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

Discussion in 'General Electronics Chat' started by electronice123, Feb 12, 2012.

  1. electronice123

    Thread Starter Active Member

    Oct 10, 2008
    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!
  2. R!f@@

    AAC Fanatic!

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

    But without will blow due to thermal run away
  3. Mr. Mho


    Jun 15, 2009
    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
  4. crutschow


    Mar 14, 2008
    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.
  5. t_n_k

    AAC Fanatic!

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


    Mar 14, 2008
    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.
  7. PackratKing

    Well-Known Member

    Jul 13, 2008
    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.
    Last edited: Feb 14, 2012
  8. bountyhunter

    Well-Known Member

    Sep 7, 2009
    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.