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From the 2N7002's data sheet, it can be shown than there is a minimum voltage threshold and maximum threshold and also a typical voltage threshold.

enter image description here https://www.electrokit.com/uploads/productfile/40327/2N7000-2.pdf

Case 1: When the MOSFET gate gets 1V, the MOSFET begins to turn ON(> 0%). When the MOSFET gets 2.5V, it's 100% turn ON?

Case 2: When MOSFET get gets 1V, the MOSFET turns on to 100%. When the MOSFET crosses 2.5V, then the MOSFET remains 100% open until Gate is conntected to ground GND.

Case 3: Between 1V and 2.5V on the gate, then MOSFET is 100% open. Above that, or under, the MOSFET is closed

Case 4: When gate gets 1V, the MOSFET turns on. But above 2.5V, the MOSFET can be harmed and breaks.

Please, keep it simple and very clear. I have read lots of post about the threshold and every body talking about theory. I just want a clear answer what min and max and typical means.

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    \$\begingroup\$ None of the above... see Spehro's answer, not the currently accepted one. \$\endgroup\$ Oct 21 '20 at 21:12
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The correct way to read this is:

  • ABOVE 2.5V the device is guaranteed to be ON
  • BELOW 1V the device is guaranteed to be OFF

Between? do not design for this case IF you are after deterministic behaviour as a ON/OFF device

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  • \$\begingroup\$ Thank you! Very clear! On threshold is also 2.5V in this case? Or what happens if I gives gate 4V and then 2.1V? Will the MOSFET be still open? \$\endgroup\$
    – MrYui
    Oct 21 '20 at 19:07
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    \$\begingroup\$ possibly, maybe... many things come into play... tolerances, temperature etc. In such a condition it cannot be guaranteed to be OFF but equally it cannot be guaranteed to be ON. \$\endgroup\$
    – JonRB
    Oct 21 '20 at 19:41
  • \$\begingroup\$ Ok. I understand. \$\endgroup\$
    – MrYui
    Oct 21 '20 at 19:45
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    \$\begingroup\$ FALSE the threshold voltage is the voltage at which it just begings to pass a tiny current. Usefully "on" is somewhat higher. \$\endgroup\$ Oct 21 '20 at 21:03
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    \$\begingroup\$ That is when the other graphs come into play where the specific gate voltage permits a higher current to flow as the MOSFETs acts like a resistor. That however does not change the fact this value is read as ABOVE and BELOW. Maybe 250uA is all something needs, we don't know about the wider cct BUT below 1V it is guaranteed to be OFF \$\endgroup\$
    – JonRB
    Oct 21 '20 at 21:18
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It is guaranteed to pass less than or equal to 250uA with 1V on the gate and drain.

It is guaranteed to pass more than or equal to 250uA with 2.5V on the gate and drain.

250uA with 2.5V across it is about 10K equivalent which is not very much 'ON'.

If you want it to be guaranteed to pass a useful amount of current greater than 250uA (like, say 50mA with a fraction of a volt across it) you will have to give it significantly more than 2.5V

How much more can be guessed at from the curves (such as figure 1), but the only datasheet guarantee is that it will have less than 5 ohms resistance with 10V on the gate, passing 0.5A, when cold, or 9 ohms when very hot.

'Typical' is what you might expect an average unit to do if you pick it off the assembly line. They don't guarantee it, it may not be valid, but usually (sometimes) it's pretty close. If you want to build many units and have all of them work reliably and over a wide temperature range and component tolerances you don't pay much attention to 'typical' numbers.

Think of it like ordering piece of lumber at your local big box store. It's nominally say 3' (1m) but it might be an inch (25mm) shorter or longer than that. Semiconductors are not individually trimmed (cheap ones anyway) so you have to live with the tolerance from the manufacturer. If you absolutely need a 3' (1m) piece to fit you'd better order it longer and cut it down.

In the same way you might want to use a 2.5V rated MOSFET* for operation at 3.3V because it has guaranteed characteristics that apply at 3.3V.

* by this I mean the Rds(on) is guaranteed with Vgs=2.5V.

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