What to use for TO-220 isolating pad?

[leadbelly]

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?

 

[Netlist]

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

 

[Peter Daniel]

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).

 

[leadbelly]

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!

 

[UrSv]

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!

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.

 

[Peter Daniel]

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.

 

[leadbelly]

Woo-hoo...thanks Peter, I already bought some of those

 

[rljones]

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

 

[cm961]

These chips are availible in isolated packages, you could try that.
LM3875TF intead of LM3875T.

Hope that helps.
Pete

 

[Matttcattt]

i used top3, and made a new hole, they are the perfect size. they are 22mm by 18mm, i just turned it sideways and made a hole at the top. see image.

 

[MWP]

You can use common TO3 insulators by cutting them in half.

 

[millwood]

There are silpads available in larger formats (100x100mm) which you can cut into the desired format.

does anyone know where I may be able to get those sheets in the US?

Thanks.

 

[JOE DIRT®]

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®

 

[dkemppai]

does anyone know where I may be able to get those sheets in the US?

Thanks.

Maybe Digikey... ...I order sillpads from there... ...but not sheets.

 

[chris ma]

Plastc screw is OK when not much pressure is required (diodes), but on ICs and transistors, I'm using metal screw (non magnetic) and a plastic washer (I buy from Supremetronic).

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?

 

[Peter Daniel]

Those are washers designed for that purpose. They have additional lip, that prevents the screw from touching the case.

 

[millwood]

I am concern about the shaft of the screw may make contact with the inside surface of the heat sink thru hole.

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.

 

[AKSA]

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

 

[Peter Daniel]

The rest of a thread is here: http://www.diyaudio.com/forums/showthread.php?s=&postid=204608#post204608