Rapid charge lithium ion battery charger
First Claim
1. A battery charging circuit for charging a lithium ion battery cell having a maximum recommended battery cell voltage, the battery charger comprising:
- (a) a charging circuit for charging a battery cell configured with a constant current during a constant current mode of operation during which a first charging voltage and a constant current is supplied to said battery cell and a constant voltage mode of operation during which a constant second charging voltage is applied to said battery cell during a charging cycle, said charging circuit configured to intermittently sense the battery cell open circuit voltage when no current is flowing in the charging circuit and maintain said constant current mode of operation until said battery cell open circuit voltage reaches a predetermined value less than said maximum recommended battery cell voltage, said charging circuit further configured to switch to said constant voltage mode when said open circuit battery cell voltage reaches said predetermined value and thereafter reduce the charging voltage to said constant second charging voltage at or below the maximum recommended battery cell voltage.
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Abstract
A rapid charging circuit for a lithium ion battery. The battery charger in accordance with the present invention compensates for the voltage drops across the various resistance elements in the battery circuit by setting the charging voltage to a level to compensate for the initial resistance of the series resistances in the circuit and an additional resistance selected to take into account the anticipated increase in resistance of the various circuit elements over time. The battery charger in accordance with the present invention periodically monitors the open-circuit voltage of the battery cell and reduces the charging voltage to when the battery cell voltage reaches the optimal value. Thus, during a constant current charging mode, the battery cell is driven at a relatively optimal charging current to reduce the charging time. As such, the system is able to optimize the charging current supplied to a battery cell during a constant current mode of operation while compensating for circuit elements whose resistance may vary over time due to temperature or other factors, such as corrosion, while at the same time avoiding exceeding the maximum recommended voltage for the battery cell.
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Citations
16 Claims
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1. A battery charging circuit for charging a lithium ion battery cell having a maximum recommended battery cell voltage, the battery charger comprising:
(a) a charging circuit for charging a battery cell configured with a constant current during a constant current mode of operation during which a first charging voltage and a constant current is supplied to said battery cell and a constant voltage mode of operation during which a constant second charging voltage is applied to said battery cell during a charging cycle, said charging circuit configured to intermittently sense the battery cell open circuit voltage when no current is flowing in the charging circuit and maintain said constant current mode of operation until said battery cell open circuit voltage reaches a predetermined value less than said maximum recommended battery cell voltage, said charging circuit further configured to switch to said constant voltage mode when said open circuit battery cell voltage reaches said predetermined value and thereafter reduce the charging voltage to said constant second charging voltage at or below the maximum recommended battery cell voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
Specification