Why Transistor is called current device

Thread Starter

Surendar

Joined Sep 12, 2005
18
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.
 

Dave

Joined Nov 17, 2003
6,970
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
 

Thread Starter

Surendar

Joined Sep 12, 2005
18
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.
 

Dave

Joined Nov 17, 2003
6,970
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.
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
 

BladeSabre

Joined Aug 11, 2005
105
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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