A power supply and a method of driving the same. A converter receives an input voltage from a battery and outputs a first voltage through an output terminal, such that a ground voltage of the output terminal changes. A pulse width modulation (PWM) controller controls the converter to adjust the voltage level of the first voltage. The ground voltage is applied to the converter as a direct current (DC) voltage during a first time and as a pulse wave having a predetermined amplitude during a second time. The PWM controller controls the first voltage to have different voltage levels during the first time and the second time.