IIRC, the collector is internally connected to the metal housing and the maximum operating Tj is increased from 125-150oC to an easy 200oC with the TO-39. Then there is the premium hermetic sealing advantage. There's no question about the superiority of that package to all else....
never
I've got Toshibas that slow down to a crawl below *twenty volts*.
They're video / chroma output transistors though.
Tim
-- Deep Fryer: A very philosophical monk. Website @
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If I had tried to incorporate the plastic package into the Geiger counters we made for the Navy to look at their reactor vessel containment areas with, we would have lost that contract, and I would have lost my job. Since our product (The 1.5kV HV source for the counter) was fully encapsulated, it had to be done with the right parts. Just breathing "coffee breath" onto some assemblies can cause a premature failure.
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If you think that's so, then I'm sure you can name a whole list. Come on then let's see it.
Metal can devices are rarely used outside military and aerospace now because they have very little to offer that's valuable in most instances.
As it happens I'm still a fan of the TO-3 can device for audio output devices since the 2 point fixing avoids mounting flange distortion that can happen with TO-3P and TO-264 style devices plus the higher die temperature allowable (200C instead of
150C) means they will dissipate more with the same die inside. Compare the MJL21193 (200W) and MJ21193 (250W) for example.So, there you are. I'll use them where they have an advantage to offer. I'm certainly not biased against them. I last used TO-18 about 35 years ago though.
Graham
The 2N2222 is in TO-18 not TO-39. TO-18 is not a useful package for power applications.
The fact that the 2N2222 in TO-18 is only good for 500mW whilst the PN2222 is good for 625mW DESPITE the 50C lower Tj only shows how poor the TO-18 can performs thermally.
Graham
I think I've bumped into a few like that too. IIRC they were a 500V transistor that was normally operated in the 200V to 400V as a linear part. It was part of a linear regulator so saturation wasn't supposed to be happening. I noticed that when the supply voltage went low, the regulator oscillated making a waveform that looked like a low passed squarewave.
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How about thermal and mechanical shock resistance?
Best regards, Spehro Pefhany
-- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
military /
changing
Since they were specifically designed originally for industrial, and hi-rel applications, I am quite sure that they excel in both.
See abse for the Motorola specs. They were the original designers of the part, IIRC.
If you make a serious attempt to heat sink the TO-18, I think you can push it harder than you can by heat sinking a TO-92. I have seen a few TO-18s soldered to a copper plane, or into a large plated through hole, or clamped into large aluminum heat sink, and those could get rid of considerable power. This was in old equipment where the choices were TO-18, TO-39, TO-66 or TO-3. Unfortunately, this adds a lot of capacitance to the collector node. I think the TO-18 may even outperform the TO-39 if properly heat-sinked, if the can construction is the same in each (not the thick base version of the TO-39).
Heat sinking a TO-92 through the epoxy case has a higher thermal resistance than metal to metal contact, but at least, provides isolation between heat sink and collector.
-- Regards, John Popelish
The data I have does not support your assertion.
The thermal resistance of the TO-18 package from junction to case is
146C/W whereas for TO-92 it is 83C/W. Will post these in abse.Graham
Thanks. I stand corrected.
Figuring out a way to hold the entire surface of the TO-92 at 25C is a bit of a problem, though. Submersion in boiling refrigerant, perhaps (i.e. putting the transistor in the wet end of a heat pipe). Simpler to get effective thermal contact between a round can and a metal heat sink. But it would be interesting to see a TO-18 operate in a heat pipe, too.
-- Regards, John Popelish
That isn't as easy as it sounds. The TO-18 is strong against compression at the ends but not in the middle. When you attempt to grip it, you tend to get a gap around the waist. Using a softish alloy and making the sink have a slit in it that a screw tightened seemed to make the best results.
The same sort of thing can be done with the TO-92 but the machining is a bit trickier. You want the sink to press against the flat face so a simple round hole and a slit doesn't work very well.
These days it is better to just use a bigger part.
Use a hard anodized sink. That is a non-conductive interface.
The REALITY of decades of design incorporation of the part, however, DOES, idiot.
U-B-Dumb. We-B-knowin-this-fact.
Well ... to be honest I don't see either package as suitable for serious power dissipation.
Graham
On TO-18 ?
You're quite mad. So, it'll dissipate about 1W now !
Graham
Designs that fail to use the correct data are flawed designs.
Graham
No one said they were, dope.
They are only good for 1 W or less, and that is pushing it.
There are mil spec heat sinks that are hard anodized that clamp or are thermally bonded right onto the can.
It will dissipate 1W in free air.
That must have been what happened to you then.
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