Is this correct? MOSFET general application?

Thread Starter

Tonyr1084

Joined Sep 24, 2015
7,997
I'm old school. Transistor were new when I started. So much has changed and I'm learning a lot. I believe I finally have this right. Please, have a look and tell me - in general - is this the way these things work? And don't worry about voltage, resistance or current, that part I'm comfortable with. Is my assumption in the diagram correct?

Gen MOSFET Rule.png
 

dl324

Joined Mar 30, 2015
17,134
You're saying THIS is correct ?
Yes. N MOSFETs turn on when the gate is more positive than the source by Vth. P MOSFETs turn on when the gate is more negative than the source by Vth. On resistance is reduced when the gate is driven harder.
 

crutschow

Joined Mar 14, 2008
34,842
Note that the normal drain-source voltage for either polarity MOSFET is to reverse bias the substrate diode.
Otherwise the device will conduct, even with a Vgs of zero.
 

dl324

Joined Mar 30, 2015
17,134
Also note that the symbol used in @Jony130's post is the correct symbol for enhancement mode MOSFETs; but it's quite common for the depletion mode symbol used in your schematics to mean enhancement.

When we drew schematics at work, we didn't draw the substrate terminal or polarity arrow; and when hand drawing circuits we frequently rounded the corners so we could draw them faster.
upload_2017-2-22_11-11-27.png
 
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