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Transistors amplification

Discussion in 'General Electronics Discussion' started by kingofjong, May 8, 2018.

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  1. kingofjong

    kingofjong

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    Aug 14, 2014
    Hello

    I know transistor amplifies current, but I am a bit confused about that. Can I power a component that requires 10A (ex. motor) using 5A and a transistor? Can the transistor increase 5A to 10A? What will happen to the voltage in this situation will the output voltage also increase?

    Thank you
    kingofjong
     
  2. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Gee, how many angels can stand on the tip of a pin? Maybe you should reconsider your "knowing" that a transistor amplifies current. It doesn't. So, no, a transistor cannot increase 5A to 10A.
     
  3. BobK

    BobK

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    What a transistor does is controls a large current based on a small current. It does not create current, the large current must come from a power source.

    There are circuits that can double the input current, but it is always at the expense of halving the output voltage. The power, which is the product of the voltage and current, remains the same, or actually it is reduced a bit because you cannot get to 100% efficiency.

    Bob
     
    Last edited: May 8, 2018
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  4. BobK

    BobK

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    All of them.

    :p

    Bob
     
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  5. LvW

    LvW

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    Apr 12, 2014
    Bob - this statement contradicts the contribution from hevans1944. In order not to confuse the questioner - perhaps you reconsider the above quoted sentence?
     
  6. BobK

    BobK

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    I do not see it as contradictory. The OP seems to think you can take a transistor and a 5A supply, and get a 10A supply from it. My point is that the output current comes from a power source, not from the input current "amplified". Perhaps you would like to phrase it better? (I have added the word is to make it grammatical.)

    Bob
     
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  7. LvW

    LvW

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    Apr 12, 2014
    Bob - what I mean is the following: The phrase "a transistor ....controls a large current based on a small current" implies that the BJT would be a current-controlled device, right?
    In contrast, the contribution from hevans (..."you should reconsider your "knowing" that a transistor amplifies current. It doesn't") implies that a BJT is NOT current-controlled.
    Do you see what I mean?
     
  8. Hopup

    Hopup

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    You can think of the operation of transistor as a dam having adjustable gates. You can't get more fluid flow out of the river than what is present in it, but you can control it using the electric gates of the dam by opening the gates wider which will let more water flow through them or closing them which will let less water flow through them.
     
  9. davenn

    davenn Moderator

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    Sep 5, 2009
    guys

    please, lets not get into whether a transistor is a voltage or current controlled device long discussion/argument again
    Has happened way too often

    @BobK 's response was very suitable for the basic misunderstandings that the OP has
     
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  10. Ratch

    Ratch

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    Mar 10, 2013
    A BJT transistor by itself is a transconductance device. So is a FET or a vacuum tube. That means a voltage controls the output current. However, those devices can be incorporated into several types and variations of circuits that can amplify current or voltage. The amplification limits are determined by the capabilities of the power supply to which they are connected.

    Ratch
     
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  11. hevans1944

    hevans1944 Hop - AC8NS

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    I hope that I have been careful over the past few years not to state or imply that the base current of a Bipolar Junction Transistor, or BJT, somehow magically controls the collector current because it simply doesn't. It is the forward biased base-emitter voltage that controls collector current. Please, let's not repeat the discussion we had a few years ago here (look it up with the search window); all the usual suspects have already chimed in on this thread.

    I can imagine a situation where a transistor has a base current of 5 A and a collector current of 10 A. That does not mean the base current was responsible for the collector current. And that would be a pretty sh!tty transistor with a beta or hFE equal to 2. Almost in the same class as the venerable 2N3055, which sports a minimum hFE of 5 with 10 A collector current.

    Can a moderator please close this thread, at least until the OP gets up to speed on BJT semiconductor theory of operation?
     
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  12. davenn

    davenn Moderator

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    Sep 5, 2009

    as you should have learnt in this thread, by now, transistors don't amplify current or anything else meaning that your opening statement was incorrect
    I suggest you go do some reading on basic transistor operation, then come back and start a new thread with specific questions
    relating to what you have read that you don't understand :)

    cheers
    Dave

    thread closed
     
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