Full charge detection circuit for a battery
First Claim
1. In an automatic battery charging circuit connected to a source of direct current, comprising:
- switch means to connect and disconnect a battery to be charged to said direct current source;
reference circuit means connected to said direct current source to provide first and second electrical reference values derived from said direct current source, comprising;
temperature responsive electrical impedance means in heat-exchanging relationship to said battery and being connected to said direct current source to provide a first electrical reference value which varies in response to changes in battery temperature;
electrical storage means connected to said direct current source in parallel with said temperature responsive means to establish a second electrical reference value when charging of a battery is initiated and to maintain said value during charging independently of a change in the first electrical reference value;
comparison circuit means including input means connected to sense each of said first and second electrical reference values and having output means connected to said switch means;
said switch means being responsive to a signal from the output means of said comparison circuit means to connect the battery to said source of direct current so long as both of said reference values remain substantially constant during charging, and to disconnect the battery in response to a variation in said first reference value upon completion of charging.
1 Assignment
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Accused Products
Abstract
A circuit for detecting the completion of the charging of a battery from a source of direct current employs two reference voltages, one of which is established by charging a capacitor when the charging of the battery begins, the other reference voltage is maintained by a thermistor connected across the direct current supply and in heat-exchange relationship to the battery. The first voltage is maintained by a diode which isolates the capacitor from discharging, but the other voltage drops when the fully charged battery lowers the resistance of the thermistor. The reference voltages are fed to the inputs of a difference amplifier whose output controls a switch circuit to disconnect the battery from the power source.
9 Citations
10 Claims
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1. In an automatic battery charging circuit connected to a source of direct current, comprising:
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switch means to connect and disconnect a battery to be charged to said direct current source; reference circuit means connected to said direct current source to provide first and second electrical reference values derived from said direct current source, comprising; temperature responsive electrical impedance means in heat-exchanging relationship to said battery and being connected to said direct current source to provide a first electrical reference value which varies in response to changes in battery temperature; electrical storage means connected to said direct current source in parallel with said temperature responsive means to establish a second electrical reference value when charging of a battery is initiated and to maintain said value during charging independently of a change in the first electrical reference value; comparison circuit means including input means connected to sense each of said first and second electrical reference values and having output means connected to said switch means; said switch means being responsive to a signal from the output means of said comparison circuit means to connect the battery to said source of direct current so long as both of said reference values remain substantially constant during charging, and to disconnect the battery in response to a variation in said first reference value upon completion of charging. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification