Insulated synchronous rectification dc/dc converter

A secondary-side controller that is arranged on a secondary side of an insulated synchronous rectification DC/DC converter, and that controls a synchronous rectification transistor, the secondary-side controller comprising:

• a first comparator that compares a voltage across both terminals of the synchronous rectification transistor with a first threshold voltage, and that asserts a set signal when the voltage across both terminals of the synchronous rectification transistor becomes lower than the first threshold voltage;
• a second comparator that compares the voltage across both terminals of the synchronous rectification transistor with a second threshold voltage, and that asserts a reset signal when the voltage across both terminals of the synchronous rectification transistor becomes higher than the second threshold voltage;
• a flip-flop that generates a pulse signal which is switched to an on level when the set signal is asserted, and which is switched to an off level when the reset signal is asserted;
• a forced turn-off circuit that forcibly turns off the synchronous rectification transistor after a predetermined time-up period elapses after the reset signal is asserted;
• a set terminal that is connected in use to an external circuit element so as to determine the time-up period based on a circuit constant of the circuit element;
• and
• an abnormal state detection circuit that is capable of detecting an open-circuit state and/or a short-circuit state that can occur in the set terminal, and that asserts a detection signal upon detection of such an open-circuit state and/or short-circuit state,
• wherein, when the detection signal is asserted, the secondary-side controller instructs a primary-side controller arranged on a primary side of the DC/DC converter to suspend a switching operation of a switching transistor.