Re: Looking for two-input comparator with hysteresis
- From: Keith <krw@xxxxxxxxxx>
- Date: Tue, 23 May 2006 13:33:42 -0400
In article <44734782.2000200@xxxxxxxxxxxxxx>,
cdt22NOSPAM@xxxxxxxxxxxxxx says...
Hi all,
I'm building a digital clock circuit which will use the AC mains
frequency for time keeping. I need a circuit (preferably a single IC)
which can be connected via a transformer to the mains supply, and will
send one output pulse to my TTL for each complete supply cycle. I think
it would be good to include some hysteresis in case the AC mains
waveform is noisy. I'm concerned about using a simple Schmitt trigger,
where the input is taken relative to the lower power rail, in case I
create a loop which causes a large current to flow back through the
linear power supply. So I'm looking for a comparator with two high
impedance inputs and hysteresis. Does such a thing exist as a single IC?
Any suggestions would be much appreciated.
Use an optical isolator to connect to the line, even if there is an
isolation transformer inbetween.
Depending on your clock circuit, it may be eaiser to do the
filtering in the digital domain. After the isolator turns on wait
1/119th of a second to look for it to go off, then 1/119th of a
second for it to turn back on...
--
Keith
.
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