What are the Different Regions of Operation for a FET? | Intermediate Electronics
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- Опубликовано: 22 май 2024
- One of the challenges when learning about MOSFETs are... what are the different regions of operation for a FET? Why can't they give each region a single name and stick with it? Why does the progression from one region of operation to another seem to change depending on how I'm looking at it? We answer these question and more as we discuss the different regions of operation, including the active region (also known as the linear region or triode region), the saturation region, and the cut-off region. While we use an NMOS in enhancement mode as an example, these regions apply to NMOS or PMOS in enhancement or depletion mode. Check out the written version of this tutorial on the CircuitBread website.
www.circuitbread.com/tutorial...
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Table of Contents:
0:00 Introduction
0:20 Review of the MOSFET structure and cut-off region
0:46 MOSFET in the saturation region
1:26 Linear, ohmic, or triode regions of operation
2:13 Reading the drain current (Id) versus drain source voltage (Vds) graph.
3:42 Comparing a MOSFET to a water spigot.
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Thank you for these easy to understand and intuitive explanations. Throughout my education, these concepts have always been presented to me directly via equations and although I was able to use the equations as tools and get good grades in exams, I never felt that I got a solid and intuitive understanding of the phenomena.
I wish that my teachers would have first introduced the phenomena in such an intuitive way like you are doing, before diving into the mathematics and the nitty-gritty equations. It would have helped me understand much better much earlier.
Couldn't agree more.
Sir you just saved my life for applied electronics course at McGill
Thanks for including the tap analogy, to allow everyone to confirm the understanding of the ID/VDS diagram.
These explanations are GOLD!! Thank you so much for creating them and making them available for anyone to watch!
Thanks for the feedback, Levente!
Absolutely Gold 🥇 :)
Extremely simple, straightforward, and clear explanation. I went through a lot of resources and problems trying to understand this in vain, but here it finally "clicked." Thanks!
Thank you so much! This was an incredible, quick refresher. Appreciate explaining it in multiple ways too. Cheers.
Oh my God thank you! I spent over an hour trying to understand this from an awful textbook and you explained it so clearly, the analogy also helped.
That tap analogy is incredible.
Simple and straight to the point. Amazing explanation sir!
This is a FANTASTIC explanation. Better than any other one out there. It really helped my intuition figure out what is going on. Thank you so much!!!!!!!!!!!! I liked how you told us how it didn't make sense to you at first, then you showed us how you made sense of it. Profs rarely step down to the students' level.
Who knew three 5 min videos is all I needed, thanks!
Saturation finally makes sense! Thank you!!!
That tap made it click. Thanks a lot!
Thanks for explaining. This really helped me understand MOSFET operating regions.
The water spigot example at the end was a huge light-bulb moment for me. I sat through a whole devs and circs course this past year and never understood this concept until now. Thanks much
I normally don't leave any comment, but this one is BRILLIANT! The best explanation and video explanation so far!
your way of explanation is sublime .Great job sir .Love You.
Have my exam in a couple of days and I just couldn't grasp MOSFET
After seeing your videos however, I have understood it very well.
You are a life saver. Thank you soooo much!!!!
This is a genius explanation!
really liked the analogy at the end of the video. Thanks!
Superb video, a true gem!
Excellent video!
Wow. After three courses that included MOSFETs to various degrees, I finally get the differences between the regions. Why is it so hard for teachers to be clear?
Thank you!
This is the BEST explanation I ever heard! Thank you! Your lessons are invaluable! 👍
Awesome, thank you for the feedback, Andrey!
Thanks man, Your water tap idea made me finally understand how the things work! And the animations, are just amazing!!
Fantastic - glad we were able to help with your understanding!
OMG!!!! Thnak you sooo muccch cleared all my doubts!!
That tap analogy is amazing. Thanks a lot.
I'm glad that was useful, have a great one!
Thank you! your videos have helped me so much :)
Fantastic. Thank you!
