This paper presents the performance of a high frequency quasi-resonant inverter using power Metal Oxide Semiconductor Field Effect Transistor (MOSFETs) as switching devices is described. This inverter circuit can output the variable frequency from 160kHz to 400kHz by power MOSFET for induction heating. The induction heating is often used for the heat-treatment of a metal work-piece. In hardening of a gear, since the bottom or tips are heated at lower frequency fL or higher frequency fH respectively, the heating at two different frequencies for uniform heat-treatment is required. Therefore, two inverters are necessary to output different resonant frequency each other. To solve this problem a single adjustable frequency quasi-resonant inverter circuits. This inverter circuit includes the first resonant capacitor and that of the second with a one-way short-circuit switch. Synthetic series capacitance is varied by manipulating the switch and then the resonant frequency can be adjusted. The power MOSFET has the disadvantages of withstand voltage and current. To solve this problem by the methods of connecting switching devices to series [2]. Voltage across the series connected power MOSFETs are balanced by magnetically coupling all gate lines using a simple two-winding transformer.
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