Mosfet drain-source voltage

[Nizar_Ib]

Hi,

I have the circuit below, when I have voltage on gate-source (~4.3V) I get voltage (~2-4V) on V12 (drain source).
why that happened? I don't face this issue on another circuits with same parameters. I have 12 circuits near each other, are totally separated from each other.
in another way of question, in which cases the FET gives me voltage on DS when I have voltage on GS?

 

[KlausST]

Hi,

Your left side voltage source is called Vgs, but in your circuit it is V_gs + V_shunt.
If it is called gate-source, why isn't it onnected to the source?

I'd rather connect the right side supply across the shunt.

Klaus

 

[Audioguru]

Your VS looks like a capacitor or a battery. What is it?

 

[Nizar_Ib]

Hi,

Your left side voltage source is called Vgs, but in your circuit it is V_gs + V_shunt.
If it is called gate-source, why isn't it onnected to the source?

I'd rather connect the right side supply across the shunt.

Klaus

Hi, sorry, here is my original circuit:



- - - Updated - - -

Your VS looks like a capacitor or a battery. What is it?

a VS is a power supply which I want to test.

 

[FvM]

a VS is a power supply which I want to test.

Sounds confused. In your simulation schematic, "V12" is a drawing item without circuit functionality. If you want to simulate a power supply, you'll place an actual voltage source.

What does it mean "I get voltage (~2-4V) on V12"? How do you measure it? Are you talking about simulation or a real circuit?

 

[Nizar_Ib]

Sounds confused. In your simulation schematic, "V12" is a drawing item without circuit functionality. If you want to simulate a power supply, you'll place an actual voltage source.

What does it mean "I get voltage (~2-4V) on V12"? How do you measure it? Are you talking about simulation or a real circuit?

I'm talking about a real circuit.
when I have voltage on Vgs I get voltage where you see V12, I measure it by DMM.

 

[FvM]

in which cases the FET gives me voltage on DS when I have voltage on GS?

Most likely explanation: drain-gate shorted, either defective MOSFET or external short.

 

[Nizar_Ib]

Hi,

Your left side voltage source is called Vgs, but in your circuit it is V_gs + V_shunt.
If it is called gate-source, why isn't it onnected to the source?

Klaus

in my circuit the "Vgs" is a regulator.
where sould I connect the negative side? directly to the source of the FET or to the ground of the circuit?

 

[KlausST]

Hi,

See the name: It is called V_GS. Therefore I assume one leg is connected with Gate, the other with Source.
I don't know what the circuit is for and who named it V_GS...therefore it's just an assumption.
****
Btw: A regulator usually needs a feedback path...but I don't see any.

Klaus