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Old 12th March 2003, 03:32 PM   #1
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Default Better transistor package?

Hi!

I'm new in this forum, most of the time I just read and find it's very informative but now I need to ask a question.

I would just like to ask your comments on which is better or easier to keep cool, transistors in TO-3 package or the plastic ones (TO-247) for output of power amps.


Tnx!

Jojo
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Old 12th March 2003, 10:00 PM   #2
MGR is offline MGR
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Hi

I am also from the Philippines,the better package is TO-3 but mounting wise the Plastic package is easier to work with.

MGR
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Old 13th March 2003, 05:38 AM   #3
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Default Hello!

MGR,

Nice to know that we're from the same country.

I guess Ill just stick with to-3s this time.
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Old 13th March 2003, 08:08 AM   #4
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TO-3 is ancient, not used anymore for new designs. Why? It's difficult to mount, that's the main reason. I think also that it's cheaper with plastic case.
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Old 13th March 2003, 09:53 AM   #5
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Actually there are a number of new designs that use the TO-3 package. Although you are right that the plastic packages are becoming more common.

If you are making in amp that is gonna get very hot (class A) then the TO-3 transistors are definatly better at keeping cool.
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Old 13th March 2003, 10:22 AM   #6
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Quote:
Originally posted by Morph
Actually there are a number of new designs that use the TO-3 package. Although you are right that the plastic packages are becoming more common.
If you really look inside power electronics (not just amps), manufactured today, TO-3 is very very rare.
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Old 13th March 2003, 10:45 AM   #7
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peranders.

so you are saying that its a good choice to choose plastic packaged transistors nowadays. i'll just be using it for an amp project.

tnx.
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Old 13th March 2003, 11:06 AM   #8
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Rare because they are more expensive than plastic and more difficult to mount. TO 3 is a very good case for heavy applications considering it's thermal characteristics.

Same story as why DIL/DIP disappears: production costs. Although I missed the explanation of producers like they give with SMD components:

- "the market demands it"
- "it has lower lead inductance"
- "better RF characteristics"
- "it is to big"
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Old 13th March 2003, 11:30 AM   #9
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Indeed Jean-Paul.

Another thing to note is that the package is only part of the story. Thermal resistance is much like electrical resistance. From the transistor chip to ambient air you first have to go from chip to package which has a certain resistance in deg Celcius/Watt, then to the washer, then to the heatsink, then to ambient. Each junction adds a thermal resistor in series. At the and you arrive at say .75deg/W for the TO3 and .80 for the plastic, not a great deal and easily compensated for by increasing the heatsink a little if it were critical. And it is only for interest in class A applications anyway.

Modern, wideband power transistors for audio are as far as I know all packaged in plastic.

Jan Didden
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Old 13th March 2003, 11:36 AM   #10
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What about things like the mj15003/mj15004, its not true that all power transistors these days are in plastic packages just most of them are.

Some of the new power opamps from burr-brown are in TO-3 packages. I saw one with 8 leads! how about that for difficult to mount.
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