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Are small signal npn transistors really so different from one another?

Discussion in 'Electronic Design' started by Paul Burridge, Dec 20, 2003.

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  1. C'mon Paul. We'll be imagining something really, really stupid. Far
    worse than your *actual* circuit, which *almost* works.

    I've seen some pretty silly-assed stuff out on the net (particularly
    with regard to bias), yours can't be much worse. Probably just have to
    add a few Rs and Cs to it to get the bias more independent of the
    transistor parameters.

    Best regards,
    Spehro Pefhany
     
  2. Jim Thompson

    Jim Thompson Guest

    If I post OT I catch all kinds of flack, setting records for thread
    length.

    Try to get ON-TOPIC and there are no takers :-(

    ...Jim Thompson
     
  3. Plus, if it's a real doozy, you could get immortalized in a "bad ideas"
    section in AoE 3ed. :)
     
  4. Walter Harley wrote...
    Indeed. But no names are mentioned. :>)

    Thanks,
    - Win

    whill_at_picovolt-dot-com
     
  5. I certainly hope to see the Williams bridge so honored.

    Best regards,
    Spehro Pefhany
     
  6. I read in sci.electronics.design that Spehro Pefhany <[email protected]
    DOTyou.knowwhat> wrote (in <>)
    about 'Are small signal npn transistors really so different from one
    another?', on Tue, 23 Dec 2003:


    What's a Williams bridge?
     


  7. The below circuit, but only when k = 0.50


    R R
    Vin ---+-/\/\/\/-----+----\/\/\/\/-------+ Vout
    | ! !
    | ! !\ !
    \ --!-\ !
    / ! --------------
    RV1= R \<---------------!+/
    / /|\ !/
    \ k*R
    / |
    | \|/
    --+----------------------------------0v

    RV1= a pot, overall value R.

    k= pot position, varying from 0 to 1.

    --
    Tony Williams.



    Best regards,
    Spehro Pefhany
     
  8. I recognise the circuit, but just can't remember the
    topic of the thread it related to.
     
  9. Fred Bloggs

    Fred Bloggs Guest

    Tuning for maximum CMR?
     
  10. Spehro Pefhany wrote...


    Indeed, a variant of AoE figure 4.14 with a variable gain from
    -1 to +1, which equals zero for k = 0.5, with zero output. :>)

    Why's it called a Williams' bridge? To jazz Tony? Is there an
    s.e.d. thread reference?

    Thanks,
    - Win

    whill_at_picovolt-dot-com
     
  11. ... to assure his immortality (almost forgot that "t")
    http://groups.google.com/groups?hl=...lm=ZgpTu1AhSik8EwIT%40jmwa.demon.co.uk&rnum=2

    Best regards,
    Spehro Pefhany
     
  12. Sorry chaps, My main computer went tits-up and I've been unable to
    connect up for 2 days. But I have revised the design and now believe
    it should work okay. Certainly by sitting down and doing the
    calculations *first* did the trick. I don't mind posting that one as
    it doesn't make me look *too* DUMB. :) And there is certainly some
    modest room for improvement yet, I'm sure...

    I'll post it later when I've re-read how to go about it.
     

  13. I'm not sure what you mean by "AC couple a diode" but maybe I
    explained it poorly. Here's what I've done in schematic form:




    output from
    final tranny

    ||
    ---------||--------->|--------+-------+
    || | |
    | |
    | |
    + | .---|
    | +-| | Meter
    --- +-| |
    --- | '---|
    | |
    | |
    | |
    | |
    +---------------+-------+--------+
    |
    ===
    GND
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de


    BTW, diode doubler idea might well be very useful if the sensitivity
    is still on the low side. Thanks.
     
  14. That's an observation I've heard throughout my life...
    Really?? I'd always assumed those non-amplified ones were only good
    for up to about one foot away. It just shows how far out one can be
    with guesses.

    [rest snipped]
    I'll check out the references, thanks, John.
     
  15. Jim Thompson

    Jim Thompson Guest

    Think on it... the meter is a resistor. The diode only allows current
    flow to the right. What happens to the charge on the input capacitor?

    ...Jim Thompson
     
  16. I read in sci.electronics.design that Paul Burridge
    >) about 'Are small signal npn transistors really so
    different from one', on Tue, 23 Dec 2003:
     
  17. James Meyer

    James Meyer Guest


    I'll be willing to bet that Paul is only doing small-signal AC analysis
    in his design. A transient analysis would quickly show up the problem with his
    output cap.

    Jim
     
  18. D'oh! :-(
     
  19. Cheeky Blighter......

    Hmm.... maybe go down to the Williams Patent Brick
    Outhouse and re-align the High Pressure Effluent
    Ejector (patent applied for). With the right subject
    (and the right curry) it could perhaps hit Toronto.
    Teach him what the phrase "Dropped on, from a great
    height" really means.
     
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