BATTERY CHARGING CIRCUIT

• US 3,854,082 A
• Filed: 06/07/1973
• Issued: 12/10/1974
• Est. Priority Date: 06/07/1973
• Status: Expired due to Term

• Current Assignee: James S. Nasby, William L. Stelter
• Original Assignee: James S. Nasby, William L. Stelter
• Inventors: Nasby, James S., Stelter, William L.
• Primary Examiner(s): Miller, J. D.
• Assistant Examiner(s): Hickey, Robert J.
• Application Number:
  US05/367,771
• Time in Patent Office: 551 Days
• Field of Search: 320/22-24,39,40,31,32
• US Class Current: 320/160
• CPC Class Codes: H02J 7/00714 in response to battery charging or discharging current
• CPC Class Codes: H02J 7/007182 in response to battery voltage

Abstract

A battery charging circuit has means for supplying a battery under charge with a constant charging current until the voltage across the battery reaches a first predetermined voltage magnitude. A constant voltage means than applies a constant charging voltage equal in magnitude to the first predetermined magnitude until the current necessary to maintain it falls below a predetermined limit, at which time, a second constant voltage means supplies the battery with a constant final voltage of a magnitude lower than the first predetermined voltage magnitude. The final constant charging voltage is maintained unless the current at the output exceeds the predetermined limit. Therefore, during those times when the constant current or the first constant voltage is supplied to the battery, the battery is charged at a maximum rate until it is fully charged, at which time the second constant voltage source maintains the fully charged battery condition.

Claims

1. A battery charging circuit comprising:

an input adapted for connection to an external power source;

an output adapted for connection to a battery to be charged;

a charging source coupled to said output and to said input, and capable of providing said output with a constant charging current and constant charging voltages of first and second predetermined voltage magnitudes at varying charging currents;

a voltage sensor for sensing the magnitude of the charging voltage at said output and for providing an output voltage having a magnitude dependent upon the charging voltage;

a current sensor for sensing the mangitude of the charging current at said output and for providing an output voltage having a magnitude dependent upon the charging current;

an AND gate comprising a pair of serially connected transistors coupled to said voltage sensor and said current sensor for combining said voltage sensor and said current sensor output voltages and for providing a control signal responsive to said combined voltages; and

means responsive to said control signal for causing said charging source to supply said output with said constant current as long as said charging voltage is less than said first predetermined magnitude, for causing said charging source to supply said output with said constant voltage of said first predetermined magnitude when said charging voltage equals said first predetermined magnitude, and for causing said charging source to supply said output with said charging voltage of said second predetermined magnitude when the current sufficient to maintain said output at said first predetermined voltage magnitude falls below a predetermined limit.

2. A battery charging circuit in accordance with claim 1 where said second predetermined voltage magnitude is less than said first predetermined voltage magnitude.

3. A battery charging circuit in accordance with claim 1 which further comprises an indicator for providing an indication when said constant current and said constant charging voltage of said first predetermined magnitude is supplied.

4. A battery charging circuit in accordance with claim 1 where said voltage sensor comprises a pair of transistors forming a differential amplifier coupled to said output and to a reference potential.

5. A battery charger circuit in accordance with claim 4 where said differential amplifier is coupled to said output through a voltage divider and wherein said battery charger circuit further comprises means for altering said voltage divider in response to said current sensor.

6. A battery charging circuit in accordance with claim 1 wherein said output is cOupled to an impedance for creating a voltage indicative of said charging current and where said current sensor comprises a pair of transistors forming a differential amplifier coupled to said output and to a reference potential.

7. A battery charging circuit comprising:

an input adapted for connection to an external power source;

an output adapted for connection to a battery to be charged;

a charging source coupled to said output and to said input, and capable of providing said output with a constant charging current and constant charging voltages of first and second predetermined voltage magnitudes at varying charging currents;

a voltage sensor for sensing the magnitude of the charging voltage at said output;

a current sensor for sensing the magnitude of the charging current at said output; and

means including a pair of serially connected transistors forming an AND circuit responsive to said voltage and current sensors for causing said charging source to supply said output with said constant current as long as said charging voltage is less then said first predetermined magnitude, for causing said charging source to supply said output with said constant voltage of said first predetermined magnitude when said charging voltage equals said first predetermined magnitude, and for causing said charging source to supply said output with said charging voltage of said second predetermined magnitude when the current sufficient to maintain said output at said first predetermined voltage magnitude falls below a predetermined limit.

8. A battery charging circuit in accordance with claim 7 which further comprises a variable current source coupled to said AND circuit and to said charging source for controlling said charging source in response to said AND circuit.

9. A battery charging circuit in accordance with claim 1 where said charging source comprises a full wave rectifier coupled to said input and a switching device coupled between said rectifier and said output.

10. A battery charging circuit in accordance with claim 9 where said switching device comprises a silicon controlled rectifier.

11. A battery charging circuit comprising:

an input adapted for connection to an external power source;

an output adapted for connection to a battery to be charged;

a charging source comprising a full wave rectifier coupled to said input and a switching device coupled between said rectifier and said output for providing said output with a constant charging current and constant charging voltages of first and second predetermined voltage magnitudes at varying charging currents, said second predetermined voltage magnitude being less than said first predetermined voltage magnitude;

a voltage sensor including a differential amplifier comprising a pair of transistors coupled to said output for sensing the magnitude of the charging voltage;

a current sensor including a differential amplifier comprising a pair of transistors for sensing the magnitude of the charging current;

a pair of serially coupled transistors, each said transistor coupled to a given one of said sensors, for providing a control signal in response to said sensors; and

means including a variable current source coupled to said serially coupled transistors and to said charging source for causing said charging source in response to said control signals to supply said output with said constant current as long as said charging voltage is less than said first predetermined magnitude, to supply said output with said constant voltage of said first predetermined magnitude when said charging voltage equals said first predetermined magnitude, and to provide said output with said charging voltage of said second predetermined magnitude when the current sufficient to maintain said output at said first predetermined voltage magnitude falls below a predetermined limit.