A New Filtering Technique That Makes Power Transistors Immune to EMI

This paper deals with the susceptibility of double-diffused MOS (DMOS) power transistors to RF interference. An nDMOS connected in the low-side configuration is considered and the failures that result from disturbances superimposed to the drain-source nominal signals are discussed. The susceptibility of power transistors to electromagnetic interference is analyzed referring to small-signal equivalent circuits and the influence of the transistor parasitic capacitances and wiring inductances is highlighted. The pros and cons of a common-filtering technique based on the use of decoupling capacitors are pointed out and a new filtering technique is proposed. The effectiveness of the analysis method used in the paper as well as that of the proposed filtering technique are proved by computer simulation and experimental test results.