Hi everyone, some advice please regarding types of insulators for TO247 transistors. They appear difficult to buy. I am fitting MJL21193/94 as outputs for a class A amplifier. I have some "rubbery" insulators for TO 247's they are grey in colour and are the correct size, I have had them a long time, I do not know make or anything about them. Or I could cut TO3 mica insulators to size. Which would give best heat transfere? Sorry to be so vague, but if anyone can offer some assistance I would be gratefull.
Thanks
Alan
Thanks
Alan
Go to Mouser Electronics and search for TO 247 thermal pads. They are easier to use and may even be better.
RS Components | Electronic and Electrical Components
Farnell element14 | Electronic Component Distributors
I like the to247 package as you don't need the bolts isolating.
Farnell element14 | Electronic Component Distributors
I like the to247 package as you don't need the bolts isolating.
TO3P insulators are much more common, cheap and you find the slight oversize is not a problem unless everything must be very neat and tidy. In that case a minute with a pair of scissors should do what you want to bring them down to TO247.
MJL21193/4 are TO264, which is larger than usual TO3P. Try searching that reference because the 2 sizes TO3P👎 and T03P(l) suffix that refer in some parts catalogues, is confusingly omitted. If you look at NJW21193/4, you'll see them also referred to as TO3P. As far as I know, MJW21193/4 types are the ones produced by On-semi in TO247, which is smaller again than TO3P.
This stocklist is typical of what's available: Transistor Mounting Kits
MJL21193/4 are TO264, which is larger than usual TO3P. Try searching that reference because the 2 sizes TO3P👎 and T03P(l) suffix that refer in some parts catalogues, is confusingly omitted. If you look at NJW21193/4, you'll see them also referred to as TO3P. As far as I know, MJW21193/4 types are the ones produced by On-semi in TO247, which is smaller again than TO3P.
This stocklist is typical of what's available: Transistor Mounting Kits
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I should have mentioned that that you'll only find mica for the older types like TO3, TO126, TO220, occasionally TO3P and rarely TOP3, MT200. Later developments like TO264, TO247/T0218 were after the change to silicone rubber, which you already have. TO247 and 264 packages were introduced with silicone in mind so there is no need to tough it out for the last joule with mica/grease within their specification.
However, if your design called for MJL21193/4 but you are actually using MJW variants, you could be making a significant error with class A's high dissipation requirements whatever insulators you use.
However, if your design called for MJL21193/4 but you are actually using MJW variants, you could be making a significant error with class A's high dissipation requirements whatever insulators you use.
Hi, thanks for the replies.
Ian, I am using ON Semi MJL devices and electrically they will be very much "under-run" , 26V rails and aprox 500mA per device. So I take it from your post that the grey insulators I have are silicone rubber and there would be no benifit to cutting down TO3 mica insulators to fit the TO 247's.
Thanks
Alan
Ian, I am using ON Semi MJL devices and electrically they will be very much "under-run" , 26V rails and aprox 500mA per device. So I take it from your post that the grey insulators I have are silicone rubber and there would be no benifit to cutting down TO3 mica insulators to fit the TO 247's.
Thanks
Alan
I'll have to ask the same question as the others.
Are you sure the MJL21193/4 are actually To247?
Read off the size/dimensions and the Onsemi size code from the datasheet.
Are you sure the MJL21193/4 are actually To247?
Read off the size/dimensions and the Onsemi size code from the datasheet.
Hi, my apologies, they are indeed TO264. Brain problem again- had one of those "senior moments"
Thanks
Alan
Thanks
Alan
Indeed the Keratherm pads are good but another alternative in Kapton film tape, a pair of scissors and a leather punch does very well too - better than typical mica at least and cuts to any type you need from a 25mm wide roll.
3M's 33 metre roll length is not cheap either but think of the hundreds of pads and an opportunity to share out the metres in group buys. Rod Elliott (ESP) has been doing just that from his website for years.
3M's 33 metre roll length is not cheap either but think of the hundreds of pads and an opportunity to share out the metres in group buys. Rod Elliott (ESP) has been doing just that from his website for years.
6thou (6mil, 0.152mm) Kapton is much worse than 1thou mica.
even 2thou Kapton is not quite as good as 1thou mica.
Many Vendors do not sell 1thou, 1.5thou, 2thou Kapton.
