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From: John Larkin on 21 Feb 2010 13:17
On Sun, 21 Feb 2010 11:46:07 +0000, Nemo
<zzz(a)nospam.nospam.nospam.nospam.co.uk> wrote:

>I said...
>
>>(I like to run caps at about double their rated voltage under the
>>impression this improves their reliability).
>
>Ahh... meant I to write half their rated voltage. Well, it shows you
>were paying attention! 8)
>
>Thank you for the advice. OS-CONs it is!

United Chem-Con makes some nice polymer caps too.

John

From: Phil Hobbs on 21 Feb 2010 14:02
On 2/20/2010 4:53 PM, John Larkin wrote:
> On Sat, 20 Feb 2010 21:07:48 +0000, Nemo
> <zzz(a)nospam.nospam.nospam.nospam.co.uk> wrote:
>
>> I am trying to evaluate whether to use tantalum versus OS-CON aluminium
>> electrolytics as the output decouplers for some linear postregulators
>> after a (relatively low noise) switcher. This is for a high gain
>> amplifier that will be operating down to audio frequencies. I've come
>> across references to aluminium electrolytics being noisy, but no firm
>> details (kind of odd as there are lots of details about ceramics'
>> problems under bias, wet vs dry tantalums etc). There's also some
>> references to "low noise" aluminium electrolytics for audio work, but I
>> don't know whether to take them seriously as audiophools believe all
>> kinds of weird stuff. So, can anyone advise if aluminium electrolytics -
>> specifically low ESR solid electrolyte types - have some kind of noise
>> problem? I know tants are NOT microphonic but I've not come across any
>> info about electrolytics and microphony one way or another.
>>
>> Assuming they do not, I favour them over tants because their ESR is
>> lower, I get the impression that tants' ESR is poorer at low
>> frequencies, and I can get electrolytics at higher voltages (I like to
>> run caps at about double their rated voltage under the impression this
>> improves their reliability). The load on these linear regs will be
>> fairly constant, so ripple current will be low.
>>
>> Thank you,
>
> I've never encountered noise from electrolytics. Considering that
> self-discharge time constants are typically days or weeks, I can't
> imagine a serious noise mechanism. Charge one up and see if it makes
> noise.
>
> The problem with tantalums is that they tend to detonate. Aluminums
> have bad ESRs at low temperatures and tend to dry out over time. The
> polymers seem OK so far.
>
> John
>

An electrolytic is trying really really hard to be a battery. There are
self-EMFs there that are horribly temperature dependent.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
From: John Larkin on 21 Feb 2010 14:10
On Sun, 21 Feb 2010 14:02:13 -0500, Phil Hobbs
<pcdhSpamMeSenseless(a)electrooptical.net> wrote:

>On 2/20/2010 4:53 PM, John Larkin wrote:
>> On Sat, 20 Feb 2010 21:07:48 +0000, Nemo
>> <zzz(a)nospam.nospam.nospam.nospam.co.uk> wrote:
>>
>>> I am trying to evaluate whether to use tantalum versus OS-CON aluminium
>>> electrolytics as the output decouplers for some linear postregulators
>>> after a (relatively low noise) switcher. This is for a high gain
>>> amplifier that will be operating down to audio frequencies. I've come
>>> across references to aluminium electrolytics being noisy, but no firm
>>> details (kind of odd as there are lots of details about ceramics'
>>> problems under bias, wet vs dry tantalums etc). There's also some
>>> references to "low noise" aluminium electrolytics for audio work, but I
>>> don't know whether to take them seriously as audiophools believe all
>>> kinds of weird stuff. So, can anyone advise if aluminium electrolytics -
>>> specifically low ESR solid electrolyte types - have some kind of noise
>>> problem? I know tants are NOT microphonic but I've not come across any
>>> info about electrolytics and microphony one way or another.
>>>
>>> Assuming they do not, I favour them over tants because their ESR is
>>> lower, I get the impression that tants' ESR is poorer at low
>>> frequencies, and I can get electrolytics at higher voltages (I like to
>>> run caps at about double their rated voltage under the impression this
>>> improves their reliability). The load on these linear regs will be
>>> fairly constant, so ripple current will be low.
>>>
>>> Thank you,
>>
>> I've never encountered noise from electrolytics. Considering that
>> self-discharge time constants are typically days or weeks, I can't
>> imagine a serious noise mechanism. Charge one up and see if it makes
>> noise.
>>
>> The problem with tantalums is that they tend to detonate. Aluminums
>> have bad ESRs at low temperatures and tend to dry out over time. The
>> polymers seem OK so far.
>>
>> John
>>
>
>An electrolytic is trying really really hard to be a battery. There are
>self-EMFs there that are horribly temperature dependent.
>
>Cheers
>
>Phil Hobbs

So someone should actually measure the noise across a charged (or even
discharged?) electrolytic cap, and maybe a polymer too. I'll try it
next week if I get time.

John

From: Baron on 21 Feb 2010 14:20
Nemo Inscribed thus:
> I can get electrolytics at higher voltages (I like to
> run caps at about double their rated voltage under the impression this
^^^^^^
> improves their reliability).
>
> Thank you,

I'm glad I'm not in your lab. :-)

--
Best Regards:
Baron.
From: Jim Thompson on 21 Feb 2010 15:22
On Sun, 21 Feb 2010 11:41:21 -0800, Fred Abse
<excretatauris(a)invalid.invalid> wrote:

>On Sat, 20 Feb 2010 18:08:52 -0800, Joerg wrote:
>
>> John Larkin wrote:
[snip]
>>>
>>> I've never encountered noise from electrolytics. ...
>>
>>
>> Oh, I sure did: pheeeooou ... *BOOM*
>
>I once got the can off one in the crotch, from across the lab. Makes yer
>eyes water ;-)

I had a Tantalum blow up in my face one time. Fortunately I had my
magnifiers down over my eyes.

(Client's board sent to me to evaluate to replace with a single chip.
Who ever threw it together inserted Tantalums backwards, so a VCC to
ground short _somewhere_. While I'm micro-probing down the rails to
find the offending element, it blew.)

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
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