Somehow I have never seen that water tap analogy. That helped a LOT.
Awesome! Glad it helped!
Hours in university and y'all explain this a million times better in 5 minutes. Thank you!
Thanks!
Thanks, this really helped.
This helped me to understand it so much better! Thank you for making this video!
You're welcome, Jenae! I'm glad it helped!
thank you. well delivered
Great Channel! The best!
Fantastic channel.
I was able to not only pass but gain much needed insight into transistors because of this video. Thank you very much!
Awesome, glad to hear it helped!
Thank you good sir!
Thank you so much sir. I was struggling on this topic for days.
Awesome, I'm glad we were able to help!
Wow that was my question exactly! I was so confused by there still being current after the conduction channel is pinched off
this wass perfect thankss!!
The water-Tap analogy best fit it.
This is perfect
Thank you sir
good job ! thx for the good work
Our pleasure, thanks!
Thank you
These explanations are very nice. How can we understand that MOSFET takes saturation region to function as an amplifier?
great content!!
Thanks!
awesome, thank you
You're welcome!
thanks dude
Thanks for these great videos! Question though: Will you do explanations of certain circuits (i.e. static circuits as source followers, current mirrors etc.) in future, too?
Hey Dex, yeah, we're planning on it but right now, we're seeing there are more topics to do than time to do them. We haven't decided if we're going to do these as part of our Circuits 1 series or if they'll be a separate series after we finish our Circuits 2 series. But yes, we'd like to get to them eventually!
@@CircuitBread Ah great, no worries, I am already happy to know that they will arrive one day! :D
Thanks for this! It is very helpful!
I was kind of lost until the water tap analogy at the end. It would help if it was somewhere near the beginning to follow along the video as the terms like drain source voltage don't make sense when the video is going by.
Thanks for the feedback! Maybe we should've done it at the beginning and at the end, to reemphasize the comparison. I appreciate your thoughts!
Damn it you're a geniuss!!
Thank you for a clear and concise explanation. I still have questions though. I have a p36nf06 mosfet controlling a 12v led flood light. I'm using PWM from Microcontroller (max 3.3v amplitude) for controlling gate voltage to get a dimming effect. Varying duty cycle of the PWM gives me the desired effect, I'm trying to understand the power dissipation of the mosfet. I assume RdsON only applies to saturation? I assume this gives the load the most of the power and there's very little power dissipation by the MOSFET. In linear mode it acts like a variable resistor? I'm trying to understand why at some points in linear mode the MOSFET seems to get hot while at other points is not hot. I guess as it approaches saturation? That part is a big confusing to me. I can measure the voltage across the lights at various duty cycles but I'd really like to understand what's going on with the MOSFET.
Thanks for the questions, it is easy to get much deeper into these topics, hopefully I can clarify. RdsON actually applies to the linear or ohmic region - in general you want your FET to be in this region when using it as a switch, you want it in saturation region when using it as an amplifier. In the linear mode, it is kind of like a variable resistor - typically the higher the Vgs, the lower RdsON (actual) is. From the datasheet of the P36NF06, you can see that doubling Vgs from 5V to 10V (keeping the drain current constant), you drop your expected resistance from .045 to .032 ohms.
As for why it gets hot in linear mode sometimes and not other times, I'm not sure without more information. As you can see with any MOSFET VI curve, there are a lot of different points within the linear region - with lower Vgs you'll have a higher RdsON, giving you more power losses. OR, with higher Id, you'll dissipate more power in the junction just because you're increasing the current in the P = I^2*R power equation. Also, as you're flicking the MOSFET on and off, while it is actively turning on or off, the resistance change isn't instantaneous but curves. You get these "power peaks" where your current and resistance are at a point where you reach maximum power dissipation. We go over that in an older tutorial we made ( www.circuitbread.com/tutorials/power-dissipation-in-circuits )
So, I can't tell you for sure why it's acting the way it's acting, but hopefully this does help.
