All You Need To Know About MOSFETS To Fix Stuff! How Mosfets Work Fail Test In & Out of Circuit

[@Philippians4vs4-8]

Before retiring, I was an electronics troubleshooter for about 30yrs. I have worked with technicians and engineers from all around the globe. This man has taught me a lot in the past hour. Thank you Sir, but where were you 20yrs ago, when I really needed you, lol?

[@dhavies]

mind if i send you a mail sir? I’m graduating in a year from college

[@alainmilette6460]

​@@dhavies been a year! Hope you graduated and have undertaken a wonderful career! 😊

[@KevlarSammy]

😦 youre so kind.

[@bikkies]

Very interesting. I only ever had the most rudimentary of electronics knowledge as a teenager, with BJTs in switching applications being the limit of my skills. AC and amplifier circuits were completely beyond me, and I barely even knew what FET stood for, let alone how to use them. Now, mumblety decades later, I'm trying to learn some of these things again. Components and test equipment have become ludicrously cheap and accessible, something that was not the case in the early 1980s for me. I'm trying to go slow-and-steady, starting to dabble with JFETs before breaking into my stash of MOSFETs, but it's good to build up some knowledge for Future Me. One thing I hadn't realised until it was explained and demonstrated here in this video, was the concept of capacitance and a MOSFET remaining switched-on when current is removed. I genuinely didn't know this. I find myself wondering whether that retained charge dissipates over time (when out of circuit) or whether the transistor effectively remains "on" for a number of minutes, hours, days or weeks. Another part of this is a loose concept bouncing around between both my braincells, about this potentially being used as a form of (perhaps short-term) non volatile one-bit memory. I can see the entrance to a particularly deep and twisting rabbit warren nearby...

[@nigelwright7557]

Well, been in electronics 43 years and still learned a little from this video.

[@davesdigitaldomain]

earlier today I sat down to watch a movie 10 minutes into the movie I got an email letting me know you'd uploaded a video so I turned off the movie and began to watch your video instead which was very interesting and I learnt something. thank you. later in the day I began to watch the movie it was very boring and I learnt nothing and it costs millions of pounds to make.🙂

[@LearnElectronicsRepair]

hahaha I actually laughed out loud at this comment 😂

[@DustinWatts]

Hi Richard, although I would call myself advanced when it comes to electronics, I love your "All You Need To Know About" series. And I still learn a lot through them. Sometimes I learn something new, but most of the time I remember something I had forgotten. Thank you for taking the time to make these series. Again, I love them!

[@autolancegega599]

So well explained , no professor could explain it rather than equations on the board.

[@MrRene1968]

Thank you soooo much, I have been working in the field for 20 years, repaired a lot of equipment by using sight, and experience. Had I known this information I would have fixed a lot more equipment. Thank you for sharing in such simple terms.

[@bienhelado204]

Wow, my head is swimming...but I know much more about the four types of mosfets than I ever did before. Inching towards making sense. Thank you so much.

[@kriswillems5661]

Depletion mosfets are used where you want to make use of variable RDSon. They are used in LED drivers, linear power supplies,constant current sources, as a resistive load in logic circuits, or in the startup circuits of switched power supplies. It's just very easy to make a constant current source with a depletion mosfet, you just need only 1 resistor.

[@andymouse]

I would like to add that a resistor from gate to source is often added as a discharge path for the gate capacitance, its good practice with N channel so the 'switching on' with the multimeter wont work in a normal design that has a gate resistor to ground (source)...cheers.

[@LearnElectronicsRepair]

Thanks for the info 🙂

[@TheEmbeddedHobbyist]

Also as the gate is such a very high impedance (not resistance there is a cap in there) if left undefined it could drift and partially turn on, going in to the linear region with a reasonable current flow will over heat the fet in an switching application in no time at all. As your relying on the very low RDS(on) to limit or remove the requirement for a heatsink. Squeak!

[@andymouse]

@@TheEmbeddedHobbyist Squeak!

