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About MOSFET, Why N-Channel are more popular than P-Channel?

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About MOSFET

Hi, Why N-Channel Mosfet are more popular than P-Channel Mosfet? Most DC/DC controllers use N-Channel Mosfets. And I saw some power path controllers use back-to-back N-Mosfets to totally isolate two power sources, it means that one N-Mosfet's Source connects to V+ and Drain connects to V-, is it allowed to exchange the Drain and Source's position? And I see no electrical characteristic descriptions about Vsd and Is in MOSFET products' datasheets.
 

Re: About MOSFET

jaffe said:
Hi, Why N-Channel Mosfet are more popular than P-Channel Mosfet? Most DC/DC controllers use N-Channel Mosfets. And I saw some power path controllers use back-to-back N-Mosfets to totally isolate two power sources, it means that one N-Mosfet's Source connects to V+ and Drain connects to V-, is it allowed to exchange the Drain and Source's position? And I see no electrical characteristic descriptions about Vsd and Is in MOSFET products' datasheets.
Click to expand...
we can positive supply but p channel need negative supply
 

Re: About MOSFET

I don't know exactly but usually N typt transistor have better efficency and greater beta and greater Gm(max about 500 in npn bjt max about 100 in pnp )
 

Re: About MOSFET

a_tek7 said:
I don't know exactly but usually N typt transistor have better efficency and greater beta and greater Gm(max about 500 in npn bjt max about 100 in pnp )
Click to expand...
input impedance is high
 

Re: About MOSFET

There are many reason. A few are: (The question and reasoning will be same for NPN transistor too).
Most of our circuits have -ive ground and most common (and used) configuration is CE or CS (so N-channel or NPN suites)
They manufacture more due to demand (and thats why they have less cost than P-channel or PNP). So people try to design circuits which have naturaly and forcely contain N-channel or NPN (unless needed otherwise) and vice versa.
 

Re: About MOSFET

P-FETs need their their gate to be more negative than source but N-FETs need to be more positive. Obviously producing positive voltage is more straight forward than negative voltage(almost in all circuits you have positive voltage but in many you don't have negative so it need more components). You can't just replace drain and source. MOSFETs have a parasitic diode so only can be used unidirectionally if you want to use them bidirectionally you have to use two of them with source connected together hence their parasitic diode are back to back and do not conduct.
regards,
 

Re: About MOSFET

N-fet are also easyier to manufacture
 

Re: About MOSFET

I think the main reason is that electron mobility (carriers in nMOSFET) is much higher (~ 2x) than hole mobility (carriers in pMOSFET). Thus, nMOSFET with the same area as pMOSFET will have higher current and lower resistance. And Rdson is one of the main parameters of power device.
 

About MOSFET

It is possible to swap the position of the source and drain.It is possible in a MOSFET....
 

Re: About MOSFET

santom said:
It is possible to swap the position of the source and drain.It is possible in a MOSFET....
Click to expand...
Have you heard anything about parasitic diode in MOSFETs?
 

Re: About MOSFET

fala said:
santom said:
It is possible to swap the position of the source and drain.It is possible in a MOSFET....
Click to expand...
Have you heard anything about parasitic diode in MOSFETs?
Click to expand...


Hi,

Since the MOSFET is basically a switch and also an symmetric device,I just told the answer as YES for our friend's question.

By the way,I too kinda clear in the concept of Parasitc Effects in a transistor.Still,I really dont mind and will be interested to read if you give me any good information about the parasitic effects which you were talking about..

thank you in advance

Cheers
santom
 

Re: About MOSFET

Power MOSFET (e.g, LDMOS) is NOT symmetric device, so source and drain can not be interchanged!
 

Re: About MOSFET

timof said:
Power MOSFET (e.g, LDMOS) is NOT symmetric device, so source and drain can not be interchanged!
Click to expand...

Can u please throw some light on what u told , something more specifically?


Cheers
santom
 

Re: About MOSFET

santom said:
timof said:
Power MOSFET (e.g, LDMOS) is NOT symmetric device, so source and drain can not be interchanged!
Click to expand...

Can u please throw some light on what u told , something more specifically?


Cheers
santom
Click to expand...

santom, why you don't download datasheet of a few MOSFETs and study them, for example IRF540, or you can go to international rectifier's website you will find plenty there.
 

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