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| clipping a fast negative pulse |
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| dzseki:
Also a question: do you need to actually clamp that pulse or you just need an output voltage as per specified during the pulse? What about a "comparator like" feedback loop using an opamp that drives a shunt transistor, if the voltage is above say 0V the transistor is closed, if the pulse gets negative the opamp and the transistor would clamp the output at the threshold voltage. |
| StillTrying:
There's not enough clear information for sensible suggestions. Such as whether it's the 64V pulse that needs to be clamped, or it just needs to be prevented from getting to the next stage. And if the next stage is only ever going to see a very stable -0.8V then that's easy. :) |
| OM222O:
--- Quote from: dzseki on May 08, 2019, 04:09:28 pm ---Also a question: do you need to actually clamp that pulse or you just need an output voltage as per specified during the pulse? What about a "comparator like" feedback loop using an opamp that drives a shunt transistor, if the voltage is above say 0V the transistor is closed, if the pulse gets negative the opamp and the transistor would clamp the output at the threshold voltage. --- End quote --- the main question still remains: WHY WOULD YOU WANT TO CLIP A PULSE TO A VERY SPECIFIC VOLTAGE WITH LESS THAN 20mv ACCURACY! if a negative rail is needed, this a really bad way of generating it, and if it's done for protection purposes, then the accuracy should not matter :-/O |
| capt bullshot:
So the circuit doesn't have to absorb the pulse energy but just to limit the negative voltage to a stable level, and you can apply a high source impedance like that 2k2 resistor shown in your circuit? So one might consider a fast enough Rail-to-Rail I/O OpAmp to buffer the signal. Apply some coarse input protection using diodes, set its negative supply voltage to the desired clamping level and have your output clamped to the negative voltage. Or do you need a signal path without active devices in the non-clamping state, like your circuit? One can speed up the OpAmp by doing some biasing tricks to prevent output saturation in the non-clamping state. This will increase the clamping action at the falling edge of your signal. |
| SiliconWizard:
--- Quote from: OM222O on May 08, 2019, 05:01:45 pm ---the main question still remains: WHY WOULD YOU WANT TO CLIP A PULSE TO A VERY SPECIFIC VOLTAGE WITH LESS THAN 20mv ACCURACY! --- End quote --- I'm not sure why either. Especially since the OP mentioned at first that it should clamp between -0.8V and -1.4V. So if 20mV accuracy is needed, does that imply that this clamping voltage is going to be adjustable? Because this is the only way I see that those two requirements would match? |
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