# Why is a transistor called a current controlled device?

1. ## Why is a transistor called a current controlled device?

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

2. ## 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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4. ## 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

5. ## 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

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6. ## 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.

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7. ## Re: Transistor

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

8. ## 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)

9. ## 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).

10. ## 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)

11. ## Transistor

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

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12. ## Transistor

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

13. ## Re: Transistor

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

14. ## Re: Transistor

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.

15. ## Transistor

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

16. ## 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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