to-220 shoulder washers

So, if Graham's suggestion won't work for some reason, why not do some digging?

I agree that there's room for more material. An absurd minimum for a clearance hole for a #4 screw is 0.110 or so -- that's about the dimension that'll jam half the time, so you want something more like

0.112. The hole in the part is 0.141; this leaves you with a hair under .03 inches to divide up between the two walls.

(the more I write, the more I wonder why you don't want to take Graham's suggestion, or use a big shoulder washer from the back to insulate the screw from the heat sink, or something. I mean -- even after you've taken care of the wall thickness of the washer, you should really use one deep enough to extend all the way through the part, or further; if you go further you have to countersink your heat sink, etc., etc., etc.)

"Most that I have seen" implies that you haven't done the kind of exhaustive web searches that one must do to find mechanical gizmos like this.

Somewhere out there is a molded plastic washer company that makes what you're looking for, so if you can't change to a more HV compatible package, it should come up with assiduous searching.

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Consider a TO-247 or some more modern package than a TO-220.

John

At your age, you need all the fiber you can get! ;-)

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Amen. Much sturdier.

Jim

It _does_ help.

My typical (weekday) breakfast is a 4-oz cup of YO-Plus and an oatmeal "chewy bar".

Weekends I splurge... like a Frittata or a "skillet" breakfast with potatoes, sausage, and bell peppers, overlaid with sunny-side-up eggs ;-)

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
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 I love to cook with wine     Sometimes I even put it in the food

I still have some mica washers in my parts drawers ;-) That plus the fiber washer has held up well even in automotive applications (Belleville washer to maintain tightness).

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

| 1962 | I love to cook with wine Sometimes I even put it in the food

That's a little better bit than a piece of 2" * 4" that's been in the blender. :)

That is a common breakfast here, minus the eggs. Quick, filling, and meets my dietitian's approval. Ten minutes in the microwave, and it's ready. I buy the red, yellow & green peppers & onions already cut up & frozen, and use the large frozen french fries, along with some heat & serve sausage links. Add some spices and it ready to cook. The whole meal is about a buck, too.

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The crazy, and the insane.
The first sign of insanity is denying that you\'re crazy.

Mouser 532-7721-3PPS has a material thickness of 0.019" between the screw and the transistor tab.

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think this has enough to choose from?

;)

most of the ones I have used, the shank have been longer than the tap is thick so the first time it is used is buckles and fill out the gap between screw and tap.

-Lasse

ea?

We buy some Teflon ones from McMaster-Carr. I think they have nylon and hard fiber too. Look under Washer/ shoulder in the index. Thickness is quoted as 0.030"

George Herold

The dielectric constant of nylon is 500-600V/.001", so you should be fine with the one you have.

Cheers! Rich

Thanks, that sounds like a good idea :) Do you have a favorite part# for to-220's out of that list?

cheers, Jamie

ea?

IIRC Microplastics makes some with a thicker top.

You can also add a second washer on top of the shoulder one. A shoulder, then a fiber washer, and then a flat washer seems to work nicely.

Yes, but the real problem isn't the thickness of the "shoulder" part of the washer that sticks down into the hole in the case, but the fact that the shoulder doesn't stick all the way down to the backside mounting surface. At SOME point, there will be an air gap between the screw and the case-collector that will be the point of primary breakdown. As I vaguely recall, the breakdown DC voltage of air at STP is something on the order of

50 volts/mil with a finagle factor for high frequency AC.

Jim