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You are here: Home / Meters and Testers / How to Check a MOSFET Using a Digital Multimeter

How to Check a MOSFET Using a Digital Multimeter

Last Updated on July 8, 2019 by Swagatam 33 Comments

The post explains how to test mosfets using multimeter through a set of steps, which will show help you to accurately learn the good or faulty condition of a mosfet

Mosfets are Efficient but Complex Devices

MOSFETs are outstanding devices when it comes to amplifying or switching of various kinds of loads. Though transistors are also largely applied for the above purposes, both the counterparts are hugely different with their characteristics.

The amazing efficiency of mosfets are to a great extent neutralized by one drawback associated with these devices.It is the involved complexity which makes these components difficult to understand and configure.

Even the simplest of operations like testing a good mosfet from a bad one is never an easy task especially for the beginners in the field.

Though mosfets usually require sophisticated equipment for checking their conditions, a simple way using a multimeter is also considered effective most of the time for checking them.

We take the example of two types of N-channel mosfets, the K1058 and the IRFP240 and see how these mosfets can be tested using an ordinary digital multimeter through slightly different procedures.

checking mosfet with DMM

How to Check N-Channel Mosfets

1)  Set the DMM to the diode range.

2) Keep the mosfet on a dry wooden table on its metal tab, with the printed side facing you and leads pointed towards you.

3) With a screwdriver or meter probe, short the gate and drain pins of the mosfet. This will initially keep the internal capacitance of the device completely discharged.

4) Now Touch the meter black probe to source and the red probe to drain of the device.

5)You should see an "open" circuit indication on the meter.

6) Now keeping the black probe touched to the source, lift the red probe from drain and touch it to the gate of the mosfet momentarily, and bring it back to the drain of the mosfet.

7) This time the meter will show a short circuit (sorry, not short-circuit rather "continuity).

The results from the point 5 and 7 confirms that the mosfet is OK.

Repeat this procedure many times for  proper confirmation.

For repeating the above procedure each time, you will need to reset the MOSFET by shorting the gate and the drain leads using meter probe as explained earlier.

How to Check P-Channel Mosfets

For P-channel the testing steps will be as per 1,2,3,4 and 5, but the polarities of the meter will change. Here's how to do it.

1)  Set the DMM to the diode range.

2) Fix the mosfet on a dry wooden table on its metal tab, with the printed side facing you and leads pointed towards you.

3) With a any conductor or meter probe, short the gate and drain pins of the P-mosfet. This will initially enable the internal capacitance of the device to discharge, which is essential for the testing process.

4) Now Touch the meter RED probe to source and the BLACK probe to drain of the device.

5) You will find an "open" circuit reading on the meter.

6) Next, without moving the RED probe from the source, remove the black probe from drain and touch it to the gate of the mosfet for a second, and bring it back to the drain of the mosfet.

7) This time the meter will show a continuity or a low value on the meter.

That's it, this will confirm your mosfet is alright, and without any problems. Any other form of reading will indicate a faulty mosfet.

If you any further doubts regarding the procedures please feel free to express your thoughts in the comment section.

How to Test an IRF540 Mosfet

The procedures are exactly similar to the above explained N-channel mosfet testing procedures. The following video clip shows and proves how it may be implemented using an ordinary multi-meter.

Practical Video Tutorial

Simple Mosfet Tester Jig Circuit

If you are not convenient with the above mentioned testing procedure using a multimeter, then you can quickly construct the following jig for checking any N channel mosfet efficiently.

simple mosfet tester jig circuit

Once you make this jig, you can plug-in the relevant pins of the mosfet into the given G, D, S sockets. After this you just have to press the push button for confirming the mosfet condition.

If the LED glows only on pressing of the button, then your mosfet is fine, any other results will indicate a bad or defective mosfet.

The cathode of the LED will go to the drain side or drain socket.

For p-channel mosfet you could simply modify the design as per the following image




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About Swagatam

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials.
If you have any circuit related query, you may interact through comments, I'll be most happy to help!

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  1. Search Related Posts for Commenting

  2. onur says

    what is difference between N and P channel test circuit ? It looks same .

    Reply
    • Swagatam says

      supply polarity and the LED polarity are opposite

      Reply
      • Onur says

        Ok supply polarity is different in P Channel circuit but LED has no any polarity label. Can you update it please ?

        Reply
        • Swagatam says

          The lower diagram is for p channel, the LED polarity are indicated in this diagram. The upper diagram is for N channel mosfet, the LED pin on the drain side will have negative polarity.

          Reply
  3. nipun sana says

    thank u sir for your tips.

