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Browse Prior Art Database

Accurate Zero Crossing Detector

IP.com Disclosure Number: IPCOM000102903D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 27K

Publishing Venue

IBM

Related People

Sylivant, JW: AUTHOR

Abstract

The circuit shown in Fig. 1 switches as Vin crosses zero volts, going either positive or negative. When a zero crossing is detected, positive feedback causes the circuit to regenerate which promotes rapid switching and immunity to noise riding on Vin. After several R1-C time constants, the switching threshold returns to zero, ready for the next zero crossing. The advantage of this circuit is that it achieves noise immunity without introducing an offset in detection threshold levels normally present in circuits with hysteresis. Switching occurs at exactly zero volts.

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Accurate Zero Crossing Detector

      The circuit shown in Fig. 1 switches as Vin crosses zero volts,
going either positive or negative.  When a zero crossing is detected,
positive feedback causes the circuit to regenerate which promotes
rapid switching and immunity to noise riding on Vin.  After several
R1-C time constants, the switching threshold returns to zero, ready
for the next zero crossing.  The advantage of this circuit is that it
achieves noise immunity without introducing an offset in detection
threshold levels normally present in circuits with hysteresis.
Switching occurs at exactly zero volts.

      Fig. 2 shows an alternate circuit which achieves the same
results without requiring a capacitor.  This circuit would be better
for incorporating in an integrated circuit.

      Disclosed anonymously.