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A guide on bypass capacitors — Parallax Forums

A guide on bypass capacitors

Paul BakerPaul Baker Posts: 6,351
edited 2005-11-09 07:56 in General Discussion
Time to time someone asks in the forums what values should be used for bypass capacitors, with the answer that it is a little bit of a black art. EDN has a new article out that discusses the issue and provides formulas for expected di/dt switching noise and the minimum value capacitor required to counteract it, the article is located here. One word of warning though, to fully understand the article you'll need to know a little theory, but they present formulas that can be used by any general hobbyist who understands basic algebraic formulas.

If anyone wants a copy of any of the IEEE articles suggusted in the "Read more about it" box, let me know and I'll get a copy of it for you, I have access to the entire IEEE and ACM databases.

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·1+1=10

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-11-08 20:27
    <sigh>· I remember the good ol' days where in a digital circuit a .1µF capacitor on the power leads to each chip would be sufficient.· Now there's formulas and such.· =)

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2005-11-09 07:56
    Nuts and Volts recently had a guide to capcitors and even mentioned using a mix of ceramic, tantanlum, and electrolitic to get the optimal filter.

    Sad to say, I came across a comment the The Art of Electronics that mentioned the combination of a ceramic and tanatanlun intended to filter can actually create a parasitic oscillator due to the inductances in the radial leads.

    This is an area where 'tweak' is the best solution and in order to do so I suspect you have to have an O-scope watching the effects of change. I also suppose it is why everything has gone to SMS as the clock frequency has climbed. If it is slow, you have less worries.

    I must say that some of it is marketing exploiting imagined ills [noparse][[/noparse]like the doctor telling you to eat more fiber]. More filters usually can't hurt. But, then there is that parasitic oscillator to ponder. Hmmmm........

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    "When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

    ······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
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