Method of and apparatus for half-cycle-average or R.M.S. load voltage control

A method for controlling the half-cycle-average magnitude of an A.C. voltage applied across a load from a higher magnitude A.C. source, comprising the steps of:

• (a) providing switching means connected in series between the source and the load for selectively completing the circuit therebetween;
• (b) enabling the switching means to allow a flow of current through the load for at least one time interval during each source A.C. waveform cycle;
• (c) sampling the magnitude of the voltage across the load at least once during each source waveform cycle to provide an adjustment signal;
• and
• (d) adjusting, responsive to the adjustment signal, the time interval during which the switching means allows the flow of load current to vary the mean-absolute-value of the load voltage magnitude to a value substantially equal to a desired value.

Apparatus for controlling a selected one of the half-cycle-average and RMS magnitude of an A.C. voltage applied across a load from a higher-magnitude A.C. source, comprising:

• switching means connected in series between the source and the load for selectively completing the circuit therebetween;
• means for enabling the switching means to allow a flow of current through the load for at least one time interval during each source A.C. waveform cycle;
• and
• means enabled by said enabling means for sampling the magnitude of the voltage appearing across the load during at least one time interval during only one half-cycle of each source waveform cycle when load current flows to provide an adjustment signal to said enabling means for adjusting the time interval during which said load current flows, to vary said selected one of said half-cycle-average and RMS load voltage magnitude to a value substantially equal to a desired value.