@@CircuitBread thank you very much for such a thorough explanation that actually explains a lot that was very fuzzy to me. By the way the link doesn't seem to work I'll try and search for it on your site thank you again.
No problem! And thanks for letting me know about the link, it was including the end parenthesis in the link - it's fixed now.
thanks a lot for this video
No problem!
Thanks alot for the incredible explanation mister ..but I have one thing that confused me.. why the direction of current flow is from source to drain though it's n-channel mosfet
That is an excellent question! The answer is quite simple - current and electron flow are opposite. So, it isn't actually current moving from source to drain, it's electron flow. Which means that current flow is from drain to source.
Am I missing something from the graph? As soon as we are above 0 Voltage for Vgs, we are no longer in the cutoff region? Don't we need a higher Vgs to escape the cutoff region? such that Vgs > Vth? Should it be Vth instead of 0?
The tap, what a life saver! who knew a tap could fix my problems lmao
Awesome! I remember when Dr. Baker was covering for my normal microelectronics teacher and he used this example. He was *so* angry with me when I didn't understand it intuitively at first. But that's one reason I loved Dr. Baker - he taught things so that they made sense intuitively before jumping into the intense math and he scared me enough that I was terrified of getting things wrong. 😂
I love the outro! Can you please edit in a couple freshly toasted PCB boards popping out of the toaster after a few seconds?
Hey Faith, we were thinking that after a year of using that outro, we'd create another outro showing either PCBs popping out or a piece of bread with a lightning bolt on it (like our logo), then after another year, we'd do another outro. That was the plan! In reality, we haven't gotten around to it 😬 Maybe we'll film the next one at the beginning of 2021 to celebrate getting out of this crazy year...
Nice. When in doubt, compare it to water.
Yeah, water isn't always the perfect metaphor but it works more often than not!
seems to be the opposite terminology in a BJT. It has similar curves, but the region names are crisscrossed
This video is helpful, but it seems like it doesn't get to the "and their applications" promised at 0:19. What I mean is, the video doesn't make the connection between these regions of operation and real uses like logic switching vs signal amplification.
What confuses me on the graph is that the omic region comes before the saturation while on the operation of the device saturation happens before omic when the inversion layer spans the channel, can you help clarifies this.
Oh, boy, do I relate, that was a huge point of confusion for me as well. This is why it's important to remember that when we're showing things physically, we're usually increasing Vgs and showing how that changes the inversion layer. With the graphs showing the different operating regions, the x-axis is Vds, with varying Vgs levels shown as well. Look at the graph again and watch the video again with that in mind and I think it'll make things a LOT clearer.
A thing about these transistor regions is that saturated and ohmic regions often confuse, most transistors operate in saturated region, which makes me wonder why is it so. Why can't it operate in ohmic region where good flow of electrons is present?
It can operate in ohmic region, that's a totally usable region! You just need to make sure that you've designed the circuit to have it operating in that region.
@@CircuitBread but why do some transistors operated in saturation region?
Great video! Would love it if you could slow it down a little.👍
Thanks! I have received this feedback a lot and am still trying to remember to actually implement it going forward.
thanks, currently doing this in school. a bit fast tho, this is complicated for someone just seeing it for the first time
after watching this a few times I think I understand more, thanks! lol
Hey Ethan - glad that it (eventually) made more sense. It's interesting, as we've gotten feedback that Josh speaks too slow and feedback that he speaks too fast. RUclips works really well at giving different speed options, so we always recommend to either bump up or drop down the speed depending on your preferences. Thanks!
I wish you had not assumed the threshold voltage was zero. It makes it a bit simpler than it really is. :-)
Hi Rob! Yeah, I always like to keep things as simple as possible, develop a foundation of understanding, and then throw in the complications. Personal teaching preference, I guess. But almost everything in electrical engineering and electronics can be made more complicated if we want it to be! 😄
TLDR: MOSFETS can be used as both transistors and current regulators
Everywhere I look says that saturation is the final region(fully open) not the middle region. Did you guys made a mistake or is it because a is a pmos??? I think he made a mistake.
