Power control circuit arrangements

Claim 1

A power control circuit arrangement for controlling the a.c. power in a load, comprising means for deriving a direct current voltage proportional to the a.c. power applied to said load from voltages proportional to the a.c. current flowing in the load and the a.c. voltage across the load, respectively; the voltage proportional to the load current is compared by a comparator with the sawtooth waveform output of a linear ramp generator and the voltage proportional to the load voltage is combined with the output from the comparator to produce a pulse train representative of the load current and voltage, the pulse train then being applied to an averaging circuit to produce said direct current voltage proportional to said a.c. power applied to the load; and means for comparing said direct current voltage with a voltage representing nominal power to the load to provide a d.c. signal the amplitude of which is utilised in conjunction with a staircase or ramp generator to add or deduct cycles of the a.c. power to or from the load circuit according to a predetermined load power rating and in dependence upon variations in the a.c. supply voltage to the load and changes in the resistance of the load.