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- Опубліковано 7 лют 2025
- Please note that towards the end of this video, where I am showing different bias conditions, that the resistor connected from base to ground is actually 4.7kohms, not 2.7k as shown in the video. This is corrected in the show notes available below. This video gives the basics of the bias point, also called operating or quiescent point, of a bipolar transistor (BJT). For a BJT, there are three operating regions: Cutoff, Active and Saturation (note, these names differ a little when dealing with FETs). The Q-point will influence the "class of operation" of an amplifier circuit. Class A, B, C and AB are discussed and demonstrated. A copy of the video drawings can be found here:
www.qsl.net/w/w...
you say " thanks for watching " and i always say to myself " thanks for watching ??? THANK YOU for providing this info !!!!" you help A LOT !
Well, you are more than welcome! Knowing that people find my videos useful and helpful is what motivates me to keep doing them. So, again, I thank you and all my viewers.
***** Just jumping into the comments to say I agree wholeheartedly with Tiago, your videos and those of a one or two others are incredibly informative and extremely useful from a practical point as well.
I would like to second Tiago's comment. Thanks for the effort, real-world stuff like this is much better than whiteboarding it in a lecture hall
@@nix324 The Q-point is not defined as Vce=1/2 Vcc. The Q-point, or quiescent point, is simply the voltage and current conditions at the terminals of the transistor without a signal applied. One may choose to set the Q-point at Vcc/2, as this will give close to the maximum available linear swing.
@@w2aewand still interesting 9 years later 😂
I basically knew everything in this video already but watching this made it so much more clear in my head. Much appreciated, and subscribed!
FINALLY SOMONE MADE A VIDEO FOR HUMANS TO WATCH 🥳🥳🥳🥳 thank you for not assuming we are all robot engineers from the future. You sir… have a nice day😊
I hope you find that most of my videos are human-worthy too!
Learned this from Professor Barry Blesser 47 years ago. You teach it the same way. The best demo i've ever seen was in his class. He set up a 2n2222 on a curve tracer showing its characteristic curves, next to it was a triode small signal tube set up the same way with a curve tracer. He held a match an inch away from the transistor and the curves went bananas. He then held a propane plumbers torch to the tube. Nothing. The tube envelope softened and and collapsed on the plate of the tube. Nothing changed on the curve tracer. The tube finally failed when it lost vacuum from the glass rupturing. Lesson 1 in thermal stability!
33 years ago when I was in college, I saw all this concepts on the book and didn’t understand well. And now in few minutes of your tutorial was more than enough. THANKS for sharing it.
sometimes, it's helful to understand things if a good teacher know his job. The most i know, don't know it or had forgotten how. That's a pitty....
Same. Back in college (40yrs ago) it was all digital switching and square waves and I'm now trying to go back and get into amplifiers and audio circuits and I was terminally stuck. Eureka in 10 minutes watching this.
Better than any university lecture. I'm teaching myself about electronics for free solely from UA-cam. Incredible.
Agreed absolutely! Hey, by the way, aren't you Mark Knopfler? LOL...
I would STRONGLY suggest 2 other resources besides UA-cam.
lushprojects.com/circuitjs/circuitjs.html
This here is a circuit simulator that runs in your browser. It's been instrumental in helping me to learn about circuits visually and understand them on a more intuitive level, as well as being able to experiment with them hands on.
www.allaboutcircuits.com/textbook/
And this is the single best written resource I've come across for electronics. It has damn near everything you need to know, but doesn't overdo the technical details to the point of it being dry or intimidating.
These combined with the many great videos on UA-cam, as well as wiki articles, datasheets and application notes make probably 90% of the material you'll ever need for your first couple of years or more of learning electronics. Videos like this are great resources, but I find they're most effective when used as a supplement to other education. If you try watching stuff like this without knowing some basics, a lot of it could potentially go over your head. And don't just limit yourself to one viewing. Nobody's gonna remember all of this stuff after watching it just once. Especially in the long term, like weeks or months down the road.
im nearly there, going to get my analogue logic done soon!!!! good luck to you my friend.
