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Are discrete transistors dead?

  1. Feb 28, 2013 #1
    ...outside integrated circuits?

    Can OpAmp's replace them?
     
  2. jcsd
  3. Feb 28, 2013 #2
    I used op-amps today and discrete transistors for controlling a DC motor :) To me they aren't dead. Also I have a magnetic levitation unit containing transistors and op-amps.
     
  4. Feb 28, 2013 #3
    They are inanimate - so yes technically..... sorry this place can become so literal!

    As for your Q -- noooo we will be using them until the day of one-off IC fabrication - even then, still needed.
     
  5. Feb 28, 2013 #4
    But their usage is in decrease. The number of transistors in todays circuits is much less than from 80s. The same with vacuum tubes.
     
  6. Feb 28, 2013 #5
    Do you have figures for your assertion? I tend to view such proclamations with skepticism.

    Being the yungin that I am who has never even seen a vacuum tube in person, I can only speculate. However, I believe the main reason vacuum tubs went away is because of size, cost, high operating voltages, and heat.

    Discrete transistors are still much cheaper and much smaller than op amps. Even if it is true that their usage is declining, they'd still have enough advantages that would make it bizarre to say they're dead.

    About a year ago I tore apart a pair of cheap $5 walkie talkies from Toys-R-Us. There wasn't a single IC anywhere in it.
     
  7. Feb 28, 2013 #6

    berkeman

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    For cost-reduction reasons, we are indeed sweeping more external discrete transistors into our mixed-signal ASIC designs. Minimizing the number of external components can help to cut down on the cost of the circuitry. But there are usually a few components outside the ASIC that cannot be pulled inside for voltage or power reasons. So there will always be a few discrete transistors outside of the ASICS in many designs.
     
  8. Feb 28, 2013 #7
    I'm not saying they are 100% dead like vacuum tubes, I mean their use is so limited outside the ICs.
     
  9. Feb 28, 2013 #8

    berkeman

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    Vacuum tubes aren't 100% dead. There are still some important applications where they are used.

    Quiz Question for you Rudinhoob -- where are they used now?
     
  10. Feb 28, 2013 #9
    Audio amplifiers?
     
  11. Feb 28, 2013 #10

    berkeman

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    That would be one, although one can certainly debate whether using vacuum tubes helps the audio quality (some argue that it does, others don't think so).

    There is a much more important application... think BIG TUBES!
     
  12. Feb 28, 2013 #11

    Redbelly98

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    I am intrigued. My first thought was displays for televisions and computer monitors, then realized that no, evacuated tubes are no longer used to make them either.
     
  13. Feb 28, 2013 #12

    trollcast

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    The magnetron in a microwave is a type of vacuum tube.
     
  14. Feb 28, 2013 #13
    I'm now thinking some military applications where vacuum tubes are not damaged by strong electromagnetic waves? What about communication transmitter/receivers?
     
  15. Feb 28, 2013 #14

    berkeman

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    Pretty close! They are used in high-power microwave and radar applications, as well as radio/TV broadcasting equipment. The power levels and high voltages lend themselves to vacuum tube circuitry better than semiconductor circuitry sometimes... :smile:
     
  16. Feb 28, 2013 #15
    My friend who plays the guitar in a metal band once told me that tube amps were preferred by almost everyone in his circles. Dumbfounded, I looked it up, and it turns out (IIRC) that tubes have a strong distorting third harmonic which "sounds good". Realizing that my exquisite rational skills couldn't probe into the domain of taste, I had to let it go, but I couldn't help thinking that his beloved tube amp did a little more than advertised (i.e., it's not simply amplification).
     
  17. Feb 28, 2013 #16

    jim hardy

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    Quite a bit of research went on in the 1990's.

    One of the better reports i recall demonstrated the differing harmonic content of tube vs solidstate pre-amplifiers when over-driven into distortion. Which is how the musicians participating in the study used them, to surprise of the investigators..

    Solidstate amps tend to provide more symmetric clipping than tubes because of the latter's cutoff and saturation behavior. Solidstate amps tend to be feedback controlled so they'll drive right to the power supply rails instead of approaching them in a gradual, nonlinear fashion. They clip both top and bottom peaks alike, and it begins suddenly.
    Recall from your Fourier that odd harmonics affect both peaks symmetrically, even ones don't.

    The investigators' Fourier analyzer showed the tube amp output when overdriven to contain more even numbered harmonic content, as a result of asymmetric clipping, than did the solidstate amp with its symmetric clipping..
    So, to a musician's ear they produce different "overtones".


    It made sense to me....
     
  18. Feb 28, 2013 #17

    rbj

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    investigators in the 90s???! pretty dumb investigators if they didn't know that guitarists were using their guitar amps for distortion.

    in other words, hard clipping instead of soft clipping. that's what we call it.

    or odd-symmetry distortion on a sinusoid will generate odd-numbered harmonics and even-symmetry distortion on a sinusoid will generate even-numbered harmonics.

    solid-state distortion was quite odd in symmetry, so no even-numbered harmonics.

    tube distortion (if it wasn't push-pull) was asymmetrical so it was a combination of odd and even symmetry distortion.

    some overtones sound nice and others less nice.

    but the softness to the clipping is also very important.

    and there are some other weird non-linear effects with an old tube amp. the poorly-regulated power supply droops when you hit a power chord, so it clips at even a lower clip level.

    there is also some reactive components in a tube amp. transformers (with hysteresis) and coupling capacitance and, in the tubes, inter-electrode capacitance. so it's a mix on non-linear components and it's not memoryless. hard to model non-linear systems with reactance or "memory". makes a very subtle difference in distortion compared to a memoryless non-linear system with the same static non-linear curves.
     
  19. Mar 1, 2013 #18

    jim hardy

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    Yes, they were not musicians....

    Thanks for your clarifications and vocabulary additions ..

    This one caught my eye
    another trait of inductors is their tendency to maintain current(Lenz), and a power pentode is rather a constant current device. So a tube amp likely is more of a current source(high impedance) than a voltage source(low impedance)... that's why the precaution never let a tube amp operate into open circit it'll wreck the output transformer's insulation...

    Amplifiers tend to be tested with resistive load so voltage and current have same shape..
    But a speaker has inductance and inertia - it's really a motor-
    and a motor responds different to a high impedance current source than it does to a low impedance voltage source. I've never seen a mathematical analysis , but amplifier impedance is a term in speaker enclosure design....

    so many projects, so little time...
     
  20. Mar 1, 2013 #19
  21. Mar 1, 2013 #20

    cepheid

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    I'm confused. Isn't the answer to the question in this thread:

    "Only if you bias them wrong.."
     
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