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Transistor AMPLifier HelP

  1. Nov 20, 2009 #1
    Transistor AMPLifier HelP !!!!

    i will start from the first
    plz clarify my doubts
    i will post my other doubts as and when i get replies and answers

    my first doubt is
    what is meaning of Vbe base emitter voltage
    and also Vce collector emitter voltage
    what is the actual meaning of these 2 voltages
    i cant visualize
    also are these voltages permanently there
     
  2. jcsd
  3. Nov 21, 2009 #2
  4. Nov 22, 2009 #3
    Re: Transistor AMPLifier HelP !!!!

    i cant understand what is voltage between base and emitter
    also the voltage between collector and emitter
    i dont understand the meaning of those two words
    voltage means a driving force of potential difference
    what is it here i want to know the physical meaning behind it
     
  5. Nov 23, 2009 #4
    Re: Transistor AMPLifier HelP !!!!

    In this thumbnail
    https://www.physicsforums.com/attachment.php?attachmentid=21960&d=1258770808
    the plot at the bottom of the thumbnail is voltage (vertical) vs. time (horizontal). The green curve is the base (input) voltage, red is the emitter voltage, and black is the collector voltage. Vbe means base-emitter voltage, and Vce means collector-emitter voltage. Note in the circuit diagram that the collector current is nearly exactly the same as the emitter current (both across a 500-ohm resistor), and the base current is very small.
    Bob S
     
  6. Nov 24, 2009 #5
    Re: Transistor AMPLifier HelP !!!!

    1) i asked what is the physical meaning behind Vbe and Vce
    is it the barrier potential

    2) if so we say that in CB junction which is reversed bias resistance is large
    but actually current flows easily into the collector
    then how can we say that resistance of collector is large

    3) the depletion region is responsible for the voltage drop in diode
    in forward bias also there exists voltage drop according to my book
    but in forward bias the depletion region would have vanished,then how will there be voltage drop.
    BOB S could u plz give ur yahoomail id we'll chat there
    i have a lot of doubts plz Sir
    All my professors and students are teasing me if i ask doubts
    could u plz help me because u r the one who is responding to my doubts instantly
     
  7. Nov 24, 2009 #6
    Re: Transistor AMPLifier HelP !!!!

    Vce is the driving potential for the amplifier.
    Vbe is the bias potential across the base-emitter junction.

    Both are applied to the device, and are not inherent properties of the transistor.
     
  8. Nov 24, 2009 #7
    Re: Transistor AMPLifier HelP !!!!

    Hi Sudar-
    I will try to answer your questions. First, study the figure
    https://www.physicsforums.com/attachment.php?attachmentid=21960&d=1258770808
    Power supply V1 is 12 volts. The base bias voltage is 1/3 of 12 volts, or 4 volts. So the emitter voltage is 0.6 volts less, or 3.4 volts. So the emitter current is 3.4 volts over 500 ohms. or 6.8 milliamps. The collector current is also about 6.8 milliamps, so the voltage drop across R2 is about 3.4 volts. So the collector voltage is 12V - 3.4V = 8.6V. Power supply V2 is ac coupled to the base. It has a 1 volt (peak) 500 Hz sinewave on it, and on the base. In this configuration, the transistor is an emitter follower, so all three sine waves (base, emitter, collector) are about 1 volt peak. I hope this helps.
    Bob S
     
  9. Nov 25, 2009 #8
    Re: Transistor AMPLifier HelP !!!!

    1) i cant understand the basics
    i want to know what do u mean by voltage between emitter and base and voltage between collector and base
    is it the barrier voltage ???
    i.e the barrier potential at the juctions EB an CB???
    the depletion region is responsible for the voltage drop in diode
    in forward bias also there exists voltage drop according to my book
    but in forward bias the depletion region would have vanished,then how will there be voltage drop.


    2)also i cant understand voltage divider bias
    i have posted the circuit diagram
    i have many doubts there about how the voltage drop between R1 and R2 gives forward bias to the base emitter
    also which current's voltage is getting dropped there
    in my diagram its showing collector current
    but collector current itself arises from the emitter
    also u have not biased the emitter till now then how did u get Ic

    forward bias provided by the voltage drop of Ic
    see u have not biased it and u r about to bias the emitter only from voltage drop of Ic
    then where did u get that Ic from
    Ic comes only after biasing EB

    plz BOB S answer first question 1 and then 2
    if u cant understand my question plz mention it i will try to ask it in a better way
     

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    Last edited: Nov 25, 2009
  10. Nov 25, 2009 #9
    Re: Transistor AMPLifier HelP !!!!

    u hav good qustons. Study bk on smicndctrs.
    bob s
     
  11. Nov 26, 2009 #10
    Re: Transistor AMPLifier HelP !!!!

    could u plz mention some good books which has answers to my question and can be downloaded for free
     
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