Analysis and Optimization of Power MOSFETs Shaped Switching Transients for Reduced EMI Generation

The abrupt change in current or voltage caused by the rapid switching action of power semiconductor devices will generate high-frequency electromagnetic interference (EMI) and needs to be located as the primary interference sources in power electronics. This paper deals with interference suppression on the basis of the study of shaped switching transients in switching waveforms and closed-loop gate drive method for power MOSFETs. The characteristics of switching waveforms with arbitrary switching transients are investigated in both time- and frequency-domain. In addition, conditions of constructing a switching waveform with optimized switching transients are put forward. An optimized Gaussian switching waveform with infinite successive derivatives is proposed which provides the deepest decreasing rate in the interference source spectrum for a given switching time. Compared with a trapezoidal waveform with single-slope transients, the proposed switching waveform has better interference suppression at high frequencies. Meanwhile, a closed-loop gate control prototype with on-state resistance compensation is presented to shape the switching transients of power MOSFETs. The simulated and experimental results show that the proposed controller is successfully implemented to shape the drain-source voltage into an optimized Gaussian reference. Spectrum comparisons show that the EMI generation is effectively suppressed as expected.