Switching power supply EMC optimisation design method

Abstract

On the basis of serious electromagnetic interference (EMI) produced by power electronic equipment, parasitic capacitance existing between transistor and heat sink is considered as the main factor disturbing common-mode loop. Calculation model of parasitic capacitance is established by using finite element method and electrostatic field principle, and computing method is also derived. EMI improvement method for converter system is proposed by controlling the parasitic capacitance impedance. Experimental results show that changing the permittivity and thickness of the thermal conductive adhesive which are filled between the transistor heat-conducting plate and heat sink to can reduce the conducted interference.