Why doesn't the mosfet simulate correctly?

[lacy]

One quick addition to this dicussion. I have done research on the bi-directionality of the FET channel  just to be sure and I am confident I am correct about  this. The only exception would be the ones with the internal diode/zener between the source and drain. The problem is that this can't be proven in Multisim as I do not believe it supports the revesal of the drain  and source. I believe this has to do with the way they are being modeled within the simulator.

If needed I can post a few websites I found with this information if anyone would like to confirm my findings (not Wiki-pedia or anything like that. These are college material like Labs and research papers, etc).

[RnDMonkey]

I have very limited experience with the terminology for FETs, so I am probably the one that is confused. For BJTs we had this old mnemonic "NPN is Not Pointing In" which refers to the direction of the arrow in a BJT. I had assumed that the arrow on FETs was the same way. I take it that is wrong then? The funny thing is that if nobody ever corrects you about such a simple thing, you can make a few very wrong assumptions, as I seem to have made.

[RnDMonkey]

Can somebody confirm that this is correct? An N-Channel FET is equivalent to an NPN transistor, right?

[kittmaster]

It depends on the application, for a common emitter/collector amplifier, sure. As a switch, sure. The byproducts are different since the JFET is a "channel" and a transistor is two stacked opposite diodes. One requires minimum current of much higher magnitude to operate (NPN) with proper biasing while the other only requires miniscewal current but proper voltage to operate. The power factor is also a bit different between the devices as well as the amount of operational noise.....but ultimately is application dependant. I don't think replacing one with the other will give a "real world" picture, but if its a basic amplifier or switch technique, then it will give an "idea" of what should happen.

The bias methods will depend on what needs to be done. And that is what makes it apples to oranges.....IMO

[RnDMonkey]

Yeah, I was clear on operation, I had just made a fundamental mistake in that I had my terminology backwards. I though that N-channel meant that the N-material was the sandwich filling, when it's actually the bread. So to speak. 🙂 I understand now that N-channel means a channel BETWEEN N-material, so I think I'm all good now. 🙂

[kittmaster]

very good,

Chris