The topic of capacitors appears fairly engaging from the standpoint of getting low values of equal sequence resistance (low ESR) however there could be a problem which we see after we extract a small portion of a chart about these capacitors as taken from the Digi-Key web site the place we discover rankings for “Lifetime @ Temp.”. Please see the next (Determine 1) excerpt from Digi-Key:
Determine 1 Polymer tantalum capacitor lifetime at temperature (proper). Supply: Digi-Key
In all these years, I had by no means earlier than seen a “lifetime” score for every other capacitor varieties. For me, this specification raised heretofore unknown issues.
From a unique URL which sadly is not energetic: https://www.vishay.com/docs/42106/faqpolymertantalumcaps.pdf. We might discover a Q & A as proven in Determine 2.
Determine 2 An software be aware excerpt from Vishay for polymer tantalum capacitors. Supply: Vishay
Please take particular be aware of the phrases “….slowly take in moisture… “.
I downloaded the Vishay-Sprague file “polymerguide” which appears to explain these capacitors fairly nicely, however I discovered no info in that doc relating to “lifetime”. Thus, the query in my thoughts is whether or not the anticipated “lifetime” of polymer tantalum capacitors is the results of getting old led to by gradual however inexorable absorption of moisture from the setting.
Would a circuit board coating (parylene or one thing comparable) quell that moisture absorption getting old course of and lengthen the capacitors’ anticipated lifetime?
I have no idea however SOMETHING is limiting “lifetime”. Taking no matter it’s to be an getting old course of opens up a believable line of reasoning by way of Arrhenius’s Regulation which briefly acknowledged is that any getting old course of takes place at a price which doubles for every ten levels Celsius rise in temperature. Conversely, the speed of an getting old course of will get reduce in half for every ten levels Celsius fall in temperature.
This getting old subject has been addressed earlier than relating to movie resistors.
Making use of Arrhenius’ Regulation to this capacitor scenario, we will estimate as follows:
Lifetime = (Lifetime at Max. Temperature) * 2^((Max. Temperature – Levels)/ 10)
The variable “levels” is the precise temperature to which the capacitors can be uncovered.
For the six instances proven on the Digi-Key chart in Determine 1, we extrapolate six “lifetime” versus temperature curves within the plots of Determine 3. The little dots alongside every curve are the place “lifetime hours” will get doubled for every 10°C drop in temperature from their respective maximums.
Determine 3 Extrapolated lifetimes versus temperature, lifetime hours are doubled for each 10oC drop in temperature. Supply: John Dunn
John Dunn is an electronics guide, and a graduate of The Polytechnic Institute of Brooklyn (BSEE) and of New York College (MSEE).
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