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What is the simplest explanation of how a transistor works?

  1. Mar 13, 2008 #1
    Just curious. For some odd reason, I don't seem to get it.
     
  2. jcsd
  3. Mar 13, 2008 #2

    mgb_phys

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    How simple do you want?
    In the simplest terms it acts like a (water/gas) valve - a small current into the base is used to control how much of a much bigger current flows between the other two pins.

    In a junction transistor the base current provides electrons which diffuse into the thin electron poor base region and allow it to conduct.
    In a FET the field in the depletion region changes it's conductance and allows a bigger current to flow.
     
  4. Mar 13, 2008 #3
    Perfect. Thanks.
     
  5. Mar 13, 2008 #4

    mgb_phys

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    That's why the glass things, used before transistors were invented, were called valves - because they worked exactly like a tap/faucet.

    This is also the property that is used in a computer.
    Power on main input + power on small input = power on output.
    But power on only one of main pin / base pin = no output.
    With just this operation, called an AND gate, you can make any other calculation
     
    Last edited: Mar 13, 2008
  6. Mar 13, 2008 #5

    berkeman

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    "glass things" -- LOL. AKA "vacuum tubes" :rofl:
     
  7. Mar 13, 2008 #6

    Danger

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    Hey, Berkeyboy... remember when the neighbourhood gas stations and drug stores used to have vacuum tube testers so you could figure out why your TV wasn't working? :biggrin:
     
  8. Mar 14, 2008 #7

    berkeman

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    I'm afraid so. I fixed a few friends' TVs using testers like that. Uh, thanks for the reminder about how "experienced" I am, Danger.... :redface:
     
  9. Mar 14, 2008 #8

    Danger

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    :rofl::rofl:
    Don't worry, pal; I'm laughing at you, not with you. :biggrin:
     
  10. Mar 15, 2008 #9

    Ouabache

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    As mgb_phys correctly asserts, they are also commonly called "valves" (coined by Ambrose Fleming, abbreviation for thermionic valve). By the way, those valves work as perfectly today, as they did back in Danger's day.:wink:

    I recently restored a broadcast receiver that uses several valves. It sounds great across the AM and SW bands and looks a lot like this one.
     
  11. Mar 15, 2008 #10

    mgb_phys

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    I described them as glass tubes because if the op didn't know how a transistor works they are unlikely to have heard of vacuum tubes.
    Is valves only a British term - are they known as tubes in the US?
     
  12. Mar 15, 2008 #11

    Ouabache

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    That is my understanding..
     
  13. Mar 16, 2008 #12

    Danger

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    We Canuks recognize either term, although 'tubes' is far more common.
    Most serious audiophiles pay a lot of extra bucks for a vacuum tube amplifier as opposed to a solid-state one. There's a bit of ambiguity to the signal processing that gives a really rich, warm texture to the music. Sometimes 'high-fidelity' can be too high and ruin the experience.
     
  14. Mar 16, 2008 #13

    mgb_phys

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    Tube/Valve amps go into saturation in a very different way to transistors - so it makes a big difference with stage amps, especially 60s era guitar amps.
    Sony used to make a redicoulsy expensive home theatre amp that used DSPs to simulate Valve amps - you could select the exact model of valve amp and it would distort in the same way. Pink floyd confirmed their nerd band image by designing a valve ADC pre-amp to record the CD of their last live album.
    Of course it only applies to amps when they are in overload so a class A valve amp shouldn't sound any different to a transistor class A.
     
  15. Apr 1, 2008 #14
    :yay: ooops, no :yay: smilie... ho hum.

    That Magnavox has got a magic eye!

    We had an old Murphy radio (a uk radio manufacturer long out of business, famed for various off the wall designs, like the single valve self oscillating line output on a tv) when I was a kid that had the same kind of magic eye.
     
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