Low leakage capacitors

P

Paul

Guest
Hi,

I'm trying to find the lowest leakage capacitor, somewhere in the
range of 0.01uF to 1uF, *might* be able to live with 0.001uF, for DC
use. I'm not sure if PTFE (teflon) is the best choice, but here's one
-->

http://www.cde.com/catalogs/MCM-MIN.pdf

It says, "Insulation Resistance: 1000 MĽŘ*ĽěF Need not exceed 100,000 MĽŘ
at 25 ¨ŹC" What exactly do they mean by "Need not exceed 100,000 MĽŘ" ?

Also I heard polystyrene is good.

I've performed various RC time constant tests on caps by placing a
voltage source on the cap for a period of time, removing the voltage
source and time it, then measure the DC voltage after a certain time
period, and calculate the parallel resistance. It appears that the
longer the voltage source is held on the cap results in more parallel
resistance-- possibly dielectric absorption.

So this makes it more difficult to find the best type of caps for this
use. IOW, perhaps one cap might have less leakage after 1 minute, but
after 10 hours perhaps another type of cap might have less leakage.

I'm looking for a cap that would contain as much charge as possible
for about one day. The voltage levels are around 1 volt.

Any help is greatly appreciated!
Paul
 
Paul <energymover@gmail.com> wrote in news:6ac514c1-4564-438d-9294-
2a824c939c6b@d19g2000prh.googlegroups.com:

Hi,

I'm trying to find the lowest leakage capacitor, somewhere in the
range of 0.01uF to 1uF, *might* be able to live with 0.001uF, for DC
use. I'm not sure if PTFE (teflon) is the best choice, but here's one
--

http://www.cde.com/catalogs/MCM-MIN.pdf

It says, "Insulation Resistance: 1000 MĽŘ*ĽěF Need not exceed 100,000 MĽŘ
at 25 ¨ŹC" What exactly do they mean by "Need not exceed 100,000 MĽŘ" ?

Also I heard polystyrene is good.

I've performed various RC time constant tests on caps by placing a
voltage source on the cap for a period of time, removing the voltage
source and time it, then measure the DC voltage after a certain time
period, and calculate the parallel resistance. It appears that the
longer the voltage source is held on the cap results in more parallel
resistance-- possibly dielectric absorption.

So this makes it more difficult to find the best type of caps for this
use. IOW, perhaps one cap might have less leakage after 1 minute, but
after 10 hours perhaps another type of cap might have less leakage.

I'm looking for a cap that would contain as much charge as possible
for about one day. The voltage levels are around 1 volt.

Any help is greatly appreciated!
Paul
Click to expand...
Exploring what people use for sample/hold circuits might be the way to narrow
it down. The requirements are very low dielectric absorbtion, usually low
voltage at DC or of moderately changing signals.

Somewhere (I forget where) I read of a sample/hold op-amp circuit that not
only had a very high resistance input, but some sort of regenerative ability
to prolong the life of the charge on the cap on its input. I'm not sure if
this is what you're after, but it might be worth hunting for.

Bob Pease has a page:
http://www.national.com/rap/Application/0,1570,28,00.html
Amongst other things it shows a way to get better than teflon's performance
witha polypropylene cap. It looks like a different scheme than the one I saw
once but the intent is the same.
 
Paul wrote:

Hi,

I'm trying to find the lowest leakage capacitor, somewhere in the
range of 0.01uF to 1uF, *might* be able to live with 0.001uF, for DC
use. I'm not sure if PTFE (teflon) is the best choice, but here's one
--

http://www.cde.com/catalogs/MCM-MIN.pdf

It says, "Insulation Resistance: 1000 MΊ*ΟF Need not exceed 100,000 MΊ
at 25 ºC" What exactly do they mean by "Need not exceed 100,000 MΊ" ?

Also I heard polystyrene is good.

I've performed various RC time constant tests on caps by placing a
voltage source on the cap for a period of time, removing the voltage
source and time it, then measure the DC voltage after a certain time
period, and calculate the parallel resistance. It appears that the
longer the voltage source is held on the cap results in more parallel
resistance-- possibly dielectric absorption.

So this makes it more difficult to find the best type of caps for this
use. IOW, perhaps one cap might have less leakage after 1 minute, but
after 10 hours perhaps another type of cap might have less leakage.

I'm looking for a cap that would contain as much charge as possible
for about one day. The voltage levels are around 1 volt.

Any help is greatly appreciated!
Paul
Click to expand...
Have you considered glass !

--
Best Regards:
Baron.
 
Baron <baron.nospam@linuxmaniac.nospam.net> wrote in
news:gtffio$ugf$1@news.motzarella.org:

Have you considered glass !
Click to expand...
I know I hadn't, but it's a cool idea:
http://www.avx.com/docs/techinfo/perform_gl.pdf
 
Lostgallifreyan wrote:

Baron <baron.nospam@linuxmaniac.nospam.net> wrote in
news:gtffio$ugf$1@news.motzarella.org:

Have you considered glass !


I know I hadn't, but it's a cool idea:
http://www.avx.com/docs/techinfo/perform_gl.pdf
Click to expand...
Post back and lets know how it goes.

--
Best Regards:
Baron.
 
re : lowest leakage caps :
a high voltage film like teflon or polysulfone would be ok if space is
not a problem.
Otherwise ELNA makes low leakage caps the size of regular RB and RT
electros,
specifically designed for timing circuits.

jcdrisc
 
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