Where to get LM4780 Thermal Pads? - diyAudio
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Old 6th June 2006, 06:52 PM   #1
lgreen is offline lgreen  United States
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Default Where to get LM4780 Thermal Pads?

I need two thermal (electrical) insulating pads for my LM4780 amp (2 chips) and then a few more for the next revision. I've searched here and seen the free sample thread (so far nothing after 2 months) and European suppliers, but there is nothing in USA that I can find.

Anyone have some to sell or know where I can get some? I thought I'd use TO-3 mica pads but after trying for 2 days the heatsink is live (negative DC rail (V-) as per footnote 14 in the data sheet) and I'm pretty sure its not caused by something else.

thanks
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Old 7th June 2006, 03:20 AM   #2
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Digikey has a fair selection.
http://www.digikey.com/

Look on pages 789 & 790 of their online catalog.
http://dkc3.digikey.com/PDF/T062/0789-0790.pdf

Fig 7 on page 789 looks about right for the LM4780... but be
aware that the Q3 material on that one is graphite... which IS
electrically conductive.

Looks like fig 5 might be a better alternative... though some
modification might be required.

There is also some bulk sheet materials listed on page 790.
But the extra thickness worries me.

Good luck. Let me know if you find something better.

Best Regards,
Head_spaz

Edit: just saw this on e-bay:
http://cgi.ebay.com/Mica-Sheet-2-25-...QQcmdZViewItem
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Old 7th June 2006, 03:28 AM   #3
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you can use a TO-3 pad, or a pair of ordinary TO-220 pads.

if anyone is interested, there is supplier of mica pads from China which will custom manufacture TO-220 for this format. The pads which would work on the LM4780 or LM4702 -- but I would have to order thousands -- GB anyone????

I should have these manufactured as well, they snug the chip up to the heatsink really well.

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Old 7th June 2006, 03:46 AM   #4
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I have a hard time finding stuff on Digikey myself. When you go to the site search "Sil Pad 400".
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Old 7th June 2006, 04:58 PM   #5
lgreen is offline lgreen  United States
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Default turning to ebay

Like I said, the TO-3 insulators are not working for me.

How about this Mica Sheet on Ebay?

Click the image to open in full size.

You could cut it to size and even remove some of the lamination thingies to make it thinner.
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Old 7th June 2006, 06:31 PM   #6
poobah is offline poobah  United States
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lgreen,

That mica doesn't really look like the stuff you want... you might be able to cleave off a nice thin piece... but... The good stuff comes from India... dead flat and almost water clear... HARD to find here (phlogopyte mica?).


Call Bergquist 800-347-4572

Tell them you can't find an insulator for this device and you need some plain jane SILPAD 400.

Once they learn that nobody has shelf stock of a precut part, they will send you a sheet. They are very nice people. They have made lots a weird dohickeys for me. Doesn't hurt to tell them you're a consultant and this is a new design... report to us... and that will be your conscience clearing consultation.

If that doesn't work, I'll clean my desk and send you a piece, try the easy way first though!

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Old 7th June 2006, 06:42 PM   #7
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dohickeys? ''
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Old 7th June 2006, 06:54 PM   #8
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yes!

and widgets. gizmos. and even deals

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Old 7th June 2006, 08:29 PM   #9
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Quote:
Originally posted by poobah
They are very nice people.
Bergquist people are so nice they'll call a day after the catalogue and sheets slide in the mail box, AND invite themselves over.
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Old 7th June 2006, 08:35 PM   #10
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