Is It SOP to Use TO-220 ..

I thought that TO-126 packages have a hole sized for 3mm metric screws, while TO-220's have holes sized for 6-32 (non-metric) screws.

You will not be able to put a 6-32 screw in a TO-126!

All of the associated insulator hardware (mica sheet, fiber or nylon shoulder washers,etc. ) for TO-220's is completely unnecessary for a TO-126, right?

Tim.

screws,

Maybe I shouldn'r have said mounting hardware, I really meant mica insulator and washer and hardware (of the appropriate size), like what you get when you buy a TO-220 mounting kit from Rat Shack.

I've seen TO-126 devices (mostly Japanese) mounted directly to a steel heatsink which is soldered to the PC board. I've seen 'em mounted to the PC board for low power apps, with a clip-on HS, or even freestanding w/o a heatsink. But I've never seen 'em mounted to a HS with a mica or other insulator.

The On Semi AN-1040/D shows 'em mounted to a HS with screw and nut and a conical washer, but no mica insulator. That's fine if you use an electrically isolated heatsink. But if you want to mount them to a chassis or bigger heatsink, say as driver transistors with the output trs on a common HS, then they have to be insulated.

I've seen several TO-220s mounted to a common HS with the gray rubbery thermopad insulators and an aluminum bar across them all to hold them to the HS. That way, there's no hassle with insulated washers, bushings, or screws. But I've never seen the TO-126 with mica insulator and white silicon goop. So I'm just trying to come up with some kind of solution. Thanks.

"Watson A.Name - "Watt Sun, the Dark Remover"" a écrit dans le message de news: snipped-for-privacy@corp.supernews.com...

Why wouldn't you do it? Just because you've never seen it before?

Just check the mica hole size against the TO126 hole isolation and go for it if it's OK.

"Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message news: snipped-for-privacy@corp.supernews.com...

The TO-126 transistors I use (BD135, BD136) are completely insulated. What TO-126 transistors are you using, that have exposed metal like a TO-220?

wrote

What

TO-220?

No, the BD135 has the flat metal area on the back, which contacts the heatsink, electrically tied to the center pin which is the collector. The BD135s I have are made by Philips. The same is true for the 2SD975. However the 2SC4934 is completely encapsulated in plastic and is electrically isolated from the heatsink. See datasheet here

what

steel

to

freestanding

or

and a

output

rubbery

them to

bushings,

white

solution.

My original Q was "Is it SOP (standard operating procedure) to use TO-220 mounting hardware for TO-126 devices?"

for it

TO-220: Use a sil-pad (the gray rubbery thermopad you mentioned), incur the wrath of John Larkin (rightly so, as experiments demonstrated), endure more heat in the device - but if you need insulation... mica would be better, sil-pad easier to modify (if needed). I haven't experimented yet to see the Rt difference between a sil-pad and mica. I've never seen a TO-3 sil-pad, but TO-3 micas abound. Makes you wonder. Mica is supposed to be a better heat conductor than sil-pad.

Ed

needed).

I've seen the spacer, looks like it may be anodized aluminum, for the TO-3. It's thicker than mica, and dark, almost black. I don't know what it's made of, because I've never had to remove one. Seems like all the PSes I've come across are cheapo, with TO-220 or similar devices. It used to be that heatsinks were massive with convection cooling and TO-3s. Nowadays in order to reduce size and weight and cost, they are all smaller and cooled with fans and use epoxy cased devices.

The On Semi AN-1040/D app note shows some good info on why the TO-220 and similar are not the best way to mount a power device to a heatsink.

"Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message news: snipped-for-privacy@corp.supernews.com...

Hmm, interesting. The BD135s I've been using are by Fairchild, and they are completely insulated, no exposed metal.

What a pain! I don't think I've seen mica insulators with the smaller TO126-sized hole myself, although Google does turn some up ("TO126 insulator").

wrote

the

collector.

they are

The Fairchild datasheet I have is dated Feb 2000 and doesn't show whether or not the 'backside' is insulated; it doesn't show the backside. Philips' datasheet does so and states so. SGS-Thomson's datasheet calls the package SOT-32, and does show a graphic of the backside, which looks like it has a metallic area that contacts the heatsink. But it doesn't state that it is connected to the collector. The general standard is that most transistor packages have the metallic area electrically connected to the collector.

ON Semi has the BD135 and says it's in the Case 77-09, what it calls TO-225. Here

Fairchild's BD135 series should conform to the rest of the industry, which is probably like Philips, since Philips or another Euro manufacturer is probably the original maker of the series. Also it seems to me that in order to dissipate that much power on a heatsink, it would have to have a metallic area on the backside.