I listen with warmth in my heart, despite the fact that I am also a radio engineer for about 30 years or like and have known all this since childhood, I am also a HAM radio guy. However, what this person does for public through the UA-cam is priceless !
73s ! Kissees and hugs !
de UT5USA.
;-)
Excellent as always!! Your explanation together with the visual demonstration really helps build understanding - Thank you!
Thanks for this short tutorial. I did all of this more the 20 years ago when I was studying electronics at bachelor level, but never really worked with it or very little. Most of the time it was for a simple application to turn something on or off... I suppose I am a generation that already has access to a lot affordable modules, op-amps, and other IC's, starting the carrier in beginning of 2000. So I will repeat these (and more others that you did) short "lab experiments" at home just for fun. You do a really good job with teaching, and also important you know very well what are you talking about! You also put the scan of the schematics 👍 You can see a lot of people already watched it, almost 300k ! Good work, thanx
I always enjoy watching your videos Alan! Thank you for sharing your insights ! 73's , Gary Grove
There are those who can and there are those who teach and then there are the rare human line output converters and you Sir are one of the best. Taking a high esoteric complexity and turning it into a lowly lament's ability to understand.
This may be the single greatest video on transistors I've ever seen, and turned on so many lights for me all at once. I've never seen anybody used a variable power supply to demonstrate the different states of a transistor. Thank you so much! (this also tipped me over for the reason of buying a signal generator and a variable power supply, lol).
4 yrs of College and i've never been this excited. I'll relearn everything now. Thanks man, a million times over.
I'm glad to hear that this video has helped inspire you to learn more! Note that there is a link to a complete video index file in the lower right corner of the header graphic on my channel's main page.
Yess I'm currently going through your entire index. Simply awsome.
I am learn more from your channel
I'm an EE, probably of a similar vintage to you Alan, and I wish it would have been possible for you to have been my lecturer at uni. Your impressive contribution toward free electronics learning is incalculable. Thank you, from all of us.
Something about seeing it in real life, not just on paper with calculations, amazes me. All the physics and stuff we learned about transistors actually works..
I was struggling with the concept of biasing a transistor and how it related to its amplification factor. I understand now that:
(1) The bias resistors only affect the operating point of the transistor and the ratio of the two biasing resistors can be adjusted to accomodate any Collector voltage and still deliver an appropriate Q-point.
(2) The voltage amplification of the transistor is dependant on the ratio of the collector and emitter resistors along with the collector voltage applied (in this case 5V)
Wow - thank you, thank you, thank you!😊
So glad you found this helpful. The only time that the base-bias resistors can enter into the gain calculation is when collector-to-base feedback is used. It's much easier to estimate gain when feedback in the form of emitter degeneration is used. You might want to check out this video on some hints & tips about common emitter amplifier design: ua-cam.com/video/VWY2WQcKJgk/v-deo.html
I can't believe you only have 50k subs, you sir are the best teacher on the tube.
Ian Darley Also check out Mr Carlson's lab, he's also great
Fermilab also didn't have much subscribe back then, hopefully this channels sub count also blows up.
There is not necessary beeing "The teacher" , but prominent is to spell things to understand. Well, I am not a professor legally, but students in my class where all !
nobody them forced to go, but anyway.
You have the best electronics tutorials. Great work!
The best teachers are not always those we have in schools... my case at least
Wow. I've been trying to re-teach myself BJT theory after being away from it for /gasp/ 40yrs, watching countless demos/tutorials and it just was not clicking. In 10 minutes watching this it's all coming back again. Thank you!
I just want to be another person to say thank you. simple concept yet so many people find it so hard to teach
The best practical explanations i ever watched on classes of amplification
Amazing explanation, you don't know how much oh help are your videos.
At 10:55 you said "Remove that transistor from the circuit" but you actually meant to say remove the "*" resistor (Voltage divider upper resistor) from the circuit.
