Battery charger

• US 4,220,905 A
• Filed: 06/27/1978
• Issued: 09/02/1980
• Est. Priority Date: 06/27/1978
• Status: Expired due to Term

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Quarton, William T.
• Primary Examiner(s): Hickey, Robert J.
• Application Number:
  US05/919,698
• Time in Patent Office: 798 Days
• Field of Search: 320/20-23, 320/39, 320/40, 320/DIG. 1
• US Class Current: 320/160
• CPC Class Codes: H02J 7/007182 in response to battery voltage

Abstract

A battery charging circuit includes a switching transistor which controls the flow of charging current to the battery at a high rate or a low rate. The operation of the transistor is, in turn, controlled by a voltage sensing circuit which includes a voltage detector module characterized in a very low current drain. The battery is, in fact, isolated from the charging circuit by a diode; the sensing circuit, however, is not isolated from the battery by a diode. This arrangement permits a more sensitive voltage detection and a more accurate control over the switching transistor. A desirable switching hysteresis is built into the sensing circuit but is operable to allow the hysteresis loop to be eliminated for purposes of calibration.

Claims

1. A battery charger circuit comprising:

a pair of terminals for connection to a battery,

a source of charging current for said battery,

control means connected between said source and said terminals for controlling the charging current from said source to said battery,

a voltage sensing circuit, including a voltage detector module, connected to said pair of terminals to be responsive to the terminal voltage of said battery, said voltage detector being characterized by having a negligible current drain,

said control means including a first means for controlling said charging current in a first mode at a relatively high rate, and second means for controlling said charging current in a second mode at a relatively low rate,

said control means being connected to be responsive to an output signal from said voltage sensing circuit for controlling the mode of operation in accordance with the sensed terminal voltage at said battery terminals.

2. A battery charging circuit comprising:

a pair of terminals for connection to a battery,

a source of charging current for said battery,

a control circuit connected between said source and said terminals for controlling the charging current from said source to said battery,

a voltage sensing circuit, including a voltage detector module, connected to said pair of terminals to be responsive to the terminal voltage of said battery, said voltage detector module having an input terminal and an output terminal and being characterized by having a negligible current drain, said voltage detector being further characterized in having a predetermined threshold voltage characteristic at said input terminal at which voltage the signal condition at said output terminal changes state, said voltage sensing circuit including a passive voltage dividing network connected across said pair of terminals with an intermediate connection to said input terminal of said module,

said control circuit including a first means for controlling said charging current in a first mode at a relatively high rate, and a second means for controlling said charging current in a second mode at a relatively low rate,

said control circuit being connected to be responsive to said signal condition at said output terminal of said module for controlling said charging current in said first mode whenever said voltage at said input terminal of said module is below said threshold voltage and for controlling said charging current in said second mode whenever said voltage at said input terminal of said module is equal to or above said threshold voltage.

3. A battery charging circuit comprising:

a pair of terminals for connection to a battery,

a source of charging current for said battery,

a control circuit connected between said source and said terminals for controlling the charging current from said source to said battery,

a voltage sensing circuit, including a voltage detector module, connected to said pair of terminals to be responsive to the terminal voltage of said battery, said voltage detector module having an input terminal and an output terminal and being characterized by having a negligible current drain, said voltage detector being further characterized in having a predetermined threshold voltage characteristic at said input terminal at which voltage the signal condition at said output terminal changes state, said voltage sensing circuit including a passive voltage dividing network connected across said pair of terminals with an intermediate connection to said input terminal of said module,

said control circuit including a switching transistor and a shunt connected resistor for controlling said charging current in a first mode at a relatively high rate through said transistor when said transistor is conductive and in a second mode at a relatively low rate through said resistor when said transistor is nonconductive,

said control circuit being connected to be responsive to said signal condition at said output terminal of said module for controlling said charging current in said first mode whenever said voltage at said input terminal of said module is below said threshold voltage and for controlling said charging current in said second mode whenever said voltage at said input terminal is equal to or above said threshold voltage.

4. A battery charging circuit comprising:

a pair of terminals for connection to a battery,

a source of charging current for said battery,

a control circuit connected between said source and said terminals for controlling the charging current from said source to said battery,

a voltage sensing circuit, including a voltage detector module, connected to said pair of terminals to be responsive to the terminal voltage of said battery, said voltage detector module having an input terminal and an output terminal and being characterized by having a negligible current drain, said voltage detector being further characterized in having a predetermined threshold voltage characteristic at said input terminal at which voltage the signal condition at said output terminal changes state, said voltage sensing circuit including a passive voltage dividing network connected across said pair of terminals with an intermediate connection to said input terminal of said module,

said control circuit including means for controlling said charging current in a first mode at a relatively high rate and for controlling said charging current in a second mode at a relatively low rate,

said control circuit being connected to be responsive to said signal condition at said output terminal of said module for controlling said charging current in said first mode whenever said voltage at said input terminal of said module is below said threshold voltage and for controlling said charging current in said second mode whenever said voltage at said input terminal of said module is equal to or above said threshold voltage.

5. A battery charging circuit as set forth in claim 4 wherein said voltage sensing circuit includes a selectively operable means for introducing hysteresis into the response characteristic in said sensing circuit whereby the transfer of said control of said charging current from said first mode to said second mode is at a different level of terminal voltage of said battery than is the transfer of control of said charging current from said second mode to said first mode.

6. A battery charging circuit as set forth in claim 5 wherein said selectively operable means includes a feedback circuit connected between output circuit means of said module and the input terminal of said module, said feedback circuit including a feedback impedance means and switch means for selectively switching said feedback circuit into operative circuit relationship.

7. A battery charging circuit comprising:

a pair of terminals for connection to a battery,

a source of charging current for said battery,

a control circuit connected between said source and said terminals for controlling the charging current from said source to said battery,

a voltage sensing circuit, including a voltage detector module, connected to said pair of terminals to be responsive to the terminal voltage of said battery, said voltage detector module having an input terminal and an output terminal and being characterized by having a negligible current drain, said voltage detector being further characterized in having a predetermined threshold voltage characteristic at said input terminal at which voltage the signal condition at said output terminal changes state, said voltage sensing circuit including a passive voltage dividing network connected across said pair of terminals with an intermediate connection to said input terminals of said module,

said control circuit including a switching transistor and a shunt connected resistor for controlling said charging current in a first mode at a relatively high rate through said transistor when said transistor is conductive and in a second mode at a relatively low rate through said resistor when said transistor is nonconductive, said control circuit further including a driver transistor the input of which is connected to said output terminal of said module and the output of which is connected to the control input of said switching transistor controlling said charging current in said first mode whenever said voltage at said input terminal of said module is below said threshold voltage and for controlling said charging current in said second mode whenever said voltage at said input terminal of said module is equal to or above said threshold voltage, and

said voltage sensing circuit further including a selectively operable feedback circuit connected between said output of said driver transistor and said input terminal of said module for introducing a selectively operable hysteresis into the response characteristic in said sensing circuit whereby the transfer of said control of said charging current from said first mode to said second mode is at a different level of terminal voltage of said battery than is the transfer of control of said charging current from said second mode to said first mode, said feedback circuit including a feedback impedance means and a switch means for selectively switching said feedback circuit into operative circuit relationship.