Understanding the Kelvin pin mitigation of the MOSFET turn-on losses by fast-switching and neutralization of the clamp diode

The super-junction MOSFETs enhanced with an additional source, called Kelvin pin (4-lead), are faster than traditional three-terminal MOSFETs (3-lead). Moreover, the former presents a lower increment in the turn-on power losses as the load increases. This paper investigates the phenomenon and explains this behavior. The drain-source voltage waveform of the 3-lead device usually presents a plateau due to the voltage drop across the parasitic inductances during the current rising and to the clamp imposed by the diode until it conducts. The higher current speed of 4-lead involves that the plateau should occur at a lower value of the drain-source voltage, then this voltage takes longer to reach this lockout value. On the other hand, the higher current speed involves a reduced time necessary for the 4-lead device to reach the boost inductor current, thus unclamping earlier the diode. Consequently, the plateau does not occur thus achieving reduced turn-on losses. The plateau extension is small in the 3-lead MOSFET at low current and it increases as the current increases, thus the advantage increases as the current increases. The formulation and argumentation supporting the understanding of this phenomenon can be applied also to faster power devices like the SiC MOSFET and the GaN HEMT.