Effect of External Gate-Emitter Capacitance on Turn-Off Loss of IGBT Devices

Abstract

Although an external gate-emitter capacitance (C_GE(ext)) has been proposed to reduce the turn-on loss of insulated-gate bipolar transistors (IGBTs), its effect on the turn-off loss (E_off) has not been investigated in detail. In this study, the effect of C_GE(ext) on E_off in an IGBT was investigated. In the case of a relatively low gate resistance (R_G), C_GE(ext) does not affect E_off; thus, the turn-off behavior is independent of C_GE(ext) and R_G. In contrast, in the case of a relatively high R_G, C_GE(ext) affects E_off. When C_GE(ext) is connected to the input terminal of an IGBT, the dV_CE/dt decreases owing to the increase in the effective gate charge (Q_G) due to the addition of C_GE(ext), thereby increasing the value of E_off.