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Old 09-17-2014, 07:49 PM   #1123 (permalink)
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Hi Dave!

A quick question about the spikes - they don't show up in the oscilloscope plots, even if I speed up the scope to where I see only part of the waveform. This shows up in the spectrum analyzer. How does that work? Am I getting paranoid about something that is barely visible? Then, at the resolver's zero crossings, there's a bunch of crap. Seriously crap - I don't know a better way to describe it. If I use my signal generator for a resolver input, it goes smoothly to zero, so I'm guessing it's not the resolver. From what I can see, there are no odd shifts or other hints that something's wrong at the zero crossing.

I'm using decoupling caps on every op-amp. You are suggesting microFarad sized caps, right?

I'm running 0.1 uF ceramic caps on every op-amp. Apparently that's not enough - the Microchip App note advised 1.0uF ceramic caps **in addition** to the 0.1uF caps.

The ST app note doesn't mention anything larger than the 0.1uF caps, although I did run two 10uF electrolytic caps on a previous design, one for the positive and one for the negative supply. This is a single supply design, and I was considering 10uF to help it out.

A few other app-note suggestions I'd like to run by folks:
1) a capacitor at the power op-amp's output, with a very small resistor to ground -because this is driving an inductive load, the "Boucherot cell" concept.
2) a high value (M Ohm) resistor to ground right after the decoupling capacitor at the filter op-amp's input

Thank you very much for your help!

- E*clipse

Originally Posted by dave koller View Post
On most of the breadboards I've tested in a noisy environment I have put massive numbers of .1 and .01 caps on all chip power leads as close as I can to the chips - and place them on all power lead, regulators etc... Helps so much to quench those transient spikes...
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