#132

This video shows a couple of methods you can use to test enhancement-mode MOSFETs. An N-channel device is used in this video, but the same procedure can be followed for P-channel by simply properly changing the polarity. The operation of the MOSFET as a switch is easily tested with just a DMM using the diode test function. Also, a very simple test circuit is shown that will give a bit more insight into the operation of the MOSFET.

[@Hopeless_and_Forlorn]

Please allow a retired avionics instructor to thank you for sharing your wealth of knowledge with the world. The clarity of your exposition is matched only by the effectiveness of your hands-on, do-it-yourself demonstrations. Every student of electronics at every level should subscribe to your channel to ease their path to mastery of the subject. Bravo.

[@RhythMickJ]

You have a way of explaining things which brings real clarity to a solid state newbie like me. Thank you for sharing your experience.

[@georgie3]

Thanks this works on many MOSFETs but you have to be careful about the voltage produced by your multimeter in diode test mode, since it may not be above the MOSFET's gate threshold voltage. Check the data sheet and if possible measure the voltage produced by your multimeter in diode test mode, using your second multimeter :) On my two multimeters it's 3V which is right around the typical threshold voltage of many MOSFETs, and well below the 4V maximum threshold many MOSFETs like the IRF520A and IRF120N might have. Keep in mind that at its threshold voltage a MOSFET is just barely on and needs a significantly higher voltage to switch fully on. A trick to measure the meter's voltage if you have only one meter: Charge a big capacitor in diode test mode then measure it in DC voltage mode.

[@ahurasim4566]

Haven't messed with this stuff in a long time, Your comment helped 🙂

[@jasoneyes01]

Absolutely love how you break down the fundamental, making understanding easy.

[@redrigger8348]

I like these straight to the point videos. Great job

[@ElPasoTubeAmps]

Alan, you have positively touched (no pun intended) the lives of many techs with this video. I worked for NASA and WSMR for twenty six years and can check BJT's and SCR's blindfolded but I never knew how to test FET's until now. I knew the basics of FET's and the "open" gate and understood why it could be damaged so easily (and the reason we were required to wear wrist straps and antistatic lab coats) but no one knew how to actually test the FET's. By the time our technology got to FET's we replaced PCA's by hexadecimal error code and never worked at the component level again on mainframes. Thanks for the information. I may never use the method but I will never forget it. Funny some of the things we can remember and some of the things we can't.... :-)

[@DanielCruz-vp7mg]

Wow

[@kvmdop]

Another awesome video! I love how you easily explain such a complex behaviour. Simple, to the point and calm. Thanks for sharing :-)

[@Rodderick45]

Great video as usual. You are presenting a wealth of knowledge at a layman’s level in such a professional manner. This is by far the best channel I have seen on you tube when it comes to electronics old school and modern day. You and I are probably the same age as I begun my electronics practice and education back in 1972 with vacuum tubes. I have my Simpson 260analog meter from back in the day which served me well while employed in industry that I use still on occasions among others as well as two analog Tektronix oscilloscopes that have out lasted my digital storage oscilloscopes. I am enjoying a watching all your videos. Keep up the good work.

[@w2aew]

You're probably a *little* older than me - I wasn't yet a teenager in 1972...

[@theduder2617]

Beautiful Simpson! And excellent explanation of the function of the mosfet. Thank you for sharing!

[@SuperFuckingname]

This is my first time needing to know how to test a MOSFET and your tutorial was very well presented and included everything i needed to know. Thank you. Subcribed.

[@patrickremis2023]

Great video. I worked my way through college being a TV repairman in the late 60's. Which we had great videos like this back then.

[@w2aew]

I also worked part time in a TV repair shop during High School and the first year or two of college (early 80s).

[@BobMellor1954]

Hi Alan, thanks for the video, I find all of them easy to understand and very useful. Cheers Bob

[@ryanbishop3343]

Thank you so freaking much. How sweet it is to hear someone explain this in clear English

[@knunne1]

Thanks for the clear concise explanation on function and testing. Great Video!

[@donaldfilbert4832]

Excellent tut. The test circuit is a great visual aid !!

[@xray364]

Very simple but detailed explanation of how Mofset work and how to test. Thankyou.

