Why Transistor is called current device

Discussion in 'General Electronics Chat' started by Surendar, Nov 14, 2006.

  1. Surendar

    Thread Starter Member

    Sep 12, 2005
    18
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    Altough i'ts the voltage that is applied to the transistor it's called a current device.

    But MOSFET's are called voltage controlled device.

    Altough both work on the principle of flow of electrons , Why there are called so??

    Please clarify.

    -Surendar.
     
  2. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    143
    A MOSFET is known as a voltage controlled device because a voltage applied to the gate controls the flow of current between the source and drain.

    For a BJT the principal is the same. It is a current controlled device because the base current controls the current flow from the emitter to collector.

    Dave
     
  3. Surendar

    Thread Starter Member

    Sep 12, 2005
    18
    0
    Thanks,

    But does it mean that voltage and current are insignifcant in Transistor and MOSFET respectively??

    Bit confused. Could it be a little bit more elaborate.

    -Surendar.
     
  4. bharathig_8

    New Member

    Nov 10, 2006
    3
    0
    Please do not hijack another members thread. If you are having posting issues send me a PM and I will help you.

    Thanks
     
  5. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    143
    Both are significant, the main difference between BJT and MOSFET (besides the physical structure of the devices) is the method of control, i.e. what is explicitly responsible for the transistor-action - current for BJT and voltage for MOSFET. In any transistor you must take account of current and voltage characteristics to fully understand the device operation.

    Dave
     
  6. Surendar

    Thread Starter Member

    Sep 12, 2005
    18
    0
    Mr.Dave,

    Thanks a lot for your response.

    -Surendar,
     
  7. BladeSabre

    Senior Member

    Aug 11, 2005
    105
    0
    A MOSFET has a high input impedence so very little current can flow into it. On a bipolar transistor the input behaves more like a diode.
     
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