| Author |
Message |
Ian
Guest
|
 Posted:
Sun Feb 13, 2005 5:50 pm Post subject:
Re: Back to Back Tantalum Caps |
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"PaulCsouls" <paulcsouls@worldnet.att.net> wrote in message
news:mght019usmjnvf2ste55vb0gvb47eo7d0j@4ax.com...
| Quote: | On Sat, 12 Feb 2005 20:10:16 -0500, "Tam/WB2TT"
t-tammaru@c0mca$t.net> wrote:
"John Larkin" <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote in
message news:f0fs01p7afasgce1bnic3pplftu7erq7op@4ax.com...
On Sat, 12 Feb 2005 10:00:09 -0500, "Tam/WB2TT"
t-tammaru@c0mca$t.net> wrote:
"PaulCsouls" <paulcsouls@worldnet.att.net> wrote in message
news:ujuq01hav3ba3d787s27hbllaqb56tisbc@4ax.com...
I was recently looking at a design that had two Tantalum caps
reversed
biased to each other to make a bipolar cap. I know tantalums can work
down to -1v and don't need a DC bias the way aluminum electrolytic
caps do but this looked strange. What are the pitfalls to this
method.
Thanks
Paul C
You might be better of putting a low Vf diode across each cap to keep
the
cap from ever conducting forward current.
Tam
Makes it more nonlinear in many situations.
John
Wouldn't the cap acting as a diode be as bad or worse? He does not say
what
this is for; so, I am assuming he wants to put 60 Hz through it, which I
have done at 24VRMS..
Tam
It was in an AGC circuit. Basically a low pass filter with the caps in
series to ground two 47uF caps and 1k resistor so a 4Hz 3dB. Not very
demanding with respect to distortion or tolerances. I was just curious
about how the limitations of the configuration.
Paul C
|
A better method would be to put a bias resistor to a sufficiently large bias
voltage
connected to the junction of the 2 capacitors. That way, both are always
operating
correctly biased.
Regards
Ian
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Nico Coesel
Guest
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| Posted:
Sun Feb 13, 2005 10:11 pm Post subject:
Re: Back to Back Tantalum Caps |
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PaulCsouls <paulcsouls@worldnet.att.net> wrote:
| Quote: |
I was recently looking at a design that had two Tantalum caps reversed
biased to each other to make a bipolar cap. I know tantalums can work
down to -1v and don't need a DC bias the way aluminum electrolytic
caps do but this looked strange. What are the pitfalls to this
method.
|
This may be interesting reading material:
http://www.epcos.com/inf/20/40/db/tec_03/01070134.pdf
--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl |
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Clarence_A
Guest
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| Posted:
Sun Feb 13, 2005 11:33 pm Post subject:
Re: Back to Back Tantalum Caps |
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"Nico Coesel" wrote
<snip>
This document IS interesting, and it seems to be good technically.
It will be useful if someone can get past the poor phrasing and
reverse orders of many statements.
Perhaps the inserted reverse logic was intended as humor?
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PaulCsouls
Guest
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| Posted:
Mon Feb 14, 2005 12:19 am Post subject:
Re: Back to Back Tantalum Caps |
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On Sun, 13 Feb 2005 16:11:04 GMT, nico@puntnl.niks (Nico Coesel)
wrote:
| Quote: | PaulCsouls <paulcsouls@worldnet.att.net> wrote:
I was recently looking at a design that had two Tantalum caps reversed
biased to each other to make a bipolar cap. I know tantalums can work
down to -1v and don't need a DC bias the way aluminum electrolytic
caps do but this looked strange. What are the pitfalls to this
method.
This may be interesting reading material:
http://www.epcos.com/inf/20/40/db/tec_03/01070134.pdf
|
Interesting. They call for the diode protection across each cap.
Paul C |
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PaulCsouls
Guest
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| Posted:
Mon Feb 14, 2005 12:32 am Post subject:
Re: Back to Back Tantalum Caps |
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On Sun, 13 Feb 2005 09:13:34 +0000, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:
| Quote: |
PaulCsouls wrote:
On Sat, 12 Feb 2005 04:38:56 +0000, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote:
PaulCsouls wrote:
I was recently looking at a design that had two Tantalum caps reversed
biased to each other to make a bipolar cap. I know tantalums can work
down to -1v and don't need a DC bias the way aluminum electrolytic
caps do but this looked strange. What are the pitfalls to this
method.
The cost of tantalum caps perhaps ?