[@twobob]

@@LearnElectronicsRepair There are actually a few fun project on hackaday for "mosfet based memory" ( I seem to recall, one managed to store something for a day, and someone built one and managed 15 minutes) JLC PCB TO THE RESCUE! ;) Eh first freebie circuit board might not be a bad plan to use a hackaday project, They usually contain at least ONE interesting talking point. Plus you could get some time flexing on EasyEDA, might be fun trying to figure out what equivalents from LSCC you can source. see if you get something 100% pick and placed? A challenge!

[@rockpadstudios]

@@TheEmbeddedHobbyist Good point - I always think there's a resistor in there - much better to think it's a capacitor. I'll remember that from now on.

[@delta-KaeBee]

I swear, whenever ive hit a spot in trying to self-teach electrical & electronics eng'ring, I've almost always found a video of yours that if it isn't actually the topic & TITLE of the episode, you at least covered it to a practical point within some other episode topic. 👏 so well done brother! 😆 lol but seriously, you've helped me MANY times over the years of building stuff, making coils, tearing things apart to harvest components for other things [

[@donk8589]

Great video! I wish I had a teacher like this. All teachers started their courses with complex mathematical equations. They failed at teaching how to think intuitively of how a component is used in a circuit. It was all about solving equations and calculus 🙄

[@spudnickuk]

This channel is a little gold mine of information and clearly explained , I have searched high and low to get a clear understanding of such, so thank you so much for making this video as i have learned so much with in the hour and have not wasted years with all the complicated Bla Bla Bla in text books that fries the brain just like an over voltage Cap.

[@Fourty_7]

@18:31 , 7 minutes were enought to understand how to test mosfets the right way .. Thanks Richard

[@GapRecordingsNamibia]

Hi Richard, I know I am a bit late to the party but I just joined so please forgive the tardiness. I feel the need to add in one point for those that might be new to mosfets, the gate resistor you have drawn in your mockup relay diagram is going to +Ve, that means that you are using the resistor to power the mosfet "on" there are other circuits in which the resistor will actually go to ground to turn off the mosfet, this depends on A: the circuit design and B: the semiconductor you are using to switch the mosfet with. In your circuit with the relay you are using whatever is driving the mosfets gate to "sink" the voltage from the gate to ground on other circuits with the resistor to ground the device driving the mosfet will be the "source" of the voltage for the gate to turn the mosfet "on" and the resistor will discharge the mosfet gate to switch the mosfet off.... The other point one might add, is that N Channel mosfets "typically" have lower resistances between drain and source compared to P channel mosfet and therefore also higher current capabilities sourcing P channel mosfets with low resistances and high current capabilities can become quite expensive compared to N channel mosfets of the same characteristics. Mostly it depends on the circuit use and design. I just thought that it might be prudent to add this point in.

[@juggernauted-ch4sr]

Love your work, well explained detail to detail. As a troubleshoot technician I found a voltage difference on a transistor and could not comprehend what was going on internally until I watched this video. 💯👊

[@jacksparrow6217]

Hello sir, you are now my fulltime teacher! Nice to meet you!

[@Lyndalewinder]

One of your best videos in my opinin Richard - thankyou for posting.

[@spelunkerd]

Thank you, I'm finding your teaching method easy to grasp and follow.

[@michaelcummings6178]

I've seen soo many vidioes on mosfets - Yours is the best so far GREAT JOB keep it up .

[@kmersi]

Thanks to this gentleman, I enjoy electronics even more. Thank you for sharing your knowledge.

[@poypiedlajego78]

Again, a seamlessly delivered compendium of knowledge. If only they had taught us this way in the technical colleges of the late socialism in eastern europe... Cheers, Richard!

[@Gersberms]

A really nice summary, thank you for being so to the point and clear.

[@janakapriyadarshana5835]

Wow...! What a beautuful presentation .....

[@theguitaramptech]

An excellent and practical overview. Thank you.

[@PurityVendetta]

These a brilliant tutorials. I'm trying to teach myself how to repair and even possibly design and build circuits, I can't tell you how much you've helped me to understand how components work. Your explanations just seem to click with me. I'm not too bright and have to watch two or three times to take it all in but thanks so much for posting these videos 👍

[@gameofquantity96]

After a year,how far could you get?

[@PurityVendetta]

@@gameofquantity96 Designing and building my own tube amps now. And I'm very pleased with the results.

