Great demonstration, practical physical view of what the MOSFET does and how it operates, clearly shows what this item does. Great teacher, you won over a new subscriber.
Thank God... FINALLY - a video that not only explains a Mosfet, but ACTUALLY shows how it works by hooking it up in real use practice.. I LOVED IT, and thanks so much for this video - I am finally starting to understand Mosfet's now because of you. I am a visual and Hands-on learner, not theory - who cares about theory and history, but yes I do understand they both have their place, but that is the only thing that most of these videos talk about, and I end up learning nothing - just getting more and more frustrated - AND confused LOL... This video has finally made it all clear, and I truly thank you for creating this video - Got my sub for sure, and a great big thumbs up!! Steven
Yes Dorian, PLEASE make some more videos, especially about diodes, transistors, capacitors - testing/checking and how to find the bad ones etc., etc., as I am starting to learn about soldering, de-soldering components, and then using some of those components to fix and repair computers etc.. I have been building/repairing computers for the past 20+ years, but have just recently decided to start learning how to go into more depth with repairs. Using the components in practice like you did here, helps me very much, to better understand what you are teaching. It would be so much better if others did that as well as you... Thanks for the quick reply, and do truly look forward to more from you that is for sure. Steven PS. I like encouragement myself (which you just did for me with this video), and am glad also, that I could be of some encouragement to you, so keep them coming ;).
berglundsimon I couldn't directly reply to you. Thank you for your inspiring comment about the video. I encourage everyone to comment - good or bad - about the videos to help keep me on track.
Great! glad you liked it. I was going for shock and awe but plan to do a more technical video on MOSFETS and other devices soon. Keep an eye out for it. Thanks for commenting.
Jared Jeanotte I know, they don't make them like they used to. It's been a hell of a battery. It's a rechargeable lead acid battery that was part of an emergency lighting system. It was intercepted by a friend before they were able to throw it away. They are required to be replaced whether they work or not. What a waste. BTW it was made by Globe.
Man. This video completely demystified the *practical* application of power FETs. I've understood some of the theory, and I've kinda sorta used them in little projects as switches, but this video, for some reason or another, just lit that bulb above my head and now I totally get it. It was like the catalyst needed to make all that stuff I've read actually make sense. Wow. Thank you so much for this video - excellently explained and excellently demonstrated. Seriously. Thank you.
As you started to show the active region I wanted to comment about heat and power dissipation there, but you explained it perfectly, nothing to add =) Like Paul electrical engineer here, doing a refresher. Thanks for the great video - it's really fun to watch how you switch the Mosfet with your bare hands.
I just saw your video now, and have subbed, thanks man, after so many years i finally get a clear and thoughtful explanation. Thank you for your creativity to create a visual for our understanding of a mosfet from our brain end, thanks man.God bless you...
Thanks for putting this together. I have basic setup where I'm using an N channel on the low side and driving the gate using an opto-isolator in a 12 VDC 1 amp configuration. My Vgs is around 12 volts and should drive the mosfet fully on. i'm driving the opto-isolator from an Arduino using PWM. If my PWM frequency is low say 1000 hz or less, the MOSFET's run cool (12 volt, 1 amp load), but the circuit has a nasty buzzing sound. If i turn the PWM frequency up to say 15K or 30K, the MOSFET's get extremely hot after a few seconds--(like 100 deg c). For my N-channel config I'm using these, CSD18536KCS and a 4N25 opto isolator. I have no clue why the mosfets get burning hot at a 1 amp load--but only when the pwm frequency is high. Thoughts?
I believe the big problem you're dealing with here is the Switching Speed and Rise Time limitations of opto-isolators. Slow rise and fall times cause the MOSFET to remainw in the active region for a longer period of time and dissipate power during that time. Bandwidth issues decrease the gate signal level reaching the MOSFET at higher frequencies also causing heating of the MOSFET. The combination of the two cause the MOSFET to become much less efficient which ultimately leads to gross overheating. With large motors a switching frequency of 1000 hz should be fine. Fine tune the frequency around 1000 hz to decrease buzzing which occurs when harmonic resonance is reached for motor mechanical parts such as laminations and windings. Good Luck.