Thanks a million my friend
Alan your way to teach is absolute impressive. You're not such a Master you're a kind of God on this.
Incredibly helpful, thank you. Seeing it on the scope is slowly starting to make this click.
You shpuld be an instructor, best explanation I"ve ever seen on
saturation. Now I finally understand, when you said two things are happening
when Vc crrashes into Ve. Both junctions become forward biased. That's why Vce approaches 0v when transistor is saturated.
GOOD JOB!!!!!!
ChueyMr11 your comment opened another perspective for me. I was thinking of the base as a valve between two potential barrier and the collector and emitter short as a short ckt. Thanks..
I'm usually a bit confused when it comes to biasing transistors, but this video was informative enough, and had the extra visual that I have been needing. Thank you for providing this great content!
This is how electronics need to be taught. That's equal to a ton of reading. Thank you sir.
The best video blog in whole internet
29DR194 Thank you!!
Agree! I watching this tutorial a third time and still getting some knowhow. Thanks.
Same here!!
Agreed.
When I saw the first video I thought this must be Forrest Mims
Incredible. Thanks, Mr Wolke.
This has to be the best demonstration of how a transistor works. Transistor operation is something that is nearly impossible to understand without a dynamic visual demonstration. Thanks!
Been binge wathcing your videos to learn as much as possible in as short a time as I can.
Thank you so much for sharing your knwoledge with the world!
This helps me to understand Biasing an amp more than anything I've seen yet. Seeing it on the scope was worth a thousand words.😃
Very clear and to the point. I think this is the best introduction to transisters I've ever seen. I agree with others here when they say you are a great teacher. I do so wish you had been around 30 years ago when I was learning electroinics. You would have been very tired of me!! Again, Great Job and lI ook forward to your future vids! You have never let me down.....vids are always informative!!!!! Thank You!!
Wow, very cool description of bias point and operation. The visuals are especially helpful. Thank you for this!
You methods are awesome. Every student basically needs a teacher like you. Desiring to learn much from your videos. Highly appreciate your work and efforts.
Thank you for the nice comments - please be sure to let me know if there is a topic you'd like to see in the future.
I've watched a lot of videos trying to explain this but none have come close formulating things so clearly. Well done, great tutorial!
Transistor BIAS is always a very hard subject to visualise. You just made that so clear, so simle and easy to understand.
It doesn't matter what you have posted or what you will be posting Alan, I'm gonna watch every single one of them. my Stay at Home goal. Back to basics and RF section are my favorites.
Thank you so much for showing the difference in amplifier classes, it is one thing to read about the classes, another to see that its just a shift in bias point.
Great description of a transistor amplification demonstration. I taught this same thing to my collage electronics class in 1980 to 2004 at Harper College in Illinois. My students love it. Thanks for caring on the great work.
Mind blown.....visualization makes the difference between a shaky grasp and solid understanding. Thanks!
Very interesting approach, quite different than the usual classical way, but, could I say, more practical, mainly for a first contact, ... or just for personal curiosity about the various points of view that we can have for this technic. It is simple, enough to position the subject, then to the point toward a result, finally, some details are added to enforce the main possible variations. And the "transition" between the various "scenes" is smooth and relevant. Really good composition, not just mastering the subject, but how to explain it too! And given that this kind of presentation is hardly doable "in a book", that is also a perfect use of the medium (youtube). A brillant technician AND a talented artist !
I had my avionics license quite a few years ago. Today I am a 2 way radio repair shop. Your tutorials are so awesome! A lot of the little things one gets away from over time. It is nice to watch and say... That works!
wow you are a great teacher. i am doing this for a hobby and you explain how components work and it is making me want to break out the bread board. It is fascinating how much precision there is to make things work. I have spent so many hours getting ready to start playing with this stuff. you really explain this stuff so well and all the applications. thanks again.
There are a ton of nuances in doing effective analog circuit design. It is amazing how many "bad" designs you find out on the web...
