Ni-Cad battery charger circuit
First Claim
1. A battery charger having a fast charging current circuit and a slow charging current circuit comprising:
- means for coupling the fast charging current circuit to a battery to provide a voltage developed across the battery and to a resistor/capacitor time constant circuit for storing a voltage in the capacitor of the time constant circuit such that the capacitor voltage tries to catch up with the battery voltage;
means for comparing the instantaneous voltage developed across the battery in response to the fast charging current with the instantaneous voltage stored by the capacitor; and
means for removing the fast charging current circuit from, and coupling the slow charging current circuit to, the battery when the voltage stored by the capacitor exceeds the battery voltage developed by the fast charging current.
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Abstract
An analog, low-cost nickel-cadmium battery charger including a fast charging current circuit and a slow charging current circuit, both of which are controlled by a comparator circuit which compares the characteristic negative change in battery voltage at the onset of overcharge to the stored charging voltage and changes the charging current from fast charging to slow charging when the battery voltage begins to decrease at the onset of overcharge, a timer that shuts off the fast charging current circuit after a predetermined period of time and reverts to the slow charging current circuit, and a thermostat that checks the temperature of the battery and, in the event of overheating or cooling below a predetermined temperature, stops all charging of the battery.
51 Citations
15 Claims
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1. A battery charger having a fast charging current circuit and a slow charging current circuit comprising:
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means for coupling the fast charging current circuit to a battery to provide a voltage developed across the battery and to a resistor/capacitor time constant circuit for storing a voltage in the capacitor of the time constant circuit such that the capacitor voltage tries to catch up with the battery voltage; means for comparing the instantaneous voltage developed across the battery in response to the fast charging current with the instantaneous voltage stored by the capacitor; and means for removing the fast charging current circuit from, and coupling the slow charging current circuit to, the battery when the voltage stored by the capacitor exceeds the battery voltage developed by the fast charging current. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A charging circuit for a battery having a charge voltage versus time curve that increases until a relatively flat portion then decreases at the onset of overcharge, the circuit comprising:
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a fast charging circuit coupled to the battery; a series coupled resistance and capacitance for receiving and storing the charging current; a comparator circuit having first and second inputs; conductor means coupling the voltage stored by the capacitance to the first comparator input; resistor means coupling the battery voltage to the second comparator input; said comparator circuit detecting a decrease in battery voltage at the onset of overcharge of the battery and generating an output signal when the voltage stored by the capacitor is greater than the battery voltage at the onset of overcharge; a slow charging current circuit; and electro-optic means coupled to the comparator circuit for receiving the comparator output signal, removing the fast charging current from the battery and coupling the slow charging current to the battery when the battery voltage decrease is detected. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A method of charging a battery with a fast charging current circuit and a slow charging current circuit, the method comprising the steps of:
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coupling the fast charging current circuit to a battery to provide a voltage developed across the battery and to a resistor/capacitor time constant circuit for storing a voltage in the capacitor of the time constant circuit such that the capacitor voltage tries to catch up with the battery voltage; comparing the instantaneous battery voltage developed by the fast charging current with the instantaneous capacitor voltage developed by the fast charging current; and removing the fast charging current circuit from, and coupling the slow charging current circuit to, the battery when the voltage across the capacitor exceeds the battery voltage. - View Dependent Claims (14, 15)
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Specification