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Post by **Nick** » Wed Feb 16, 2011 11:00 pm

The thing is, I doubt that in future electronics there will be little need for 63v caps.

Mike H · Post by **Mike H** » Thu Feb 17, 2011 12:53 pm

I am often fascinated how they get capacitors into integrated circuits. E.g. LM317 has got 2 x 30pF, and a 20pF, I think. Or something like.

Must be something like a reversed diode, 'cause if you think about making 30pF out of sheets of stuff, it's actually quite large, certainly on an chip scale.

Post by **Nick** » Thu Feb 17, 2011 1:44 pm

Must be something like a reversed diode, 'cause if you think about making 30pF out of sheets of stuff, it's actually quite large, certainly on an chip scale.

And I will say it again, not if you can get the plates close together, which is easy on a chip scale. And if you can fill the area between the plates wich a material with a high dilectric constant.

From the above, if you half the distance between the plates, you can half the area and get the same capacitance.

If we use a 4um Si02 dilectric (which has a dilectric strength of 40v) then a 30pf cap would need square plates 1.8mm a side (if I got the numbers right)

Looking at this

http://www.usmicrowaves.com/voltreg/LM317.htm

I can see a couple of 10pf caps, so that would be about 1mm a side. The above die size is 2.45mm * 1.8mm. And I am sure there is a lot more cleverness than what I know about it.

http://www.siliconfareast.com/sio2si3n4.htm

Mike H · Post by **Mike H** » Thu Feb 17, 2011 5:43 pm

Whoo....

OK I was slightly off on the cap count

chris661 · Post by **chris661** » Thu Feb 17, 2011 9:18 pm

Okay, a quick search reveals...

http://en.wikipedia.org/wiki/Electric_d ... _capacitor

So, they're putting many, many farads into something reasonably sized. 10, 20 years ago, how big would such a capacitor have been?

I pulled a 2,200uF capacitor out of an old amplifier (think it was 35v rated), and it was more than twice as tall as a 35v 10,000uF capacitor bought recently. I can't see how they're not getting smaller.

Chris

pre65 · Post by **pre65** » Thu Feb 17, 2011 9:45 pm

Does size matter ?

jack · Post by **jack** » Fri Feb 18, 2011 6:41 am

ed wrote:
Its surface area AND distance between plates, so if they are closer together they dont need to be bigger.
is it possible to get a 10000uf 63v cap in smd format? for example. Or, will it be possible in the future by getting the plates closer together, with the application of Moore's law or some such?

My understanding is that the surface finish of the plates (and even the gel) can dramatically increase the effective surface area - it really is down to nano-technology... http://en.wikipedia.org/wiki/Energy_app ... en_and_now

Power will be an issue for a long time - basic physics about heat, small surface area and convection - case in point, my daughter loves her GHDs (look it up), but they have a design flaw which leads to an SMD resistor overheating and going o/c - its a 1W 100R 2512 case one - I had a devil of a time finding a suitable 2W in the same footprint - 2W is about as big as any SMD resistor gets...
http://uk.farnell.com/jsp/search/produc ... KU=1376985

al newall · Post by **al newall** » Fri Feb 18, 2011 7:44 am

case in point, my daughter loves her GHDs

More than one design flaw methinks.
I'm forever trying to rewire the things.

jack · Post by **jack** » Fri Feb 18, 2011 8:31 am

al newall wrote:
case in point, my daughter loves her GHDs
More than one design flaw methinks.
I'm forever trying to rewire the things.

Daughters?

jack · Post by **jack** » Fri Feb 18, 2011 8:36 am

chris661 wrote: I pulled a 2,200uF capacitor out of an old amplifier (think it was 35v rated), and it was more than twice as tall as a 35v 10,000uF capacitor bought recently. I can't see how they're not getting smaller.

Ripple & pulse current rating are major factors wrt size. I have some quite small 3300uF @ 400V caps, and some ABSOLUTE BEASTS which need M5 bolts as terminals with the same basic specs. The small ones cost about GBP 1.50, the big RIFAs cost about GBP 90 (if you buy them from Farnell or RS).

However, possible current density & capacitance are definitely improving - just look at what's happening to supercaps.

Apples vs. pears.

al newall · Post by **al newall** » Fri Feb 18, 2011 8:59 am

Daughters?

Two.

Not worth the money those GHD things. IMHO.

IslandPink · Post by **IslandPink** » Thu Dec 22, 2011 6:55 pm

Just to plug 'Rapid' again .
Put in an order for some carbon resistors and a bag of ferrites ( no, not a bag of ferrets , for those listening in Yorkshire

).

I put in the order about 8pm last night .
Received the parcel today - bearing in mind the Christmas post !

ILPS

Andrew · Post by **Andrew** » Thu Dec 22, 2011 7:21 pm

al newall wrote:
Daughters?
Two.

Not worth the money those GHD things. IMHO.

I got two boys so didn't know what a GHD was, I 'fort it was a disease

Mike H · Post by **Mike H** » Fri Dec 23, 2011 12:13 am

I had to look it up! Even that wasn't straightforward

al newall · Post by **al newall** » Fri Dec 23, 2011 8:11 am

Andrew wrote:I got two boys so didn't know what a GHD was, I 'fort it was a disease

It is a bit like a disease. Girls seem to be brainwashed into believing that GHD are the ones to have.
The power of advertising i suppose.

audio-talk

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