Battery charger having temperature compensated charge rate
First Claim
1. Apparatus for charging a battery comprising:
- a switching type voltage regulator having a current sense output wherein said regulator is connected in a series circuit between a power source and a first terminal of said battery, said regulator receiving unregulated dc power from said power source and delivering regulated power to said first terminal of said battery;
a controller for said regulator operatively connected to provide switching signals to said regulator, said controller having a voltage adjust circuit and a current limit circuit, and having a first external voltage input and a first reference voltage input associated with said current limit circuit, and having a second external voltage input and a second reference voltage input associated with said voltage adjust circuit, said voltage adjust circuit and said current limit circuit being operatively connected to modulate said switching signals in response to the potential applied to said first and second external voltage inputs;
a current sense resistor having a first terminal connected to said current sense output of said regulator and a second terminal connected to a second terminal of said battery;
means for connecting a current sense output voltage from said regulator to said first external voltage input of said controller for modulating said switching signals in response to said current sense output voltage;
a resistive voltage divider network connected across said first and second terminals of said battery;
a thermistor disposed to measure the temperature of said battery, wherein said thermistor is connected in parallel with a resistor of said resistive voltage divider network;
means for operatively connecting a node of said resistive voltage divider network to said second external voltage input of said controller for modulating said switching signals in response to said thermistor and the voltage of said battery;
means for connecting a ground potential to said first reference voltage input; and
means for connecting a reference potential to said second reference voltage input wherein said reference potential corresponds to the maximum modulation of said switching signals that can be provided by said controller.
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Accused Products
Abstract
A battery charging circuit is disclosed which rapidly charges a battery from some level of discharge, including fully discharged, to fully charged without endangering the battery. The charging circuit includes a control circuit which provides switching type regulation responsive to current, voltage and temperature signals from the battery, and also a timer circuit for automatically halting the charging current to a defective battery. The control circuit receives a temperature compensated voltage signal (TCVS) which is useful for effectively implementing a charging program which includes a low constant current mode, a high constant current mode, and a constant voltage mode. The TCVS is generated by connecting a thermistor responsive to battery temperature in parallel with one resistor of a resistive voltage divider network which is connected across the battery terminals. The output of the thus modified voltage divider network when plotted against temperature is a nonlinear curve which, with proper selection of ohmic values for the resistors and thermistor, corresponds to a temperature/voltage relationship for the battery which is known from experimental results to be effective for charging the battery.
218 Citations
7 Claims
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1. Apparatus for charging a battery comprising:
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a switching type voltage regulator having a current sense output wherein said regulator is connected in a series circuit between a power source and a first terminal of said battery, said regulator receiving unregulated dc power from said power source and delivering regulated power to said first terminal of said battery; a controller for said regulator operatively connected to provide switching signals to said regulator, said controller having a voltage adjust circuit and a current limit circuit, and having a first external voltage input and a first reference voltage input associated with said current limit circuit, and having a second external voltage input and a second reference voltage input associated with said voltage adjust circuit, said voltage adjust circuit and said current limit circuit being operatively connected to modulate said switching signals in response to the potential applied to said first and second external voltage inputs; a current sense resistor having a first terminal connected to said current sense output of said regulator and a second terminal connected to a second terminal of said battery; means for connecting a current sense output voltage from said regulator to said first external voltage input of said controller for modulating said switching signals in response to said current sense output voltage; a resistive voltage divider network connected across said first and second terminals of said battery; a thermistor disposed to measure the temperature of said battery, wherein said thermistor is connected in parallel with a resistor of said resistive voltage divider network; means for operatively connecting a node of said resistive voltage divider network to said second external voltage input of said controller for modulating said switching signals in response to said thermistor and the voltage of said battery; means for connecting a ground potential to said first reference voltage input; and means for connecting a reference potential to said second reference voltage input wherein said reference potential corresponds to the maximum modulation of said switching signals that can be provided by said controller. - View Dependent Claims (2, 3, 4)
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5. A method of charging a temperature sensitive battery without damage to the battery comprising the following sequential steps:
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(a) generating a temperature compensated voltage signal representative of a voltage for safely charging said battery at the exisitng temperature of said battery; (b) supplying a constant current having a first magnitude to said battery until said temperature compensated voltage signal attains a first predetermined voltage level representative of the minimum voltage that said battery should attain within a predefined time period in response to said constant current having said first magnitude if said battery is undamaged; (c) supplying a constant current having a second magnitude which is greater than said first magnitude to said battery, said second magnitude of constant current being applied to the battery until said temperature compensated voltage signal attains a second predetermined level representative of a predetermined voltage which can be applied across the terminals of said battery for safely and efficiently charging said battery at the existing temperature of said battery;
said second predetermined voltage level being higher than said first predetermined voltage level; and(d) impressing a constant voltage across the terminals of said battery, said constant voltage corresponding to the voltage attained by said temperature compensated voltage signal in step. - View Dependent Claims (6, 7)
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Specification