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When is a uF not a uF ?
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mzzj:

--- Quote from: tautech on October 04, 2019, 02:13:40 am ---

Simply, because tants are fast you need a much larger capacitance to absorb the same spikes that a tant can.


--- End quote ---
Define "speed"

I see tantalum drop-ins more like fashion during certain period..

compared to electrolytics:
+more stable ESR vs aging vs. temp?. Not necessarily any lower ESR than al-electrolytic and the ones that I managed to find from my parts drawer actually had higher ESR than bog standard al-electrolytic!
+lower leakage? (haven't actually measured and historic specs of tantalum drop-in ignitors are scarce so this is more of hear-say)
+"longer life" (but NASTY failure mode)
+possibly higher capacitance in same size... again very much debatable what benefit you have left after you derate the tantalums below volcano-mode. 
tautech:

--- Quote from: mzzj on October 04, 2019, 05:32:14 am ---
--- Quote from: tautech on October 04, 2019, 02:13:40 am ---

Simply, because tants are fast you need a much larger capacitance to absorb the same spikes that a tant can.


--- End quote ---
Define "speed"
--- End quote ---
Comparable to ceramics.


--- Quote ---I see tantalum drop-ins more like fashion during certain period..
--- End quote ---
You might but they still have a place in designs like todays SMD high value tantalums.



--- Quote ---compared to electrolytics:
+more stable ESR vs aging vs. temp?. Not necessarily any lower ESR than al-electrolytic and the ones that I managed to find from my parts drawer actually had higher ESR than bog standard al-electrolytic!
+lower leakage? (haven't actually measured and historic specs of tantalum drop-in ignitors are scarce so this is more of hear-say)
+"longer life" (but NASTY failure mode)
+possibly higher capacitance in same size... again very much debatable what benefit you have left after you derate the tantalums below volcano-mode.
--- End quote ---
It might appear you are happy with using part parameters on the edge of reliability whereas once designers were much more conservative.
Tants are a good example where it is wise to overate them and a lesson the industry has learned.

They still have the advantage of offering the designer a single part that can provide both bulk capacitance and bypassing capability. They'll be with us until better technologies are developed.
mzzj:

--- Quote from: tautech on October 04, 2019, 06:47:55 am ---
--- Quote from: mzzj on October 04, 2019, 05:32:14 am ---
--- Quote from: tautech on October 04, 2019, 02:13:40 am ---

Simply, because tants are fast you need a much larger capacitance to absorb the same spikes that a tant can.


--- End quote ---
Define "speed"
--- End quote ---
Comparable to ceramics.



--- End quote ---
Bullshit.
I asked you to define "speed" because it doesn't really specify anything.

Tantalums and especially typical "classic" tantalum "drops" are much closer to al-electrolytic than ceramics for "speed"  >:D (high frequency bypass) .
Similar inductance and ballpark same ESR vs. ceramics that have something like 1000x lower ESR. 

Low ESR SMD tantalums are bit different animal but average tant drops are not that special.

http://datasheets.avx.com/tap.pdf  16v 10uF ESR 2.5ohm 1,2uA 5x10mm

vs. al-electrolytic
https://www.nichicon.co.jp/english/products/pdfs/e-upw.pdf 16v 10uF ESR 0.6ohm  4.8uA 5x11mm
or smaller version 16V 22uF ESR 0.95ohm 4x7mm

So al-electrolytic is both smaller size and lower ESR..
Lower leakage tho.
T3sl4co1l:
Heh no, ordinary (MnO2 electrolyte) dry tants have modest ESR.

Speed is:
τ = ESR*C

It's around, ohh, what's a typical figure for tant, 1uF and 2Ω, so 2µs?

Ceramics are easily 1/10th-1/100th of that.

Polymer tants improve this figure a bit, though you might opt for polymer aluminum because of price and conflict minerals.

It's noteworthy that tants of the same value as electrolytics, do tend to outperform them -- the electrolytic's impedance is complex, and rises at low temperature, while the tant is simple and stable.  This made them an excellent, premium-quality alternative back in the day, but we have many more options available today. :-+

Tim
mzzj:

--- Quote from: T3sl4co1l on October 05, 2019, 06:58:34 am ---Heh no, ordinary (MnO2 electrolyte) dry tants have modest ESR.

Speed is:
τ = ESR*C

It's around, ohh, what's a typical figure for tant, 1uF and 2Ω, so 2µs?

Ceramics are easily 1/10th-1/100th of that.

Polymer tants improve this figure a bit, though you might opt for polymer aluminum because of price and conflict minerals.

It's noteworthy that tants of the same value as electrolytics, do tend to outperform them -- the electrolytic's impedance is complex, and rises at low temperature, while the tant is simple and stable.  This made them an excellent, premium-quality alternative back in the day, but we have many more options available today. :-+

Tim

--- End quote ---

Typical esr numbers for 1uf tants look much worse than that, ie 10ohms for 1uf 25v drop.
http://datasheets.avx.com/tap.pdf
Old ones I had in junk boxes were about same range or even bit worse.
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