Column: EMC


Designing filters with simulation By Dr Min Zhang, EMC consultant at Mach One Design, and design engineers at REO UK


M


ost noise is generated by high-frequency, fast-switching devices, such as drive inverters, DC-DC converters and


microcontrollers. For this reason, filters are oſten designed to suppress noise caused by switching events. In the past, IGBTs and MOSFETs


were the main switches; MOSFETs were predominantly used in low-voltage applications, with IGBTs in medium-voltage ones. For voltages above 800V, insulated gate commutated thyristors (IGCTs) and gate turn-off thyristors (GTOs) are preferred. MOSFETs switch quicker, but they are


limited by their voltage rating and thermal properties. Typically, they are limited to switching frequencies up to 150kHz; their rise time is oſten in the tens of nanoseconds. IGBTs have a tail-current, which limits


their switching frequency (generally to about 60kHz) and switching speed. Tis will soon change as wide-band-gap


Figure 1: Spectrum of a 60kHz switching event with a rise time of 5V/ns


Figure 2: 10V/ns rise time spectrum (blue) vs 5V/ns rise time (green) 10 March 2023 www.electronicsworld.com


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