Isolating DC-DC converter

An isolating DC—DC converter comprising a main transformer isolating a primary-side circuit and a secondary-side circuit, a main switching element disposed in the primary-side circuit, the main switching element being turned on/off by charging and discharging an input capacitance by a control pulse, and at least one synchronous rectifier disposed in the secondary-side circuit, the synchronous rectifier being turned off by synchronizing to the turn-on of the main switching element, wherein the turn-on of the main switching element and the turn-off of the synchronous rectifier are synchronized, and the turn on/off of the main switching element allows energy to be coupled from the primary-side circuit to the secondary-side circuit, the secondary side circuit rectifying and smoothing the energy so that a DC voltage is outputted from an output end;

• and further comprising a series circuit comprising a primary coil of a drive transformer and a capacitor connected to a path for charging the input capacitance of the main switching element in parallel to the input capacitance of the main switching element, and further comprising an early-off drive circuit for the synchronous rectifier disposed on a secondary side of the drive transformer to turn off the synchronous rectifier before the input capacitance of the main switching element is charged to turn on the main switching element when the main switching element is provided with the control pulse, by using a secondary-side output of the drive transformer.