Yeah, the terminology in your question actually implicitly identifies some of the challenges with this topic. The "final" region or even the idea of being "fully open" is not really clear. The video goes through explaining from the perspective of changing the gate voltage while keeping VDS the same but then moves to address the fact that the region is defined by the *interaction* between the gate voltage and VDS.
草，模电学了10年，今天终于悟了
why do these videos have so few views?
I think you have no idea how current flows during the pinch-off. During the pinch-off, current flows because there is a large electric field in the depletion region between the channel and drain terminal. You say current will hardly follow during pinch-off which is wrong. Second, linear operation mode depends on the relative values of Vds and Vgs-Vth. Your explanation says when Vgs is higher than Vth, the linear operation occurs. This is a wrong understanding. You also need to set Vds below Vgs-Vth to get the linear operation. As long as Vds is higher than Vgs-Vth, pinch-off occurs resulting in saturation mode operation.
I think we're having a terminology confusion here, which is extremely common in any conversation about these. Pinch-off != cut-off. And yes, part of the challenge of showing any of this relationship on a 2 dimensional graph is the fact that there are three dominating variables, so you are correct that the different regions do not only depend on Vgs in comparison to the threshold voltage but also needs to take into account the drain-source voltage. This is addressed towards the end of the video and in the written tutorial.
@@CircuitBread he is right though. As long as Vgs > Vth, the mode of operation is dependent on Vds.
The intuitive explanation in the first part of the video is not correct! Your explanation implies that saturation is caused by a gate-source voltage that is not sufficiently large. However, saturation depends on both the gate-source and drain-source voltages. For example, with Vgs=3 V and threshold voltage=0.7 V, the MOSFET can be either in saturation or triode region depending on Vds. For a given Vds, increasing Vgs can actually make the transistor into triode.
Yep, you're exactly right, which is why we talked about that later on in the video (2:20 to 3:35).
I like the formatting of your videos, but just speaking as a novice, I find it often difficult to grasp the concept of some of these videos when there is an assumption that I have an intrinsic understanding of the terminology.
It is a "chicken an egg" problem... Do I watch a video to learn a subject or do I have to learn the subject to watch the video 🤷♂️.
I bet if you A/B tested this same video with the bare minimum electronic terms to explain the concept the average person would find it far easier to grasp.
Essentially if I don't understand the concept the terminology is irrelevant.
Thanks for the feedback! We have created tutorials that build up to this one and create the foundation in both concepts and terminology that someone needs to understand this particular video. That being said, we've found two issues with our approach. 1) that many people who watch these don't watch them in order and 2) that is, at least in part, our fault as we aren't clear in this particular series about the order. We've been more focused on creating linearity (where applicable) with our more recent attempts. And we need to go back and make the journey more clear for those people who would like to start at the most basic and work up to this point.
@@CircuitBread Sounds like you are aware of the issue and if you're able to effectively solve it you will be quite unique in your format.
I can only say this as a novice in the subject because as I learn more it will inherently be less and less obvious what a novice would or wouldn't know.
As a general rule I have see 4 main issues with the educational material available in most channels on the subject.
1.) Assumed familiarity w/ terminology (even if it's an advanced topic it can be hard to take a math test & vocabulary test at the same time)
2.) Too much focus on the math before the concept is REALLY EXPLAINED
3.) Most single topic videos hyper focus on functionality of the component without actually giving multiple examples of its practical use. I get to the end and say "Wow, that's something... Wonder what it or its variations are ACTUALLY used for 🤔"
4. Linearity of the educational material so you can start learning somewhere and build on it in one place (as you mentioned).
Hope the feedback helps and keep up the good work.
That's great feedback, thank you! I agree with you 100% on #2 and think I need to do better about #3 as well.