I have to agree with "Evgeniy asd", plenty of easy understandable information. Im new to electronics so this was perfect for me. Thanks from Simon in Sweden
Would you be able to show how to build a multi pc fan / multi water pump controller with tach, temp, and output to a local lcd screen with a wifi or blue tooth module to communicate to a pc for controlling the speeds of all independently and get a data output from each. I realize this is a complicated build, one i have been struggling to realize how it would all go together with a ardunio. Thank in advance either way. Love the detailed information you provide, Keep it up :)
I have just come across your tutorials and I am most impressed with your clear explanations. The first one that I saw was the one showing the interaction between an inductor and capacitor and you are quite right to say that the interaction between the two is not emphasised enough. Your video of this explains a lot about the two devices, so well done.
The charge stayed on the gate because there is an internal capacitance between the gate and source. Discharge the capacitor and the MOSFET will turn off
Thank you for this very helpful video. You have a teaching gift - clear, informative explanation with interesting and understandable demonstration. Bravo!!
Been watching a lot of videos to understand how MOSFETs work. Until now didn't realize how sensitive they were. Great job on explaining this and the fundamentals. Thanks!
A word about mho... As you say it's the old name for siemens. Old meaning mho was renamed siemens already in 1881. But some are slow to take up new conventions! Also there's no "siemen", it's "1 siemens". :)
+renxula The mho should have never been renamed. Siemen was an industrialist who had to nothing to do with research in conductance or resistance. It was all about politics and has confused people every since.
You might notice even bipolar transistors come in antistatic plastic these days. Some say even bipolars live longer if taking care over static. Doubtless a 2N3055 won't be harmed. Even that might not be true as the ones sold today might be higher grade devices than in the past. One type of FET that seems better from this point of view is the JFET. JFET input opamps like TL071 seem to perform OK if handled. CMOS ones not.
There is a lot of folklaw about FET's that isn't totally true. One it they will not suffer thermal runaway like bipolar transistors. What might be said is they seem to run nearer there calculated maximums better than bipolar devices. Audio MOS FET's seem to fit the folklaw better. They can be biased with just a resistor. BUZ900/905 being typical.
guys I have seen ppl using mosfets in electric cigarettes?? why?? is it because of the on of switch that their mod is using or is it something else?? pls explain... and if possible, please provide a proper set up to use common rechargeable batteries that are not lithium...
I just learned more in 15 minutes then several hours of other electronics videos. But why does touching it work to turn it on if the data sheet says it needed a minimum of 2 volts? There is that much voltage going through your fingers from the battery? I would have thought only millivolts would pass through skin.
Only a few microamps of current are required to build up a high voltage on the Gate of the MOSFET. If you leave you finger on the MOSFET the voltage will rise up to 12 volts.
The capacitance of the gate is very small and the Gate is completely insulated from the rest of the MOSFET so no current escapes from the Gate. This means that the small current flowing through my fingers will remove enough electrons from the Gate to eventually reach the turn-on voltage for the device. This voltage will eventually reach the full 12 volts which will fully turn the device.
It is a Field Effect Transistor (FET) and it does not need current to it. Voltage is the only thing it needs. That is why you should know the difference between current and voltage. When you touch the battery pole your body, being a conductor of electricity, becomes the voltage of the pole you touched. That voltage is impressed on the gate, thus activate the drain.
You cant have voltage without current or current at zero volts. Thats like having a water faucet thats on but saying it has no water pressure. Current might be minimal but its certainly not nonexistent.
