MULTIPLEXING_LED_DRIVERS

Published:2009/7/1 21:41:00 Author:May | From:SeekIC

Duty cycle of each display digit can be varied from 10% (full on with strobing) to less than 1% (almost off).Circuit uses 7490 and 7442 as 1-of-10 multiplex driver to strobe cathodes of display digits through Q1, Q3, etc and tum on required 7400 multiplex gate through Q2, Q4, etc. Outputs of7447 are polarity-inverted by QA, QB, etc, which can be Sylvania ECG 159 rated at 200 mA. Q1,Q3, etc can be EGG 123 or HEP S0002, while Q2, Q4, etc can be any silicon PNP transistor.-B.Hart, Cument-Saver Counter Display, 73 Magazine, June 1977, p 174-176.



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