Jay wrote:
Q3: The open-ended question: How do I improve on this? I suspect the
main place for improvement will be in the trigger, but I'm not sure
where to go with that. Most designs I've seen involve a schmitt
trigger, generally with reference voltages set by things like
voltage dividers. This seems dubious at best, to me, since that
means the reference voltage will be affected by the same effects I'm
calling out above. Is there a *specific* design (rather than "make a
zero crossing detector!" or something similarly vague) that someone
can point me to, that would minimize this kind of trigger noise?
Q3.1: Is there a better way to get mains voltage down to something I
can work more directly with? I saw at least one design that just
used a couple of megaohm resistors inline -- does that introduce
appreciably less phase noise than random AC/AC power brick?
I posted a very simple circuit that performs very well some time
ago. It can be found here:
<http://www.ko4bb.com/getsimple/index.php?id=download&file=02_GPS_Timing/4_App_Notes_and_Articles/Simple_AC_mains_zero_cross_detector.pdf>
This circuit was designed specifically to avoid the problems with
Schmitt triggers and with iffy input circuits. It is transformer
isolated, but uses the second primary winding of a small dual-voltage
power transformer for input (i.e., 120v), which is immediately
dropped by resistors into a diode clamp. Why? Because the higher
the voltage you start with, the faster it slews through the zero
cross and, therefore, the more precise the trigger point will
be. Using a 120v winding gives you a 10x slew rate advantage
compared to using a 12v winding. Free gain, free precision!
There was some on-list discussion starting on 12/16/14, with the
Subject: "Simple AC mains zero-cross detector". (I'd include a link
to the first message in the thread, but febo.com appears to be down
at the moment. Use the link at the bottom of this message, choose
list archive, then choose December 2014 and display the messages by date.)
Best regards,
Charles
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
