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I have learn that the FET looks like this:

enter image description here

However industrial FETs are not built like that.The source and the substrate have common potential.However if the source and substrate have common potential that means the conductive channel formed is not wide enough to connect the source with the drain there is a gap between the n type channel formed and the source.So how does it really work?

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  • \$\begingroup\$ Can you tell us why you think the channel won't reach the drain? Did you read this somewhere, and if so please give us a link. \$\endgroup\$ Jan 14, 2021 at 13:41
  • \$\begingroup\$ However industrial FETs are not built like that. The MOSFETs in the ICs I design for Industrial purposes are exactly constructed like this. There Source and Substrate do not have to be connected. Maybe you actually want to ask about Power MOSFETs which have a different construction, see: ecee.colorado.edu/~bart/book/book/chapter7/ch7_8.htm \$\endgroup\$ Jan 14, 2021 at 13:46
  • \$\begingroup\$ I don't just imagine the black line named source has to touch the p type substrate there fore the yellow lines must be a little bit more right and therefore , the n type conducting channel appears just below the yellow line so the source won't 'touch' the conducting channel \$\endgroup\$
    – Clone Wars
    Jan 14, 2021 at 13:46
  • \$\begingroup\$ Bimpelrekkie I have bought FETs myself and it had 3 pins not 4. \$\endgroup\$
    – Clone Wars
    Jan 14, 2021 at 13:47
  • \$\begingroup\$ However if the source and substrate have common potential that means the conductive channel formed is not wide enough to connect the source with the drain Source and Substrate being connected has nothing to do with the size of the channel. The channel is formed when enough positive voltage develops between Source and Gate: \$V_{GS} > V_{Threshold}\$. May I suggest that you read a book or tutorial on how MOSFETs work because I sense that you lack some knowledge there. \$\endgroup\$ Jan 14, 2021 at 13:48

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The source and the substrate have common potential. However if the source and substrate have common potential that means the conductive channel formed is not wide enough to connect the source with the drain there is a gap between the n type channel formed and the source. So how does it really work?

It works precisely how you say it does not. The conductive channel formed is wide enough to connect the source with the drain. The channel might be a little asymmetrical, like this:

enter image description here
(image from electrical4u.com)

Provided the gate voltage is high enough there is no gap and the conductive channel is, well, conductive.

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