JPS5784621A - Alternating current two wire type proximity switch - Google Patents

Abstract

PURPOSE:To reduce leakage current and to decrease the residual voltage at the same time, by providing a series control type voltage stable circuit at a DC output terminal of a rectifying bridge and providing a current shunt path in parallel with a current limit element. CONSTITUTION:When an output of a detection circuit is at H level, a transistor (TR)Q4 of a driving circuit 5 is conductive, and a thyristor SCR2 is conductive and an on output appears at AC input terminals (a), (b) of a rectifying bridge 1. In this case, a base current flows to a Qs of shunt path and a comparatively larger shunt current flows in parallel with a resistor 22, then even if the conduction angle of the SCR2 is increased, a sufficient driving current can be supplied to a detection circuit and the residual voltage can be reduced. When the output of the detection circuit 2 is at L level, the Q4 is nonconductive and the SCR2 is also nonconductive. An off output appears between the output terminals (a), (b). Thus, since the base current of the Q3 is interrupted, the output of a stable circuit 4 passes through only a resistor R22 and the leakage current can be reduced.