An isolating DC-DC converter has a main switching element (2) disposed on the primary side of a main transformer (4) and a synchronous rectifier (6) disposed on the secondary side thereof. The synchronous rectifier (6) is turned off by synchronizing to the turn-on of the main switching element (2) and is turned on by synchronizing to the turn-off the main switching element (2). The isolating DC-DC converter has a drive transformer (11) connected to a charging circuit (12) of the main switching element (2), the drive transformer (11) outputting a pulse when an ON signal of a control pulse driving the main switching element (2) is outputted, and an early-off drive circuit (30) receiving the pulse of the drive transformer (11) to turn off the synchronous rectifier (6) before the main switching element (2) is turned on.
展开▼
