Patent ID: 7894217

Claim:
A direct current (DC) to DC converter comprising: 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 comprising a first transistor, 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, an output terminal configured to output the second DC voltage, and a storage capacitor connected between the output terminal and ground; wherein the first transformer comprises a primary winding and a secondary winding, a terminal of the secondary winding being connected to the output terminal, the other terminal of the secondary winding being grounded via the control circuit and the first transistor; and the DC to DC converter further comprising a second transistor connected in series with the primary winding of the first transformer, the PWM circuit being configured to switch on or switch off the second transistor; wherein the control circuit comprises a second transformer, a first resistor, a second resistor, a third resistor, a third filter capacitor, a protecting diode, a third transistor, a fourth transistor, and a fifth transistor, the second transformer comprising a primary winding and a secondary winding, the first resistor and the third capacitor being connected in parallel with the secondary winding of the second transformer, a base electrode of the third transistor being connected to a first terminal of the secondary winding of the second transformer via the second resistor and the third resistor in series, and being connected to a second terminal of the secondary winding of the second transformer via the second resistor and the inverse protecting diode in series, an emitter electrode of the third transistor being connected to the first terminal, a collector electrode of the third transistor being connected to a terminal of the secondary winding of the first transformer, a base electrode of the fourth transistor being connected to the first terminal, an emitter electrode of the fourth transistor being connected to the gate electrode of the first transistor, a collector electrode of the fourth transistor being connected to ground, and being connected to a base electrode of the fourth transistor.