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....
See details at:
Rich
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.
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.
What is it you've captured? That signal has a period of 100us (10kHz), but a standard ringing signal is usually 20Hz.
Bob
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
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.
LOL- subtle...
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]--+---|>|---+----|
Hmm, I guess my first question would be: 1. Are you using a 10:1 probe to measure that?
---------------- 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?
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
-- Deep Fryer: A very philosophical monk. Website @
How about an analog scope - could the digital sampling be playing tricks?
joe
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