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    Why is a transistor called a current controlled device?

    Why is a transistor called a current controlled device?
    Pl detail with the theory..

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    Transistor

    Transistor .. i suppose you are referring to Bipolar Junction Transistor .. Here you know that the
    collector current is proportional to the base current
    as

    Ic = ( Beta ) Ib hence .. here Ib is the input current
    ane Ic is the output current .. so we called it a current
    controlled device.



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    Transistor

    If you want learn more about this topic, you can read Boylestad, Sedra, Rashid, among others.



    •   Alt30th November 2006, 13:45

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    Re: Transistor

    Transistor .. i suppose you are referring to Bipolar Junction Transistor .. Here you know that the
    collector current is proportional to the base current
    as

    Ic = ( Beta ) Ib hence .. here Ib is the input current
    ane Ic is the output current .. so we called it a current
    controlled device.
    besides, if u see in active region the collector current is independent of collector voltage and only depends upon the base current. so we could say the device out put depends upon the input current ie base current



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    Re: Transistor

    hi because in transistor there are primarily 3 currents ,ie,Ib,Ic and ie=ib+ic for further refernce u can see the working and explanation of" TRANSISTOR CURRENT FLOW MECHANISM" IN ANY OF THE STANDARD book in electronics



    •   Alt3rd December 2006, 06:43

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    Re: Transistor

    A bipolar transistor is said to be current controlled because when it is biased in the active region the output (collector) current is controlled from the input (base) current.

    A bipolar trasistor is said to be in the active region when BE junction is forward biased while CB junction is reverse biased (or viceversa)

    In this situation the collector current depends mainly on base current via β (Ic=β*Ib) and only marginally (second order effect) from collector Voltage (Early effect). Also β depends on Ic.



    •   Alt3rd December 2006, 07:38

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    Re: Transistor

    It's probably best seen in a small signal model. IB can be said to control IC.



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    Re: Transistor

    the bjt transistors are best respons for u
    they have ic and ib and ie
    ic=(beta)ib
    ie=(alfa)ic
    alfa=(beta)/(beta+1)



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    Re: Transistor

    Because voltage at input Vbe(base to emmiter voltage) remains at about 0.6V and variation of current into the base contros output variations(current, voltage both).



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    Re: Transistor

    The Transistor was described as " Trans-fer of current across a re-Sistor" by its inventor.

    No matter what you do , The base bias voltage may remain same or vary slightly but the base current can be varied widely, resultingin a corresponding increase in Collector current.
    (The Base-Emitter junction(diode) has a fixed Forward V of ~0.6 to 0.65vdc. like any other pn junction)



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    Transistor

    cuz the the current in the base controls the voltage at the collector



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    Transistor

    cuz the the current in the base controls the voltage at the collector



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    Re: Transistor

    for Mosfet,i think is because of this equation
    ID=1/2Kn'W/L(Vgs-Vth)^2



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    Re: Transistor

    Quote Originally Posted by zhangseong
    for Mosfet,i think is because of this equation
    ID=1/2Kn'W/L(Vgs-Vth)^2

    MOSFETS are not current controlled devices. They're voltage controlled, cause ID depends on Vgs.



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    Transistor

    because o/p current is contrlled by base current..............



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    Re: Transistor

    I think it's too clear from previous posts. An input current, the base current in the common emmitter stage is the parameter that makes the output variable, the collector current goes up or low. So the collector current follows the variations the input (base) current dictates.



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