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Old 20th February 2019, 10:09 PM   #11
chris719 is online now chris719  United States
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Originally Posted by MarcelvdG View Post
I avoid tantalum capacitors whenever I can because tantalum ore is a conflict mineral (see Coltan - Wikipedia ) and the datasheets almost never mention where the tantalum comes from. Unfortunately the same holds for tin and gold, but I don't know any good alternatives for those.
Kemet claims to source 100% conflict-free tantalum, but I don't know the exact details.

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Old 22nd February 2019, 03:39 PM   #12
Vovk Z is offline Vovk Z  Ukraine
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1 uF - "usual" low voltage rated film (63-100 V, not PP), 10 uF - tantalum with large enough rated voltage margin ( 2x ), or polymer.
Non-NP0 ceramics in time-dependent circuits - it's not right, I think.

Last edited by Vovk Z; 22nd February 2019 at 03:46 PM.
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Old 22nd February 2019, 04:19 PM   #13
RJM1 is online now RJM1  United States
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The last year that I worked for Rockwell-Collins They issued a directive that all new designs using
tantalum capacitors must have a 10 ohm resistor in series with the capacitor. (Pilots tend to freak out when they smell smoke in the cabin.)
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Old 23rd February 2019, 12:29 AM   #14
wg_ski is offline wg_ski  United States
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I’m thinking ceramic is the way to go in the pulse coupling position. I ordered 22 uf, to go where 10 uf aluminum electro used to be. It has to deal with charging 13000pF worth of hexfet input capacitance thru a 15 ohm resistor. And has to do it at the audio rate. Mostly subwoofer trequencies, but I don’t want any stupid behavior at 20kHz either. I was somewhat concerned about the 25 rating on caps that big, but it seems the rating is more driven by capacitance loss than by “it will blow up if you hit it with 30 volts” (which is 2X what it would normally see) or “one amp for 200ns at a time is bad news”.

The other target applications won’t see much stress, but I really don’t want to deal with caps getting leaky over years of use. A 1 megohm charging 1 to 2 uf on a 555 timer for instance - works pretty well initially. Then it takes longer and longer for the relay to kick in, and eventually it just won’t anymore. I’ve had to replace too many of them, both in DIY and store bought amp supervisor circuits and I’m sick of it. I doubt a tantalum would catch on fire, but if it’s just as unreliable as aluminum I’d rather use something else. Stay with the ceramic (with only 5 volts on it where it ought to have well over half it’s capacitance) or go to a fractional-uf green mylar chicklet and up the resistor to 10 meg?
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Old 23rd February 2019, 12:01 PM   #15
indianajo is offline indianajo  United States
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Ah, yes, timer circuits. I've been using ceramic 1 uf up in timers since the late seventies. Those circuits are still working, whereas the power up silence circuit in Allen organs pretty much silences all of them by 25 years due to the electrolytic cap they used.
Voltage modulation of the capacitance is not critical in non-amp circuits.
My use of 50 v ceramics in amps for couplers for 2 v signals indicates to me the fear of them is oversold. Any affordable speaker covers distortions in the 2nd decimal place and probably the 1st also.
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