Voltage controlled variable capacitor based snubber for the further reduction of IGBT´s turn-off loss

A voltage controlled variable capacitor based snubber is proposed in this paper for the further reduction of IGBT´s turn-off loss. The variable capacitor is composed of two capacitors and an auxiliary MOSFET with both turn-on and turn-off automatically. This kind of voltage controlled variable capacitor (VCVC) snubber performs large capacitor characteristics in the early turn-off period while the auxiliary MOSFET turns on automatically and switched to a small capacitor performance when the auxiliary MOSFET turns off. At the same time, the voltage across the capacitor, which is in series with MOSFET, is reached to the turn-off threshold voltage. The additional loss of the auxiliary MOSFET is very tiny and can be negligible. The operating principles of VCVC based RCD snubber is analyzed in detail and the additional loss is derived in this paper. The advantage of this kind of snubber is verified experimentally with a prototype of Buck converter.