US Patent 7894217 DC to DC converter

An exemplary direct current (DC) to DC converter includes a first rectifying and filtering circuit configured to receive an alternating current (AC) voltage and transform the AC voltage to a first DC voltage, a pulse width modulation (PWM) circuit, a first transformer configured to receive the first DC voltage and transform the first DC voltage to a second AC voltage under control of the PWM circuit, and a second rectifying and filtering circuit including a first transistor and a control circuit for switching on or switching off the first transistor so as to transform the second AC voltage to a second DC voltage.