I have had the mosfets in my power inverter explode when I transmitted a portable radio too close to the inverter. There were four mosfets. 2 were on the positive side and two were on the negative side, I believe they are used for breaking the dc power from positive to negative at 60hz to create a square wave AC signal. I think the radio charged the mosfets gates on one side while out of phase with the other sides mosfets which caused a direct short between them
Kudos to you for getting this to work. I'm trying the exact same thing but using a car headlight (10 amp draw) but my MOSFET gets super hot on any setting other that 0 or 100% duty cycle (and my MOSFETS are mounted on a big heatsink. If I send 5v to the gate i can run the light for 30 min and the MOSFET temp never gets over 100 deg F, if in change the PWM to say 50% duty cycle, the temp goes way up. my PMW frequency is 32250 or so, but if i lower the frequency, the bulb hums. My MOSFET is a a CSD18535KCS, others tell me "its not logic level" but it works fine with a pure 5v at the gate. Thoughts?
+Kris Kasprzak A few possibilities... Make sure the ground for your headlight is connected to the Arduino ground. Make sure the output pin you're using is configured as an output. These are the most common problems I've seen.
+Kris Kasprzak Can't remember, I just picked the first power MOSFET I saw on my bench. Unfortunately the video quality is too poor to make out the part number on the video. What power supply voltage are you using? You are using a monster MOSFET, it's possible that the input capacitance is keeping the MOSFET in the active region too long and causing the overheating. The Arduino can only supply 40 ma and you may need a larger gate drive current to charge the MOSFET. The gate threshold for your MOSFET looks good - logic level capability is not necessary. Are you powering the MOSFET from USB or a separate power supply. If your powering it from USB try using a battery pack or wall transformer to power the Arduino instead to ensure you're getting maximum output current to the MOSFET for a quick gate charge. Let me know how it goes. Thanks.
+Dorian McIntire I'm using the output from the Arduino directly (5 VDC)--just like you but as you say my MOSFET may not be well suited for TTL level voltage and current. I'm not sure what to do in order to get higher voltage and current to the gate--experienced people would build some transistor circuit--but that is way over my head. my only other guess is to use an optocoupler. The reason i picked this MOSFET is that I *was* going to build a DC motor controller (locked rotor amps = 130, but general operation in the 50-70 amp range. I *was* going to parallel 3-4 of them together. This simple circuit was to see if I can even control a light--ive not yet even gotten into handling the spikes from the motors impedance. I'm no longer going to build a controller--i''l just buy one. But it bothers me something so simple as a light dimmer is so hard to make.
+Kris Kasprzak Try driving a smaller MOSFET to a smaller load (12 Volt Bulb) to make sure the connections and Arduino are set up properly. If you still experience the same problem look for connection and Arduino issues. If you plan to drive more than one MOSFET you will need a gate driver to get the gate charge established quickly since you will need a drive current larger than the Arduino alone can provide. Check the following link for more information. www.quora.com/What-is-the-purpose-of-a-MOSFET-gate-driver
Use a grounding strap when soldering up MOS FET's. Some static charges will harm them. Our bodies often carry enough charge to harm them. Some say even bipolar devices suffer if zapped. MOS FET's were suggested in 1925 before bipolar devices. Really nice video. I didn't exspect the detail about transconductance.
I wasn't as clear on the points you were trying to make at the end of this tutorial... probably because I have a specific context in mind for MOSFETs. You were talking about the active region of the device and power dissipation. Is a power MOSFET (N channel/enhancement mode) acting like a BJT when it is operating in the active region? From what I have pieced together so far, it looks like the fet operates like a BJT if it is kept under the max safe operating area, DC-line on a Drain Current vs Drain Source Voltage graph on a datasheet. Am I missing something here?
The active region for MOSFET or BJT is simply the region in which a further increase in the control signal (input current or voltage) will cause a corresponding increase in the controlled current. Once a MOSFET or BJT is saturated no further increase in the controlled current is possible by changing the control (input) signal. Any control device will dissipate power only if both voltage exists across the device and current exists through the device. When the device is saturated minimal voltage exists across it and when the device is cutoff no current exists through it. You must have both voltage and current to produce power.
