Cap heating on P2P Gainclone

[Werner]

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.

[JOE DIRT®]

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

DIRT®

[matth]

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

I would be reluctant because that also hinders the natural induction of the die substrate to the metal tab

Can you explain this futher??

[peranders]

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.

[joensd]

Every capacitors get worse when it's hot, no parameter gets better.

You´re right saying that but at least the capacitance rises slightly with temperature.
I repaired so many TV´s 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 it´s that cap and put a new one in.

But don´t get me wrong here!
We don´t want to heat our caps permamently.

Cheers
Jens

[matth]

Thanks for the replies guys.

A pic to clear things up:

[joensd]

I wouldn´t 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 it´s OK for those.

That´s one I like.

Cheers
Jens