Study on the C OSS Dynamic Loss of Superjunction MOSFETs in Quasi-Resonant Flyback Converters

In this article, we study the output capacitance dynamic loss,EDISS, of superjunction (SJ) MOSFETs in the quasi-resonant (QR) flyback converter for the first time. A calorimetric method is used to measureEDISSof different SJ MOSFETs and numerical simulations are used to explore the electrothermal behavior ofCOSSin OFF-state SJ MOSFETs. Based on measured results, we find that theRCbuffer can reduceEDISS, and the more advanced the device is, the more effective theRCbuffer is. Based on simulated results, we find thatEDISSis mainly caused by the carrier movements in the lightly doped drift region during the charging and discharging processes. Each device has a critical voltage,V_ DS_CRL. If the minimal resonant drain voltage,V_ DS_MIN, is lower thanV_ DS_CRL, the neutral islands can be merged and a large current density occurs in the channel, leading to increasedEDISS. IfV_ DS_MINis higher thanV_ DS_CRL,EDISSis small or even negligible. The more advanced the device, the smaller the cell-pitch, the lowerV_ DS_CRL, and the largerEDISS.