Published:2009/7/15 2:06:00 Author:Jessie | From:SeekIC
AC line voltage is rectified by D1 and filtered by C1. R2 and R3 form voltage divider that holds one meter terminal at half of rectified line voltage. DC is also applied to low-voltage calibration pot R6 through 3-W 117-V lamp or equivalent resistor PL1 which limits zener current. Any increase in line voltage increases voltage at R2-R3 junction while voltage at slider of R6 remains constant, so bridge unbalances and meter reads upscale. Zener is 70 to 100 V at 10W. R2 and R3 are equal and are from 8.2K to 15K. C1 is 50 to 100 /μF at 200 V, and diodes are power silicon with PIV above 200 and 100-mA rating.-W. P. Turner, Expanded Range Line Voltage Monitor, 73 Magazine, Jan. 1974, p 39.
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