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.
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.
peranders said:
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.
It's pressure depended. Drops when tightly screwed, with metal clamp or spring over chip body.Bazukaz said:
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.
jackinnj said:
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.
Hello,
thanks for your responses.
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...
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...
thanks for your responses.
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...
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...
A T03P/T0218 pad (25.4 x 19.1) will fit the chip OK. Using the aluminium (or copper) heat spreader instead, look out for sheet material like this, but it's fairly expensive and seems to be getting harder to find.
The spreader doesn't need to be enormous in area, too big and you'll have problems with plate:sink flatness. Main thing is the heat reservoir action to get heat out of the chip quickly, so mass is good.
The spreader doesn't need to be enormous in area, too big and you'll have problems with plate:sink flatness. Main thing is the heat reservoir action to get heat out of the chip quickly, so mass is good.
DigiKey sell suitable to LM3886 pads; this is Bergquist P/N K10-114 (DigiKey stock No. BER118-ND). They are 24x21mm, with hole.
If you need a big thermal sheet.
- Use smaller pads, with same thickness. Just arrange them to all area without overlapping.
- Visit web sites of companies who's make things for thermal management: Wakefield, Thermagon, Bergquist, Fujipoly, Chomerics, AAVID Thermalloy. Just google for exact web addresses. Probably there are dealers in your region. Also, for 1 amp you can get samples of sheet materials.
- Kapton (polyimide) film is excellent insulation material with good thermal conductivity. No idea who make or sell it.
- Exotic.way. Take big unused paper-in-oil capacitor and open it. Oiled paper has good thermal properties. And easy to cut. After assembling you must check it for shorts, at room temperature and heated to estimated maximum (use heat gun).
Vidalgo said:
Kapton is a DuPont plastic of the nylon family.
Digikey sells Kapton pads:
http://dkc3.digikey.com/PDF/T061/0747.pdf
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.