A battery charger includes a microcomputer operable to receive an input value corresponding to a value of charging current. A thyristor has the gate connected to an output port of the microcomputer. The microcomputer operable to adjust the firing angle of the thyristor for controlling the value of the charging current through a phase control of the charging current in response to the input value. A capacitor has a first electrode connected to the gate of the thyristor. A transistor has the collector connected to a second electrode of the capacitor, the base connected to the output port of the microcomputer, and the emitter connected to a power source voltage for the microcomputer.