Electrolytic vs Tantalum
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Posts: 46,084
Looking for a decent explanation on filter caps.
I completly understand the concept of the small .1 uf cap close to the power
supply for decoupling (at least I think I do). Also I think I have a decent
handle on why to use an electrolytic (much higher value) in tandem with the
0.1uf cap.
However, it seems more and more I am seeing tantalum caps on the output next
to the power supply to work in tandem with the 0.1uf ceramic.
For example, in the case of the SX demo board from parallax, the cap on the
input side of the 5v reg is electrolytic and the cap on the output of the 5v
reg is tantalum. I am sure this probably has something to do with the
characteistics of the different caps.
Can anybody give a quikie "caps 101" explanation on when and why to use
electrolytic verses tantalum?
Thanks
Dummy
[noparse][[/noparse]Non-text portions of this message have been removed]
I completly understand the concept of the small .1 uf cap close to the power
supply for decoupling (at least I think I do). Also I think I have a decent
handle on why to use an electrolytic (much higher value) in tandem with the
0.1uf cap.
However, it seems more and more I am seeing tantalum caps on the output next
to the power supply to work in tandem with the 0.1uf ceramic.
For example, in the case of the SX demo board from parallax, the cap on the
input side of the 5v reg is electrolytic and the cap on the output of the 5v
reg is tantalum. I am sure this probably has something to do with the
characteistics of the different caps.
Can anybody give a quikie "caps 101" explanation on when and why to use
electrolytic verses tantalum?
Thanks
Dummy
[noparse][[/noparse]Non-text portions of this message have been removed]
Comments
> electrolytic verses tantalum?
Tantulums are physically smaller. That may be one reason. In the
balloon program I use tants because they are sealed. Standard
aluminuim electrolytics can leak electrolyte.
Paul
Tantalum capacitors have many excellent qualities, but in this case you
are probably seeing them replace an electrolytic to reduce size. There
are other factors such as ESR and leakage, but in this case, that
probably isn't a factor.
Tantalum capacitors have higher failure rates at high temperature than
low temperature, and also their MTBF decreases as you run closer to
their rated voltage.
Read this:
http://www.illcap.com/pdf/papers/A_Comparison_Of_Surface_Mount_Aluminum.
pdf
From that paper:
Among the advantages [noparse][[/noparse]of tantalum] are:
! Small size
! No liquid electrolyte
! Superior temperature stability
! Wider operating temperature range (up to +125°C)
! Long storage (shelf) life
! Larger reverse voltage tolerance
! Low dissipation factor
! Self healing
Aluminum electrolytic capacitors do have several advantages over
tantalum capacitors.
Most prominently:
! Lower cost
! Higher availability
! Shorter production lead times
! Low leakage current
! Higher voltage range (up to 400 VDC)
Some of the most prominent electrical performance differences between
tantalums and aluminum electrolytics
that should be resolved before substituting an aluminum electrolytic for
a tantalum capacitor are:
! Aluminum electrolytic’s higher dissipation factors/ESR, which in turn
reduces their ripple current
capabilities.
! Aluminum electrolytic’s larger capacitance change over temperature.
Electrolytics can change up to six
times more than tantalums.
! Aluminum electrolytic’s capacitance change over frequency.
! Aluminum electrolytic’s changes over time -- up 20% after 2,000 hours
for aluminum electrolytics.
### end quote
Years ago, electrolytic capacitors were largely regarded as junk parts.
But modern advances have made them much more robust, although they are
larger than a comparable tantalum.
One interesting note about electrolytic capacitors. Do you know why
electrolytic caps can reach such high values? Capacitance is determined
by the surface area of the plates and the spacing between the plates.
The closer the plates, the higher the capacitance. To maximize space
when using metal films (like in a metal film capacitor) you roll the
metal and the insulator like a tootsie roll, so that unrolled it would
be a big sheet of metal and plastic.
Electrolytics are different. The capacitors contain a conductive fluid
(as you know if you've hooked one up backwards). When you apply current,
the fluid "plates' a thin insulating layer on one electrode. That's why
the capacitor has a polarity. So one plate is the electrode, and the
other plate is the fluid. The dielectric is the extremely thin plated
layer that is thinner than you could reasonably build with mechanical
means. This very thin gap is where electrolytics get their high values.
Al Williams
AWC
* Floating point A/D
http://www.al-williams.com/awce/pak9.htm
>
Original Message
> From: smartdim@a... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=dqvuDvGgI2MmOEflQiE8LYho5g2MlHt5sDLqusdFIKotmux3LYaPWjgADNZY38vGoddqA5ec8x6daQ]smartdim@a...[/url
> Sent: Thursday, February 20, 2003 9:19 AM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Electrolytic vs Tantalum
>
>
> Looking for a decent explanation on filter caps.
