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

LER #243 *All you need to know about MOSFETS to fix stuff* This is the 9th video in this series looking at common components and circuits, from the perspective of a repair hobbyist / technician.

In each video I hope to teach you all you need to know about the most common way in which components and circuits fail, and how to test and diagnose these faults.

00:00:00 Chapter 1 - Introduction
00:06:47 Chapter 2 - MOSFETs vs Bipolar Transistors
00:13:59 Chapter 3 - Understanding P Channel MOSFETs
00:18:28 Chapter 4 - Testing MOSFETs
00:25:17 Chapter 5 - The Body Diode
00:30:23 Chapter 6 - Why We Need Gate Resistors
00:32:40 Chapter 7 - Gain vs Rdson
00:36:25 Chapter 8 - Enhancement & Depletion
00:38:57 Chapter 9 - Switching Properties
00:40:13 Chapter 10 - What Goes Wrong
00:41:56 Chapter 11 - ESD
00:43:23 Chapter 12 - Floating Gates
00:50:04 Chapter 13 - Testing MOSFETs In Circuit
00:54:55 Chapter 14 - Epilogue

Mentioned in the video - The Amazing $1 Short Circuit Finder
The ALL YOU NEED TO KNOW Series
*Resistors*

*Capacitors*

*Inductors*

*Diodes*

*Zener Diodes*

*Transistors*

*ATX PSU*

*Amplifiers*

*MOSFETs*

*Thermal Cameras*

*Power Adapters*

These are affiliate links, you pay the normal price and I make a small commission.

TEST METERS
Aneng AN8009
KM601
VC480C+
MESR-100 ESR METER
XC6013L CAPACITOR METER
TM-902C TEMPERATURE METER
LCR-T4 LOW COST COMPONENT ANALYZER
FNB58 USB ANALYZER
PCI POST ANALYZER
TL460S Plus PCI_E ANALYZER
TOOLTOP ET829 SCOPE METER
MULTIMETER PROBE KIT KET05
OSCILLOSCOPES
FNIRSI 1014D
FNIRSI DPOX180H
BENCH PSU
NPS3010W
SOLDERING
T12 Station with M8 9501 Handle
M8 9501 HANDLE
T12-BC3 Tip
SUGON T26D
QUICK 861DW
PROS'KIT SS-331H
THERMAL CAMERA
Infiray P2 Pro
MICROSCOPES
Amscope Optical Microscope (copy)
ANDONSTAR AD407

EEPROM Programming
TL866 II+
CONSUMABLES
NC-559-ASM FLUX
DESOLDER BRAID (I use size 8045)
MECHANIC HX-T100 Solder 63:37 (I use 0.6mm)

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Thank you for your support.
Richard

[Philippiansvs-]

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?

[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...

[nigelwright]

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.🙂

[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!

[autolancegega]

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

[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 [<- that was the majority of my early DIY & Electrical/-tronics self-education days, aside from reading and watching different videos to understand concepts... and, now that I think about it, my real entrance into actual serious DIY electrical/tronics was yearsss ago, when I stopped smoking & starting vaping, and MOST of the vapes at that time were "mechanical mods", or basically a metal tube with a battery connected to a switch, with a threaded '510' connector. Lol. But i had to learn and understand Ohms Law, to be able to actually wrap & build my own coils. Ah, the good old days of vaping 👍 😅], repair different things, build power supplies, Tesla coils & more.
BUT ANYWAY thanks for all the experience & knowledge you share! Those simple things that just 'click' into place when someone explains or demonstrates something really well, they're truly invaluable. Much appreciated 🙏 💯

[bienhelado]

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.

[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.

[jacksparrow]

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

[Fourty_]

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

[poypiedlajego]

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!

[MrRene]

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.

[michaelcummings]

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

[Lyndalewinder]

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

[donk]

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 🙄

[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.

[janakapriyadarshana]

Wow...! What a beautuful presentation

[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.

[juggernauted-chsr]

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. 💯👊