LM3886: TF Version or rather T + isolation pad? - diyAudio
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Old 11th April 2006, 05:46 PM   #1
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Default LM3886: TF Version or rather T + isolation pad?

Hello
See Topic.
What will give the better heat flux?



Thanks,
Stephan
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Old 11th April 2006, 06:50 PM   #2
Bazukaz is offline Bazukaz  Lithuania
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For sure , T + mica insulator + thermal paste will have better thermal conductivity.Silicone pads are worse than mica for thermal transfer.

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Lukas
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Old 11th April 2006, 09:09 PM   #3
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If you have normal demands, just use the TF version with some heat compound.
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Old 12th April 2006, 09:50 AM   #4
Vidalgo is offline Vidalgo  Israel
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T with good silicone pad will be better. Thermal resistance of good silicone pad can be as low as 0.2 K*in2/W. Look for Bergquist thermal pads "Sil-Pad K-10", selling by Digikey.
Also, with T case you will have another nice option - cooling both sides of metal tab. Why no? Use an insulator pad for large, main heatsink and add small heatsink to front side of the tab, without insulator but with thermal greese. This simple trick give lot of help.
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Old 12th April 2006, 01:03 PM   #5
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It seems that Sil-Pad K-10 has thermal resistance of 0.41 C*in2/W...
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Old 12th April 2006, 01:33 PM   #6
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Quote:
Originally posted by peranders
If you have normal demands, just use the TF version with some heat compound.
The TF part requires a heatsink with 1 C/W lower thermal impedance. This is a pretty big difference if you are using nominal 30 vdc rails -- practically speaking the heat sink for a TF part has to be 70% larger with 30VDC rails.

You can figure this out with National's Overture Series design calculator, and Aavid Thermalloy's heatsink calculator.
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Old 12th April 2006, 04:03 PM   #7
Vidalgo is offline Vidalgo  Israel
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Quote:
Originally posted by Bazukaz
It seems that Sil-Pad K-10 has thermal resistance of 0.41 C*in2/W...
It's pressure depended. Drops when tightly screwed, with metal clamp or spring over chip body.
But I'm surprised. In my printed catalog (5yr old), K-10 listed with 0.2 K*in2/W.
Anyway, K10 is far away better than a regular cheap glass-filled silicone pad.

Another cooling trick.
Make an aluminium brick - says, 30x50x10mm. Screw 3886 to it without insulation, only with thermal grease applied (you can get extremelly good one from computer world, like Arctic Silver).
Now screw this assembly to the main heatsink, with insulator pad. Well, you need big pad, as big as your brick. But it can be made from less-perfomed material and cheap. Don't forget about insulation washers under the screws.
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Old 12th April 2006, 04:27 PM   #8
cpemma is offline cpemma  United Kingdom
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Quote:
Originally posted by jackinnj
The TF part requires a heatsink with 1 C/W lower thermal impedance...You can figure this out with National's Overture Series design calculator...
The NS spreadsheet does show a big required HS difference between T & TF, but the figures are for grease only, no "extra" insulator pad, so need an isolated sink with the 'T'.

Otherwise you need to factor in a "typical" 0.4-0.5C/W pad (and as said, there are better pads), so if you're pushing the limits and don't want the bigger HS use the 'T' with good quality interface media.
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Old 13th April 2006, 01:36 AM   #9
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Arctic Silver Ceramique is non-conductive; it would work very nicely with mica pads. I've used it before; it's good stuff, and a 4$ tube will last you months if you use it properly.
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Old 13th April 2006, 06:13 PM   #10
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Hello,

thanks for your responses.


Quote:
Another cooling trick.
Make an aluminium brick - says, 30x50x10mm. Screw 3886 to it without insulation, only with thermal grease applied (you can get extremelly good one from computer world, like Arctic Silver).
Now screw this assembly to the main heatsink, with insulator pad. Well, you need big pad, as big as your brick. But it can be made from less-perfomed material and cheap. Don't forget about insulation washers under the screws.
I already thought about that. I've got some big aluminium plates here, 10mm thick.
But I dont know how to isolate them from the Heatsink.
There seems to be no dealer in germany who sells that big silicone or mica plates...


Quote:
If you have normal demands, just use the TF version with some heat compound.
Hmm... What are "normal demands"

I want to use 4 Ohm speakers and I'm going to use a transformer with a least 18V AC, rather 22V AC.
It should bear that.

But if I cant get suitable mica or silicone sheets, wich seem to bee extremly rare in germany, since the IC is not a regular TO220, i'll have no other choice then using the TF...
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