The Spark Gap Podcast - Episode 25

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Show Synopsis

Karl and Corey are joined by James Lewis of Kemet Electronics to talk about capacitors.

James was nice enough to setup a landing page for our listeners.
The best place to go to learn more about capacitors would be here!

General Capacitor Info:

Sparkfun has a really nice wirte up on capacitors.
There are plenty of basic tutorials out there, but I like this one best.

Wow! I had to go back to episode 33 to find Dave Jones talking about capacitors.
Still worth a watch even with his old, grainy camera:

Ceramic Capacitors:

Basic Info:

This app note from Johanson Dielectric is pretty easy to digest.
I like the assembly line pictures and explanations of the process steps for creating MLCCs.

Temperature Ratings of Capacitors:

One of the biggest things I took away from my conversation with James was that all capacitors are not the same.
Maxim seems to agree with me. Their basic premise of this article is that not all X7R capacitors are the same.

DC Bias Lowers Capacitance:

We talked about how applied DC Bias on a capacitor lowers its capacitance.
I found numerous articles on the web saying the same thing.

I particularly liked this article from Murata. For one, it has nice pictures. ha!
Also, I thought the second to last paragraph concisely answered the Why? question.
I’ll quote it here:

“Without a DC voltage, spontaneous polarization can happen freely. However, when a DC voltage is externally applied, spontaneous polarization is tied to the direction of the electric field in the dielectric, and independent reversal of spontaneous polarization is inhibited. As a result, the capacitance becomes lower than before applying the bias.”

Full article here:

Now, if you haven’t already checked out the landing page at http://www.kemet.com/sparkgap at least check out their webspice tool.
It does seem to be the best way to easily observe the effect that a DC Bias has on capacitance.

Microphonics in Ceramic Capacitors:

I was quite suprised to find this excellent demonstration of capacitors inducing a voltage on TI’s website.
But there it was:

Electrolytic Capacitors:

Aluminum Electrolytic

I am a sucker for cutaway views of capacitors. This App Note from Cornell Dubilier has them and tons more information about their Aluminum Electrolytic Capacitors.

Also, not direclty related, but I saw they have a ton more applications notes.
The even have an app-note on designing RC snubber circuits. Which are typically used to quiet switching noise of transistors.

Why does everything have to be so hard? Even a simple question like, “How long is this cap going to last?” has a complicated answer.
This app note from Nippon Chemicon spends a great deal of time discussing all of the factors that reduce the lifetime of Aluminum Electrolytic Capacitors.

Dielectric Absorbtion

Bob Pease wrote a couple times about Dielectric Absorption or “Capactior Soakage”.

Another thorough article written by Bob Pease on the subject of Dielectric Absorption.

Here is an article where they setup a simple experiment to see the effect of this phenomenon.

Tantalum Capacitors:

Obligatory Wikipedia Article on the topic.
There article actually includes a lot of information about the Polymer based Tantalum capcitors we spoke about.
Honestly though all the wikipedia articles on capacitors are really good.

Here is a whitepaper talking about Kemet Replacing MnO2 with Conductive Polymer in Tantalum Capacitors.
It definitely reinforces the information James told us about.

Vishay has a relatively succinct FAQ about their Solid Tantalum Capacitors.
Interestingly, they have Solid Tantalum Capacitors with built in “electronic” fusing mechanisms.

I also like the cutaway views of their Wet Tantalum Capacitors.

I don’t mean to downplay the safety concerns of using MnO2Tantalum Capacitors though.
So, here is a friendly reminder that they should be used only when proper to do so.
Beware! This could happen to your board if you even get near a Tantalum Capacitor:

Sparkfun hating on Tantalums. Now we know better than to dismiss all types of Tantalum capacitors.

Bypass Capacitors:

There is a ton of app notes about bypass capacitors.
To the point where I am slightly overloaded.
Here are just some app notes on different ways to increase the effective filtering bandwidth of your bypass capacitor circuits:

More Cool Stuff to Checkout!

I was quite impressed by the production value of Jame’s Electronic Tutorials.
Check them out here:

Also, James blogs at:


Personally, I really like his Open Source Reflow Oven Controller called Open Vapors:


If I had more time, I would have asked him about it.