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

#### disturbed123

Joined Jun 11, 2020
122
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.

#### DickCappels

Joined Aug 21, 2008
10,067
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.

#### disturbed123

Joined Jun 11, 2020
122
if i want to turn this battery to universal turning on the mosfets what resistance to insert to limit the current?

#### disturbed123

Joined Jun 11, 2020
122
in the manual am i looking for Gate Threshold Voltage ?

#### DickCappels

Joined Aug 21, 2008
10,067
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
6,155
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.