A circuit for charging a battery pack includes a power converter and a charger controller. The power converter is operable for receiving an input power, and for providing a charging power for charging the battery pack. The power converter provides galvanic isolation between input circuitry and output circuitry of the circuit. The input circuitry shares a first ground potential with the input power, and the output circuitry shares a second ground potential with the charging power. The charger controller in the input circuitry includes a modulator for generating a driving signal to drive the power converter and control the charging power.