Question

What are the differences between a BJT and a FET?

Answer 1

Hi subanwit :)

How are you?

Welcome to Openstudy.

Answer 2

If you are related to electronics field then I feel shame that you are asking just a little thing, because I am 100% sure, you have read BJTs and FETs. So you must be able to detect differences.

BTW: Most important difference is the input impedance, FET has high and BJT has low.
Another is BJT is a voltage controlled device and FET is a current controlled,
Another one, BJT is used for low power circuts, FET is use for high power circuits, especially for switching circuits.
Another difference I prefer to say about its construction i.e. about their channels.
Another is their terminal differences.

Any question?

Answer 3

Thanks :)

Answer 4

bjt is a bipolar and fet is a unipolar

Answer 5

@Shayaan_mustafa

"...Another is BJT is a voltage controlled device and FET is a current controlled..."

Precisely, the other way around

Answer 6

And the channels are a difference in terms of BJT not having channels
BJT works through injection of carriers from Emitter to Collector, being the recombination controlled through base current. FET polarizes the gate to change the resistivity between source and drain by modulating the witdth of the depletion zone

Answer 7

BJT is a current-controlled device!

Answer 8

@carlosgp
Yes yes, BJT is current controlled and FET is voltage controlled. Thanks for correction dear.

Answer 9

@subhanwit

As you can see there are many differences. I prefer you to detect these by your own self.

Answer 10

paking density of FET amplifier is much much lesser thn BJT.

Answer 11

For the BJT transistor the output current IC and input controlling current IB were related
by beta, which was considered constant for the analysis to be performed
A linear relationship exists between IC and IB. Double the level of IB and
IC will increase by a factor of two also.

Unfortunately, this linear relationship does not exist between the output and input
quantities of a JFET

Answer 12

@onkar_rahul. "...Unfortunately, this linear relationship does not exist between the output and input quantities of a JFET..." is not quite a correct statement. That would exclude FET's of linear amplification and this is not true

Answer 13

@CarlosGP.
m just talking abt a FET not a system in which it plays a role of amplifier.
"Unfortunately, this linear relationship does not exist between the output and input
quantities of a JFET. The relationship between ID and VGS is defined by Shockley’s
equation.
The squared term of the equation will result in a nonlinear relationship between ID and
VGS, producing a curve that grows exponentially with decreasing magnitudes of VGS.":)

Answer 14

Thank u all :)