They *don't* need bias ? I rather thought they did to perform properly. In
fact, under the right condirions, aluminium electrolytics work well for
audio coupling under zero bias conditions. You need a big cap to ensure
that the ac component of the signal is essentially miniscule but you might
be interested to know that almost every single top-end modern audio mixing
console uses unbiased aluminium electrolytics to couple signal - right at
the very top-end too. I'm talking $100,000 + products here.
I do know an audio company that ( many years ago ) used back to back
tantalums for coupling that biased their centre junction to ensure biasing
polarity. Today that would be considered esoteric overkill and financial
suicide for a large product.
I have used that technique with a pair of aluminium electros though, where
the DC offset voltage at the source is subject to tolerances. Works
nicely.
Graham
I'm just following Ian Sinclair's Passive Components for Circuit
Design.
Any link ?
He says that Alumunium Electrolytics require a DC polarizing
voltage to maintain the insulating film
Oh well. That means almost every piece of current pro and consumer audio is
built wrong then !
and for Tantalum Caps he says
"Tantalum electrolytics can be used without any DC bias and can accept
a small reverse voltage, typically less than 1.0v."
Alumiums are good for a few 100mV reverse volts typically. Perfect for split
supply audio apps.
But he doesn't get
into the frequency characteristics and I would guess biasing would
improve the usable bandwidth.
What 'frequency characterisitcs' ? Bias affects bandwidth ? Some very strange
ideas here.
Maybe this Mr Sinclair is one of those audiophool gurus ?
Graham
|
The bias / bandwidth idea is one of my fool ideas. Ian Sinclair's book
is recommended by Bob Pease in his Troubleshooting book, so it has
been proofread by someone with some experience in the field.
Paul C
I'd be really smart, if I wasn't so stupid. |
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John Larkin
Guest
|
| Posted:
Mon Feb 14, 2005 1:20 am Post subject:
Re: Back to Back Tantalum Caps |
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|
On Sun, 13 Feb 2005 16:11:04 GMT, nico@puntnl.niks (Nico Coesel)
wrote:
| Quote: | PaulCsouls <paulcsouls@worldnet.att.net> wrote:
I was recently looking at a design that had two Tantalum caps reversed
biased to each other to make a bipolar cap. I know tantalums can work
down to -1v and don't need a DC bias the way aluminum electrolytic
caps do but this looked strange. What are the pitfalls to this
method.
This may be interesting reading material:
http://www.epcos.com/inf/20/40/db/tec_03/01070134.pdf
|
Section 4.8 is oversimplified. For the back-to-back config with
diodes, small-signal AC (unbiased) series capacitance is indeed C/2,
but large-signal (when the diodes are being useful) it approaches C.
Nonlinear as hell.
John |
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Pooh Bear
Guest
|
| Posted:
Mon Feb 14, 2005 6:28 pm Post subject:
Re: Back to Back Tantalum Caps |
|
|
PaulCsouls wrote:
| Quote: | On Sun, 13 Feb 2005 09:13:34 +0000, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote:
PaulCsouls wrote:
On Sat, 12 Feb 2005 04:38:56 +0000, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote:
PaulCsouls wrote:
I was recently looking at a design that had two Tantalum caps reversed
biased to each other to make a bipolar cap. I know tantalums can work
down to -1v and don't need a DC bias the way aluminum electrolytic
caps do but this looked strange. What are the pitfalls to this
method.
The cost of tantalum caps perhaps ?
They *don't* need bias ? I rather thought they did to perform properly. In
fact, under the right condirions, aluminium electrolytics work well for
audio coupling under zero bias conditions. You need a big cap to ensure
that the ac component of the signal is essentially miniscule but you might
be interested to know that almost every single top-end modern audio mixing
console uses unbiased aluminium electrolytics to couple signal - right at
the very top-end too. I'm talking $100,000 + products here.
I do know an audio company that ( many years ago ) used back to back
tantalums for coupling that biased their centre junction to ensure biasing
polarity. Today that would be considered esoteric overkill and financial
suicide for a large product.
I have used that technique with a pair of aluminium electros though, where
the DC offset voltage at the source is subject to tolerances. Works
nicely.
Graham
I'm just following Ian Sinclair's Passive Components for Circuit
Design.
Any link ?
He says that Alumunium Electrolytics require a DC polarizing
voltage to maintain the insulating film
Oh well. That means almost every piece of current pro and consumer audio is
built wrong then !
and for Tantalum Caps he says
"Tantalum electrolytics can be used without any DC bias and can accept
a small reverse voltage, typically less than 1.0v."
Alumiums are good for a few 100mV reverse volts typically. Perfect for split
supply audio apps.
But he doesn't get
into the frequency characteristics and I would guess biasing would
improve the usable bandwidth.
