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transistor 2n3055

Discussion in 'Electronic Basics' started by Bob Clark, May 11, 2007.

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  1. Bob Clark

    Bob Clark Guest

    The transistor 2N3055 is packaged in a TO3 case. It has its collector
    "grounded" to the case, and the base and emitter to the two pins. NPN
    transistors are usually used with the emitter going directly to ground, and
    the collector somewhere far from ground. Can someone give me a typical
    application for this 2n3055 transistor, showing how it is typically used in
    a circuit? What am I missing? The MJ2955, it's mating PNP, is the same
    way, and this, in a PNP makes sense.

    Thanks for the help.

    Bob Clark
  2. Meat Plow

    Meat Plow Guest

    Power amps, pass filter.
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  3. There is no such thing as a typical use. Transistors are
    used in all sorts of applications. The collectors are
    connected to cases because of the way transistors are made
    from slices of silicon. The slice becomes the collector,
    and the base and emitter are formed as islands on one side
    by successive masking, doping, heat treatment and
    metalization steps. Then the slice is bonded to the metal
    part of the case for heat sinking, as well as electrical
    connection to the collector, and flying leads are bonded to
    the top surface to make connection to the emitter and base
    The leads are not connected to make sense, they are
    connected in the only way that is feasible from a
    manufacturing standpoint.
  4. Many/most power transistors are not common emitter.

    For instance, in a power supply the power transistor is used to
    pass the voltage to the output, so the collector is connected to
    the "raw" voltage source, and the emitter is the output. The transistor
    needs to supply current, it doesn't need to do any real voltage amplification.

    In power amplifiers, it is rare to see a common emitter configuration.
    (You'd see them in the early days of transistors, but not in decades.)
    Again, the collector goes to the positive supply, and the emitter is
    connected to the output (and usually there is a complementary PNP transistor
    doing the mirror image to the negative supply voltage). The power output
    transistors do not need to supply much voltage gain, earlier stages
    take care of that, but the output transistors do have to supply current,
    and with a low output impedance. You won't get that with a common emitter

    Since in neither case neither the collector nor emitter are grounded, it
    doesn't particularly matter which is connected to the case. It may be
    convenient, in terms of internal arrangement, to have the collector
    connected to the case.

  5. Chuck

    Chuck Guest

    Hey Bob, a Google search on 2N3055 gives
    720,000 hits. There's a world of
    fascinating information out there on the

    81,000 hits from a search on "2N3055

    That's a skill you need to master.

    Good luck.

  6. Bob Clark

    Bob Clark Guest

    When seeing an NPN transistor used in a circuit, as a switch, the load is
    usually connected to "VCC", the current goes from +, through the load
    resistance, then to the collector, through the NPN transistor, and out the
    emitter to ground. Wouldn't it be nice if the transistors in the TO3 case
    had the emitter connected to the TO3 case which we could ground to the
    apparatus case. But since the transistors in the TO3 case are the reverse
    of this, one has to isolate the TO3 case from ground so as to be able to use
    an NPN transistor in the TO3 case. Maybe John Popelish is right, this is
    the only way a transistor can be made in the TO3 case. Hard to believe!!!

    Thanks, Bob Clark
  7. John Larkin

    John Larkin Guest

    The collector is the chip substrate, and they solder that to the can
    to let the heat out. The emitter and base leads are on the top of the
    chip, so are connected to the pins by wire bonds. That's how most
    planar silicon transistors (and mosfets) work.

    GaAs fets are nice for RF, because the source is the substrate and is
    convenient to bolt to a big grounded heatsink. I think there are some
    silicon npn RF transistors that have grounded emitters soldered to the

  8. Eeyore

    Eeyore Guest

    It's only grounded if the case is grounded. In any case (lol) you may very well
    not want the current to flow to chassis/frame. Most power devices are isolated
    from chassis.

    No they're not.

    How about a quasi-complementary audio output stage ? Google it.

    Not especially.

    What makes sense is that the back of the transistor die is the collector and
    when soldered to a heatsink, the heatsink tab or header also becomes the
    collector connection.

  9. Eeyore

    Eeyore Guest

    As a switch and only as a switch. Think amplifier instead of switch.

    No. To the negative supply (power return). Not ground.

