Question 40E6

Switching mode power supplies (SMPS) operate by rapidly switching the input voltage on and off to regulate the output. This rapid switching causes the SMPS to draw current from the AC line in short, non-sinusoidal pulses, rather than a smooth sine wave. Any non-sinusoidal waveform, according to Fourier analysis, can be decomposed into the fundamental frequency and numerous harmonics (multiples of the fundamental frequency). Thus, the input current has high harmonic content. Additionally, because these sharp current pulses are not smoothly in phase with the sinusoidal input voltage, and the current waveform itself is highly distorted, the apparent power drawn is significantly higher than the true power used. This phase difference and waveform distortion result in a low power factor. High harmonic content can be a source of electromagnetic interference (EMI) and radio frequency interference (RFI), which is a critical consideration for amateur radio operators. Options B, C, and D are incorrect because a basic SMPS inherently generates significant harmonics and operates with a low power factor without active power factor correction.