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Message |
PaulCsouls
Guest
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 Posted:
Sat Feb 12, 2005 6:11 am Post subject:
Back to Back Tantalum Caps |
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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
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Pooh Bear
Guest
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| Posted:
Sat Feb 12, 2005 6:11 am Post subject:
Re: Back to Back Tantalum Caps |
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PaulCsouls 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.
|
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 |
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John Larkin
Guest
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| Posted:
Sat Feb 12, 2005 6:11 am Post subject:
Re: Back to Back Tantalum Caps |
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On Sat, 12 Feb 2005 03:46:20 GMT, 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.
Thanks
Paul C
|
If there's an unknown DC polarity and a small AC signal, it's OK. If
the AC across the combination gets to be larger than a volt or so the
the capacitance will change during each AC cycle (as the
reverse-biased cap goes from being a capacitor to being a resistor)
and that can cause distortion and other weirdness.
The potential nonlinearities are complex and depend on the situation.
John
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Tam/WB2TT
Guest
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| Posted:
Sat Feb 12, 2005 9:00 pm Post subject:
Re: Back to Back Tantalum Caps |
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"PaulCsouls" <paulcsouls@worldnet.att.net> wrote in message
news:ujuq01hav3ba3d787s27hbllaqb56tisbc@4ax.com...
| 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.
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 |
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John Larkin
Guest
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| Posted:
Sat Feb 12, 2005 11:26 pm Post subject:
Re: Back to Back Tantalum Caps |
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On Sat, 12 Feb 2005 10:00:09 -0500, "Tam/WB2TT"
<t-tammaru@c0mca$t.net> wrote:
| Quote: |
"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 |
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PaulCsouls
Guest
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| Posted:
Sat Feb 12, 2005 11:32 pm Post subject:
Re: Back to Back Tantalum Caps |
|
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On Sat, 12 Feb 2005 04:38:56 +0000, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:
| Quote: |
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. He says that Alumunium Electrolytics require a DC polarizing
voltage to maintain the insulating film 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." But he doesn't get
into the frequency characteristics and I would guess biasing would
improve the usable bandwidth.
Paul C |
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PaulCsouls
Guest
|
| Posted:
Sat Feb 12, 2005 11:34 pm Post subject:
Re: Back to Back Tantalum Caps |
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On Fri, 11 Feb 2005 20:37:54 -0800, John Larkin
<jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote:
| Quote: | On Sat, 12 Feb 2005 03:46:20 GMT, 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.
Thanks
Paul C
If there's an unknown DC polarity and a small AC signal, it's OK. If
the AC across the combination gets to be larger than a volt or so the
the capacitance will change during each AC cycle (as the
reverse-biased cap goes from being a capacitor to being a resistor)
and that can cause distortion and other weirdness.
The potential nonlinearities are complex and depend on the situation.
John
|
That's my intuition. I would pay for a bipolar cap with a data sheet
to give me that warm fuzzy feeling of knowing what's going on.
Paul C |
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PaulCsouls
Guest
|
| Posted:
Sat Feb 12, 2005 11:38 pm Post subject:
Re: Back to Back Tantalum Caps |
|
|
On Sat, 12 Feb 2005 10:00:09 -0500, "Tam/WB2TT"
<t-tammaru@c0mca$t.net> wrote:
| Quote: |
"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
|
Yes, or clamp the signal to +/- 0.7 volts.
Paul C |
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Rich Grise
Guest
|
| Posted:
Sun Feb 13, 2005 6:11 am Post subject:
Re: Back to Back Tantalum Caps |
|
|
On Sat, 12 Feb 2005 23:45:06 -0500, Tam/WB2TT wrote:
| Quote: | "PaulCsouls" <paulcsouls@worldnet.att.net> wrote in message
On Sat, 12 Feb 2005 20:10:16 -0500, "Tam/WB2TT"
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
What I had done was put 2 caps back/back with diodes to get a NP 200uF
capacitor for use with a reversible 2 phase electric motor in an antenna
rotator. Worked fine. I know of people who have don this with speaker
crossover networks, but as John points out, probably not a good idea.
|
Aluminums can do this all day - that's what a "non-polar" cap is -
essentially two aluminum electrolytics back-to-back in one package.
The OP was asking about doing that with tantalum.
Nobody seems to know. ?:-|
I'd say, look for followups on the performance of the circuit design the
OP saw with that configuration, or put a couple on the bench in the
breadboard with some kind of test setup, and see what happens.
