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Introduction

Let me start by saying that I know what a snubber is and how to implement one. I learnt how to use them when developing power electronics. Needed to reduce EMI in switchers, but they are even more needed in order to not have exploding power FET's. Also often a trade-of between clean and efficient.

Example

So while being aware of the usefulness of snubbing, I was thinking about a filtering schematic that is used often in one way or another:

power supply -> Pi filter -> buck converter for point of load supply.

In the schematic below it's represented with a ferrite bead equivalent on the left hand side and input cap of buck on the right hand side, with an equivalent load of the buck of 1.5W on 12V supply rail. There's the 1nH inductor in between to represent a PCB track. Just look at the terrible 20dB peak, smack in the middle of the audio band. I wouldn't like anything like that feeding audio circuitry. without snubbing

Add 2 snubbers and look how clean it can be: with snubbing

Question

Other than accross switching elements with parasitic capacitance (mostly FET's and diodes), I don't ever see mentioning of snubbers. Why is that? Am I overcomplicating things, being paranoid, or do I have a blind spot somewhere that would render the snubbers in above example useless?

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  • \$\begingroup\$ That’s not a snubber. \$\endgroup\$
    – winny
    Dec 5, 2020 at 10:44
  • \$\begingroup\$ You can't be serious, right? Please read the more informative answers below. \$\endgroup\$
    – gommer
    Dec 5, 2020 at 11:05
  • \$\begingroup\$ The opposite. You read DKNguyens answer below. \$\endgroup\$
    – winny
    Dec 5, 2020 at 13:42

2 Answers 2

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They're referred to as damping components in this context, not snubbers. I assume because in power switching you're dealing with inductive kick from interrupting current, whereas in signal applications you're dealing with resonant peaking.

https://www.analog.com/en/analog-dialogue/articles/ferrite-beads-demystified.html

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  • \$\begingroup\$ So it was a blind spot after all, because I never knew the correct term for it. Although a (real) snubber could be caused by kickback, I always saw it as taming (parasitic) LC that gets excited somehow (by steep dV/dt). In that sense it works exactly the same as LC dampers. Ah well, same technique, different name by application. \$\endgroup\$
    – gommer
    Dec 5, 2020 at 11:25
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Implementing suitable DAMPENING of power rail filters has been discussed by several people here on stackX.

Curves with and without lossy components are excellent visual aids.

I found Rdampen = sqrt (L / C) to be a good starting value.

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  • \$\begingroup\$ I can only choose one answer. Damping seems to yield more on-topic results than dampening. So I choose the other one. But thanks for pointing out anyway. \$\endgroup\$
    – gommer
    Dec 5, 2020 at 11:28

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