Animated BJT - How a Bipolar Junction Transistor works | Intermediate Electronics
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- เผยแพร่เมื่อ 6 มิ.ย. 2024
- Bipolar Junction Transistors, or BJT's, have been around for decades and are a fundamental portion of modern electronics and computing. For something as simple as two back-to-back PN junctions, these can be difficult to understand how they actually work at the semiconductor level. After laying the foundation for how they're built, we use some basic animations to demo how the electrons and holes move within the BJT to hopefully give you a more intuitive feel for what's going on when you apply a voltage at the different nodes. If this doesn't make sense - go check out our other intermediate electronics tutorials about semiconductors and PN junctions. I also highly recommend reading JB's written tutorial here for more in-depth information: www.circuitbread.com/tutorial...
Table of Contents:
0:00 Introduction
0:23 Introduction to the bipolar junction transistor
0:41 The different physical regions of a bipolar junction transistor
0:54 The two junctions that are created in NPN and PNP interfaces
1:29 How a BJT is configured to be an amplifier
1:57 Simplified animated demonstration of how the electrons flow through the different portions of an NPN BJT
3:13 Verbal overview of how a PNP compares to the animated example of the NPN version
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Why did I have to scroll so much to find such a good video. Curse the algorithm
I just love the sound clarity, your accent is just so comfortable to follow. Animations make things so much easier to comprehend. Excellent work. Thanks.
I was very much stuck on this concept, especially why only a small amount of the electrons actually make it through the base. I now get it! Thanks for the high quality explanation and visuals.
It's really helpful ... Within 4 minutes , you covered almost all the things.. Thank you brother
An underrated channel 👍
Thank you for these lectures! Really helpful, looking forward to seeing more content from you guys :)
How to use a Bipolar Junction Transistor (BJT) as a Switch?: www.circuitbread.com/tutorials/how-to-use-a-bipolar-junction-transistor-bjt-as-a-switch
Loved the delivery of concepts. Although, I'd love (so would other people watching these videos), if they were delivered a little slower. I felt like there was no time for me to think. Loved it. Kudos!
Thanks Subbalakshmi! We've often talked about pacing because a lot of people think Josh is actually pretty slow. This may be weird but TH-cam has the ability to change the playback speed. We usually playback the videos at 1.25x, but if he's too fast for you (instead of too slow, as he is for some of us), you can drop it down to .75x. Let us know if that's actually helpful. Thanks again!
How to use a Bipolar Junction Transistor (BJT) as a Switch?: www.circuitbread.com/tutorials/how-to-use-a-bipolar-junction-transistor-bjt-as-a-switch
Agreed, its too fast and I've had to replay & pause many times....we shouldn't have to slow down the speaker by changing the default speed in order to follow the material.
goto settings (Gear symbol) and set the speed to .75, sounds fine and its much slower.
@@aceloth Just slow down the video dude!
Absolutely wonderful explanation. Thank you.
I love your videos😄
They are always on point!
This channel has been really useful to my subject of Electronic Fundamentals, thanks a lot!!
How to use a Bipolar Junction Transistor (BJT) as a Switch?: www.circuitbread.com/tutorials/how-to-use-a-bipolar-junction-transistor-bjt-as-a-switch
Thanks man. Infinitely more helpful than a university professor!!!
Your every video is such a masterpiece .
This was incredibly helpful. Thank you so much.
You're welcome!
Great information!
Dude, you're a genius.
Hi everyone! If you want to go over this topic at your own pace, we have the written tutorial with pertinent images on our website for your review: www.circuitbread.com/tutorials/bipolar-junction-transistor-bjt-basic-structure-and-operation Also, at :43, the junction names on the PNP are swapped, sorry about that... I hope you're having a great day!
excellent!!
Nice explanation. A video on exactly how the current is amplified in bjt amplifier?
The 1940s was filled with fascinating firsts, from the invention of the Bipolar Junction Transistor to the-ZACK!!!!
This was delivered at a speed of one million light years per second lol!
We're always pushing the boundaries of science around here!
Sir can you explain about CE configuration
Josh, I would have liked to also see the PNP mode of operation discussed in detail - I felt that the 30 second blurb at the end to say that 'everything is reversed compared to the npn' did not do it justice. There's something to be said for actually seeing the electron/hole movement - any chance you could include this as an addendum or in the text ?
