Fourier Series Triac Switching Waveform

Cuthbert Nyack

When used in power applications, a Triac switches during both the positive and negative half cycles( voltage waveform is shown in yellow in the applet below). The resulting current waveform is shown in red. The even coefficients of the spectrum are shown on the left and the odd coefficients to the right. With a gain of 1, vertical range for the spectrum is from +1 to -1. Waveform has unit amplitude. It is assumed here that switching occurs at the same point on positive and negative half cycles. In practice this may not be the case.
The applet shows the value of the spectral component at ndb as a ratio of the component at n = 1. If the Fundamental is at 50Hz then ndb from 10,000 to 30,000 corresponds roughly to the AM band. The attenuation in this range is ~ -87 to -97dB. If the fundamental is ~ 100V then the component at ndb is still ~ 3mV. Depending on the radiation characteristics of the circuit and the current in the circuit, this is still large enough to affect an AM receiver.

When activated the following gif image show how the applet should appear.

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