Abstract: A quasi-resonant PWM inverter performs stable resonant operation utilizing a simple control system and a highly efficient inverter operation. A first condenser is connected between a connecting point between first and second main switches and to the first side of the first main switch. A second condenser is connected between the connecting point and the second side of the second main switch. The respective first and second sides of the first main switch and second main switch are connected to a DC power source having a first dividing point for the first potential and a second dividing point for the second potential. A terminal of a first auxiliary switch is connected to the first dividing point; and a terminal of a second auxiliary switch is connected to the second dividing point. A reactor is connected between the connecting points of the first and second auxiliary switches and the first and second main switches.

Abstract: A direct current power unit has main and secondary direct current power supplies, a serial circuit, and first and second parallel circuits. One terminal of the secondary direct current power is connected to one terminal of the main direct current power supply. The serial circuit consists of a choke coil and a first capacitor, of which each terminal is connected to each terminal of the main direct current power supply. The first parallel circuit consists of a first diode and a first switching element, of which each terminal is connected to each terminal of the first capacitor. The second parallel circuit consists of a second capacitor, a second diode, and a second switching element connected between the serial connected point of the choke coil and the first capacitor and the other terminal of the secondary direct current power supply. Each terminal of a third capacitor is connected to each terminal of the secondary direct current power supply.