I am a little confused by vgs and g, if the min vgs is 2v, why is g min 11? at 21a/v and min vgs 2v I would think that means that min current you can drive is 42A? Is VGS a charge threshold you have to overcome, but not actually min? Just a little confused by that.
Vgs is the minimum voltage required for transconductance to begin. Nothing happens until this threshold is exceeded and then transconductance begins. So the min is zero until 2 volts on the gate is exceeded. With 21S of transconductance the Drain Source current will change by approximately 21 amps for every volt applied to the gate. This means the device is pretty sensitive once VGS(th) is reached.
Hello sir, Can you help me for Dimming COB DC lamp with 28V 670mA? 1. TIP41C BJT [100V 6A 65W] it is getting to much hot. 2. IRF540 MOSFET[100V 30A 150W] it is not giving effective dimming Other Option is to use TIP120C BJT[60V 5A], IRF520 MOSFET[100V 10A] Which is best IC to use with 4N35 Optoisolator to dim DC with ARDUINO ?
I would use a 555 timer for the PWM signal to drive a MOSFET. Be careful not to apply 28V to the 555 since it can only handle a maximum of 15 volts. Do not control the MOSFET with a DC signal like I did on the video since the MOSFET will be hot. The video was information purposes only and not for real designs. www.electroschematics.com/8759/dim-light-bulb-555/ Good luck.
Thank you very much for producing this video. I have recently started working with small Chinese ZVS induction heating circuits that use Mosfets and your video has made them very understandable. I am also a member of a small Arduino group and, for a recent meeting, I duplicated your test setup. the demonstration was enlightening to all. Pete Stanaitis ---------------------
Glad to hear you found the video useful. I'm currently working on an Arduino series of videos so please stay tuned in. Thanks for watching and commenting.
Great video! My first ever project since starting hobby electronics,and it worked! All be it in reverse but that's something else I will "fix" later!:) Next stop designing iPhone 8! :)Thanks!
Excellent job on the video and explanation. For the longest time my vehicle's lights (headlights and dome lights) were turned on using mosfets. But I was young and not well educated at the time. I forgot to consider the constant drain on the battery due to the high, but existent resistance between the drain and source. Believe it or not, it would drain a car battery beyond it's ability to turn over the starter motor with only 2 days of not driving the vehicle at most. I viewed adding a physical switch on the source would defeat the entire purpose of using mosfets in the first place. lol As I said, young and dumb. Anyway, I will be recommending your channel to everyone I know. I am a horrible teacher, but you are able to explain things very well. Thank you for sharing!
Hi, I am trying to power an rs775 DC Motor(12 volts, stall current 60 amps) with a 195 amp MOSFET and 7.4 liPo. The MOSFET got hot and shorted itself. Do you think it is possible for a rs775 to even work with any MOSFET, or is it just to Much? and if it should will I need a transistor to amplify the gate?
There are several factors to consider. What is the threshold voltage of the MOSFET? Are you driving the MOSFET in the active region or saturated? If you drive the MOSFET in the active region you must have a large heat sink connected to the transistor since much power will be dissipated by the transistor.
MOSFET "saturation" does NOT generally mean fully on. It refers to the region of operation where a changing voltage does not result in a changing current.
I'm well aware of the concept of saturation. "Fully On" means the same thing as Delta ID/Delta Vg = 0. The MOSFET cannot become more "on" than "fully on" - so no more change in Drain current will occur with increasing Gate voltage - and this imparts the same meaning for saturation. I try not to confuse beginners too much by getting too rigorous with definitions when I'm attempting to convey a concept for the first time.
