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Old 27th April 2011, 11:07 PM   #1
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Default Help isolating LM4780

So, I finally bought my LM4780 chip off of DigiKey. I mindlessly forgot that it is a non-insulated type chip, so now I'm confused about proper isolation etc.

I'm using a wood chassis with some beefy copper heatpipe computer heatsinks doing the cooling. I know since my case is wood, it won't conduct (duh), but just incase I or someone else forgets somewhere in the future not to touch the heatsinks while it's running, I'd like to isolate them.

I'm kinda dumb with this entire concept so bare with me. What would happen if I ran a wire screwed in my heatsink to the safety ground pin on my IEC jack? Would that isolate it? Or do anything?

Thanks.
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Old 27th April 2011, 11:15 PM   #2
Minion is offline Minion  Canada
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You need a Mounting kit , it will come with a Mica or Sil pad that isolates the chip from the heatsink and a Plastic washer type thing that isolates the mounting bolt from the chip and heatsink ..... you should put some heatsink compound between the Pad, chip and heatsink .....

They are pretty cheap and you should be able find them at any electronics shop .....


Cheers
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Old 27th April 2011, 11:24 PM   #3
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I'm not going to be screwing them in unfortunately...
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Old 27th April 2011, 11:29 PM   #4
Minion is offline Minion  Canada
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Then you just need the Mica or sil pad ...... how are you mounting them ?? are you putting a bar across the chips ??
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Old 28th April 2011, 01:43 AM   #5
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Yes essentially a bar. The 2x LM3886s that are part of the same amp (powering the satellites) will be screwed, but the LM4780 (sub amp) can't be because of the positioning of the heatpipes which cannot be punctured. So I'm kind of using a bar/bolt thing.
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Old 28th April 2011, 03:07 AM   #6
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You say they sell these at some place with Radio Shack (the Source)? I can't say I've ever seen them there, though I've never looked. Also there is like 0 thermal pads on Mouser/Digikey. It's so lame.
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Old 28th April 2011, 03:35 AM   #7
infinia is offline infinia  United States
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the heatsink metal portion on back of the part is internally electrically connected to -Vee.
1 ) use 0.002" (2 mil) kapton film or 0.003 kapton tape. it comes in 0.5 and 0.75 widths, clean the tape with solvent and apply very thin coating of thermal grease both sides. EDIT>I think polyamid is the generic term for kapton
2) use only grease and take precautions to isolate the entire heatsink. (only recommended for advanced users )
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Last edited by infinia; 28th April 2011 at 03:51 AM.
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Old 28th April 2011, 04:05 AM   #8
infinia is offline infinia  United States
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Quote:
Originally Posted by TheLaw117 View Post
Also there is like 0 thermal pads on Mouser/Digikey. It's so lame.
Thermal interface products
I'd just buy one of these and cut it to make 8 or so
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Last edited by infinia; 28th April 2011 at 04:13 AM.
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Old 28th April 2011, 01:55 PM   #9
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I requested some samples from Berquist which makes Sil-Pad. Hopefully I can get some for free then...
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Old 28th April 2011, 02:18 PM   #10
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Try Ebay Item No. 200600615657

This is a 3" x 4" sheet of Mica Sheet which can be cut to size. It's brittle so be gentle when cutting it, sharp scissors are the best tool for the job.
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