[@GulfSouthGene]

Alan, you produce some very good videos, and explain things very well. I have been a engineering technician for 45 years and still enjoy it, but your teaching skills are top gun. KC5WS

[@jeanious2009]

Thanks for the educational video. Thanks a lot for taking your time and explaining it very well.

[@brendanzotto1239]

Amazing video, so easy to test a mosfet with the DMM. Thank you.

[@patrickmorin7693]

Very informative and easy peyzy to follow. If only all my school teachers would have been this clear! Thanks from a North American, French Canadian, bilingual Ottawa valley guy. :-)

[@jesseweaver2113]

Amazingly easy DMM test for FET's. Thanks for sharing.

[@bend0matic]

Great video! Content is always quality in resolution and in information.

[@KAFA2020]

Masha-Allah. Zazakallah Khyer. You are very helpful for every engineering students.May you live a long life with Full of gladness and health.

[@dandearman2871]

I never thought to charge the gate using the meter. Great idea. I hook up the meter to the drain and source and use a 9V battery and my fingers to complete the circuit to the gate. Great video. Thanks.

[@hardergamer]

Thank you, been a big help finding my blown 2 fets out of 18!

[@emgab]

Excellent video and explanation - thanks for sharing !

[@Pwaak]

Watch video...take notes...go to workbench...remain at workbench until lesson learned! (sometimes many, many moons!) Thanks so much for these videos!

[@lltb67]

Very clear explanation with good video. Thanks

[@briantumor9390]

Excellent tut. Thanks for the test circuit.

[@mikedalakis5292]

Clear explanation, beautifully presented. Thanks much.

[@mauserman48]

this is great video.. very informative..I'll be using these tests on the many mosfets I"ve pulled

[@tcpbox]

Good video thank you for share, it is the best one I have seen in years.

[@MrMac5150]

Very Very Good, I was waiting on this one. thumbs up.

[@electrofly23]

excellent - clear and simple! thank you

[@nevartojau]

Thanks, was really helpful to detecting faulty mosfet semiconductor

[@musmodtos]

The DMM tip is great, thank you for taking the time to share! Sub'd!

[@AndrasBato]

Thanks a lot! Very nice explanation in Oxford style.

[@electronicsradiovideo]

These techniques are so useful. Thanks.

[@ka8syv203]

Practical, informative, excellent!

[@okechukwuanwasia9968]

Thank you for the tutorial. It was well done! Regards, Cyprain

[@tcarney57]

Thanks, Alan! Nice fade in/out editing. I'll be giving a presentation at our next club meeting about online Elmers such as yourself. You're on my list of a dozen or so I'll show clips of including K7AGE, VK3YE, EEVblog, and so forth.

[@w2aew]

Thank you, Todd! I hope your club enjoys it.

[@XCALIBUR4326]

GREAT VIDEO,VERY SIMPLE & INTERESTING TIPS TO CHECK MOSFET thanks for sharing information-------

[@arshamskrenes]

Fantastic video! Thank you!

[@vleolml]

Nice video. You trick with the finger is great! I was messing with some metal tool, like a screwdriver. In fact - one finger has low enough resistance to reliably discharge the gate capacitor. There is another simple DMM test - the internal diode of MOSFET, there should be a normal diode (0.6V) voltage when DMM probes connected (+) to S, (-) to D (in DMM diode testing mode). Also, if your DMM has a BJT tesing socket (the one with EBCE pnp npn text) - you can connect the mosfet there this way: S to E, G to B and D to C - it should show infinite hFE, since there is no current needed to keep MOSFET open).

[@solderbuff]

Best MOSFET video. Thanks.

[@LeoBercoff]

Look at that "glorious" Simpson! :) Great video!

[@ElectronFunCom]

Your video is great! Finally I know how to test MOSFETs :)

[@txsharpshooter85]

Nice video, thanks for posting.

[@magickandre]

Another great lesson!

[@MrWaalkman]

Gotta love those old 260's! :)

[@AzMetsFan]

Great idea to use your finger to discharge the stored energy in the gate capacitance. I'm a bit surprised you didn't discuss the body diode of the MOSFET and how that could effect some readings if the DMM leads are reversed.

