Reference voltage circuit for personal computer capacitive discharge switch - uses reference voltage derived from primary side of computers isolating transformer to supply capacitive discharge switch

摘要

A variable reference voltage produced from a high-resistance variable potential divider (25, 27, 29) is fed to the secondary side (23) of a main isolating transformer (21, 11, 23) via a remotely controlled switch (31). The latter is governed by a relay (39) which ensures that the reference voltage is alternately added and subtracted from the alternating secondary voltage, this being in turn defined by a polarity switching current supplied via a triac (37) connected across the primary circuit. The reference voltage bypasses the PC power supply via two capacitors (73) and fed to a capacitive sensor circuit comprising a discharge plate (47), detector amplifier (51), integrating amplifier (53) and switching circuit (69). When the discharge plate is touched, the rise in potential caused by the stray charge flow to the plate is amplified and integrated to provide a signal to operate the switching circuit. ADVANTAGE - Provides accurate reference voltage that is not subject to variations found in earth/chassis reference circuits.