Please forgive me if I am misunderstanding the information or am missing something. Most of the tutorials I see for using mosfets are for low power situations where they just suggest a general mosfet that is easy to use and easy to obtain for basic hobby purposes. How do I use the data sheets to select what kind of mosfet I need that doesn't fit in those examples so I'm able to use something of the proper specs? For example: I'm wanting to drive a 48V 1000 watt motor rated for 26.7A
Most MOSFET manufacturers provide the ability to specify the voltage and current rating and will suggest MOSFET that will work. In your case you use the following MOSFET: www.jameco.com/z/RFP50N06-Fairchild-Semiconductor-Transistor-MOSFET-N-Channel-60-Volt-50-Amp-3-Pin-3-Tab-TO-220-AmpB-Rail_875051.html Make sure the Threshold voltage of the MOSFET is also adequate. If you are driving a MOSFET with an Arduino you would need a threshold voltage of less than 5 volts for the MOSFET. Google the term MOSFET Ratings for more info.
Super informative and interesting! More so than most any other videos I've seen while trying to learn about mosfets and/or IGBT'S, etc... with the exception of @subcooledheatpump ... if you haven't seen his channel yet and you enjoy this video's content, I can guarantee you that you'll like watching his content as well... super young guy who seems to be nearly entirely self-taught as I don't think he is old enough to even have a formal education just yet. Well, maybe now but not when he first started making vids... who knows, all I know for sure is that both of you guys are awesome and you have a new Sub. Cheers!
Excellent tutorial Dorian, but I have a question for you about a commentary in your video regarding to avoid operate the device in the active region. I am trying an application where it is necessary not to turn totally on the transistor and obviously the device get hot, around 45°C. Does it this condition eventually destroy the device? or there is a high temp margin to operate the device?
+juarezvivo Operating A MOSFET in the active region will not harm the device. The danger only exists if the device is not sufficiently cooled with a heatsink while doing this. Many great-sounding Class-A audio amplifiers use MOSFETs in the active region but these use heatsinks to keep the device cool. The video was mainly aimed at those who needed the MOSFET to act as a switch. When using the MOSFET as a switch you want to avoid the active region since energy is wasted in the device and overheating of the device can occur.
I think this is one of the best MOSFET related video on youtube. I was wondering if you could make another one that touches MOSFET amplification? Have a good one!
Thank you for producing these videos, very educational for a new guy (Subscribed). As a side note, I find your videos to be soothing, as they remind me of watching my Dad at his workbench when I was young. Wish I could've picked these skills up back then, but who knows what runs through the minds of children?
tahsyr No. I really wanted to get across the concept of driving a motor with PWM without overcomplicating things. The motor was not under load so the current was very low. Also the PWM switching frequency for the Arduino is pretty low and because the MOSFET gate charge current is low the motor current is actually dissipated in the MOSFET before the device can completely shut off through the supply rails.. If I was putting large current demands on the motor I would have added a flyback, or snubber diode (there are other possibilities also). In future videos I will show why this is important, what can go wrong and why. There is actually much more to know about PWM motor driving, back EMF and motor freewheeling than people learn from the typical RU-vid video.
can a potentiomter be used across the gate and source too control the voltage and speed of the motor? im building an electric scooter from scrap parts. need a way too adjust motor speed.
+dan childers It can be done but is a very inefficient way to control the speed of a motor. At half speed half the power will be used to heat the MOSFET instead of driving the motor.
when you use mosfet with microcontroleur does a signal is long enough to make fully saturated ? do you need to use 2 resistor ?(one between gate and masse ) and another one between microcontroller output and the gate (or just this one ? ) ? (are they both 10 k ? ) thanks for the video
bac302 No resistor is necessary between controller output and gate. No other resistor should be necessary between mosfet and load unless load is an LED. The output voltage from the controller must be higher than the threshold voltage to turn the mosfet on. Hope this helps.
i want to use a mosfet as cutoff for a 200 watt audio amplifier, by placing mosfet between power supply and amplifier. Does the mosfet need to be rated for 200 watts dissipation, even tho i'm never using it in the linear region? If not, how to select correct mosfet? Current-handling rating?
