Current Controlled Li-Ion Battery Charger Circuit


 Here we discus a current controlled Li-ion battery charger circuit which has been specifically
designed for charging all types Li-Ion Batteries very safely and without
any considerations.

It is generally advised that a Li-ion battery should be charged with utmost care and caution as these type of batteries are prone to instant damages or explosions if the specified charging measures are not employed.

Thanks to TEXAS INSTRUMENTS for providing us with this
wonderful chip, the LM3622 which is an excellent Li-Ion charger, controller
device.

The IC has been designed for generating a constant current at constant
voltage, a basic prerequisite for all Li-Ion batteries. The IC may be configured
for charging a single Li-Ion cell or a pack of many.

The circuit using the IC LM3622 can be fed with voltages
right from 5 to 24V depending upon the charging needs and the connected battery.

The IC does not require any precision external resistors for implementing the
functions. Moreover, the IC has a negligible drain of less than 200nA of
current from the battery in the absence of an input voltage.

The in built circuitry of the chip accurately regulates the
charging current through the principle of temperature compensated band-gap
reference. The current is regulated, however its done via an external current
sensing resistor.
The band gap principle results in an efficient operating control
performance of the circuit and also of the input supply voltage.
The shown current controlled Li-Ion battery charger circuit illustrates a low drop out linear Li-Ion
battery charger design which is capable of charging a single 3.7V Li-Ion Cell.
For enabling low voltage detection, the switches J1 and J2
may be appropriately selected.
The IC starts the charging process by first detecting the
voltage of the cell and “enable status” of the low voltage detection.
The transistor Q2 immediately comes into the operating
condition as soon as the connected battery hits target regulation level, determined
by the internal setting of the IC.
Q2 now begins supplying a regulated voltage to the connected
battery, initiating a constant voltage charging mode of the circuit.
In the above situation the battery receives a constant
regulated voltage across its terminals, while the charging current is monitored
depending upon the level of charge over the battery.
On reaching a full charge condition, the charge current to
the battery is significantly reduced to a safe value.
For more information, you may refer to the following LM3622 IC datasheet.

Current Controlled Li-Ion Battery Charger Circuit