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Old 18th August 2014, 03:23 AM   #1
ammel68 is online now ammel68  United States
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Default Which Capacitors Should I Use?

When bypassing rectifier diodes and electrolytic filtering capacitors, is it better to use polyester film capacitors or X7R ceramic caps.?

Also, is it safe to assume that X7R ceramics are good for op-amp supply decoupling?

Thanks...
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Old 19th August 2014, 02:13 AM   #2
ammel68 is online now ammel68  United States
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Hmm...96 views and no replies.

Doesn't anyone here use capacitors in power supply circuits and op-amp circuits??
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Old 19th August 2014, 03:37 AM   #3
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For rectifiers almost anything beats nothing. Ideally it should be an RC snubber, but I just use a 0.1 uF polyester.

There should be other threads on bypassing electrolytics, with opinions on all sides. I believe if a bypass there accomplishes anything measurable, it means you either need the bridge bypass caps (at the bridge where they can do some good) or you need better bypassing at the circuitry (where it can do some good). The only advantage of bypassing big electrolytics is you usually have handy lugs to solder to. Unfortunately the inductance of the wiring makes them pretty much useless, compared to putting them at the other two locations.

You can't fix a big bad capacitor by putting a negligible-by-comparison capacitor across it, no matter how good, and you risk creating a resonator that you didn't want. Don't like that opinion, worry not, there are many others.
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Old 19th August 2014, 03:48 AM   #4
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X7R are good for local decoupling of opamps. As far as I understand it, the ESR of X7R dielectric lends itself well to this role.
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Old 19th August 2014, 03:49 PM   #5
ammel68 is online now ammel68  United States
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Gentlemen, thank you for the replies.

I'll use .1uF polyester caps across the rectifiers and X7R ceramics for op-amps.
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Old 19th August 2014, 05:51 PM   #6
RJM1 is offline RJM1  United States
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Please see this thread!
Simple, no-math transformer snubber using Quasimodo test-jig
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