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.
How the Circuit Functions
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.