transistor or mosfet?

[rookie]

:? what makes mosfet are batter than the transistor?

 

[Mosfet]

They have very high input impedance.
This means they have very high gain.
They have less problem with charge storage.
This means they have wider bandwidth and higher switching speeds.
Their current is inversely proportional to temperature.
This means no thermal runaway problems.

 

[MaxKiLLiNG]

transistors are availible in faster versions then mosfets
Even some radio tubes outperform the best highspeed mosfet
:roll:

 

[Mosfet]

Different not necessarily better.
Faster than 'most' conventional bipolars.

Tubes have many uses that surpass transistors (BJT & FET).
A favorite is my Dynaco ST35.

regards

 

[rookie]

thanks,
I would like to learn more about this "mosfet" espicially for propotional switching or pwm switching.is't true that mosfet also have a lower internal resistance compare to transistor?

I collected a few mosfet (I gues)from some broken mechine,how to confirm a pnp or npn mosfet with a DMM.is't the same way the tr's checked.

 

[miro]

for the bipolar transistors, they r known as current contol current sourse...as u can control them by entering a base current...bur for the mosfets...they are voltage control current sourse..that u control them by voltage only and they dont drow any current..so they have a very large impedance better than the bipolar ones....but the switching time of the bipolar is much better than mosfets

 

[rookie]

chosing the right mosfet

how to chose a good mosfet,are this true?

Vds -the higher the batter.

Rds(on) -the lower the better

Id cont@25'C -the higher the batter

 

[stevez]

The word "better" takes on many meanings and this is especially true in electronics. While some technologies have significant advantages over others there are very few that are "all purpose" in the sense that they do all the things that need to be done better than anything else. Each type of device here is different and while some may appear to have many "ideal" characteristics each of them also "suffers" in one way or another and is less suited for some applications.

 

[rookie]

yup :roll: you are right stevez,sorry I did't mantion that ..I would like to build a speed controller for a dc motor.