[@sinjhguddu4974]

Another gem of a class. Thanks a lot.

[@RolandV3922]

Pretty thorough and yet practical. Job well done sir 🙂

[@ionix2000]

Thank you for the video. Very nice explained.

[@opacky1411]

Another top one Richard! I am amazed how much we can learn from you.

[@howardatherton3889]

Many thanks for sharing your excellent knowledge and posting this video. Really appreciated

[@malcolmboyley2334]

Great presentation Richard, thank you

[@cristianpopescu78]

What a great teaching! Best ever found on you tube!

[@skysurfhf]

Thanks, Greatings from Portugal 🇵🇹🌟

[@nsb1524]

Thanks for Sharing you knowledge Mr.... Great Thought!

[@robertheim352]

Great explanation, especially the in circuit cases and open gate hazard. I'm guessing you could test in circuit using a temporary weak gate drive so as not to harm the in circuit gate driver.

[@NewbFixer]

Amazing rich, Keep that knowledge flowing 🧠

[@getitdone6694]

Youare the best lecturer on all issues electronics in my humble opinion and you're a brit that's a plus, go Liverpool. Do you have any videos on tracing a problem where you don't have power to the VCC. I am dealing with a power supply for an Anton Bauer quad charger. And I cannot seem to trace the root of the problem. No Power to both switching chips, they share the VCC and it gets 16V. I traced it to a W1P transistor that gets 17V at the collector but it doesn't release it to the emitter which would go to the VCC as probably 16V.

[@ravenclawavenger2170]

very interesting.I learned a lot about MOSFETS. I know junction transistors and vacuum tubes.

[@BlackOpsJuJu]

great vid learned alot from it in a easy to follow well explained vid thanks very much for sharing

[@aturogs1954]

Can you please do an all you need to know article on IGBT's? Really love the way your explanation made me understand easily. Thanks.

[@esecallum]

This not a pron channel.

[@tyronewalker5764]

Well done, sir. I was kind of fuzzy on how to bias MOSFETs. I want to 6:21 use one in a sample/hold circuit. 😮😮😮😮

[@skmplanet9591]

Very clear and to the point lecture. Thanks a lot.

[@Patecabraltica]

When testing, I just can't turn the gate on with the multimeter. But if I use my bench variable supply set at 9 V, it works fine. Another thing, probably mentioned somewhere else, but if you work with an antistatic mat it won't do to test the Mosfet over that. These mats are conductive and they will discharge the gate capacitor as soon as the terminals touch the surface.

[@edwardcharron2610]

Wow, awesome video. Thank you.

[@niaceri1]

Your training videos are usually good, but I think that you excelled in this one. It was excellent - simultaneously informative and entertaining ( wow ...do I miss your type of *dry* humour having grown up in N.Wales and now living in North Carolina!!). THANK YOU!!!

[@JS-fd7se]

Excellent, thank you for this. Your videos are a big help, thank you thank you thank you.

[@gerryfowler6128]

Great video Richard you answered a lot of questions for me for sure,keep the good videos coming.

[@VandalIO]

I was waiting for this ! ❤️

[@zedcarr6128]

Another reason why resistors on the gate are a good idea is in the case of the gate going short circuit. Whenever I test MOSFETs or IGBTs on the bench with a load like, say, a 21W 12V auto lamp and a lead acid battery or a PSU. If the gate has gone short circuit, the package of the device will explode. If you put a resistor in there, it won't.

[@retronexusnet]

fantastic channel!!! thank you! binge watching the videos now

[@steveo44]

Great video. Pure gold. Thanks again

[@kinjalmacwan4866]

Loved this! It was very helpful! Thank You and please keep making such videos.

[@nsb1524]

your lessons are awesome, Thanks.

[@AceNZ1964]

Very nice vid, learnt a lot, Cheers from New Zealand

[@mike-yp1uk]

Very good and this is an awesome explanation.

[@Plan-C]

Wish there had been this channel years ago!

[@christianmusso629]

Awesome tutorial, loved it! Thank you!

[@stiefbeen22]

At 4:35 you have just drawn the P-Channel version MOSFET. Since in all of the drawings the power has the plus on top, the source and drain seem reversed although the symbol in itself is correct. This is rather counterinuitive (for me at the least). Thanks for the video, very informative.

