A probe for measuring the propagation of conducted EMI in power converters

Conducted EMI compliance is based on a single frequency measurement at the mains input of a power converter, using a line impedance stabilisation network (LISN). A measurement method based on a new probe is proposed with which the sources and propagation of noise can be measured. The characteristics of the probe are compatible with the LISN. The method adds time and frequency measurements within the converter circuit, to the standard LISN measurement. This added measurement flexibility assists in the identification of the noisy switching transients. Attenuation is added in the probe as a means to contain the power dissipation in the 50 /spl Omega/ instrument input impedance. The working of the EMI probe is illustrated with some practical measurements.