Reduction of EMI in Switched Mode Converters by Shaped Pulse Transitions 2007-01-0361
An idea of reducing the amplitude of higher order harmonic frequencies from PWM switching pattern is presented and analyzed in this paper. For experimental studies a flexi-ble curve shaping circuit was developed and implemented for achieving and controlling smooth transitions in a DC/DC PWM controlled converter for a 12 V system. A comparison between trapezoidal and sinusoidal transitions is made and it is found that a sinusoidal transition gives better EMI performance without increasing the switching losses. In order to further reduce the EMI, a strategy of controlling the output voltage transitions in a MOSFET by “pre-charging” its gate is derived and investigated.
The developed practical circuit is tested with sinusoidal reference for a purely resistive load and an R-L load. Frequency responses obtained from simulations and measurements are compared and discussed.