[@TheEmbeddedHobbyist]

You brushed over the fact the FETs acts in the same way as an old style valve, it has voltage gain and can be operated in its linear region. They are used in amplifier just as much as they are used as switches. Also a point of note that can bite your butt is that logic level fets were designed for 5V logic and may not work on today’s 3.3V logic levels. You have to check the VGS(th) value in the data sheet to make sure it will switch on at 3.3V. Note that the low RDS(on) may not be met with a low VGS even if it’s above VGS(th) threshold. Also they may never be able to carry the current the data sheet claims. In practice you can’t make a heatsink that could carry the heat away fast enough. nice introduction.

[@LearnElectronicsRepair]

I certainly know that MOSFETs act like thermionic valves ,but as most viewers would not understand the analogy yeah I skipped over it I could also have mentioned thermal runaway and the fact this is another area where mosfets are opposite to bipolar transistors . What you say about 3.3V logic levels makes perfect sense, though I never really thought about it as I am a circuit repairer rather than a circuit designer. Nice to see you liked the video. This is a big topic and the video is intended specifically for those who's primary intention is to fix stuff so I kinda concentrated on those aspects. There are plenty of videos on YT that will go more into the theory and circuit design aspects of MOSFETS

[@vicmac3513]

Thanks for all these superior quality videos! Could we get an episode about motherboards?

[@misterbonzoid5623]

Your videos are very informative and I'm grateful to you. However why you would leave errors in (like at 16:30) instead of re-filming and editing them out I don't understand.

[@rahulmechatronics]

Very good video Richard. Can you make video for Mosfets selection criteria?

[@LearnElectronicsRepair]

I can have a go but usually I use alltransistor.com as it will give you the datasheet and then also find substitute devices.

[@knightwar3]

Nice explanation thank you

[@josephdewuhan]

I found your videos really educational for someone like me. I wonder if you check questions here. I got a question hoping to get your answer. I recently mistakenly connected an old PC power supply’s 12v output to a 26v battery, I hear two loud explosions and the supply was burned. I found the 16v rated 1000uf capacitors were blown open. But after replacing the two capacitors, the power supply is still broke. What else do you think could be damaged?

[@garypoplin4599]

4:26 - I just figured out a way to remember the difference in schematic symbols for N-channel and P-channel MOSFETs: for the N-channel MOSFET, the arrow point iN.

[@gustavocontreras6202]

Great video, Thanks!

[@erichertsens]

Thank you, this was quality info.

[@gameofquantity96]

Extremely great channel

[@ParsMaker]

Thanks for sharing this, just one question, for p channel MOSFET let's say it switch on by 10v to source and 5v to gate, from another power source I want to put 50v to source and connect it to load from drain, would this work or no?

[@jbear40]

I just watched an ad that literally was explaining mosfets and thought i was watching the video for about 15 minutes hahaha

[@wtfucrazy]

Good video (as always)

[@rahmanocawni5618]

hi over there .I appreciate your video from Casablanca ,where i led you to open a technic school why not make a change ,

[@surgingcircuits6955]

Excellent!

[@ricerob]

The gay resistors are also used to bias the gate.That is to bring it up to like 2.5 boltclose.The signal only has to provide half a bowl to turn the transistor on In that case, they use 2 resistors, one to positive 1 to negative.It forms a voltage divider that can set the gatevoltage at whatever you please

[@ampuh214]

Hello rick. Perhaps you can make a video about pwm drive logic and the mosfet power sequence

[@LearnElectronicsRepair]

Yeah I'll do AYNTKA VRMs at some point 😉

[@paulmorrey733]

Cheers Rich

[@Dutch_off_grid_homesteading]

Heya not sure if I understand all of it gone watch this a agin on a later time stip but still learned a few things ( because of my autism I need to see it a few time to understand)

[@lattehour]

as i tracked his pen 26:27 i was sure he will make a mistake 😁 ps an absolute masterpiece of teaching and he is very lucid with alot of experience , btw that diode is the result of shorting the source to the body of the transistor in order to avoid the turn on of the parasitic internal bjt (yes there is a bjt transistor in vertically and laterally diffused mosfets if i remember well) that is why altough a bidirectional device you are forced to connect it only in a single way since that diode Will Conduct

[@AB-yu2tj]

This was effing awesome

[@roncooke2188]

Great video interesting thank you

[@softbytesunlimited]

❇ Very informative 👏

[@paparazzo80]

Finally!

