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Old 11th September 2003, 12:34 PM   #11
Werner is offline Werner  Europe
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Quote:
Originally posted by peranders
I
If you have an inverting amp this is waaaay too much.
Way too little, you mean.

2.2uF, 10k ==> 7Hz.

Have a look at the group delay.
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Old 11th September 2003, 12:41 PM   #12
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My opinion is that I would not epoxy anything to the substrate because it needs thermal contraction and expansion and the epoxy will hinder it....if you must place the cap there then I suggest a high heat silicone but even then I would be reluctant because that also hinders the natural induction of the die substrate to the metal tab

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Old 11th September 2003, 12:52 PM   #13
matth is offline matth  United Kingdom
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Thanks for the reply Joe, OK a couple of things, the parts are glued with CA and can break apart very easily. The P2P wiring should hold all componants in place, the glue is just for a little bit more mechanical reinforcement. So any thermal expansion or contraction should still be able to take place.
The other thing is that the IC is the TF insulated version

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I would be reluctant because that also hinders the natural induction of the die substrate to the metal tab
Can you explain this futher??
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Old 11th September 2003, 04:40 PM   #14
Electrons are yellow and more is better!
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Ok, I didn't exactly understand you, now I do. A plastic capacitors can take rather high temperature but I think it's not so wise to glue an electrolthic capacitors on top of a hot surface. Try at least mount it so it is as cool as possible. Every capacitors get worse when it's hot, no parameter gets better.

Think of this:

85 deg C = 3000 hours
60 deg C = 30000 hours (roughly)
40 deg C = a decade at least

I recoemmend that you use a glue which is somewhat soft, not hard epoxy.

BTW: 2.2 uF as input coupling capacitor is OK.
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Old 11th September 2003, 04:55 PM   #15
joensd is offline joensd  Germany
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Quote:
Every capacitors get worse when it's hot, no parameter gets better.
Youīre right saying that but at least the capacitance rises slightly with temperature.
I repaired so many TVīs with just a hairdryer.
Heat the suspicious cap with the dryer, capacitance rises to original value and the switching supply starts working again.
Then cool it down again to be sure itīs that cap and put a new one in.

But donīt get me wrong here!
We donīt want to heat our caps permamently.

Cheers
Jens
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Old 11th September 2003, 05:26 PM   #16
matth is offline matth  United Kingdom
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Thanks for the replies guys.

A pic to clear things up:
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Old 11th September 2003, 05:36 PM   #17
joensd is offline joensd  Germany
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I wouldnīt put it all "above" the chip.
It can get so hot your foil caps probably melt or get slightly brown on the sides and probably also have a failure one day.
Electrolytics dry out relatively fast but if you mount your heatsink vertical I think itīs OK for those.

Thatīs one I like.

Cheers
Jens
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