[@johncorrigan2942]

Cool testing method!

[@maxxsmaxx1901]

Wonderful Demo. Thanks

[@christopherbergner7519]

Thanks very much, a very useful tutorial.

[@user-jg2xf3pj1z]

Great. And simple explanation.

[@andrewferg8737]

Very informative. Thanks for sharing!

[@Beretta96Dan]

Very nice instruction. Thanks!

[@ziadfawzi]

Thx and much appreciated for sharing this info.

[@TheCrazyStudent]

Wonderful tutorial, as always. First you did BJTs, now MOSFETs. I look forward to the next video which I assume will be about how to test JFETs? :)

[@juliencourrejou9211]

Very usefull video. Thanks

[@yoramstein]

Great video(s) like the calmand clear way you explain which make it possible to follow.

[@evil17]

Great vid, thanks for the share!

[@ikocheratcr]

I had never ever tried the touch the gate for a second to charge, and see the Drain Source to continue flowing with Gate open. I could not resist, and just grab a 2N7000 and tried it, pretty cool. I also tried it on a IRFP450 and IRFZ44N, same thing. Wow. Gate keeps the charge.

[@GeorgeTsiros]

it's a capacitor, what would you expect?

[@hackeritalics]

It's cool regardless of his expectations. LOL actually have a fan I made with a little PCB with touch pads controlled with a surface mount fet. Super useful little switch without any moving parts. :-) every single time I touch it and the fan turns on I think, "damn that's pretty f****** cool actually." LOL

[@jarrellestes1793]

Great job

[@steveedwards90]

thanks a lot this video was very helpful been working on an mfj259 not b with a frequency generation fault is it possible to test this mosfet with a scope and octopus in xy mode just a thought love the videos thanks

[@evgeniyasd2740]

Thank you, nice tips :)

[@electroman1556]

omg you are the answer of my problem! thanks

[@homemade83]

hello from the other side of the earth no words will show my thankfulness i have watched and learned a lot from most of your videos i need a video also about MOSFET false turn on due to the dv/dt i will repeat this comment in videos i have seen this morning in my country so you can them also this is the only support i have for you for now

[@sssttt6533]

Your video is great!

[@verbatimrecorder13]

Thank You very much, your video helped me :)

[@Damothedevo]

I have that same battery charger in the background I'm trying to troubleshoot, hence watching this infomative vid, thanks.

[@ashpowell9451]

Excellent, thanks!

[@loremipsum3454]

Help needed.. When I do Negative to S, and Pos to D =0, briefly Pos to G and back to D I get 0 reading !!! When I reverse and connect Neg to D and Pos to S I get a reading of 0.49 Its an HY1001P ( N channel mosfet 70V/ 75A, / RDS(ON)=7.8mOhm (typ.) @ VGS=10V) Can you please advise if according to first part of the test it's busted ? And How should I look for a replacement ( I have full data sheet) .... I can;t find an exact mach , and I was wondering if I should go higher in voltage and current or lower...? I really appreciate any advice.

[@losingyou8360]

Thanks so much mate.

[@habiburrahman-yx7xy]

Thank you Brother, i like your video.

[@naftalihaskell3310]

Short & clear

[@hyparh]

Recently I purchaset 10 new IRFP250, but all of them seem to be in an "off" state. I put negative lead to Source, charge the Gate by touching it with the positive lead, and then when I touch Drain with the positive it shows around 900 ohms. And thist is for all of the 10 brand new mosfets :( Why this could be happening?

[@synthcopathofftheair1148]

Should the MOSFET be also tested with reverse polarity, i.e. positive on source and negative on drain?

[@TheEtbetween]

Thank you so much,

[@pauledwin2955]

clearly explained thanks

[@Martin1519]

Does the mosfet need to be pulled off the circuit board to test it? Or can you test it before pulling it off to save the extra work of detaching and soldering the mosfet back on.

[@w2aew]

Testing in-circuit can sometimes be done, but not always. It depends on the rest of the circuit connected to the device - so it's impossible to say just yes or no.

[@sanchocabatay]

How about a mosfet installed in a powered amplifier? should I pull it off? Thank you!

