Inductor or Capacitor? Need help!!!

[jrd78ep]

Hello i am new on this forum....i am troubleshooting an intrument...i found a mosfet with inductor (label L3) connects at drain and source...when i check the inductor it is fuse-open (read in Mohms). Wondering if it is really an inductor or not...because it is not normal to me to see inductor at drain & source...

Any idea guys? thanks for the help. (PLEASE SEE ATTACHED FILE FOR THE PHOTO).

 

[Electrobrains]

Could be an SMD varistor to protect the MOSFET from voltage peaks.

 

[jrd78ep]

Could be an SMD varistor to protect the MOSFET from voltage peaks.

So you mean varistor also can be labeled "L3" ? thanks for the reply.

 

[Electrobrains]

So you mean varistor also can be labeled "L3" ? thanks for the reply.

No, that would be very strange, but placing an inductor over Drain-Source of a MOSFET would be even stranger!

It could happen in some rare oscillator circuits or the MOSFET could be used as a variable resistor to change the Q-factor of the inductor.

Anyway, the component sure looks like an smd inductor.

 

[jrd78ep]

Now i'm getting confuse :-(
Please help get a conclusion...since i measured it fuse-open and looks like smd inductor...do i need to replace it?

Just to add up..this mosfet source pin is connected to ground. Thanks.

 

[Electrobrains]

Well. some things in life are not so obvious, especially if we don't have a handbook...
Maybe you have to analyze the circuit a bit more. What kind of instrument is it? What is the name of the MOSFET (cannot read it)? Where does the drain connect to? Can you get a circuit diagram from the manufacturer?

 

[jrd78ep]

Yes you're right...so i drawn the schematic to give better insight...please see attached file....hoping u can share now exact idea....thanks alot.

 

[Electrobrains]

Seeing that schematic, it's most probably a protection component. The varistor alternative definitely got support.
What is the name of the MOSFET?

 

[jrd78ep]

The mosfet is L540NS....thanks

 

[jrd78ep]

Any update from you today Electrobrains??? I had sent u already the mosfet number....thanks

 

[Electrobrains]

Probably it's an IRL540NS, a rough power MOSFET.
What is the problem? What doesn't work in your "instrument"?
Does the output not switch?