[time-nuts] Line Frequency

Chris Albertson albertson.chris at gmail.com
Sun Feb 9 19:48:51 EST 2014

On Sun, Feb 9, 2014 at 3:11 PM, M. Simon <msimon6808 at yahoo.com> wrote:

> Hal,
> The resistor H bridge with a capacitor in between sounds like a good idea.
> Yes - I'm starting with a wall wart. About 12 VAC.  Maybe a couple of back
> to back diodes (zeners?)

The normal clamp design uses two normal diodes both pointing the same
direction and in series.  Theses span the power supply rails.  Of course
they are installed in the direction where they do not normally conduct.
 Your signal goes to the point where the two diodes connect.  No Zeners.
 The 1N4000 series or anything like it  would be fine.  If the signal goes
higher than the higher voltage rail then the diode that connects to that
rail will conduct.  A resister in series with the input signal will limit
current to what the diode can handle.  Knowing that you can limit current,
a smaller (and faster) switching diode made be used.

I use this diode clamp setup an an Anemometer that produces AC current with
frequency proportional to wind speed.  The diodes clamp the voltage (which
can get up to 12V i a storm) just fine.  I'm using a cheap lm311.

But if this is feeding an RS232 port, the port is designed to handle about
+/- 12 volts so you'd only be protecting from shorts and other accidents.

Zeners are good for lightening protection.  So are MOVs and you might want
these on anything connected to mains power but in your application I'd just
use a handily "spike bar" aka "surge protector".


Chris Albertson
Redondo Beach, California

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