Isolated synchronous rectification-type DC/DC converter

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

• a transformer having a primary winding and a secondary winding;
• a switching transistor coupled to the primary winding of the transformer;
• an output capacitor being charged by a current flowing in the secondary winding of the transformer;
• a photocoupler having a light emitting element and a light receiving element;
• a feedback circuit structured to drive the light emitting element of the photocoupler such that a detection voltage corresponding to an output voltage of the output capacitor approximates to a reference voltage;
• a primary controller coupled to the light receiving element of the photocoupler and structured to control the switching transistor corresponding to a feedback signal based on a state of the light receiving element;
• a protection circuit structured to be activated and to drive the light emitting element when detecting an abnormal state;
• an auxiliary power supply circuit including a power supply capacitor provided separately from the output capacitor and structured to supply a power supply voltage generated in the power supply capacitor to at least a part of a power supply line of the protection circuit;
• and
• a rectifier element provided between a cathode of the light emitting element of the photocoupler and the power supply line.

A method for controlling an isolated synchronous rectification-type DC/DC converter, the method comprising:

• controlling a switching transistor coupled to a primary winding of a transformer;
• rectifying a current flowing in a secondary winding of the transformer to charge an output capacitor and generating an output voltage;
• generating a power supply voltage by a power supply capacitor provided separately from the output capacitor;
• supplying the power supply voltage to a secondary controller which drives a light emitting element of a photocoupler and a cathode of the light emitting element;
• maintaining a state of driving the light emitting element when detecting an abnormal state;
• and
• supplying power from a cathode of the light emitting element of the photocoupler to the secondary controller when supply of the power supply voltage to the secondary controller is interrupted.