Energy transmission device and semiconductor device for energy transmission control

An energy transmission device, comprising:

• a transformer having a primary winding and a secondary winding;
• a switching element connected in series with the primary winding to switch a first DC voltage inputted through the primary winding;
• a control circuit for controlling switching of the switching element;
• and
• an output voltage generating section for converting to a second DC voltage an AC voltage generated on the secondary winding by switching control of the control circuit, and supplying power to a load,
• wherein the control circuit comprises:
• a voltage clamping device for outputting a voltage signal clamped to a clamping voltage when a voltage applied to a DRAIN terminal of the switching element is not lower than the clamping voltage, the clamping voltage being lower than a minimum point of the voltage applied to the DRAIN terminal of the switching element in a period during which a secondary current passes through the secondary winding after the switching element is turned off by the switching control of the control circuit;
• and
• a turn-on detection circuit for detecting, from the voltage signal obtained by the voltage clamping device, a specific voltage of ringing voltage generated after passage of the secondary current is stopped, and controlling a signal for turning on the switching element.