> I completly understand the concept of the small .1 uf cap
> close to the power
> supply for decoupling (at least I think I do). Also I think I
> have a decent
> handle on why to use an electrolytic (much higher value) in
> tandem with the
> 0.1uf cap.
>
> However, it seems more and more I am seeing tantalum caps on
> the output next
> to the power supply to work in tandem with the 0.1uf ceramic.
>
> For example, in the case of the SX demo board from parallax,
> the cap on the
> input side of the 5v reg is electrolytic and the cap on the
> output of the 5v
> reg is tantalum. I am sure this probably has something to do with the
> characteistics of the different caps.
>
> Can anybody give a quikie "caps 101" explanation on when and
> why to use
> electrolytic verses tantalum?
>
> Thanks
>
> Dummy
>
>
> [noparse][[/noparse]Non-text portions of this message have been removed]
>
>
> To UNSUBSCRIBE, just send mail to:
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> http://docs.yahoo.com/info/terms/
>
>
>
Thanks much for the capacitor information. Excellent information!!!
I am sure many others will also benefit from the information.
[noparse][[/noparse]Non-text portions of this message have been removed]
In general, tantalums can not withstand high ripple voltage and therefore
not suitable for main filtering in power supplies.
Jim
Original Message
From: verhap@o... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=wi1VbASINr18eAE7WMydENkpDlLe9qMVLkWtkzQ-aSvOsO2DM3e3esWjo4hgZfVlxo9vUIyOBANAOZxz34UAdLmndZs]verhap@o...[/url
Sent: Thursday, February 20, 2003 11:21 AM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] Electrolytic vs Tantalum
> Can anybody give a quikie "caps 101" explanation on when and why to use
> electrolytic verses tantalum?
Tantulums are physically smaller. That may be one reason. In the
balloon program I use tants because they are sealed. Standard
aluminuim electrolytics can leak electrolyte.
Paul
To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
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jjf@p... writes:
> Paul,
>
> In general, tantalums can not withstand high ripple voltage and therefore
> not suitable for main filtering in power supplies.
>
> Jim
>
Jim,
When you say main filtering in power supplies are you talking about your
typical power supply that rectifies AC and the "first" caps seen after the
rectifier?
My main concern is using 3 terminal regulators such as a 7805 or a LM317....
[noparse][[/noparse]Non-text portions of this message have been removed]
stamp. Is this the best way to go?
Ian
Original Message
From: Jim Forkin [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=U3SCUdwWyYuaoW4aElTEpxdHT9SnsbMeRPyeHAfPV_Cx5K5eSRGxtO2gkr1iuo-kDcj4xfkAMROFsg]jjf@p...[/url
Sent: February 20, 2003 1:01 PM
To: basicstamps@yahoogroups.com
Subject: RE: [noparse][[/noparse]basicstamps] Electrolytic vs Tantalum
Paul,
In general, tantalums can not withstand high ripple voltage and
therefore
not suitable for main filtering in power supplies.
Jim
Original Message
From: verhap@o... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=2zQ22IFpOasnwmk0ibMpsxirblGUk1-dTT3ke9IThvVs4e6G2RNdXVhegF9VOsORxZ8TkAlnUquEaR4k9X8bsyaafQ]verhap@o...[/url
Sent: Thursday, February 20, 2003 11:21 AM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] Electrolytic vs Tantalum
> Can anybody give a quikie "caps 101" explanation on when and why to
use
> electrolytic verses tantalum?
Tantulums are physically smaller. That may be one reason. In the
balloon program I use tants because they are sealed. Standard
aluminuim electrolytics can leak electrolyte.
Paul
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If memory serves the data sheet for the LM7805 and many other regulator chips
says to put at least a 1 uF tantalum cap on the input
and the output placed physically close to the chip. I think this is to
stabilize the chip and the good high frequency performance
of the tantalum caps is the reason they are used for this app.
Brooke Clarke, N6GCE
http://www.precisionclock.com
> typical power supply that rectifies AC and the "first" caps seen after the
> rectifier?
> My main concern is using 3 terminal regulators such as a 7805 or a LM317....
I think it applies only to the first caps seen. I use tants on linear
voltage regulators without a problem.
Paul
yes, I was talking about the main filter after the rectifier and mostly in
much higher current supplies than would typically use a 7805 or similar
regulator. The filter cap used near the 7805 regulator is for circuit
stability and may be eliminated if the regulator is located very near the DC
source. Incidentally, tantalums sometime make great firecrackers when
exposed to high levels of RF energy even though operating within specs.
