Battery charger with charging current variation based on a temperature difference between the battery and its environment
First Claim
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1. A battery charger for charging a rechargeable battery, comprising:
- power supply means (PS) for converting a supplied input voltage (Vi) into a charging current for the battery, said conversion generating heat which raises the ambient temperature of the battery, the generated heat increasing as the supplied input voltage (Vi) increases;
a first sensor for generating a first signal which is representative of the ambient temperature of the battery;
a second sensor for generating a second signal which is representative of the internal temperature of the battery; and
means for changing the charging current produced by said power supply means (PS) in accordance with the difference between the first and second signals;
characterized in that said battery charger further comprises;
means for generating a third signal which is representative of the supplied input voltage (Vi); and
means for modifying the difference between the first and second signals in accordance with said third signal, so as to compensate for a change in ambient temperature of the battery due to heat generated by conversion of the supplied input voltage (Vi) into charging current for the battery.
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Abstract
A battery charger whose charging current is shut off on the basis of the temperature difference between the ambient temperature, measured by means of a first sensor (RA), and the battery temperature, measured by means of a second sensor (RB). The error in the measurement of the temperature difference, which is caused by the input voltage dependent heat generation by the power supply (PS) in the battery charger, is compensated by a third signal (k*Vi) which is representative of the anticipated additional heat generation as a result of a varying input voltage (Vi).
22 Citations
9 Claims
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1. A battery charger for charging a rechargeable battery, comprising:
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power supply means (PS) for converting a supplied input voltage (Vi) into a charging current for the battery, said conversion generating heat which raises the ambient temperature of the battery, the generated heat increasing as the supplied input voltage (Vi) increases; a first sensor for generating a first signal which is representative of the ambient temperature of the battery; a second sensor for generating a second signal which is representative of the internal temperature of the battery; and means for changing the charging current produced by said power supply means (PS) in accordance with the difference between the first and second signals; characterized in that said battery charger further comprises; means for generating a third signal which is representative of the supplied input voltage (Vi); and means for modifying the difference between the first and second signals in accordance with said third signal, so as to compensate for a change in ambient temperature of the battery due to heat generated by conversion of the supplied input voltage (Vi) into charging current for the battery. - View Dependent Claims (2, 3, 4, 5, 6, 8, 9)
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7. A battery charger as claimed in claim wherein the second sensor is a resistor having a negative temperature coefficient, which resistor is in thermal contact with the battery.
Specification