How much power can a TO-3 transistor package dissipate w/o a heat sink?

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electronice123

Joined Oct 10, 2008
311
How much power can a TO-3 transistor package dissipate w/o a heat sink?

Can anyone give me a reference also?

I just don't know where to look.....Tried searching but no results....

Thanks in advance!
 

R!f@@

Joined Apr 2, 2009
9,647
Lessee ..it can dissipate it's rated power with or without heatsink...

But without heatsink..it will blow due to thermal run away
 

Mr. Mho

Joined Jun 15, 2009
15
Fairchild makes a FET in that package... suggest you check its data sheet. Max power will depend on ambient temperature and whether the air is still or there is a fan.

Fairchild SSH70N10A
 

crutschow

Joined Mar 14, 2008
23,159
This LM317 datasheet on page 5 states the thermal resistance of a TO-3 case to a still free-air ambient is 39°C/W. Thus for a 25°C ambient air and typical 125°C maximum junction temperature, the absolute maximum dissipation is 100/39 = 2.5W. At the point the case will be hot enough to readily burn you.

That must be derated, of course, for a higher air temperature such as a warm day or in a box.
 

t_n_k

Joined Mar 6, 2009
5,448
For a simple transistor example the 2N3055 might be of interest. Data sheet attached - page 2 particularly important with respect to your question.
 

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crutschow

Joined Mar 14, 2008
23,159
For a simple transistor example the 2N3055 might be of interest. Data sheet attached - page 2 particularly important with respect to your question.
The junction-to-case thermal resistance is not helpful for the device in free air and not on a heat sink. You need the junction-to-ambient thermal resistance as shown in the reference I posted.
 

PackratKing

Joined Jul 13, 2008
843
Here is the partial spec sheet for some TO-3 transistors I have for sale in the "flea market " forum..................:D

2n5302 -- BiPolar NPN -- TO-3 -- Vceo max 60v -- Pd 200w --
DC Collector/Base Gain hfe Min: 40
Maximum DC Collector Current: 30 A
Maximum Operating Frequency: 2Mhz
Maximum Operating Temperature: +200 C
Minimum Operating Temperature: -65 C

200 watts, especially enclosed in a chassis or project box, is a considerable bunch of heat..........I would suggest forced ventilation at the very least, and my overkill habit would park it on a substantial heatsink.. based on its expected duty cycle.
 
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bountyhunter

Joined Sep 7, 2009
2,498
How much power can a TO-3 transistor package dissipate w/o a heat sink?

Can anyone give me a reference also?

I just don't know where to look.....Tried searching but no results....

Thanks in advance!
I recall the package thermal resistance is ballpark 45C/W. In 25C ambient, you can dissipate about 2.5W safely without heatsink. But that puts the junction temp at about 150C where most IC's go into thermal shutdown.
 
that's like how long can I hold it over a candle before it fails? answer=if you never power it up, it will never fail.

your answer lies with surface area as in volume of heat created vs dissipated. cheap ,no money for parts. I can buy that. too hard to fix I can't.... an empty pop can can do a lot. plus you haven't given enough info to let the piers here help.

example: resistive on value is heat. (not taking measurements) guessing total surface area about 1.125 sq inch. dissipation to calculate heat loss created by a chimney affect. cold, no problem . the longer in use the more it heats up, the faster it looses heat. the closer it get to failure.

rule of thumb (ha ha) put your thumb on it, chances are if you can't stand it, it won't ether, much longer.

This thread is more than 4 years old...... OK, but it still shows up on searches.
I am aware that this thread is old, but I still want to make a reply.
 
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