    Reply
  4. Patrick says

    Dear sir
    Thank you so much for the above simple circuit.Cramming the above 7 steps can be challenging when one needs speedy solution to a circuit problem.I would like you showcase steps for analog testing.most electricians- (electronics) use them.Please is there such a simple circuit for testing inductance and capacitance.I have one inductor i got from scrab which i want to use in a circuit but couldnt find the value on its body.is not here i would have given you what is writen on its body.its a toroid one about 2cm or more in diameter .
    Thank you.

    Reply
    • Swagatam says

      Patrick, inductance meter and capacitance meter circuits are already published in this website, please use the search box to find them.

      Reply
  5. miracletech says

    Will the Circuit using the LED work for BJT too?

    Reply
    • Swagatam says

      Yes it will, but it won’t check the hFE

      Reply
  6. Vidit Ranka says

    The pic you have shown above is wrong
    its shown source as middle pin but its drain instead
    you can confirm and thank me.

    Reply
    • Swagatam says

      Which pic are you referring to? The last two pictures indicate the wire connections only, not the pin orientation.

      Reply
  7. Irulan says

    Doing the test on a NPN Mosfet, I have the continuity between source and draing after having charged the gate but this configuration is quickly (within few seconds) going to a open configuration, without touching anything. My understanding is that there is a parasitic resistance that discharge the gate and thus Mosfet is faulty. Could you confirm my understanding ? For notice, my NPN Mosfet has an integrated zener diod protection.

    Reply
    • Swagatam says

      You may be right, because any other result than the explained one indicates a faulty MOSFET, you can further confirm this using the LED jig circuit as shown at the bottom section of the article.

      Reply
  8. Aevolet Gravesd says

    Hello,
    We have extend this offer for you to provide us with a price quote for the item listed below:

    Extech EX350 Digital Multimeter or Compatible————186 pieces

    Payment mode ——————–Net 30

    Looking forward to doing business with your company

    N.B: This offer for quote is only for USA based companies

    Thank you.
    Sincerely yours,
    Aevolet Gravesd
    President, Student Affairs
    CITY COLLEGES OF CHICAGO
    180 N. Wabash
    Chicago, IL 60601

    Reply
    • Swagatam says

      Sorry, presently we are not involved with selling or manufacturing electronic items.

      Reply
  9. hery ephrem says

    Bonjour
    quel est le rôle de diode entre gate et source intégré dans le mosfet?

    Reply
    • Swagatam says

      It’s probably for safeguarding the MOSFET gate from reverse spikes and over voltages.

      Reply
  10. subha says

    how I know n or p channel mosfet when it is connected to PCB without looking at ckt?

    Reply
    • Swagatam says

      If the source side gets the positive then it’s a p channel.

      Reply
  11. Matthew V says

    First you say short the gate and the drain to reset, then you say short the gate and the source to reset. I know it’s gate and drain just a small typo I’m sure.

    Reply
    • Swagatam says

      Thank you, yes that was a typo, I have corrected it now!

      Reply
  12. Oludare says

    Pls, I’ll like to know if the pin configuration above is same for irf840 and irf1404. Bcos I use your method to test these mosfets bUT they’re not behaving as you said. What do you think am doing wrong. I guess the pins are not in the above order. You can reply through my email if you wish Sir. Thanks.

    Reply
    • Swag says

      The pinout of the two mentioned mosfets are the same.

      Just now I checked the IRF540 as per the above explained instructions and I could check it perfectly, I will the upload a video soon for everybody.

      Reply
  13. Rajesh Yadav says

    Sir,
    After connecting supply MOSFET has burning how can I check it in microtek hb1125

    Reply
    • Swagatam says

      Rajesh, a mosfet will mostly burn due to a short circuit at the output, connect a fuse in series with the battery to verify the issue…

      Reply
  14. Olanya Kay Amos says

    But I think this article is talking on SO3 MOSFETs,how do I to with SO8 MOSFETs both P & N Channel II meet them on Laptop circuit boards
    Thanks,
    Amos.

    Reply
    • Swagatam says

      the process will be identical and will need to be done twice for the pair…

      Reply
  15. Boo says

    I Have Irfp260n giving me read even after I touched the gate is that mean I have to replace it ?

    Reply
    • Swagatam says

      No, it looks OK to me..

      Reply
  16. 1 bestofyoutub3 says

    I cant have any institute in my country
    i need your help to give me some of method to be able to repair any device

    Reply
    • Swagatam says

      you can feel free to ask anything about electronic circuits I will try to sort it out for you.

      Reply
  17. anbarasan durairaj says

    Sir i want to learn inverter service ,help me to send inverter circuit diagram with service tips

    Reply
    • Swagatam says

      anbarasan, it's not that easy, you'll have to go an institute or a relevant coaching classes to learn it theoretically and practically

      Reply


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