What 'frequency characterisitcs' ? Bias affects bandwidth ? Some very strange
ideas here.
Maybe this Mr Sinclair is one of those audiophool gurus ?
Graham
The bias / bandwidth idea is one of my fool ideas. Ian Sinclair's book
is recommended by Bob Pease in his Troubleshooting book, so it has
been proofread by someone with some experience in the field.
|
When does it date from ?
I can barely remember when I last saw a tantalum cap !
Graham |
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PaulCsouls
Guest
|
| Posted:
Tue Feb 15, 2005 2:21 am Post subject:
Re: Back to Back Tantalum Caps |
|
|
On Mon, 14 Feb 2005 12:28:05 +0000, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:
| Quote: | PaulCsouls wrote:
On Sun, 13 Feb 2005 09:13:34 +0000, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote:
PaulCsouls wrote:
On Sat, 12 Feb 2005 04:38:56 +0000, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote:
PaulCsouls wrote:
I was recently looking at a design that had two Tantalum caps reversed
biased to each other to make a bipolar cap. I know tantalums can work
down to -1v and don't need a DC bias the way aluminum electrolytic
caps do but this looked strange. What are the pitfalls to this
method.
The cost of tantalum caps perhaps ?
They *don't* need bias ? I rather thought they did to perform properly. In
fact, under the right condirions, aluminium electrolytics work well for
audio coupling under zero bias conditions. You need a big cap to ensure
that the ac component of the signal is essentially miniscule but you might
be interested to know that almost every single top-end modern audio mixing
console uses unbiased aluminium electrolytics to couple signal - right at
the very top-end too. I'm talking $100,000 + products here.
I do know an audio company that ( many years ago ) used back to back
tantalums for coupling that biased their centre junction to ensure biasing
polarity. Today that would be considered esoteric overkill and financial
suicide for a large product.
I have used that technique with a pair of aluminium electros though, where
the DC offset voltage at the source is subject to tolerances. Works
nicely.
Graham
I'm just following Ian Sinclair's Passive Components for Circuit
Design.
Any link ?
He says that Alumunium Electrolytics require a DC polarizing
voltage to maintain the insulating film
Oh well. That means almost every piece of current pro and consumer audio is
built wrong then !
and for Tantalum Caps he says
"Tantalum electrolytics can be used without any DC bias and can accept
a small reverse voltage, typically less than 1.0v."
Alumiums are good for a few 100mV reverse volts typically. Perfect for split
supply audio apps.
But he doesn't get
into the frequency characteristics and I would guess biasing would
improve the usable bandwidth.
What 'frequency characterisitcs' ? Bias affects bandwidth ? Some very strange
ideas here.
Maybe this Mr Sinclair is one of those audiophool gurus ?
Graham
The bias / bandwidth idea is one of my fool ideas. Ian Sinclair's book
is recommended by Bob Pease in his Troubleshooting book, so it has
been proofread by someone with some experience in the field.
When does it date from ?
I can barely remember when I last saw a tantalum cap !
Graham
|
Copyright 2001. I use tantalum caps all the time but just for power
supply decoupling.
Paul C |
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Pooh Bear
Guest
|
| Posted:
Wed Feb 16, 2005 7:13 pm Post subject:
Re: Back to Back Tantalum Caps |
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PaulCsouls wrote:
| Quote: | I use tantalum caps all the time but just for power supply decoupling.
|
Utter waste of money.
I hope you use current limiting Rs - the disposition of tantalums to self-ignite in
this aplication has long been discussed in this group.
My advice - tantalums are a waste of money and a source of unreliability.
Graham |
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Rich Grise
Guest
|
| Posted:
Wed Feb 16, 2005 11:52 pm Post subject:
Re: Back to Back Tantalum Caps |
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|
On Wed, 16 Feb 2005 13:13:48 +0000, Pooh Bear wrote:
| Quote: | PaulCsouls wrote:
I use tantalum caps all the time but just for power supply decoupling.
Utter waste of money.
I hope you use current limiting Rs - the disposition of tantalums to self-ignite in
this aplication has long been discussed in this group.
My advice - tantalums are a waste of money and a source of unreliability.
|
Oddly, I've never had an adverse experience with a tantalum cap. Then
again, I once fell into a gold mine of "surplus" parts - a company where I
consulted had just bought out another company, for a lump sum. Ergo,
everything in the old company's stock room was, essentially, free. There
were bins of LEDs, bins of transistors, bins of resistors, bins of caps,
even some exotic stuff like 10-turn precision pots, and optical
interruptors.
