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EMC Basics #3: Voltage regulators as crucial circuits

Posted: 23 May 2011 ?? ?Print Version ?Bookmark and Share

Keywords:EMC board? voltage regulator? parasitic oscillations?

After clocks and resets, we like to focus on voltage regulator circuits when doing an EMC board review. Voltage regulators can cause both radiated emissions and susceptibility problems. Emissions are the result of parasitic oscillations, and susceptibility is the result of radio frequency interference.

The first problem, parasitic oscillations, are due to high-frequency feedback from the output to the input. The criteria for an oscillator are (a) 180 phase shift from output to input, and (b) gain greater than one at the feedback frequency. Or, as the old saying goes, "Oscillators won't, but amplifiers will."

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