An Approach to Identify Noise-Source Parameters of DC–DC Converter and Predict Conducted Emissions With Different Loads

The black-box equivalent-circuit model is generally used to predict electromagnetic interference (EMI) from dc–dc converters for assisting with filter design. We previously proposed a Norton-based two-port equivalent-circuit model excluding load to investigate the load effect on EMI. The EMI prediction presupposes constant internal impedances independent of the load change with only the noise current source change dependent on the load change. Under these conditions, the noise current source at any load can be calculated by using the numerical interpolation method. In this work, we used a dc–dc buck converter with a switching frequency of 200 kHz and identified the model parameters precisely by applying the waveform decomposition method. The internal admittances were found to be almost constant with respect to load change and only the input-port current source decreased with load. We then applied the cubic spline interpolation method to fit the input-port current source and calculate it at any load. This approach was verified by predicting the input-port noise voltage for loads between 3.3 and
$15.6~\Omega $
. Below 80 MHz, where the input-port current source decreased with load, the input-port voltage predicted using the input-port current source fitted by interpolation was in good agreement with the measured one.