Description: Optocouplers simplify logic isolation from the ac line, power supply transformations, and the control of polyphase power systems. They help solve problems by keeping ac line noise and transients out of sensitive logic. Fairchild?s 6-Pin Dip Optocoupler family, with high surge voltage capability (7500 volts peak ac, 60 Hz, 1 second duration), allows designers to achieve their goals. This paper presents a power triac phase control circuit and contrasts it with the traditional zero- crossing circuit. The example circuit isolates the low level control circuitry from the ac line. It is able to control the speed of a universal motor or brilliance of a lamp. The universal motor is capable of high starting torque and wide speed range - commonly used in mixers, blenders, floor polishers, electric hand and woodworking tools, etc.