The recent article Soldering iron – temperature control failure gave a plot of V’rms vs conduction angle for a simple full wave phase controlled AC waveform, and I have been asked to explain the derivation.
The phase controlled switch turns on at some delayed time from the zero crossing of the AC waveform, and conducts until the next zero crossing.
With the simplest circuits, there is a practical limit to the achievable stable range of conduction angle, and a minimum of about 50° to a maximum of about 160° is typical.
The RMS voltage is the square root of the mean of the square of the instantaneous voltage. We can write an expression for the normalised RMS voltage as a function of conduction angle θ. Continue reading Normalised RMS voltage of a full wave phase controlled power waveform