first i make a short G and D after that measure D to S(black) and look for OL

after that charge with G(+) and S(-) and measure with mutimeter searching for short or not?

Please be patient with me. I dont want to post 100 threads just need answers and when i find them i will stop.

thanks

 

With the gate shorted to the drain and a multimeter with the correct polarity connected to the drain and source, then the multimeter should read a very low resistance for a moment moment since the Mosfet will be turned on.

But does your multimeter produce enough voltage (when measuring Ohms) to turn on a Mosfet? My Fluke uses 0.2V I think which is not enough. Many Mosfets need a Vgs of at least 4V to slightly turn on (the max threshold voltage) with a fairly high resistance.

I would first short the gate to the source then measure the resistance from drain to source to see if the Mosfet can properly turn off. Then I would connect 5VDC or more (if the Mosfet needs it) between the gate and source with the proper polarity then measure the low resistance from drain to source to see if the Mosfet can properly turn on.
With the gate shorted to the source I would use "diode test" to check the drain-source diode.

 

When the gate is shorted to the drain, you are putting an unknown voltage on the gate for that measurement. Different meters and different MOSFETs will not result in a consistent reading, so that is not a valid measurement.

When the gate is shorted to the source, you have 0V on the gate, so the MOSFET will be off. But the measurement will depend on which polarity the meter uses to measure resistance. Again, not predictable for a random meter.

So this is not a good way to test the MOSFET.

 

When the gate is shorted to the drain, you are putting an unknown voltage on the gate for that measurement. Different meters and different MOSFETs will not result in a consistent reading, so that is not a valid measurement.

True.

When the gate is shorted to the source, you have 0V on the gate, so the MOSFET will be off. But the measurement will depend on which polarity the meter uses to measure resistance. Again, not predictable for a random meter.

The polarity results in a reading of OL or maybe the conduction of the D-S diode if the multimeter Ohms voltage is high enough.

So this is not a good way to test the MOSFET.

True.

 

The correct polarities to be used, of course, depends upon whether it is an N or P MOSFET.

 

I have always been confused trying to test MOSFETs with only a DMM so I just use a BB and a DMM.

 

what is bb?

in theory it is basic check in fact my hear is falling from nerves. i can use esr meter but it`s not comfortable puting every item in its sockets, thats why i want to do it with multimeter.

 

what is bb?

in theory it is basic check in fact my hear is falling from nerves. i can use esr meter but it`s not comfortable puting every item in its sockets, thats why i want to do it with multimeter.

Do you really think this post conveyed any information?

 

If don't understand read again.have nothing to edit

 

I do not understand what you intended to tell us.

What is your hear and what does that have to do with MOSFETS?

 

BB= Breadboard, meaning I use an active circuit to test MOSFETs.

 

BB= Breadboard, meaning I use an active circuit to test MOSFETs.

Which is a far better way to do it. Or, get a component tester that has 3 test leads like I have. Takes seconds to find that you have a working MOSFET.

 

BobTPH
can you take a shot of this item?

 

A BB is a breadboard that has rows of contacts and wires all over the place acting like antennas for radio and TV transmitters and other interference. The probes on a multimeter are also antennas.
Instead of measuring a Mosfet, you are measuring interference.