Replacing Poorly Reputed Aluminum Electrolytic Capacitor with Aluminum Polymer Capacitors

For a several years now, I have strayed away from the use of wetted Aluminum Electrolytic capacitors (aka e-cap) in most of my SMPS designs.  Tantalum Capacitors are decades gone from my repertoire. This is namely a result of personal experience, where I had a very expensive flat panel TV blow out literally days before the warranty expired.  I will never forget my early experiences, way back in the 80’s, where goggles were recommended attire when designing high power switch-mode power supplies.

The downside to using a bank of Multi-Layer Ceramic Capacitors (MLCC’s) is the cost, and real estate.

Enter a newer technology, Aluminum Polymer Capacitors.  Yah, these babies were really introduced in the early 2000, but were extremely expensive. They are not only slightly higher in cost relative to e-caps, but well below the cost of banked MLCC’s of similar µF.

These come in the same form factor as the wetted e-cap cousins, yet are not susceptible to drying out as a factor of time.  This has a huge impact on lifetime derating.  e-caps generally double for every reduction of 10 degrees.  Yes, I know there are secondary affects, such as ripple current, etc that may contribute, but first order of magnitude is simply based on operational temperature.  I’ll cover the ripple current as well later.

For Al-Poly capacitors, the rule of thumb is a 10X increase for every 20 degrees, and this is multiplicative.

Considering a 1000h, 125C rated capacitor, the following tabulates out:

Operating Temperature	Aluminum Electrolytic Capacitor	Aluminum Polymer Capacitor
125C	1000h	1000h
105C	2,000h	10,000h
85C	4,000h	100,000h

Here is a chart available at Wurth:

So, as you can see the purported longetivity is way higher.

Ripple Current. Another scourge for e-caps. This is because they have roughly 10X the ESR of the new Al-Poly cousins. Higher ESR, higher heat. So, there is a magnitude of improvement with the new Al-Poly cousins.

Here is a good video explaining all of this:

I will continue to study these as time goes on, and update with any new learnings. Tah-Tah!