Re: Looking for two-input comparator with hysteresis

On Wed, 24 May 2006 17:57:47 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@xxxxxxxxxxxxxxx> wrote:

On Wed, 24 May 2006 17:52:04 -0700, Don Lancaster <don@xxxxxxxxxx>
wrote:

Christopher Tidy wrote:
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.

Best wishes,

Chris Tidy

And the problem with a CMOS schmidt trigger is...?

Not much, really, except for crappy predictability.

Exactly one square output cycle per sine input cycle, forever, sounds
fairly predictable to me.

And, in the OP's case, some risk of sending a signal that's over-rail,
making the predictability problem even tighter.

Some day I'll explain ESD diodes to you, if you ask real nice.

John

.

Relevant Pages

  • Re: Looking for two-input comparator with hysteresis
    ... I'm building a digital clock circuit which will use the AC mains ... Not much, really, except for crappy predictability. ... Exactly one square output cycle per sine input cycle, forever, sounds ...
    (sci.electronics.design)
  • Re: Looking for two-input comparator with hysteresis
    ... I'm building a digital clock circuit which will use the AC mains ... I need a circuit ... Not much, really, except for crappy predictability. ... Exactly one square output cycle per sine input cycle, forever, sounds ...
    (sci.electronics.design)
  • Re: Looking for two-input comparator with hysteresis
    ... I'm building a digital clock circuit which will use the AC mains frequency for time keeping. ... I need a circuit 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. ... 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... ...
    (sci.electronics.design)
  • Re: Looking for two-input comparator with hysteresis
    ... I'm building a digital clock circuit which will use the AC mains ... Not much, really, except for crappy predictability. ... making the predictability problem even tighter. ...
    (sci.electronics.design)
  • Re: Looking for two-input comparator with hysteresis
    ... Christopher Tidy wrote: ... I'm building a digital clock circuit which will use the AC mains frequency for time keeping. ... I need a circuit 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'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. ...
    (sci.electronics.design)
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