How to use 9v battery for charging MOSFET before it will be measured ?

Thread Starter


Joined Jun 11, 2020
I think my DMMs are not able to charge mosfet good enough. Before time i was using 9v battery to charge the item before puting Positive probe to D and negative probe to Drain. I just don`t remember what resistor should i apply on 9v battery plus connector.

thanks in advance


Joined Aug 21, 2008
Check to see what the maximum Gate to Source voltage is for your MOSFET first. If it is 9 volts or more, just connect the battery between the Gate and Source to turn the device on (observing polarity). No resistor needed.


Joined Aug 21, 2008
Here is what the specification looks like on a Fairchild datasheet:

Just do not exceed the specified maximum voltages and you will be ok.

if i want to turn this battery to universal turning on the mosfets what resistance to insert to limit the current?
I think you are asking about limiting gate current. If you do not exceed the maximum Gate-Source Voltage the MOSFET should exhibit an input resistance on the order of a trillion ohms, and not need any current limiting. A bipolar transistor like the 2N2222 needs to have its base current limited, but not a MOSFET.

Just a note: The ON resistance of a MOSFET is a function of gate-to-source voltage. Just so you know : -)

Audioguru again

Joined Oct 21, 2019
The "threshold voltage" on a Mosfet datasheet says it is the gate-source voltage that causes a Mosfet to begin turning on.
The datasheet for most Mosfets say the drain-source current at the gate-source threshold voltage is only 0.25mA.
The word "threshold" has a definition that says "something starts to happen".

The datasheets for Mosfets specs the "on resistance" at a gate-source voltage of 10V for most Mosfets.