A portable IGBT (Insulated Gate Bipolar Transistor) of high reliability, compact size, and low cost includes a main circuit to which a control circuit and an auxiliary power supply circuit are connected. The main circuit includes, in sequence, an input rectifier filter circuit, an inverter circuit, a high-frequency primary transformer, and a secondary output rectifier circuit. The control circuit includes a PWM regulation circuit, an IGBT driving circuit, a current feedback circuit, and a current setup circuit. The inverter circuit includes a full-bridge hard switching structure, which has IGBTs constituting bridge arms that are sequentially conducted, so that their alternating conduction converts direct current into high frequency square wave alternating current, which flows through the high-frequency primary transformer and is then subjected to rectification to supply an output of low voltage direct current. Each IGBT is connected in parallel to resistor and capacitor, which constitute a peak voltage absorption circuitry.