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I have a datasheet for a MOSFET but can't find the \$\mathrm{V_{GS}}\$ to get the rated \$\mathrm{R_{DS(on)}}\$. It only shows the \$\mathrm{V_{GS}}\$ maximum rating which is the usual ±20V. The \$\mathrm{V_{GS}}\$ threshold is 4V.

Where is the \$\mathrm{V_{GS}}\$ that is required to the advertised \$\mathrm{R_{DS(on)}}\$?

AUIRF9540 datasheet

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    \$\begingroup\$ Gate voltage for what? it is whatever you set it to. \$\endgroup\$ – Voltage Spike Mar 21 at 18:24
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    \$\begingroup\$ We generally use a MOSFET by applying a Vgs to is. For using the MOSFET as a switch: Vgs = 0 V: Switch open Vgs = 10 V: Switch closed. That 10 V is just an example. For a conducting MOSFET the Vgs must be larger than Vt (threshold voltage). \$\endgroup\$ – Bimpelrekkie Mar 21 at 18:26
  • \$\begingroup\$ Your question is poorly worded, but I assume you are looking for the Vgs required to achieve the listed RDson of the MOSFET. Find the RDson in the table and look in the "Conditions" column. Furthermore, Figures 1, 2, and 3 list Vds vs Id curves for multiple Vgs from which you can calculate RDson. Do not neglect Figure 4 either that shows how the RDSon increases as the MOSFET gets hotter; Often 1.5x to 2x it's RDSon at room temperature when it is running at its thermal limit. \$\endgroup\$ – DKNguyen Mar 21 at 18:42
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    \$\begingroup\$ Yes, thanks it was poorly worded...my experience is limited. Correct, I was looking at it as a switch and wanted to know at what voltage the gate needed to be for it to fully conduct. Rds(on) says it, 10v. Since Rds(on) increases with higher temps, should the gate voltage be more than 10v in anticipation of a heat event? Maybe 12-15v? \$\endgroup\$ – Kizersoze Mar 21 at 19:47
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    \$\begingroup\$ Yes, the gate voltage at higher than the rated voltage (but below the maximum of course) to get a lower Vds. I try and run at 15V usually. Halfway between the rated and maximum. \$\endgroup\$ – DKNguyen Mar 21 at 23:12
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As pointed out, \$\mathrm{V_{GS}}\$ is something that you set. I assume you want to know the \$\mathrm{V_{GS}}\$ at which the part is rated.

Usually the best place to look is the \$\mathrm{R_{DS}}\$ spec. That will give the \$\mathrm{V_{GS}}\$ at which the thing is rated. For logic-level FETs, you might see multiple \$\mathrm{R_{DS}}\$ listed, each at a different \$\mathrm{V_{GS}}\$ (e.g. 3.3V, 5V, 10V).

Typical is 10V -- if it doesn't say it's logic-level, and if it's a silicon device (as opposed to silicon carbide), you're safe to assume that its rated for 10V.

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