Cheers!
Rich |
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Tam/WB2TT
Guest
|
| Posted:
Sun Feb 13, 2005 6:11 am Post subject:
Re: Back to Back Tantalum Caps |
|
|
"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
What I had done was put 2 caps back/back with diodes to get a NP 200uF |
capacitor for use with a reversible 2 phase electric motor in an antenna
rotator. Worked fine. I know of people who have don this with speaker
crossover networks, but as John points out, probably not a good idea.
Tam |
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| Back to top |
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John Larkin
Guest
|
| Posted:
Sun Feb 13, 2005 6:11 am Post subject:
Re: Back to Back Tantalum Caps |
|
|
On Sat, 12 Feb 2005 20:10:16 -0500, "Tam/WB2TT"
<t-tammaru@c0mca$t.net> wrote:
| Quote: |
"John Larkin" <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote in
message news:f0fs01p7afasgce1bnic3pplftu7erq7op@4ax.com...
On Sat, 12 Feb 2005 10:00:09 -0500, "Tam/WB2TT"
t-tammaru@c0mca$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
|
Without knowing the DC bias, AC current and frequency, and the
capacitance it's impossible to say how weird or maybe not weird this
would behave. It's complex.
John |
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Tam/WB2TT
Guest
|
| Posted:
Sun Feb 13, 2005 6:11 am Post subject:
Re: Back to Back Tantalum Caps |
|
|
"John Larkin" <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote in
message news:f0fs01p7afasgce1bnic3pplftu7erq7op@4ax.com...
| Quote: | On Sat, 12 Feb 2005 10:00:09 -0500, "Tam/WB2TT"
t-tammaru@c0mca$t.net> wrote:
"PaulCsouls" <paulcsouls@worldnet.att.net> wrote in message
news:ujuq01hav3ba3d787s27hbllaqb56tisbc@4ax.com...
I was recently looking at a design that had two Tantalum caps reversed
biased to each other to make a bipolar cap. I know tantalums can work
down to -1v and don't need a DC bias the way aluminum electrolytic
caps do but this looked strange. What are the pitfalls to this
method.
Thanks
Paul C
You might be better of putting a low Vf diode across each cap to keep the
cap from ever conducting forward current.
Tam
Makes it more nonlinear in many situations.
John
Wouldn't the cap acting as a diode be as bad or worse? He does not say what |
this is for; so, I am assuming he wants to put 60 Hz through it, which I
have done at 24VRMS..
Tam |
|
| Back to top |
|
|
PaulCsouls
Guest
|
| Posted:
Sun Feb 13, 2005 6:11 am Post subject:
Re: Back to Back Tantalum Caps |
|
|
On Sat, 12 Feb 2005 20:10:16 -0500, "Tam/WB2TT"
<t-tammaru@c0mca$t.net> wrote:
| Quote: |
"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 |
|
| Back to top |
|
|
Pooh Bear
Guest
|
| Posted:
Sun Feb 13, 2005 3:13 pm Post subject:
Re: Back to Back Tantalum Caps |
|
|
PaulCsouls wrote:
| Quote: | 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 ?
| Quote: | 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 !
| Quote: | 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.
| Quote: | 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 |
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Nico Coesel
Guest
|
| Posted:
Sun Feb 13, 2005 3:49 pm Post subject:
Re: Back to Back Tantalum Caps |
|
|
Rich Grise <richgrise@example.net> wrote:
| Quote: | On Sat, 12 Feb 2005 23:45:06 -0500, Tam/WB2TT wrote:
"PaulCsouls" <paulcsouls@worldnet.att.net> wrote in message
On Sat, 12 Feb 2005 20:10:16 -0500, "Tam/WB2TT"
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
What I had done was put 2 caps back/back with diodes to get a NP 200uF
capacitor for use with a reversible 2 phase electric motor in an antenna
rotator. Worked fine. I know of people who have don this with speaker
crossover networks, but as John points out, probably not a good idea.
Aluminums can do this all day - that's what a "non-polar" cap is -
essentially two aluminum electrolytics back-to-back in one package.
The OP was asking about doing that with tantalum.
Nobody seems to know. ?:-|
|
I don't even want to know. If possible, I avoid tantalum caps because
they short out when they fail. They can also burn a hole right through
the PCB if you are unlucky.
When it comes to distortion, I think the best idea is to read the
datasheet and determine how the capacitance changes with the voltage.
--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl |
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