Fundamental wave

The lowest-frequency sine waveform that composes the AC waveform. An AC waveform, excluding the sine wave, is composed of the fundamental sine wave and harmonics. When a distorted AC waveform is expanded by Fourier series, it can be separated into the fundamental wave and harmonics. In switching power supplies, this fundamental wave is used as the basis for on/off operations, making it a critical waveform that determines the behavior.