Hello, I am trying to wrap my head around mosfets and there is something I just dont understand. I am looking at this mosfet: http://aosmd.com/res/data_sheets/AO4484.pdf It has a VGS of +/- 20V and a VGS(th) of 1.7-3v. I understand that VGS(th) needs a max of 3v to open up the gate. What is th…

mmimadi: I understand that VGS(th) needs a max of 3v to open up the gate. Wrong. That would be "minimum of ~2.2volt (typical) to start opening the gate". "Threshold" is the point where the fet just starts/stops conducting. The gate/source voltage where the fet only can conduct 250uA. It needs…

You also need to check what SECTIONS of the datasheet the parameters are stated in. Vgs is in "Absolute Maximum Ratings" i.e. exceed these and you will probably kill the device. Vgs(th) is in "Static Parameters" i.e. working values. Steve

Wawa: Wrong. That would be "minimum of ~2.2volt (typical) to start opening the gate". "Threshold" is the point where the fet just starts/stops conducting. The gate/source voltage where the fet only can conduct 250uA. It needs at least two to three times that voltage to fully conduct. Gate/sour…

If you look at figure 5 of the device spec you can see the effect of various gate voltages on the FETs ability to conduct current (i.e. Rds on). 3 volts is the transition area when a small change in Vgs can make a large change in conductivity. The figure is "typical" but from it you can probably ge…

No calculation involved really. Given that you have the FET in a circuit with source to ground and drain to some supply voltage with a load resistor, as you apply increasing voltage to the gate, it will turn on just sufficiently to allow 250 μA to pass (that is, drain current) when you apply a volt…

mmimadi: Hello, I am trying to wrap my head around mosfets and there is something I just dont understand. I am looking at this mosfet: http://aosmd.com/res/data_sheets/AO4484.pdf It has a VGS of +/- 20V and a VGS(th) of 1.7-3v. I understand that VGS(th) needs a max of 3v to open up the gate. …

VGS vs VGS(th) Mosfet confusion

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LarryD December 27, 2019, 10:20pm 2

Look at the RDS(ON) line.

RDS(ON)
Static Drain-Source On-Resistance
VGS = 10V, ID = 10A
TJ=125°C
8.2
10
mΩ
12.5
16
VGS = 4.5V, ID = 8A <———<<<<
10
12.5

For those cold winters night:

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VGS vs VGS(th) Mosfet confusion

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