Charles Steinmetz wrote:
Every so often, the subject of logging the zero-crossings of the AC
mains comes up. There are any number of ways to couple the AC mains
to logic circuitry (coupling with very high value resistors,
capacitor coupling, and optical isolation have been mentioned). A
simple AC mains ZCD that is transformer isolated and gives excellent
results, is posted at ko4bb.com:
<http://www.ko4bb.com/manuals/download.php?file=05_GPS_Timing/Simple_AC_Mains_Zero_Crossing_Detector.pdf>
The ZCD uses a small, dual-primary power transformer, two
transistors, and a few diodes, resistors, and capacitors. It
produces a ~100uS logic-level pulse at every positive zero-cross, the
leading edge of which is predictably and stably related to the AC
mains zero-cross.
Best regards,
Charles
I'm not trying to downplay the circuit in the link above, but I want to
offer another possible solution to Zero-Crossing needs.
Here's an Idea For Design from EDN magazine that I've used a couple times in
non-time-nut circuits, and I must say that it works beautifully. I have no
measurements that would satisfy a time-nut's curiosity, so if someone wants
to Spice it or otherwise tear it apart, please do..
My use for the circuit was in a spot welder control; the output was used to
sync and cycle a counter-driven trigger for an alternistor, all of which
controlled the number of power line cycles that the welder transformer
received for the weld. It worked well for me until I sold the whole
contraption. Don't know whatever happened to it after the guy moved away
from the area; never heard from him again. I hope it's still working.
http://electronicdesign.com/analog/differential-line-receivers-function-analog-zero-crossing-detectors
Dave M
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