Testing Components

[Guaro]

Hi. I have been asked to test several components and do not remember how to test FETs and relays. I know that FETs are basically two diodes (huge simplification there, but the electrical characteristics match), using a continuity test should be enough, right?

Please help,

Thanks

 

[IRstuff]

Wouldn't you want to test it for its transistor characteristics?

Are we talking JFET or MOSFET?

TTFN

 

[Guaro]

What I need is a way to test if the fets are working. The fets are Hexfet power MOSFETS.

 

[IRstuff]

Then, you'll need to run it like a transistor, which means applying a gate-source voltage larger than the threshold and measuring the drain-source current.

Do you need to verify breakdown voltages?

TTFN

 

[IRstuff]

What are you using for stimulus/measurement hardware?

TTFN

 

[lcsjk]

If you are just testing to see if the mosfets work or not, then get a power supply or battery of about 6 to 12 volts and connect a series resistor to the plus terminal. Then connect this source to the drain-source terminals of the mosfet.

Then connect a voltmeter across the drain-source terminals. Then connect a 10k ohm resistor to the gate of the mosfet.
Now connect the gate resistor to the + battery (not the mosfet) and the mosfet should turn on so its drain-source voltage is almost zero volts.
Next connect the gate resistor to the - battery terminal and the mosfet should turn off and the meter will read the battery voltage.
If you happen to connect the mosfet in reverse drain-source, it will not be damaged. However the meter will read a diode forward voltage when it is off and will read close to zero when it is on.


To test the relay for functional operation:
1. Determine the relay coil voltage rating and adjust a power supply to that value.
2. Connect an ohmmeter to the contact terminals and apply the coil voltage to the coil. The contacts should close (or open if they were already closed).

 

[Guaro]

Thank you all. I got the job done.