B. Switching Characteristics of Npt- and Pt-igbts under Zero-voltage Switching Conditions

Recently, the demand for high voltage and high power IGBTs has been increasing. In order to achieve a device structure with high voltage blocking capability in the 1,200V range, the non-punch-through (NPT) type with non-buffer layer IGBT has become popular. Commercially available devices today in the 600 V range are mainly PT type, and in the 1,200 V range are mainly NPT type. These two device types behave differently in on-state voltage drop and dynamic switching because of their physical structure and carrier lifetime control. In a practical application circuit, the switching characteristics can be affected by parasitic components, temperature, and diode reverse recovery characteristics [1]-[2], [4], [8]-[11]. In general, the fundamental switching characteristics that are of concern in applications are: 1) di/dt and dv/dt device stresses, 2) turn-off tail current and switching energy, 3) high switching frequency capability, and 4) interaction with diode reverse recovery. Such fundamental characteristics can be changed with externally connected circuitry. Recently, it was found that the IGBT switching characteristics were further influenced by external soft-switching circuitry [3]-[6]. However, different types of devices behave differently under soft-switching conditions. In a resonant snubber inverter (RSI) [3], the IGBT output is paralleled with an external snubber capacitor to reduce turn-off loss and turn-off dv/dt. This capacitor interacts with the output capacitance of the IGBT and affects the turn-off tail current magnitude and duration.