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Recommend transistor?

Discussion in 'Electronic Design' started by Satan's Little Sister, Nov 3, 2004.

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  1. I need a PNP transistor for switching 5 A/20 V at audio frequencies or
    a bit higher. I've been through a dozen parametric searches and
    downloaded scores of datasheets - there are too many candidates with
    nearly identical characteristics, I can't try them all.

    How do you go about picking the right power transistor? Anyone have a
    favorite with a low Vce(sat) and a DC gain >30?
  2. Leon Heller

    Leon Heller Guest

    Why not just choose the cheapest one that meets your spec., is readily
    available, has a SPICE model (in case you want to simulate your circuit),
    and buy a couple. That's what most people do.

  3. Ban

    Ban Guest

    You cannot switch AC with a bipolar junction transistor, it has a built-in
    diode function, that will rectify and induce a horrible distortion. However
    you can try two Mosfets in series, because they have a parasitic diode from
    drain to source. But best will still be a relais, and that is what is done

    If it is pulsed DC then you can do what you want. Have a look at switching
    times too, because BJT tend to be pretty slow. They will need a lot of
    current drive to achieve low Vce, so a good driver stage is a must.
    If the transistors have almost identical data, they will also behave
    similar, so probably all of your candidates will work nicely.
    Please be a little more specific about what you want to do, you will get
    better advise then.
  4. Sounds like a BD132 might fit the bill.
  5. Rich Grise

    Rich Grise Guest

    Maximize/minimize the "important" paramaters, then go for price and

  6. Clarence

    Clarence Guest


    She said nothing about switching AC.
    "switching 5 A/20 V at audio frequencies "
    Is still a DC signal.
    The level is 20Volts. The rate is "Audio frequencies."
  7. Ban

    Ban Guest

    How do you know? To me 5A/20V sounds more like the output of an audio power
    amp with 100W into 4 Ohms, but if it is supposed to be a switched power
    supply or something similar you might be right. A low Vce_sat supports your
    understanding. That is why I wrote the last sentence above.
    The transistors for both applications might be quite dissimilar, in fact.
  8. Clarence

    Clarence Guest

    Well I "Know: because I read English.
    What it "Sounds like" is that you didn't get it.
    All audio Amps operate with DC, even "Class 'D'"

    If you didn't know why didn't you just ask?
  9. We have to make allowances for these unfortunate dipshits who don't
    have English as a first language. Ban's one of them. He obviously
    doesn't understand the concept of an audio signal riding on a DC bias.
    Or class B audio either, presumably. Still, no matter...
  10. For that current and voltage it might be better to use a power MOSFET.

    However, if you want to stick with bipolar, maybe the ON MJD45H11
    (0.36 in 1K). It's an ON "preferred device".

    Best regards,
    Spehro Pefhany
  11. What? You mean it's hard to switch OFF? ;-)

    (NB: see "latch-up" in CMOS devices)
  12. me

    me Guest

    How do you go about picking the right power transistor? Anyone have a
    I ususally just use one that works out of my junk box stock. You might
    consider a higher DC gain depending on what you are driving the transistor
    with. Maybe a darlington or two transistors hooked as darlington...
  13. Ross Herbert

    Ross Herbert Guest

    Why not ask "how long is a piece of string?" You'd get the same
    answer. You don't specify how much space is available because this
    determines the mounting and heatsinking arrangement. There are
    literally hundreds of candidates in all different packages but unless
    you know the space requirements you can't start to make a choice.
  14. Rich Grise

    Rich Grise Guest

    2N3055. ;-)

  15. Hey Rich, when did a 2N3055 become PNP ?
  16. Ken Smith

    Ken Smith Guest

    Thats an NPN, but it would make a good driver for a TIP-36.
  17. Rich Grise

    Rich Grise Guest

    Oops. Guess I missed that part. MJ2955 then. :) (or is that MJE?)

  18. Rich Grise wrote...
    Depends if you want the metal TO-3 or the plastic version. But there
    are much better choices than those old poor-performance transistors.
    Is that why you put up the smiley? Very well, give us an alternate.
  19. Rich Grise

    Rich Grise Guest

    As OP said, there are billions and billions of them. :)

    I was going by the term "favorites", which reminded me of the days as
    a Radio Shack repair technician: The shop's entire budget was covered by
    warranty repairs, mostly high-end stereos with blown output trannies, and
    quasi-comp-sym was so common, that on my first one of these, the boss
    said, "Just use 3055's." So 2N3055 was our first choice for replacement
    output trannies.

    When I started there, they had about a 3-month backlog, and kept telling
    customers, "It's waiting for parts". There were two other techs plus me,
    and the boss, who worked occasionally. I practically single-handedly
    cleaned up the backlog in about three weeks.

    I know there are sh!t-hot complementary trannies now, but as for
    recommendations, all I can say is, start from the spec, and pick
    and choose based on ranges of parameters to narrow down the range
    of choices, and then go by price and availability.

    But heck, if I can get other people to do my homework for me, why
    should I bother? ;-)

  20. Pooh Bear

    Pooh Bear Guest

    Too true.

    The TIPs were pretty popular too and would doubtless have filled the bill for
    the OP if he wanted a TO-220 device.

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