A few that do sell the thin Kapton only sell the self adhesive style and tell you nothing about the thermal properties of the adhesive that is sometimes even thicker than the thin Kapton !!!
I tried looking for a UK Vendor of 1thou 25mm wide non adhesive Kapton tape a couple of years ago. I failed.
even 2thou Kapton is not quite as good as 1thou mica.
Many Vendors do not sell 1thou, 1.5thou, 2thou Kapton.
A few that do sell the thin Kapton only sell the self adhesive style and tell you nothing about the thermal properties of the adhesive that is sometimes even thicker than the thin Kapton !!!
I tried looking for a UK Vendor of 1thou 25mm wide non adhesive Kapton tape a couple of years ago. I failed.
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Mssr Finch: Thank you !
Was in need of non conductive isolators on a heat sink.
Great info.. I have a Roll of above Kapton tape, on hand
Was in need of non conductive isolators on a heat sink.
Great info.. I have a Roll of above Kapton tape, on hand
Andrew, the Kapton commonly used is 1-1.5 thou. RS sell Tesa brand which is quoted at 0.065mm. The stuff I use is similar to that offered by ESP which is 25uM - thin enough? ESP - Complete Price List (last item, KAP 1)
Most mica on sale is also far thicker than 1 thou. Yes, you can get out a razor blade and slit it if you wish or only order from a specialist manufacturer. A year or so ago, I did buy a batch of MT200 micas from Taiwan which were average 1.0 thou, measured with a dial gauge but they were thinner than any other mica I have been able to buy since 1970, when I also first used mica and compared Kapton type film (polyimide).
The problem with DIY mica slitting is non-uniformity and the fact that mica itself is not truly flat. The result for DIYs generally is inferior due to a stepped surface when using mica. If you have exclusive supplies that are ideally flat and thin, then I would agree that it is entirely possible for it to be superior. For most of us who just buy imperfect products because that's all they can buy, it's just not so.
Most mica on sale is also far thicker than 1 thou. Yes, you can get out a razor blade and slit it if you wish or only order from a specialist manufacturer. A year or so ago, I did buy a batch of MT200 micas from Taiwan which were average 1.0 thou, measured with a dial gauge but they were thinner than any other mica I have been able to buy since 1970, when I also first used mica and compared Kapton type film (polyimide).
The problem with DIY mica slitting is non-uniformity and the fact that mica itself is not truly flat. The result for DIYs generally is inferior due to a stepped surface when using mica. If you have exclusive supplies that are ideally flat and thin, then I would agree that it is entirely possible for it to be superior. For most of us who just buy imperfect products because that's all they can buy, it's just not so.
How's this for suitability, min quantity and price? Freight is something else, I'm afraid.
1-mil Polyimide (Kapton) Film No Adhesive | PIT1N-Series
1-mil Polyimide (Kapton) Film No Adhesive | PIT1N-Series
I don't know if this helps. Some people use uninsulated heat-sinks and the transistor grease. They then isolated the heat-sinks from the chassis and outside world. It means a little thought doing things this way. All PNP on one heat-sink and NPN on another. When TO3 and flying leads not a bad idea.
Arcam when A+R for the A60 used high grade anodizing to isolate them. It always worked!!!!!!! They said it made a big difference to size of heat-sink. A60 was a genuine 40 + 40 watts and very few blow ups. Great amp if asking.
There are cheaper versions of this product in the link. This one looks very top spec. Hope the links open. CPC UK if not.
Those grey ones you speak of are most likely very good.
SIL-PADK10 304X304 SHEET - BERGQUIST - SIL-PAD, 304X304 SHEET, K10 | CPC
Insulators | CPC | Results
Arcam when A+R for the A60 used high grade anodizing to isolate them. It always worked!!!!!!! They said it made a big difference to size of heat-sink. A60 was a genuine 40 + 40 watts and very few blow ups. Great amp if asking.
There are cheaper versions of this product in the link. This one looks very top spec. Hope the links open. CPC UK if not.
Those grey ones you speak of are most likely very good.
SIL-PADK10 304X304 SHEET - BERGQUIST - SIL-PAD, 304X304 SHEET, K10 | CPC
Insulators | CPC | Results
Those are roughly the dimensions of a TO264 package but the metal heat spreader is slightly narrower than the package outline. They are quite thick at 15 thou though.
What about these ceramic?Transfer Multisort Elektronik - On-line Catalogue | Over 120 000 products offered.