measuring current through a bf981

[neazoi]

how to measure current flowing through a bf981 which is loaded with drain and source resistors?
also how to measure current if it is loaded with a drain transformer and a source resistor, or with a drain resistor and a source transformer?

 

[rfredel]

Hello neazoi,

If you want to measure the DC current, you can measure the voltage drop across the resistor with a normal multimeter. For measuring the AC current, you need a oscilloskop or a multimeter, which can measure the AC voltage across the resitor.

Regards

Rainer

 

[neazoi]

Hello neazoi,

If you want to measure the DC current, you can measure the voltage drop across the resistor with a normal multimeter. For measuring the AC current, you need a oscilloskop or a multimeter, which can measure the AC voltage across the resitor.

Regards

Rainer

The datasheet states a 10mA current through the transistor to achieve the lowest noise. I think this is DC current right?
But which resistor, the drain or the source one?

 

[FvM]

If you can explain me why you assume drain and source current of a MOSFET to be different, I'll try to answer the question.

 

[neazoi]

If you can explain me why you assume drain and source current of a MOSFET to be different, I'll try to answer the question.

Ok, so it does not matter where to measure it.
Is it DC current I have to measure?

 

[FvM]

Yes I presume you want to measure the DC current.