The full charger feedback control circuit can be seen in Figure below. This circuit implements a three stage charger algorithm: constant current state, constant voltage full charge state, and constant voltage float charges state. This circuit will require an input voltage of at least 17 volts to output the 14.7V for charging because of the 2V drop across the regulator.
The comparator is used to provide feedback of the current that the battery is
drawing from the circuit: as the battery charges, the current drawn decreases. The current sensing resistor is used to convert that current into voltage, which can be used to compare to a reference within the circuit. This will be the logic needed for the state switching mechanism. The full charge state will provide 14.7V or 2.45V/Cell on the battery and float charge will provide 13.8V or 2.3V/Cell. The battery will try to draw maximum current, in this case:
(14.7V-10.5V)/.1Ohm= 42A (assuming the battery is completely dead)
The current limiting of the voltage regulator will force the current to 3A. The
charger will continuously pump this 3A until the battery current falls below the limit of 500 mA. This will bring the voltage of the battery above the reference point, therefore causing the comparator to turn on the transistor switch, pulling the output voltage to the float charging level.
The full charger feedback control circuit can be seen in Figure below. This circuit implements a three stage charger algorithm: constant current state, constant voltage full charge state, and constant voltage float charges state. This circuit will require an input voltage of at least 17 volts to output the 14.7V for charging because of the 2V drop across the regulator.
The comparator is used to provide feedback of the current that the battery is
drawing from the circuit: as the battery charges, the current drawn decreases. The current sensing resistor is used to convert that current into voltage, which can be used to compare to a reference within the circuit. This will be the logic needed for the state switching mechanism. The full charge state will provide 14.7V or 2.45V/Cell on the battery and float charge will provide 13.8V or 2.3V/Cell. The battery will try to draw maximum current, in this case:
(14.7V-10.5V)/.1Ohm= 42A (assuming the battery is completely dead)
The current limiting of the voltage regulator will force the current to 3A. The
charger will continuously pump this 3A until the battery current falls below the limit of 500 mA. This will bring the voltage of the battery above the reference point, therefore causing the comparator to turn on the transistor switch, pulling the output voltage to the float charging level.
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