Insulated synchronous rectification type dc/dc converter, and power adaptor and electronic device

An isolated synchronous rectification type DC/DC converter, comprising:

• a transformer including a primary winding and a secondary winding;
• a switching transistor connected to the primary winding of the transformer;
• a synchronous rectifying transistor installed between the secondary winding of the transformer and a ground line on the secondary side;
• a photocoupler including a light emitting device and a light receiving device;
• a feedback circuit configured to drive the light emitting device of the photocoupler such that an output voltage of the DC/DC converter approaches a target voltage;
• a primary side controller which is connected to the light receiving device of the photocoupler and switches the switching transistor depending on a feedback signal from the photocoupler;
• a synchronous rectification controller configured to control the synchronous rectifying transistor;
• and
• a protection circuit including a temperature detection element, one end of the temperature detection element connected to a drain of the synchronous rectifying transistor, the protection circuit configured to detect an overheated state of the synchronous rectifying transistor depending on a first signal generated by the temperature detection element.