EMI Reduction Using Symmetrical Switching in an Application with an Unshielded Wire between the converter and the load

Abstract

An EMI reduction technique using two MOSFETs instead of a single MOSFET in a Buck converter has been investigated in this thesis. A circuit that implements this technique was designed, constructed on a surface-mounted technology printed circuit board and tested. The designed circuit is made up of an IRF 7307 consisting of a p-channel and an n-channel MOSFETs; plus the input circuit for the MOSFETs and a “errorhandling” circuit containing a p-regulator responsible for approximating the turn-on and turn-off times of the p-channel MOSFET and n-channel MOSFET, and also correct the effect of differences in the threshold voltages between the two MOSFETs. The analyses of simulations and measurements results show that the symmetrical switching (or double MOSFET switching) technique may successfully be applied to reduce the RF emission in the low frequency and medium frequency range when compared to the single MOSFET switching.