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How would one use NPN transistors only?

Discussion in 'Electronic Design' started by B, Jun 8, 2004.

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  1. B

    B Guest

    All:

    I am familiar with the typical amplifier using NPN, and PNP
    transistors. It just makes good common sense, even to lay people like
    me.

    What about amplifiers that use ONLY NPN transistors? How would that
    work? It may be elementary, but when I am trying to theorize that, it
    just doesn't make sense to me.

    There are a few people now building amplifiers with only NPN
    transistors, and I understand the advantages, but I don't understand
    how they make it work.
     
  2. Hank

    Hank Guest

    What type of amplifier are you talking about? I can build a class A amplifier
    all day long with just one npn transistor.
     
  3. Activ8

    Activ8 Guest

    On Tue, 08 Jun 2004 16:19:42 GMT, Hank wrote:

    It takes you all day? ;)
     
  4. John Larkin

    John Larkin Guest

    Advantages?

    John
     
  5. Activ8

    Activ8 Guest

    Speed, sinks more, smaller Vce, easier to get out of saturation,
    IIRC.
     
  6. MikeM

    MikeM Guest

    How did they manage when all they had is tubes?
    Tubes are like NPNs; there were no PNP tubes...

    MikeM
     
  7. MikeM wrote...
    In the early Ge transistor days, everything was all PNPs. :>)

    In tube days the issue of making multistage dc amplifiers (that's
    where one runs into a problem) was handled with fixed-voltage
    level shifters, made from resistors, or from neon lights. In
    more recent times with early ICs that were NPN only, resistors
    were used, both as voltage dividers and with current sinks, as
    well as 6V zener diodes (made from reversed-BE junctions).
    Examples can be seen in the old uA702, uA709 and uA715 opamps.

    Thanks,
    - Win

    (email: use hill_at_rowland-dot-org for now)
     
  8. Tim Wescott

    Tim Wescott Guest

    Yea, it's a bitch keeping the antimatter tube elements connected up to
    the rest of the device - but heating the cathode really isn't a problem.
     
  9. Hank

    Hank Guest

    It takes about 1 minute. I spend the rest of the day wasting my time on the
    internet. :)
     
  10. Activ8

    Activ8 Guest

    At least you have your priorities straight ;)
     
  11. Activ8

    Activ8 Guest

    With a transformer. You can find plenty of Marshall and Fender Amp
    schems out there as examples.
     
  12. Del  Cecchi

    Del Cecchi Guest

    Don't need transformer. But no one said what kind of amp. If you talking
    audio amp, go to the library and look at old old late 60's issues of
    "popular electronics" or "radio Electronics" or evne the british "wireless
    world".

    I might even have one in my file. Basically the output stage is an emitter
    follower for the pull up and a common emitter stage for the pull down.
    Drive the bases out of phase, and away you go.

    del cecchi
     
  13. NPNs are cheaper and there's a better choice.
     
  14. Ken Smith

    Ken Smith Guest

    Consider this circuit:
    Vcc
    !
    \
    /R1
    \
    !-----------------------
    ! !
    \ Vcc -----
    /R2 ! ----- C1
    \ !/ !
    !----------! Q2 !
    !/ !\ !
    -! Q1 !------------------- To load
    !\ !
    ! !/
    !----------! Q3
    \ !\
    / R3 !
    \ GND
    !
    GND

    If Q1 is on, Q3 is also on and Q2 is off so the output swings down to
    ground. If Q1 os off, Q3 is alos off and R1 and R2 pull up on Q2 turning
    it on and the output swings up near Vcc. If Q1 is partially on, Q3 is
    also partailly on so some current flows through it. There is some voltage
    drop on the R1, R2 combination so the base of Q2 is at some middle voltage
    and thus the output will be somewhere in the middle.

    This circuit doesn't work in real life because as the temperature changes,
    the current through Q2 and Q3 goes all over the place. At least, a
    resistor in the emitter of Q3 should be added before you tinker the
    circuit together.

    "What does C1 do?" I hear you ask. Well imagine the circut is making a
    small sinewave on its output and that C1 is huge. How much AC current
    flows in R2?
     
  15. John Larkin

    John Larkin Guest

    Then why does anybody use PNPs at all?

    John
     
  16. Because the decent ones are dearer and there's not such a range. :)
     
  17. Ian Bell

    Ian Bell Guest

    Same as when all they had was PNPs - they used transformers.

    Ian
     
  18. On a sunny day (Tue, 8 Jun 2004 21:28:16 +0000 (UTC)) it happened
    How about specifying what is emittor and collector, and NPN and PNP?
    JP
     
  19. B

    B Guest

    Hank:

    Just an audio amplifier. One wwith considerably more power than can
    be had with a single transistor. I just have no clue how you wowuld
    pair them, or use more than one b/c of the nature of the transistor.

    Thanks!
     
  20. Activ8

    Activ8 Guest

    That's the other one I was thinking of, but I couldn't say
    push-pull, cause it's different and it's not complementary symmetry
    or if it is, is not the same as the complimentary symmetry amp that
    *does* use a pnp.
     
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