A Frequency-Domain Study on the Effect of DC-Link Decoupling Capacitors

DC-link decoupling capacitors are generally placed near the power switches in the converter to minimize the parasitic ringing and voltage overshoot on the devices. In this paper, the influence of decoupling capacitors on the turn-off parasitic ringing of power MOSFETs is studied in the frequency domain based on a small-signal modeling approach. This new angle helps explain the effect of these capacitors in a simpler and more straightforward way compared to the traditional time-domain analysis, and provides a deeper insight into the problem. A rule of thumb about the selection of effective decoupling capacitance value can also be derived from this study.