ABSTRACT
Power supplies are both a source and a conduit for interference. Power supply filters are usually designed for frequencies below 30 MHz, often ignoring the high frequency power supply noise, which is often significant up to 50 MHz, and completely fail to filter higher frequency system noise. Linear supplies are the simplest. Start with a transformer to provide a voltage output of sufficient amplitude to provide adequate voltage for the worst-case conditions. Ferroresonant supplies insert a resonant circuit in the line transformer, then feed a rectifier circuit and ripple filter. Switching supplies consist of two basic elements, the Alternate current (AC) to Direct current (DC) conversion, followed by the DC to DC conversion. The approach to filter design is to design the CM and the DM filter separately, then combine them into one. Filter design needs to be compatible with power supply design.
