This simple battery charger, with overcharge protection, can be used to charge multiple cells in a battery. It indicates when the cells are fully charged. The charger requires minimal components, which can be procured easily. The author’s circuit wired on a breadboard is shown in Fig. 1.
The circuit of the Li-ion battery charger, shown in Fig. 2, has three parts—charging and balancing circuit, current limiter, and constant voltage source. The circuit is capable of providing a maximum of 1.5A current and can take input up to 27 volts.
The most important part of the charger is the charging and balancing circuit that incorporates Zener diode TL431, which acts as an adjustable shunt regulator to control the PNP transistor BD140. The TL431 works as a linear regulator whose threshold voltage can be adjusted through trim pot VR1.
This project will be published in a few weeks. If you want to access it now, refer to Electronics For You’s October 2022 Issue–print or ezine edition.