[@amikhimji]

Great video thanks

[@74LS324]

How about testing mosfet with dumping diode? (My cd800a Sanwa cant test mosfet and scr, so not all dmm can test that component)

[@marcomeli9821]

Thank you!

[@burningions]

Simple and great

[@mikeTmurray]

Many thanks for the video - would the test work with the mosfets in situ (in the circuit but no power) or do i need to de solder and remove?

[@w2aew]

Not for in-circuit testing

[@power-max]

Are BJTs more linear than MOSFTs, my understanding is that they are. Is is possible to make some form of negative feedback to the input of the MOSFET to make it operate linearly, to minimize distortion?

[@w2aew]

It depends on how you look at it. BJTs are fairly linear with regards to collector current vs. base current. But, their quite non linear w.r.t. collector current vs. Vbe. MOSFETs are more linear in this mode (drain current vs. Vgs). Feedback can be used with either to improve linearity. This typically works better with BJTs since the transconductance is much higher, increasing loop gain and thus closed loop linearity.

[@FullElectronic]

Thank you. I made this test on a D90N0 and it works great.In case of channel P is just to invert the probes right?

[@w2aew]

+CYBERRD58 Yes, just reverse everything for P channel

[@kapilawickramasinghe1895]

Thank you Sir

[@electronic7979]

Excellent

[@babumanikuttan2258]

So nice video

[@shelby50411]

damn i had my hopes up no maybe not....i tested some other mosfets in circuit on another laptop board and it seems most D-S diode test shows open..but a few show low reading like 15....so you are correct ..testing in circuit can mislead bad for good....but in your opinion the high 550 reading both ways D-S is definitely worth going further to test? removing from board?

[@w2aew]

The only reliable way to test them is out of the circuit (or by verifying proper circuit operation).

[@Laughinggray]

I've got a FR18N15D here but can't find info on the source and gate points (had a look at the data sheet but it is probably very well hidden somewhere?). Is there a way to find out which is which, using the multimeter?

[@w2aew]

Pinouts are shown on page 8 and 9 for the two different packages: www.datasheetspdf.com/datasheet/download.php?id=692712

[@Laughinggray]

Thanks for your quick response and for the link, but that's the sheet I have been looking at and the only thing I can see on page 8 and 9 are the dimensions, or am I missing something?

[@w2aew]

There is a small list showing pin number and function on each page, on the right side of the page. www.mouser.com/Search/Refine.aspx?Keyword=FR18N15D&FS=True&Tb=datasheets

[@Laughinggray]

Ah! Found it! Finally! Thanks very much for your quick replies and your patience:-)

[@BinjKomisar11]

Thank you for sharing this... You have saved me many, many hours! :)

[@fardellp]

How about testing the MOSFET as an RF amp? (Another very common application).

[@badshah_pro]

Good video but I have a question, I have a clamp meter 266FT with no diode test mode but it has ohm test labeled 2M, 20K and continuity test labeled 200. Can I use it to test Transistors? Or I should purchase another multimeter

[@trevorjames5493]

Does the same principle and tests work for surface mount mosfets ? because they also have the drain source and gate?

[@w2aew]

Yes, packaging doesn't change a thing.

[@roimark358]

With that good MOSFETs, in the On-state, or low resistance reading, how long would that be On or on 0.003 or low resistance keeping your test probe on that Drain and Source? have you tried keeping that test probes on that pins for a couple of minutes or hour and monitor the reading? does all good MOSFETs must have that reading and it will keep that reading forever until we discharge the gate?

[@w2aew]

It's difficult to say - it all depends on how long it takes the charge to leak off of the capacitance formed by the gate-source. This could be due to internal leakage, thru external contaminants on the package, etc.

[@W1RMD]

Thank You!

[@REDBARRON2424]

great little video.. but i can't get any readings at all no matter what connections i make . the G, D and S are the same as in your video .. i am testing a STW80NE06-10 Mosfet .. . does this mean it's completly blown ..

[@w2aew]

Might be, but test it in the circuit shown at 2:45 in the video to be sure. It is possible that the "diode test" on your DMM might not produce enough voltage to make the D-S channel conduct.

[@REDBARRON2424]

i don't have the means to put together a test set up like yours ..