

averaging means for averaging the sensed voltage to produce an averaged sensed voltage;

comparison means comprising an opto-isolator connected between the comparator and the switching device, the opto-isolator responding to the control signal to control the duty cycle of the switching device for comparing the averaged sensed voltage to a reference voltage and for controlling the duty cycle of the switching elements to maintain a preselected constant charge current through the battery if the averaged sensed voltage deviates from a value corresponding to the preselected current; and

overvoltage protection means comprising a voltage comparator circuit having at least one input and an output, the voltage across the battery terminals being applied to one input of the voltage comparator circuit and the output of the voltage comparator being connected to the comparison means to flexibly decrease the duty cycle of the switching elements controlled by the comparison means to flexibly decrease the charging current when battery voltage equals or exceeds said predetermined threshold voltage, in proportion to said voltage excess.

14. A circuit as defined in claim 13 wherein the switching elements comprise silicone controlled rectifiers.

15. A circuit as defined in claim 13 wherein the sensing means comprises a resistive element connected in series between the battery and the switching device.

16. A circuit as defined in claim 13 wherein the averaging means comprises an amplifier.

17. A circuit as defined in claim 16 wherein the averaging means further comprises an RC circuit connected to the output of the amplifier.

18. A circuit as defined in claim 13 wherein the comparison means comprises a comparator configured to compare the averaged sensed voltage to a first reference voltage and to produce a corresponding control signal.

19. A circuit for maintaining a constant average charge current through a rechargeable battery and for preventing overcharging of the battery, the circuit comprising:

(a) a switching device connected in series with the battery for permitting current flow in a single direction therethrough, the switching device comprising first and second semiconductor switching elements each having first and second current carrying terminals, the semiconductor switching elements being connected parallel one to another at one terminal of the battery by said first current carrying terminals;

(b) a sensing element adapted for producing a sensed voltage proportional to the charge current;

(c) a current control loop comprising;

(i) averaging means comprising an amplifier, and further comprising an RC circuit connected to the output of said amplifier for averaging the sensed voltage to produce at an output thereof an average sensed voltage;

(ii) comparison means for comparing the average sensed voltage to a reference voltage to produce a corresponding control signal;

(iii) isolation means comprising an opto-isolator, the output of the opto-isolator being connected to the switching device and being responsive to the control signal for controlling the switching device to maintain through the battery a constant charge current; and

(d) an overvoltage protection loop comprising;

(i) means for comparing the voltage across the battery terminals to a reference voltage; and

(ii) means for flexibly reducing the charge current to a level equal to or greater than a trickle charge when the voltage across the battery terminals reaches a predetermined threshold voltage, and maintaining said battery terminal voltage at a level equal to or below said predetermined threshold voltage.

20. A circuit as defined in claim 19 wherein the first and second semiconductor switching elements comprise silicon controlled rectifiers.

21. A circuit as defined in claim 19 further comprising a transformer secondary winding having first and second end terminals and a center tap, the center tap being connected to one terminal of the battery, the first end terminal of the transformer secondary being connected to the first end terminal of the first switching element and the second end terminal of the transformer secondary being connected to the first end terminal of the second switching element.

22. A circuit as defined in claim 19 wherein the means for reducing the charge current is connected to the output of the averaging means.

23. A circuit for charging a battery from an AC power line, the battery having first and second terminals and the circuit comprising:

a transformer having a secondary winding provided with first and second end terminals and a center tap, the center tap being connected to the first terminal of the battery;

a resistive element having first and second terminals, the first terminal of the relative element being connected to the second terminal of the battery;

two semiconductor switching devices for permitting current flow in a single direction through the battery, each of the semiconductor switching devices having first and second current carrying terminals and a control terminal, the first current carrying terminal of each of the switching devices being connected to the second terminal of the resistive element, the second current carrying terminal of the first semiconductor switching device being connected to the first end terminal of the secondary winding, and the second current carrying terminal of the second semiconductor switching device being connected to the second end terminal of the secondary winding;

averaging means for averaging the voltage across the resistive element to produce as an output an averaged sensed voltage;

means for producing a reference voltage;

comparison means comprising an opto-isolator connected between the comparator and the switching device, the opto-isolator responding to the control signal to control the duty cycle of the switching device for comparing the averaged sensed voltage to the reference voltage and for producing a corresponding control signal, the control signal being applied to the control terminals of the semiconductor switching devices to control the duty cycle of the semiconductor switching devices and maintain the current through the battery at a constant level; and

overvoltage protection means comprising a voltage comparator circuit having at least one input and an output, the voltage across the battery terminals being applied to one input of the voltage comparator circuit and the output of the voltage comparator being connected to the comparison means to monitor the voltage across the terminals of the battery and to maintain the voltage across the terminals of the battery at a level equal to or less than a predetermined threshold voltage by modifying comparison means control of the duty cycle of the semiconductor switching devices to flexibly reduce the duty cycles thereof, according to the relationship between said battery voltage equal and said threshold voltage.