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clipping a fast negative pulse
David Hess:
There is another way to make a precision clamp with diodes and it is very fast.
Use the signal, now low impedance, to drive the input of a diode bridge. Set the top and bottom currents through the bridge to produce the correct clamp levels into the load impedance. Some oscilloscope input protection circuits used this method as shown below in the Tektronix 1GHz 7A29 vertical amplifier.
Marco:
That's more a clipped voltage follower, the input does not provide the power and is not itself clipped.
The only reason I can think of for the requested circuit is that the flyback voltage on the primary of a transformer needs to be limited to a precise voltage to also generate a precise voltage on the secondary.
T3sl4co1l:
Wait. Why are you clipping the pulse you fought so hard to perfect?
Tim
brumbarchris:
--- Quote ---Wait. Why are you clipping the pulse you fought so hard to perfect?
--- End quote ---
In order to further signal process it and feed it to an ADC eventually.
--- Quote ---A basic simulation here:
http://tinyurl.com/y4eeqnjd
it shows that the negative edge is clipped well, but so is the positive edge due to the supply rails of the op amp (+-15v) so that can be a limitation.
Also it has so sink / source considerable current in order to do that (about 30mA which is on the high side for op amps, they're not meant for driving loads)
--- End quote ---
Hey, nice simulation. But it actually suggests the circuit would work. Clipping the positive side of the signal is not a problem, as I do not need to clip a sinewave, but a mostly negative waveform, as indicated in the OP. The opamp will have to be appropriately selected, of course, speed and current output are critical, offset and other usually important parameters not so much, in this case.
--- Quote ---See that quick and dirty schematic, hope you get the point. Component choice is up to your requirements, choose R2 to limit the current into the OpAmp input to a level typically lower than 5mA, better 1mA (check the datasheet and appnotes).
--- End quote ---
Thank you for the suggested schematic, kapitän, but would that circuit be any more accurate than the clamping diodes? Their forward voltage varies quite a lot!
Best regards,
Cristian
Marco:
What's there to ADC if your clipping circuit works?
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