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I have a signal that's output from a summing amplifier that can change between 200mV to 500mV. I would like to clamp this signal to 350 mV. That's to say that the output of clamping needs to vary as per input up to 350mV and then not increase beyond this. How can this be done?

As I understand Zener diodes don't operate at these voltage ranges. And a resistor in series with a Schottkey diode in forward bias doesn't have a sharp transition between conducting and non-conducting, so much so that LT spice simulation is showing it more like a resistor voltage divider.

What other simple options are there to achieve this goal?

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  • \$\begingroup\$ Is it to protect a device? Can you clip signals prior to the addition? Can you amplify the signal from the summing amplifier then clip it then attenuate it? \$\endgroup\$
    – Julien
    Commented Jul 26, 2023 at 15:04
  • \$\begingroup\$ Would you consider an op-amp plus a diode 'simple'? How fast has it got to work? What's the load resistance? How accurate does it need to be? Temperature stability? Is a negative rail available? \$\endgroup\$
    – Neil_UK
    Commented Jul 26, 2023 at 15:05
  • \$\begingroup\$ How sharp do you need? \$\endgroup\$
    – Tim Williams
    Commented Jul 26, 2023 at 19:21

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You could use a Zener diode of, for instance 3V plugged to a negative voltage rail of -2.7V.

You could increase the gain of your summing amplifier then use a diode, then place a voltage divider.

You could also use a mosfet with a feedback from the output voltage that drives or not the fet.

You could use a transistor as an amplifier clipped.

I can think of many circuits that could do that but without knowing exactly your issue, my only recommendation is don't work with such small signals! All the components will bring you significant voltage tolerance. I would definitely try to amplify it before conditioning it.

Edit: Not all those solution will work well in any circuit. My point is without knowing more about the circuit, there are many ways one can accomplish OP's goal.

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    \$\begingroup\$ Oh, I like the add gain to the summer, pass it through a Zener and then go through a voltage divider to attenuate. This way only one more active component! Will try simulating this. \$\endgroup\$
    – EarthLord
    Commented Jul 26, 2023 at 15:23
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    \$\begingroup\$ A 3 V zener has a really, REALLY soft knee, probably worse than the schottky you dismissed. The idea of amplifying before the clip, then attenuating, is sound. If the signal is already coming from an amplifier, then you can change its gain simply, or better put the clipping components round the opamp. \$\endgroup\$
    – Neil_UK
    Commented Jul 26, 2023 at 15:49

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