MC14081

Used in three-phase applications in which direction of rotation of phases is critical, as in three-phase motors where reversal of two phases can provide disastrous reversal of motor. Line voltages are stepped down and isolated by control-type transformers, Each phase is half-wave rectified and shaped by 1N4001 diode and MPS5172 transistor, with additional shaping by MC14572 inverter. Shaped outputs of all three phases are combined in AND gates G1-G3 to give pulse out-puts sequentially. D flip-flops are connected to sense change in sequence of pulses caused by reversal of one or more input phases. Flip-flop output can be used to trip relay or other protective device for removing air conditioner or other equipment from line before it is damaged.-T. Malarkey, "A Simple Line Phase-Reversal Detection Circuit," Motorola, Phoenix, AZ, 1975, EB-54.