Be careful using a MOSFET to accomplish your task since a single MOSFET can only switch DC voltages. If you are switching a DC voltage, the power rating of the MOSFET does not need to be 200 watts since you are either opening it or closing it. If you want to switch the amps AC voltage I would use an AC Solid-State relay.
@@DorianMcIntire DC only. I think I have to look at RDSon, Id, and maybe Tj or Tja. I can ignore all switching losses, since I'm not continually "switching" at high frequency.
Hey cool video , very good and informative , is it safe to touch the battery terminals ? I thought you might get a shock ? Will the current not be passing through your body ?
+miller88ize You will not receive a shock from a 12 volt battery. The threshold for feeling a shock is about 1 milliamp but condition have to be just right for this amount of current to flow through your hands with a 12 volt battery. You could probably feel a small shock from a 30 volt battery if you made good contact. A tiny amount of current will always flow, if you complete the circuit, but this current is harmless and usually cannot be felt. Thanks for watching.
paack3 Yes, many DIY inverters are done this way but it's far more efficient to create an inverter using PWM. Running a MOSFET in the active region causes the device to dissipate energy in the form of heat. New inverters convert 12 VDC into 120 VDC and then chop up this 120 VDC using a PWM bridge into 120 VAC.
You can use any logic level (Threshold Voltage less than 5 volts), power MOSFET. Just Google the specification sheet for any power MOSFET to make sure it meets the Gate voltage threshold requirement.
Applying sine wave single between gate and source what will be the wave across the load?how the mosfet work during the positive and negative part of the sine wave?
ayman zayed A single, N-Channel MOSFET will only amplify the positive portion of the sine wave with quite a bit of distortion. There is more to amplifying a sine wave than just using a single MOSFET. To do it properly you must build at least a Class A amplifier. Class A amplifiers are very inefficient so for best results you may want to build a Class B or Class AB amplifier. This is especially true for amplifiers with both positive and negative inputs. In Class A mode the MOSFET will get hot if you try to drive a large load so you must connect the MOSFET to a large heat sink. If you drive a speaker you must use a transformer or large capacitor to couple the amplifier output to the speaker. Below are a few links about Class A amplifiers: diyaudioprojects.com/Solid/ZCA/ZCA.htm ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-t6NNLzgIwV4.html Amplifier design is fairly complex so I recommend Googling the following terms: Class A MOSFET amplifier Class B MOSFET amplifier Class AB MOSFET amplifier Class D MOSFET amplifier Hope this helps
For an enhanced MOSFET (the most common ones), if Vg = Vs, there is no current through the canal ( between pins D and S, any direction). So, if both waves are synchronized at the same phase AND to be at the same voltage, Id, the current through the canal, will always be almost zero. For a NMOS (N Channel MOSFET), Vg has to be greater than Vs by at least Vgs(th) ( a value taken from the datasheet of the particular NMOS), and preferably two or more times that value, to have possibly a significative Id (the curent through the canal of the MOSFET). So you will have to add a DC offset to your original pure wave signal, applied to the gate (or to use a negative rail, lower than the lower voltage of your signal, applied to the Source pin of the NMOS). It is then possible to amplify your signal at the gate of the NMOS, but there are some other limitations, such as avoiding clipping. Note also that MOSFET are not as linear as BJT.
Hello, I want to use a micro controller to control the timing of a high powered electromagnet. Probably a few hundred volts and a few hundred amps. Is something like this what I would use?
There are very high powered versions of MOSFETs and IGBTs that can do such things. The IGBT is probably the most useful device for controlling high voltage and current.
