Abstract: An electrical power control apparatus in which power to a load is shared between a plurality of power semiconductors, only one of which is shown. Each power semiconductor forms part of a separate servo loop comprising, in its simplest form, a current sensor whose output signal modulates the output pulse width of a signal generator. The output from the signal generator is used to control the conduction times of the power semiconductor via drive circuit. Although it is possible, indeed desirable, to synchronise operation of the signal generators of the different servo loops, the loops are completely independent of one another, and the instantaneous pulse width of the drive pulses in any one servo loop is controlled only by the characteristics of that loop.

Abstract: A welding wire feeder system for an electric arc welder in which the wire feed motor M is powered from a pulse width modulated power supply comprising a power transistor Q10 controlled by a pulse signal on line 31 from a pulse width modulator comprising an integrated circuit A3. A control voltage proportional to the arc voltage and a feedback voltage indicative of the feed motor speed are generated and applied to respective inputs of a high gain amplifier A4-1 whose output error signal is either high or low dependent upon the relative values of the control and feedback signals. Control is effected in such a manner that an increase in welding arc voltage causes a corresponding increase in the welding wire feed rate, and vice versa.