Passive Balancing of Peak Currents Between Paralleled MOSFETs With Unequal Threshold Voltages

Abstract

The peak switching currents of two paralleled MOSFETs turned on/off by one gate driver could differ significantly owing to the mismatch in threshold voltages (Vth). The passive balancing method described herein employs one inductor and one resistor per MOSFET to force the currents to track with negligible penalty in loss. Sensors, feedbacks, and knowledge of gate-related parameters (such as gate charge, polarity of Vth difference, gate impedances, etc.) are not required. The passive components are designed using an inequality involving Vth, rise time, and unbalance percentage. The mismatch in peak currents is reduced from 15% to 1% between SiC MOSFETs tested at 20 A and 300 V with 19% Vth variation.