RING_DETECTOR

Published:2009/7/14 21:54:00 Author:Jessie | From:SeekIC

Optoisolator using neon lamp and light-dependent resistor serves as interface between telephone line and line-operated remote bell. Neon fires reliably from nominal 100-VAC ring signal, while capacitor C1 provides isolation required to prevent latch-up by sustaining voltages within range of phone-line quiet battery. If optional protective varistor RIC1 is added, rating of capacitor can be reduced to 400 V. Triac Q1 in series with primary of line transformer provides synchronization to 20-Hz ringing frequency of phone system.-W. D. Kraengel, Jr. Ring Detector Optically Interfaces Phone, EDN Magazine, Aug. 5.1978, p 80 and 82.



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