I did a lot of breadboarding in those days. I had a proto-board that I
populated with a 10 uF tantalum about every three inches along the power
buses. Admittedly, for the 100 uF at the board power entry point, I've
always used aluminum.
But I can't understand the bad rap Tantalum seems to have. I don't think
I've ever seen a tantalum cap fail. (of course, neither has Lassie, but
I _have_ seen stuff, like a selenium stack in a pressurized power supply
clearing the room when you open the unit...)
Cheers!
Rich |
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keith
Guest
|
| Posted:
Thu Feb 17, 2005 6:10 am Post subject:
Re: Back to Back Tantalum Caps |
|
|
On Wed, 16 Feb 2005 13:13:48 +0000, Pooh Bear wrote:
| Quote: |
PaulCsouls wrote:
I use tantalum caps all the time but just for power supply decoupling.
Utter waste of money.
|
Nonsense. I'e used *thousands* of them. As long as you can get your
manufacturing under control and buy for a reliable supplier they're fine.
They're a *lot* better than the bogus aluminums that have been festering
in the supply chain.
| Quote: | I hope you use current limiting Rs - the disposition of tantalums to
self-ignite in this aplication has long been discussed in this group.
|
Sheesh, we haven't had that problem for 25 years. You must be an antique
who never grew up or are buying shit from who knows where.
| Quote: | My advice - tantalums are a waste of money and a source of
unreliability.
|
Nonsense. They're very usefull devices. One must be careful with them
but they're just fine. Hard to come by at times, but there is a reason
for that.
--
Keith |
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Winfield Hill
Guest
|
| Posted:
Thu Feb 17, 2005 8:37 pm Post subject:
Re: Back to Back Tantalum Caps |
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keith wrote...
| Quote: |
They're a *lot* better than the bogus aluminums that have
been festering in the supply chain.
|
We know who makes the bogus aluminums; don't buy 'em.
--
Thanks,
- Win |
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Spehro Pefhany
Guest
|
| Posted:
Thu Feb 17, 2005 9:16 pm Post subject:
Re: Back to Back Tantalum Caps |
|
|
On Wed, 16 Feb 2005 13:13:48 +0000, the renowned Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:
| Quote: |
PaulCsouls wrote:
I use tantalum caps all the time but just for power supply decoupling.
Utter waste of money.
I hope you use current limiting Rs - the disposition of tantalums to self-ignite in
this aplication has long been discussed in this group.
|
They can be used reliably without the series R if the regulator has a
reasonable output current limit, and there are no "hot plug" issues
(like a BFC on the other side of a connector). Using them outside of
the manufacturer's recommendations (no series R and very high
potential source current) can lead to tears. Following the
manufacturer's recommendations to the letter prohibits their use in a
lot of bypass applications. Eg. "Do not use tantalum electrolytic
capacitors in power supply applications.".... "if you must".. (derate
by at least 3:1 in voltage.
| Quote: | My advice - tantalums are a waste of money and a source of unreliability.
Graham
|
Aluminums and ceramics can do a better job for less money in most
cases. The tantalums might be a better choice in some subminiature
portable applications (eg. cellphone handsets) because they are easier
to get and cheaper than the equivalent ceramics, but that's quickly
changing in favor of ceramics. And good riddance.
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com |
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Michael A. Terrell
Guest
|
| Posted:
Thu Feb 17, 2005 11:57 pm Post subject:
Re: Back to Back Tantalum Caps |
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|
Spehro Pefhany wrote:
| Quote: |
They can be used reliably without the series R if the regulator has a
reasonable output current limit, and there are no "hot plug" issues
(like a BFC on the other side of a connector). Using them outside of
the manufacturer's recommendations (no series R and very high
potential source current) can lead to tears. Following the
manufacturer's recommendations to the letter prohibits their use in a
lot of bypass applications. Eg. "Do not use tantalum electrolytic
capacitors in power supply applications.".... "if you must".. (derate
by at least 3:1 in voltage.
Best regards,
Spehro Pefhany
|
Another good rule: Don't let someone try to save money by changing
your 25 volt parts to 10 volts on the 12 volt rails. One place I worked
tried it and it wasn't pretty!
--
Beware of those who suffer from delusions of adequacy!
Michael A. Terrell
Central Florida |
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Pooh Bear
Guest
|
| Posted:
Sat Feb 19, 2005 6:11 am Post subject:
Re: Back to Back Tantalum Caps |
|
|
Winfield Hill wrote:
| Quote: | keith wrote...
They're a *lot* better than the bogus aluminums that have
been festering in the supply chain.
We know who makes the bogus aluminums; don't buy 'em.
|
Care to let me in on this snippet of info ?
Graham |
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