Power polarity tester

Published:2012/8/24 22:46:00 Author:Ecco | Keyword: Power polarity, tester | From:SeekIC

This circuit can detect positive and negative polaritywith the power supply between 3V-30V and LED indicator. The test circuit is a constant current source. When the polarity of inputmeasured power iscorrect, T1 , T2are also turned o , the LED emitslight. The diode D2 allows T2 base voltage to maintain constant current . Thus, regardless of the size of conduction currentfromT1, T2will substantially send constant current. If the measured powerhas opposite polarity, the diode D1 is turned on, T1, T2 arecut off, LED goes out , the switch S1 can self-test the internal circuit of LED.



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