DVM_POLARITY_INDICATOR

Published:2009/7/15 3:51:00 Author:Jessie | From:SeekIC

Designed for use in low-cost digital voltmeters. With input polarity as indicated, arrows on connections indicate direction of current flow. When NPN Q1 is on, LED 2 will be on; with PNP Q2 on, LED 1 will be on. Darlingtons Q1-Q2 draw very little current, so choice of type is not critical. AC supply is usually available in lab but can be replaced by internal clock of DVM driving small transformer to give required floating AC source, A, B, C, and D identify nodes of bridge.-R. A. Snyder, Polarity Indicator Minimizes Parts Count, EDN Magazine, Feb. 20, 1977, p 121.



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