Spikes on Zener Clamp Circuit

I am using a zener clamp to regulate a messy signal down to a level that will cause an interrupt in a microcontroller. The circuit works fine but I am seeing some troubling spikes on the output, both negative and positive. The input signal is a reoccurring ~150Vpp ringing signal.

I would appreciate any ideas....

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Rich

Reply to
rich
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Those spikes look uncorrelated with your CH2 input signal. Do you still get them even if you touch the CH1 'scope probe to ground at the diode anodes? In electrically noisy environments, you can pickup huge impulses on a single-turn loop formed by connecting the probe ground lead to the tip.

You could add a little filtering to your input circuit using series inductance (e.g. ferrite beads) and/or shunt capacitance.

Reply to
Andrew Holme

High slew rate signals might result from inductive coupling of wiring near the clamp. The Zener clamps the conducted signal, but the wire in series with that signal can couple, as a transformer winding, to the input.

Reply to
whit3rd

What is it you've captured? That signal has a period of 100us (10kHz), but a standard ringing signal is usually 20Hz.

Bob

Reply to
BobW

I think you may be on to something. I will ground the scope probe right next to the tip and see what it looks like. The ferrites are a good idea too.

thanks

rich

Reply to
rich

On a sunny day (Wed, 19 Dec 2007 09:06:04 -0800 (PST)) it happened rich wrote in :

Why use a diode? A zener is a diode the other way around.

Reply to
Jan Panteltje

LOL- subtle...

Reply to
Fred Bloggs

Is it really necessary to dissipate a full Watt to drive a micropower input? This circuit has a fairly huge working input range of amplitudes it will handle at your frequency: View in a fixed-width font such as Courier.

. . . . . .-------------------> to INT . | . | . | . | Vdd (5V) . | D1 D2 | . sig >-[470k]--+---|>|---+----|

Reply to
Fred Bloggs

Reply to
Fred Bloggs

Hmm, I guess my first question would be: 1. Are you using a 10:1 probe to measure that?

  1. Do you have near by R.F. and maybe the diodes or uC input is rectifying depending on what side you check?
  2. Did you account for parasitic conditions with the construction of the traces, components etc... ?

---------------- P.S. Zeners are know to be slightly slow. Don't know if this is an issue on your end but it might be worth looking into?

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Reply to
Jamie

How slow? I've tested reverse recovery and 1N52xx's come out on par with

1N4148, which is to say, faster than my generator's falling edge I'm testing with. Just a little capacitance is all I get. If this is what you meant, then yes, big zeners (1N47xx, etc.) will slow things down a bit.

Tim

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Reply to
Tim Williams

How about an analog scope - could the digital sampling be playing tricks?

joe

Reply to
Joe G (Home)

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