Dorian McIntire thanks for the quick reply. A little background of me, I'm 2 classes away from a B.S. in Physics and have taken a few Electrical engineering classes but we haven't gotten into MOSFET's and transistors much, we only touched on it in physics so I know a bit, and I have a few books, the big one which we only covered a chapter or so of is Microelectronic circuits by Sedra/Smith...if you know that book. So I know a little but not a lot. When I look at spec sheets of power MOSFET's and IJBT's, it seems like IJBT's have a larger power loss. Also, I can't quite tell because there are so many terms I haven't seen, but I can't find a clear base voltage to turn it on or off, however it seems higher (around 10-20V) for IJBT's but only 2-4 Volts threshold for the base voltage of power MOSFETS. On top of that IJBT's seem to cost 4-5x more than Power Transistors. Am I correct in these assumptions?
There are many factors that determine losses in these devices. IGBTs typically exhibit a low Collector-Emitter saturation voltage of 0.2 volts - regardless of current magnitude. MOSFETs - on the other hand - exhibit a Source-Gate resistance that decreases with higher gate voltage. IGBTs are currently used extensively in Variable Frequency Drives due to their ruggedness and relatively low losses at low frequencies. Remember that the Gate threshold voltage for MOSFETs is the voltage required to just begin turning on the device but a much higher gate voltage is typically required to control large currents efficiently. As you mentioned, the cost of IGBTs is greater than MOSFETs since they fill a special niche in electronics. Your project can be controlled with MOSFETs with no problem if you select a device with the voltage and current ratings required. I typically select devices with voltage ratings twice as high as the supply voltage to guard against voltage spikes damaging the device.
It's a good point. I didn't think about the fact that viewers might think you could use a MOSFET that way. It does make for a great demonstration of how sensitive MOSFETS can be. Thanks.
Fantastic job explaining it. I didn't get it all, but I can tell it's all there and I just need time to process it. As a practical question, I've heard that as you reach its upper rated voltage, the MOSFET can become quite hot. I believe you were saying that the gate being in active state (i.e., not fully "open" or "closed") causes heat as well. Is there a relationship between these two causes for heat accumulation?
If the MOSFET is off there is no current flow through the device so no power is dissipated by the device (P = V x I). If the device is fully on there is very little voltage dropped across it so again very little power is dissipated in the device. In the active region the device is acting like a resistor so there is current flow and voltage which means the device must dissipate power. MOSFET can break down and start conducting if the maximum voltage is exceeded and get hot as a consequence of an overvoltage. Hope this helps.
So in both cases, for different reasons, energy is pooling and turning into heat? In the active state it's because is acting as a resistor (creating voltage drop between the terminals) and thus the restricted current has to go somewhere, right? Where as in overvolting, the materials cannot "fit" that much current and it's spilling into other forms of energy (namely, heat)? I'm not an engineer, I just like to learn things. Hence why I am using kinda hokey language to cross this barrier, haha.
Yes, in the active region the MOSFET is acting like a variable resistor. Resistors turn electron flow into heat because they provide obstacles for electron flow. When electrons collide with these obstacles they lose energy and pass the energy into the material in the form of heat. The loss of electron energy creates a voltage drop (energy drop). It's great that you enjoy learning. Those who enjoy learning will always have a great advantage in life. I enjoy learning and sharing what I learn even more.
Gordon Freeman Thanks. We live in amazing times. When I first show this demonstration to my students it boggles their minds but it does help explain how electricity works.
Can u explain how to test the mosfet by ohmmeter, some time the reading between drain and source is on, but sometime the reading is off , whats readon for that?
ayman zayed It's generally not a good idea to test a MOSFET with an ohmmeter because the meter may not be able to turn the MOSFET on and you will get unpredictable results. Results will depend on multi-meter test voltages and MOSFET threshold voltage. Use the method I show in the video but use a 9 volt battery for the power source and and LED (in series with a 300 ohm resistor) for the load. If you touch the positive terminal and the Gate the MOSFET and LED will turn on, if you touch the gate and the negative terminal the MOSFET and LED will turn off. If you still want to test the MOSFET with a meter see the following video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-gloikp9t2dA.html
If you just test by touching the D and S pin, the result depends on the charge in the capacitor at the gate. That capacitor can hold its charge for a more or less long time.
