Patent ID: 7245087

Claim:
A power conversion device comprising: a DC power supply; a series circuit of a main switching element and a sub-switching element sequentially connected between the positive electrode and the negative electrode of the DC power supply; an insulating transformer having a primary first coil connected via a series circuit of a capacitor and an inductor between the positive electrode of the DC power supply and an interconnection of the main switching element and the sub-switching element, and a secondary second coil connected to a load via a rectifier smoothing circuit; a main control circuit for controlling the main switching element to turn on and off; and a sub-control circuit for controlling the sub-switching element to turn on and off, wherein the main control circuit and the sub-control circuit turns the main switching element and the sub-switching element on and off alternately to convert a voltage generated in the second coil and supply converted DC power via the rectifier smoothing circuit to a load, wherein the insulating transformer includes a primary third coil, wherein the main control circuit turns the main switching element on and off such that a DC voltage supplied to the load becomes constant, with the voltage of the primary third coil being a signal voltage, wherein the sub-control circuit turns the sub-switching element on when a voltage at both ends of the sub-switching element is lower than a reference voltage, and wherein a power supply voltage of the main control circuit is taken as a voltage obtained by subjecting a voltage generated in the primary third coil to smoothing rectification, and a power supply voltage of the sub-control circuit is obtained by an on operation of the main switching element.