The post explains how to check 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 checked using an ordinary digital multimeter through slightly different procedures.
How to Check N-Channel Mosfets
(Remember the following explanation is for the above mentioned Mosfets, for other mosfets the pinout assignments may change, and you may have to proceed accordingly)
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 piece of insulated wire stripped at the ends, short the extreme left lead and the extreme right leads of the mosfet (gate and drain). This will initially keep the internal capacitance of the device completely discharged.
4) Now Touch the meter black probe to center lead (source) and the red probe to right lead (drain) of the device.
5)You should see an "open" circuit indication on the meter.
6) Now keeping the black probe touched to the center lead (source), lift the red probe from the right lead and touch it to the left lead (gate) of the circuit momentarily and bring it back to the right lead (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 source leads using a piece of wire as explained earlier.
How to Check P-Channel Mosfets
Follow the procedure exactly as given in the steps 1,2,3,4 and 5.
Next remove the red and the black probes from its positions and touch the red to the left pin (gate) and the black to the center pin (source) of the mosfet.
After a few seconds, put the red probe and the black probe back to the center (source) and the right pin (drain) of the mosfet respectively.
This time the meter should show a short circuit, proving that the mosfet is in a good condition.
If you any further doubts regarding howto check a mosfet with multimeter 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.
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.
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.
Rajesh Yadav says
Sir,
After connecting supply MOSFET has burning how can I check it in microtek hb1125
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…
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.
Swagatam says
the process will be identical and will need to be done twice for the pair…
Boo says
I Have Irfp260n giving me read even after I touched the gate is that mean I have to replace it ?
Swagatam says
No, it looks OK to me..
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
Swagatam says
you can feel free to ask anything about electronic circuits I will try to sort it out for you.
anbarasan durairaj says
Sir i want to learn inverter service ,help me to send inverter circuit diagram with service tips
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
Anonymous says
HI sir .
I tested the MOSFETs in the above link the 12v bulb(two 6v / 300mA in series ) the bulb glows with full bright. i think the MOSFET is all right.
sir ,can you tell why these 7 points given above was not applicable with multimeter, for these MOSFETs.
-GIRISH.
Swagatam says
Hi Girish,
Can't say actually why it's not working for you, because when I checked the mosfets k1058 and j162 with the above methods, it gave me perfect results as explained in the article.
Anonymous says
Hi sir i am girish. i brought two IRF540N and two IRFZ44 it was new MOSFETs , for my inverter. first i used IRFZ44 it gave me very low output. i checked it with multimeter first 5 points given above was ok , but it did't give any shot circuit. then the two unused MOSFETs IRF540N gave the exactly same result i,e it did't give any short circuit . then i again brought two MOSFETs IRF540 from the same shop but, it gave the exactly same result i,e it did't give any short circuit. i checked all the MOSFETs without using in my inverter so ,we can say that the inverter did't damage it. i have all ready checked many MOSFETs successfully. but here totally confusing .and i have conformed the pin outputs of the MOSFETs. there could be any possibility of manufacture's defect?
Swagatam says
Hi Girish,
The best and simple way to check them is by testing them practically. You can make the first circuit shown in the following article. Put a 12 lamp in the "load" section. If pressing the switch triggers the load and vice versa would mean your mosfets are OK.
https://homemade-circuits.com/2013/04/simple-mosfet-switch-circuit-with-delay.html
network advise says
hi swagatham this srinivas
ihave to know the six band resister value of these colours brown,black,black,silver,brown,green
plese tell me the above resister value
thanks & regards
Swagatam says
Hi Srinivas,
It's
1 ohms, 1 % tolerance, 20 ppm temperature coefficient
Anonymous says
Hi. how to check for p-channel mosfet?
Swagatam says
just change the prod polarity in the above explained procedures
Anonymous says
HELLO. is this is applicable for all kind of n-channel mosfet?
Swagatam says
yes but first make sure about the pin assignments, might be different for different brands.
Anonymous says
hi. after test, need to dicharge pins? Before use like short circuit? Or reverse probs? Thx
Swagatam says
see step no.3
Anonymous says
According to alldatasheet.com the pins of K1058 are GSD, yet U stated here GDS. So I'm confused.
http://www.alldatasheet.com/view.jsp?Searchword=K1058.P.S’ defer . excuse my english. A big thanks to you Swagatam