I'd have to check to see if we still have the assets for this, it's possible we could animate the movement for PNP and throw that animation on our website. The written tutorial actually does go a little more in depth on what happens with the PNP BJT, hopefully it's more helpful - let's me know! www.circuitbread.com/tutorials/bipolar-junction-transistor-bjt-basic-structure-and-operation
Your illustration represent conventional current as electrons movement direction
Thank you nice TH-cam man
You're welcome, nice TH-cam comment man! And thank you for all of your kind comments 😀
Thanks
We want like this types of explaination ,,with animation's very better as compare to our coaching and collage professor's ,,we want like this kind of deep knowledge.thankyou very much sir.
Thanks, we're discussing how to increase the amount of animations we have as they are incredibly time consuming but also extremely helpful. Hopefully we'll get more and more and better and better at these!
amazinggg
Thank you for that video and for the effort, but is still have a missunderstandig here:
BE junction is foward biased. Electrons move from n to p. they move in the n-current band and later in the p-valence band according to the diode theory. Now there are the other electrons which do not recombine with hole from the base. According to much detailed theory they diffuse into the BC junction and get accelerated by the depletion region and also by the +potential out of the transitor.
If you now increase the current of the holes from the base to the BE junction, why does the diffusion of electrons into the BC junction increase, so that the current can increase?
very good good sir
I heard some terms like drift current and diffusion current in relation to BJT , is the current in the collector considered diffusion or drift ?
You have both occurring in BJTs, often at the same time. Susie put together a quick overview of the difference, it should help. While the article is talking about semiconductor materials in general, it is exactly what's going on in a BJT as well: www.circuitbread.com/ee-faq/what-is-the-difference-between-drift-and-diffusion-currents-in-a-semiconductor
I was confused how collector base junction flow current in reverse bias , cleared my doubt now
This really helps, but I don't understand why if the base-collector junction is reverse-biased in the NPN, free electrons from emitter to base would cross the reverse-biased base-collector junction and return to the emitter, since reverse-bias does not allow electron flow. Does it have to do somehow with the relative doping density of base, emitter and collector? Please elaborate on that.
If you reverse bias the emitter-base junction then there would be no electron flow but if you reverse bias the base-collector junction then this actually helps speed up the electrons from the base into the collector. Just look at the direction of the electric field of the depletion region in base-collector and you'll see why.
Sorry, a little confused. at 0:45, the PNP diagram, why the junction between the base and emitter is labelled as Base-Collector junction, while the bottom is labelled as Base-Emitter junction?
Because that's a typo that I didn't notice until now! You're correct, with the pnp junction, the top one should be the Base-Emitter, and the bottom one should be the Base-Collector.
At 0:43 isn't the labels for the PnP junctions wrong? Should they be the other way around with the top right label being base-emitter and the bottom right being base-collector since that would align with their respective port names.
Correct! We added a pinned comment to this video a few years ago to address that as we didn't want to pull and repost the entire video. TH-cam does not make minor changes possible, unfortunately. Thanks for the feedback!
Great video. A question: it seems that there are two possibilities as to what can happen (in the npn case) to an electron that was injected by the emitter into the base: (1) it gets swept into the collector or (2) it recombines with a hole in the base, contributing to base current. Isn't there also the following possibility? (3) the electron, without recombining with a hole, is attracted to the base wire (after all this has positive voltage) and thus also contributes to base current without having recombined with a hole? Or is this component negligible?
Good question! I'd be open to someone disagreeing with me but I believe you are correct - both that it's possible and that it's negligible. There is physical distance to travel and for the p-doped region, which is somewhat inimical to electron movement, it is a shorter distance between the two n-doped regions and it's easier for them to flow from the emitter to the collector unless they fall into a hole and then move out the base. This is my understanding but I do want to make the caveat that the original content was created with the help of a gracious professor who has since retired and I'm not as smart as she is. So take this with a grain of salt.
@CircuitBread makes sense! Thanks for answering
Thanks for teaching me what my profs can't lol
Haha, thanks! I like to think of it as teamwork between us and your professors, though - we're just trying to help out however we can. 😄
you said that valence electron move to wire from base but as i know that the valence electrons are attached to its nucleus and didnot move ?corrent me if i am wrong ?
Hi Aina! In wire (any metal), the valence and conduction bands actually overlap. And yes, valence electrons in a semiconductor don't move unless they either jump up into the conduction band OR they are moving but we consider it as hole movement.
i have watched several of your tutorials. They are excellent. My one and only suggestion - please don't speak at the speed of the electrons or holes. Allow a short moment for comprehension of the reader. Please bring more such tutorials. Outstanding stuff.