Jim
Original Message
From: smartdim@a... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=Tof09uRxRak5D_9TfOyuCdQ0M3rsbMODAAM--Uw_d9vpqFmmkV2CLmr3UrbMGCLzpHAYtguN0o8]smartdim@a...[/url
Sent: Thursday, February 20, 2003 1:07 PM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] Electrolytic vs Tantalum
In a message dated 2/20/2003 10:00:32 AM Pacific Standard Time,
jjf@p... writes:
> Paul,
>
> In general, tantalums can not withstand high ripple voltage and
therefore
> not suitable for main filtering in power supplies.
>
> Jim
>
Jim,
When you say main filtering in power supplies are you talking about your
typical power supply that rectifies AC and the "first" caps seen after the
rectifier?
My main concern is using 3 terminal regulators such as a 7805 or a LM317....
[noparse][[/noparse]Non-text portions of this message have been removed]
To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
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case of industrial espionage gone awry):
http://www.spectrum.ieee.org/WEBONLY/resource/feb03/ncap.html
The book, Art of Electronics has a good discussion of capacitor types.
If you have an amplifier or power supply that misbehaves,
electrolytic capacitors are not far down the list of probable causes.
They lose their capacitance with time as they dry out, and they
become electrically leaky, and they leak physically and destroy
circuit boards.
Surface mount ceramic capacitors have their problems too, because
they are very brittle and subject to cracking during the soldering
process or when a circuit board is flexed. Surface mount tantalum and
plastic capacitors are more flexible. Ceramic caps are easy to
handle and you don't have to worry about polarity.
Some voltage regulators will not be stable (i.e., they oscillate like
crazy at some loads) looking into a low ESR capacitor, and they
prefer a tantalum or electrolytic. Older PNP, low dropout regulators
like the LM2940 require large electrolytic capacitors at their
outputs in order to be stable at heavy load currents.
Some plastic film capacitors have very low losses, and they may not
make the best bypass capacitors. The trouble is, they resonate with
the inductance of circuit board traces. It is not much of a problem
at basic stamp frequencies of less than 1 megahertz. 0.1 uf X5R
ceramics and 2.2 uF tantalums make a good combination for bypassing.
-- Tracy
tracy@e... writes:
> Here is a cautionary article about bad electrolytic capacitors (a
> case of industrial espionage gone awry):
>
> http://www.spectrum.ieee.org/WEBONLY/resource/feb03/ncap.html
>
> The book, Art of Electronics has a good discussion of capacitor types
Stupid me!!!!!!!!!!!!!!!!!!!!!!!!!
I do have the book you mentioned and from what I have read about "other
stuff" I should have consulted that book before this forum. The information
that I previous read in that book is very good. I will read up!
Sometimes this forum has its bad points, that is sometimes people get lazy
(like me) and want thier canned answer without doing any work!!
Thanks for the tip.
Also thanks to all others who posted good answers.
Ken
[noparse][[/noparse]Non-text portions of this message have been removed]
interesting and have looked over the links referred to several times.
The one question that I have, which I have not been able to clarify for
myself is whether using a .1uF Tantalum (polarized) capacitor in place of a
standard .1uF non-polarized capacitor used as a by-pass capacitor (across
the 5v/gnd rail of an IC) would work as well, better or worse - the
assumption is that the tantalum would be correctly polarized when installed.
Any feedback??
mail2web - Check your email from the web at
http://mail2web.com/ .
electrolytics (including tants) until you reached 1 uF and larger.
Paul
> I found the whole discussion of Electrolytic vs Tantalum capacitors very
> interesting and have looked over the links referred to several times.
>
> The one question that I have, which I have not been able to clarify for
> myself is whether using a .1uF Tantalum (polarized) capacitor in place of a
> standard .1uF non-polarized capacitor used as a by-pass capacitor (across
> the 5v/gnd rail of an IC) would work as well, better or worse - the
> assumption is that the tantalum would be correctly polarized when installed.
>
> Any feedback??
>
>
>
> mail2web - Check your email from the web at
> http://mail2web.com/ .
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
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of the message will be ignored.
>
>
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>
>
>Do they make them that small? I thought you didn't see
>electrolytics (including tants) until you reached 1 uF and larger.
Check with an on-line catalog from someone like DigiKey or Mouser.
But yes, 0.1 uF tantalum is a standard cap in many of my designs. 0.47 uF
radial electrolytic caps are often seen inside consumer audio gear.
dwayne
--
Dwayne Reid <dwayner@p...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax
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