What are you guys using to isolate your wide TO-220 packages like the LM3875?
Checking stores, all I can find are the thin flexible TO-3 pads (wrong shape) or the thick aluminum oxide for narrow TO-220 (too narrow).
Is there something more specific out there which I can't find?
How crazy would it be to drill 2 more holes in the 3875 and just use 3 TO-220 insulators?
Checking stores, all I can find are the thin flexible TO-3 pads (wrong shape) or the thick aluminum oxide for narrow TO-220 (too narrow).
Is there something more specific out there which I can't find?
How crazy would it be to drill 2 more holes in the 3875 and just use 3 TO-220 insulators?
The ultimate in DIY!!! It would be like drilling holes in ones brain to fasten its head before going under a scanner.
There are silpads available in larger formats (100x100mm) which you can cut into the desired format. Your local supplier must be able to provide them.
This for example: http://www.angliac.com/product_search/product_range/datasheet_search/cat_page.asp?cat_number=500
/Hugo 😉
I'm using TO-220 aluminum oxide pads under LM1875. It works fine and sounds better than silpads (less damping, I guess, results in more airy sound).
Peter, do you mean just the regular narrow TO-220 pads? So you are experiencing no issues with having some of the LM3875 mounting surface not in contact with the pad? If so, I would love to hear it!
leadbelly said:
Peter was talking LM1875 which is in TO-220. LM3875 is in 11 pin MultiWatt which is small enough to fit on a TO-3P (not TO-3) pad. To use TO-220 pads under a LM3875 seems pointless since TO-3P are readily available. The MultiWatt size is hard to come by and the only place I've seen it is Schuro.
I got everything mixed up. I meant LM3875 and TO-247 pads pictured below. They measure 14 x 19.5mm and I think are sold indeed as TO-220, but fit TO 247 and are the same as TO-3 P (I guess). The sides of a chip are sticking out a bit, but I didn't have any problems because of that so far. I really like to use those aluminum oxide pads here, as I said before, they sound better and provide extra clearance between heatsink and pins for a feedback resistor.
Attachments
I've used the Multi size, like digikey part BER118-ND for the LM3875 or the TDA7294. A less expensive option is BER190-ND in the same size.
regards, robert
regards, robert
These chips are availible in isolated packages, you could try that.
LM3875TF intead of LM3875T.
Hope that helps.
Pete
LM3875TF intead of LM3875T.
Hope that helps.
Pete
silpad is very expensive.....I purchased a 12" wide roll for a production run and it was a 1000CAN.....we used a paper cutter to cut the required size which increased labour costs....I regret approving the decision now
DIRT®
DIRT®
Peter Daniel said:
Are those plastic washer are just normal flat ones, I am concern about the shaft of the screw may make contact with the inside surface of the heat sink thru hole. May be I have to use heat shrink on the screw first?
Those are washers designed for that purpose. They have additional lip, that prevents the screw from touching the case.
chris ma said:
Chris, like Peter said, those washers have extra-long "sleeves" that do precisely that: preventing the screw from touching the heatsink.
I have been using plastic tubing for that purpose as well.
Since TO-220s normally run around 1W dissipation or thereabouts, I normally just use a simple bolt on heatsink like a THD6080 and don't even bother with insulation. This improves thermal coupling, and since the heatsink is small anyway you can usually tolerate it being at collector potential.
Cheers,
Hugh
Cheers,
Hugh
The rest of a thread is here: http://www.diyaudio.com/forums/showthread.php?s=&postid=204608#post204608
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