A DC to DC converter includes: first and second switching elements connected in series at a first connection point between a first input/output terminal and a first ground terminal; third and fourth switching elements connected in series at a second connection point between the first input/output terminal and the first ground terminal; a resonant capacitor and a resonant inductor connected in series between the first and second connection points; fifth and sixth switching elements connected in series at a third connection point between a second input/output terminal and a second ground terminal; seventh and eighth switching elements connected in series at a fourth connection point between the second input/output terminal and the second ground terminal; a transformer; and a control circuit. The transformer has a primary winding connected in series to the resonant capacitor and the resonant inductor between the first and second connection points, and a secondary winding connected in series between the third and fourth connection points. The control circuit is operable to adjust the pulse waveforms for switching the fifth to eighth switching elements when voltage at the second input/output terminal is stepped down and output from the first input/output terminal.