    It would be no more convenient at all. In fact case to collector is better since
    where multiple devices are used in parallel the collectors tend to be commoned
    and the heatsink does that for you.

    It's true. Most of the bulk of the die (chip) is collector.

  10. Hey, back when the TO-3 case was first designed and planer
    transistors were something pretty new, They were just
    tickled to have a high power package with a big transistor
    in it.

    But the difficulty of isolating and mounting it, especially
    with high voltage on the collector, or with low capacitance
    to a heat sink, it fairly quickly was realized that
    something better would have to be designed. The power tab
    TO-220 (pin compatible with the TO-66, the smaller version
    of the TO-3) and TO-218 (pin compatible with the TO-3) and
    all their variants, carry most of the trade, today, that
    isn't surface mount.

    But all but very specialized devices still have the
    collector to the heat sink surface, because that is the way
    planer transistor die are still made.
  11. Bob Clark

    Bob Clark Guest

    Thank you all,

  12. Marra

    Marra Guest

  13. Jamie

    Jamie Guest

    Unity gain amplifiers (current boosters), just about anything a
    large transistor can do..

    The case style does not govern the electrical use of the part other
    than maybe physical placement and heat dissipation.

    You use a mounting kit that gives you an insulated sheet etc..
  14. sparky

    sparky Guest

    Ever hear of insulators? They make em all the time and can be used
    to isolate the transistor case from the heat sink. When you learn how
    to design transistor circuits you will also learn how to physically
    the devices.
  15. Phil Allison

    Phil Allison Guest

    "John Popelish"

    ** Nonsense.

    Plastic " flat pack " power devices are not " better " than TO3 - they
    are merely cheap and nasty substitutes.

    TO3 pack devices are now mostly found in professional / industrial
    equipment, on grounds of their higher reliability and where low cost is not
    so crucial.

    ........ Phil
  16. Ross Herbert

    Ross Herbert Guest

    I'm not sure, but you seem to be labouring under the misconception
    that since the collector of the NPN die is connected directly to the
    case, this constitutes an electrical "grounding". If it were mounted
    directly to a metal heatsink without isolation washers and insulator
    pad, and depending upon the connections to the base and emitter, it
    might result in fatal destruction of the device or other associated
    circuitry. Provided that any heatsink is isolated from circuit
    "ground" then you can mount them directly to a heatsink without
    insulation and no problems will arise, but in most situations this is
    not the case. As long as the three terminals C - B - E are connected
    as per a well designed circuit there will be no deleterious
    interaction and the device will perform as intended.

    As to applications - there are many and varied and you should do some
  17. Eeyore

    Eeyore Guest

    Agreed. The single mounting hole is alone cause for concern since it is
    realtively tricky to ensure a good thermal path. I use a large diameter washer
    on top of the device to help with this.

    The same die can be reliably run at a higher Tj in a metal can too. This gives
    extra power rating.

    A guy I used to work with annoyed the f**k out of me by insisting that we had to
    use TO-3Ps because he said they were (a) cheaper and (b) because everyone uses
    them now (as if that was a reason).

    When I actually checked On-Semi's site, the TO-3 device is *CHEAPER* !!!! $2.17 for 250W
    (0.87 cents/W) $2.40 for 200W
    (1.2 cents /W)

    It's also easier to cool metal can devices since they can operate at higher

  18. cdd

    cdd Guest

    The 2n3055 was very common in audio amps in mid 80's- about 50w with
    two and about 100w with 4 on the output stage-quite rugged transistors
  19. John Larkin

    John Larkin Guest

    The really big die simply won't fit into the antique TO-3 can, and the
    wirebond situation is awkward. The clamp-mount (no hole) TO-247's are
    much better.
    Off-center packages, like TO-220 and TO-3P, are pretty bad.
    The chip is the limit, not the epoxy.

  20. Eeyore

    Eeyore Guest

    Really ? Those must be damn big dies in that case !

    What do you prefer ?

    That's not what On Semi says.

    The TO-204AA (TO-3) MJ21193/4 and the plastic TO-3P (TO-264) MJL21193/4 use the same
    die but it's derated in the plastic package.

    Tj max = 150C in plastic vs 200C in TO-3.

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