A DC/DC converter has a transformer having a primary winding, a secondary winding, and an auxiliary winding, a switching transistor connected in series to the primary winding, a control transistor for turning the switching transistor on or off, and a feedback control circuit connected to the control transistor and the auxiliary winding. The feedback control circuit includes a Zener diode having a substantially zero temperature coefficient. The Zener diode has a Zener voltage which lies in a range between 5 volts and 6 volts. In order to cancel a temperature characteristic of the control transistor, the temperature coefficient of the Zener diode is selected.