# Understanding Vgs(th) on a datasheet [duplicate]

I am trying to understand the Vgs threshold on this datasheet. it says that the maximum is 1.45v but I have switched with 3.3 from a microcontroller. am i damaging the mosfet using this voltage?

• That particular one is best with 4.5V minimum 'on' Vgs. Maximum is 12. Commented Jul 12, 2018 at 14:29

Maximum voltages and other limit values are specified under "Absolute maximum ratings" usually: -

So the gate-source voltage should not exceed + or - 12 volts and, as a design recommendation I'd keep below +/- 10 volts. And, if you look at the forward characteristic of the device here: -

There is very little reason to go to a gate-source voltage beyond 5 volts. If you need that extra bit of conductivity with higher than 5 volt operation on the gate you should consider a better device.

• thanks very much (everyone) for this. i have another question which is very much related but about p-channel mosfets. would it be better to start a new thread? Commented Jul 12, 2018 at 11:21
• @user2105725 yes it probably would be best to ask a new question. Commented Jul 12, 2018 at 11:30

Note that on the data sheet, Vgs(th) is specified at Vds = Vgs, and the current level is 250 uA.

In this case, the maximum is simply the maximum required to produce 250 uA. If you give the gate less voltage, you may get less current (or maybe not, depending on the unit). It's possible that you might get lucky as low as 0.65 volts (the minimum).

So in this case, if you like, "maximum" sort of means "minimum", in the sense that it is the minimum required to guarantee 250 uA. This is entirely different from the maximum limits found elsewhere, which define what you can do without potentially damaging the device.

No, the FET's doing great!

The threshold voltage is the minimum voltage at which the MOSFET even starts to turn on (see the $V_{gs(th)}$ line, where they specify the $V_{gs(th)}$ at $I_d$ of 250 µA). You're doing fine. Heck, even on the first page of the datasheet, they mention some specs at $V_{gs}$ of 10V!

On the contrary, the gate voltage may even be too low for some purposes. Check out the first chart on page 3 of the datasheet, the $I_d$ vs $V_{ds}$ at select $V_{gs}$ voltages.

From the first page of the datasheet, the maximum Gate-Source Voltage ±12 V

So no, you are not damaging the mosfet.

• This answer doesn't exactly explain what the Gate-Source threshold is though, which is what OP is having trouble with
– MCG
Commented Jul 12, 2018 at 9:55
• @MCG the question was "Am I damaging the mosfet" Commented Jul 12, 2018 at 9:58
• Granted, that is the sentence with the question mark at the end. However, reading the whole post, this doesn't address the main point of the post, which is understanding Vgs(th), hence the downvote. I thought it best to let you know why rather than just downvote and leave without saying anything!
– MCG
Commented Jul 12, 2018 at 10:10
• @MCG No problem. Just thought I would give a straight forward answer to the question. Commented Jul 12, 2018 at 14:06