434Views9Replies

Author Options:

How is a standard transistor different from a mosfet? Answered

So I have been teaching my self the basics of electronics and I find my self confused on the differences between a standard transistor and a mosfet. 

I understand the physical differences but what I do not understand is the differences in their applications?

A transistor is either ON or OFF which is controlled from the BASE and is normally OFF.
A mosfet is either ON or OFF which is controlled from the GATE and depending on the type is normally ON or OFF.

I think I might be over complicating things but based on my description of the two above.

Am I missing anything important?

Discussions

0
None
iceng

Best Answer 6 years ago

A mosfet is a transistor too.
Some transistors are enhanced to be on / off  devices.
Most transistors junction and mosfet have a linear response area
that is useful for analog signal amplification ( Audio too ).

Junction transistors work with a base-emitter input current controlling
a greater output collector-emitter current, while a mosfet transistor
works with a base-source input voltage controlling a large output
drain-source current.

Hope this makes it more clear for you.

A

0
None
atrumblood

6 years ago

Thanks for the answers guys. I am making progress slowly.

0
None
rickharris

6 years ago

A mechanical analogue to a transistor would be a valve of some kind that you can turn on and off or anywhere in between with little effort and control the flow of high pressure water through it.

A MOSFET would be more like doing the same by pinching the hose pip shut to control the flow of water.

In practical terms the MOSFET will have a much higher input impedance than the transistor. It draws very little from the input circuit. and is voltage controlled whereas the transistor is a current controlled device.

0
None
steveastroukrickharris

Answer 6 years ago

A MOSFET is STILL a transistor ! Its a transferred resistor, only the mosfet is voltage controlled and the BJT is current controlled.....

0
None
atrumbloodsteveastrouk

Answer 6 years ago

I am not sure if that makes sense to me or not about how a BJT is current controlled and a Mosfet is voltage controlled. Aren't both voltage and current values dependent on the resistance in a circuit?

Also I should have stated in my original post that I knew both were transistors.

0
None
steveastroukatrumblood

Answer 6 years ago

Basically, look at it mathematically.

Ic = Hfe x Base current for a BJT (Collector current= Hfe x Base current

But for a Mosfet.

Id= Gfs x Vg ( Drain current = transconductance x gate voltage)

Steve

0
None
steveastrouk

6 years ago

NO a transistor is NOT "on or off". It is an AMPLIFIER. Without feedback, and with enough ampliification, it can give the appearance of being "on and off".

0
None
atrumbloodsteveastrouk

Answer 6 years ago

So what is being amplified is the input or output on the base right? So a small signal on the base is mirrored in the larger input on the emitter and collector?