AC CURRENT CONTROL SYSTEM

PURPOSE:To attain continuous variable control to AC with comparatively simple constitution by connecting a common electrode of each FET in series via a feedback resistor, connecting an AC power supply to both ends and connecting one end of the feedback resistor to each input terminal of an operational amplifier. CONSTITUTION:In giving a potential of the same polarity and same amplitude to operational amplifiers 25, 26, a drain of a FET is at a positive potential by a potential of an output of the operational amplifiers, then a FET 41 is conductive and a FET 42 is nonconductive, for example. The nonconductive FET by the polarity of a certain time of an AC power supply 6 is conductive via a parasitic diode. In this case, the equivalent resistance of the conductive FET 41 is changed by the input signal to the operational amplifier 25. Thus, the current from the AC power supply 6 is controlled by the input signal to the operational amplifier 25 and proportional to the voltage value of the AC power supply 6. The state of the operational amplifiers and the FETs is inverted by the polarity after a half cycle of the AC power supply respectively, a current flows reversely and the value is controlled.