[@royradburn9527]

Hi I'm very new to the channel And absolutely thoroughly enjoying The videos So thank you for all the time you spend on them I was wondering if It's possible for you to do a video on 100v line amplifiers I have Recently purchased one to use as a outside garden audio system But it is very limited on output wattage I would really appreciate and love to see a video on these and how to Increase the output wattage Thank you

[@LearnElectronicsRepair]

100V Line amplifiers are not intended to be high wattage, they are meant to distribute background or ambient sound over longer distances than 4 ohm or 8 ohm speaker systems, often using multiple speakers

[@royradburn9527]

@Learn Electronics Repair Thank you for your reply sorry I may have misled you my goal was to increase the wattage/ Output so I could have more speakers On the chain with different zones Rather than paying expensive prices for higher wattage/Output 100v amplifier I.e. a cheaper option But I would enjoy a vide on this subject To understand how they work either way Thanks 😁 👍

[@frankdearr2772]

great , thanks for sharing 👍

[@hobonickel840]

I have a hexfet part number IRF2204S that seemed to have been smoked from an overloaded small motor on tennisball machine .. rendered the entire PCB and system unresponsive to input

[@aku7598]

My ups using 4 mosfet. Just buy 4 units and replace all irrespective if there are still good ones. Its cheap and all brand new that will longer.

[@GoSlash27]

3:57 The way to remember that: The arrow always points to the N- type material.

[@LearnElectronicsRepair]

Ahh OK, thanks.

[@realMattGavin]

I don't know how I remember this since I was 5 or 6 but your logo is a recreation of the Rareware logo from Donkey Kong 64.

[@alejandroalzatesanchez]

the fact that the pen is at 1% makes me both anxious and surprised is quite the feeling

[@stevepr100]

Wonderful content all round, I've had a gander around your vids, but not found my problem...a meanwhile 750w server psu with just a relay pulsing on1 off3 seconds, a live wire touched the casing internally. Any ideas young sir? was thinking ptc/diode/feedback loop..

[@seniorwill]

Mosfet N- channel possible failed when it warm? Because when its cold I have negative signal and when it warm is nothing.

[@שרותמאיר]

Great video if you can also make a lesson about ipm driver

[@alejandroalzatesanchez]

What's up with laptop mosfets when a laptop dies generally i go after the mosfets, i always mock them on laptops, but why they fail so much? but especifically on laptops i mean a desktop has a pc that has like 3 or 4 mosfet on the power supply to push a lot of power, i know that is not fair since them work at 3 digit voltage hence lower current but a desktop motherboard has mosfets for the cpu that are beaten up to ridiculous amounts of current and a desktop motherboard (at least in my experience) rarely dies of that. so what's is going on with laptop mosfets? they doesn't go overkill on laptops as on desktops?

[@ecwcauto]

Fantastically

[@ElectronicCity715]

Hi Richard. Did you mean input resistance high on bjt? I'm lost on that point. To keep base current low would the resistors need to be high? Thankyou

[@LearnElectronicsRepair]

I meant the input resistance (or impedance) of the BJT base-emitter junction is low, that is why a resistor is required to limit the base current. With a Mosfet gate-source junction it is very high resistance, practically infinite so a resistor is not needed, at least for the purpose of limiting gate current.

[@ElectronicCity715]

Thankyou for clarifying. That makes perfect sense to me know. All the best Richard

[@AnthonyDunstan]

fantastic!

[@mauanderuk]

Nice one.

[@Mcfreddo]

MOSFETS act just as the old values do- a field device (that's my understanding.)

[@surgingcircuits6955]

32:33 / Supposedly, the Gate/Dielectric/Channel creating a capacitor effect, can slow the switching speed due to charge time. So, they add resistors to the Gate. Doesn't make sense to me as in that case, it would seem that more current would charge the "capacitor" faster than using resistors and restricting current more ... slowing the charge speed.