The op amp(s) I have in mind do not allow rail to rail inputs. Some of them will reverse the output if the input goes too negative. Since I'm only interested in signals near zero a couple of back to back diodes across the op amp input is the way to go.
Engineering is the art of making what you want from what you can get at a profit. On Monday, February 10, 2014 12:49 AM, Chris Albertson <albertson.ch...@gmail.com> wrote: > > > > >On Sun, Feb 9, 2014 at 3:11 PM, M. Simon <msimon6...@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 > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