Thanks for the feedback! I have gotten that from quite a few people and I'm trying to slow down but I'm still spotty at times. I will continue to try and do better!
@@CircuitBread thank you for the efforts. The material and message is so well prepared and delivered. The ideal pace of delivery will make it top notch
How does a free electron which has recombine with hole of base reagion causes a base current as it is in valence band and not conduction band.
valence electrons can move if there are holes in the valence band. Also, the positive voltage on the base will attract the electrons.
At 0:43, on the pnp, aren't the junction names swapped?
Yep, we missed that for the longest time until someone else pointed it out to us recently as well... 🙁 I wish we could just make that change really quick and swap out the video but TH-cam, understandably, doesn't allow that. Good catch and thanks for pointing it out!
Cách Elecron di chuyển trong Transistor: 2:00
Plz explain for pnp I know it is opposite to npn but still don't understand.
I just sent this over to JB to get his thoughts on putting together a PNP illustration and maybe some explanation - I'm not quite sure what we'll do yet but I'm hoping to put some more clarification on the written tutorial on the CircuitBread.com website. We probably won't do another video, though, as we're in the thick of creating some other series at the moment.
@@CircuitBread yeah thanks for your efforts man. The thing why I am asking for this is nobody has made a video on pnp they explain npn and tell that in pnp it is just the holes that do the work of electrons and thats it.
I want to understand how a pnp works based on the movement of electrons.
But what happens inside a BJT when we increase base current in linear region and the collector current increases ok but why the collector emitter voltage starts to be decreasing and after a time both junctions would be forward biased.what happens inside a transistor when it happens?
Hi Raza, the collector emitter voltage shouldn't start to decrease unless there's a series resistance in there that causes a larger voltage drop prior to the BJT due to the increase in current. However, when both junctions are forward biased, this is when you switch to a different region of operation (saturation region - I think you might find this video helpful: th-cam.com/video/VuxAz0fvMnA/w-d-xo.html ) and the base current is no longer the overriding factor, but the collector emitter voltage is.
@@CircuitBread thanks
But at PN junction, you taught us that when free electrons diffuse across the depletion layer, they lose their energy in overcoming the depression layer, so when they enter the P region, they become valence electrons. But here you said that free electrons pass through the depletion layer easily and they remain free electrons?
Hi Aina! It may be helpful to review the written tutorial as it gives you more time to review certain phrases that (hopefully) clarify things. I'm thinking particularly of the line, "The free electrons that entered the base region but didn’t recombine with the holes move toward the reverse-biased base-collector junction." Not all electrons that cross into the P region become valence electrons. Those that don't, are the ones that continue onward. Does that help at all?
Slowing down just a little bit would help a lot! Other than that these are great!
Thanks Brandon, I've been getting more feedback about needing to slow down, so I'll try and take it down a notch. In the meantime, I'd recommend using TH-cam's tools to slow it down if I'm going too fast. Thanks for letting me know!
@@CircuitBread thanks for the response! I love your openness!
Delivered at the speed of light 😂
Thanks but still you would have taken us through that pnp transistor😮😮😮😮
did anyone notice he resembles prince williams alot
We've noticed that Josh is not touchy about the amount of white hairs he's been getting the last few years but he is very self-conscious about his receding hairline. Let's try to avoid the Prince William comparisons 😂
@@CircuitBread 😅
Lol damn all the yrs we been taught that current flows from emitter to collector in a npn now this 🤔
Current flow versus electron flow is a serious pain when dealing with semiconductor devices. You truly have all my sympathy. Or is empathy? Whichever one it is where you feel bad because you've experienced it (or are experiencing it) yourself.
I guess so lol
I tell you this you guys dont get enough credit
FET are best
I think they're way easier to understand/work with but there are benefits of BJTs in certain applications.
@@CircuitBread They're not easier but they are more stable. Which explains why they are getting replaced. Nowadays learning about BJT is only interesting for basics about op amps design and IGBT. I would never used a BJT in a project even if, it is easier to command using current. FET are very good low power amplifiers.
esta ingles la wea
I appreciate some others of your videos but threating such interesting and complex subjects in a few seconds without showing what you say step by step with images and formulas it risks to be a useless effort both for advanced viewers who need to refresh some concepts and for intermediate ones which are invested by tons of concepts in a small amount ot time without learning anything.