Very interesting and I have been in electronics for many years but am not 75 years old and just playing around with solid state circuits. This video brings a lot of theory and practice back to mind. Thank you so much for a job well done and well explained, 73 W2AEW from Ka3lTN! I do still hold an extra class ticket!
Exceptionally well explained! Thank you!
very good explnation, the uses of visual and experimental tools are too too helpful.
Unbelievable tutorial. Principles of Operation taught as well as video display of voltages & signals that demonstrate those principles. Congrats.
certainly one of the best tutorials on transistor biasing on youtube....very clearly explained...thankyou
Thanks a lot Mister, I believe you are very talented as a electronics teacher. Clear, simple, easy and, above all, pleaseful to follow. Fogs about transistors are now dissipating! Waiting for more, riccardo -Italy
I have watched many videos on transistor biasing, but this one has finally made the concept completely clear. Thanks for presenting this tutorial!
A very good explain and demonstraition how a transistor works.
RF-Amplifiers are not use class C mode in regular case - that's depend on the used channel coding or modulation mode. Every modulation mode who detects the frequency instead the amplitude of the carrier, can be use a class C mode amp - all other don't.
Very clear and much easier to understand the way explain it than what I have read in books. Great video!
I'm a huge fan of the demos that you do with the lab equipment! It really helps to bring your point home and allows me to conceptualize the lesson.
Thanks. That's exactly why I try to mix theory and practice into each of my tutorial videos.
Amazing stuff Alan, THANK YOU !
I know I'm late to this party but this was very helpful indeed for a hobbyist like myself! Your examples w2asw are much easier to understand than others here on YT. Thanks very much for sharing your knowledge!
You have a gift for explaining a very complicated subject. The way you use the oscilloscope to illustrate electronic theory is amazing. Thanks.
This is so much clearer than any other explanation I've seen yet. A testament to how well you understand the material.
Thank so much this really helped me understand amplifiers!
Jesus, now I finally understand. Thank you, thank you a million times, easy to watch and understand
I'm happy to hear that this video helped you.
This is a great explanation of operation of amplifiers. Not used to hearing voltages to describe transistors because they are current amplifiers but if you just remember the resistor values it makes more sense... The saturation comment about the base to collector voltage is something that i think isn't well known.
LOVED THIS PRATICAL DEMONSTRATION
So adorable teaching ..... seriously ......The Best teaching I ve seen .....Thank you so much !!!
Yes I have re-watched this video, You are explaining the classes while operating you camera. My mind was amazed at your multitasking and thus did not take much in this time. I'll re watch later.
Again very interesting.
how I wish I watched this when I was still a student..Great video,,very clear and very understandable..,good combination of lecture and actual implementation
+marhsall 27777 Yes, opamps and general amplifier circuits were explained very poorly at my uni, this video covers more than I learnt from the course :p
I absolutely agree; this is better than any lecture I received on DC transistor biasing from my University education.!
Thanks for teaching us so practically by demonstrating what's really happening in there , u r the best of all you tubers on making us understand this topic
You produced a wonderful video and made technical stuff very understandable! Very impressed and I am going to use this demo with my students. Keep up the excellent work.
Thank you! I hope your student benefit from some of my videos!
Man... I just discovered your channel today and I learned more in 4hours than in 4 weeks searching on UA-cam and Google... wow keep going!!
Excellent Video - you are truly one of the best instructors, ever ( of course you have more great test gear in order to demonstrate these circuits than any instructor I've had- even in my electrical engineering classes at a major state university, which is a shame, but true).
Just stopped by your fantastic channel. I must admit that I relearn a lot of stuff that should recall from my engineering studies but back in the days (late 80ies) it wasn‘t presented that good. Keep up the good work.
Great video. I've taken electronics classes in my EE program that break down all the math and believe me I've worked all the theory and math. This simple vid really helps clear up the physical design understandings and to see how the changes work.
5 years before i attended my engineering classes had a week of class for this subject, but today i understand what and How this things working... thanks alot.
A very succinct explanation of amplifier classes . Always appreciate these tutorials, many thanks for your time.
Very well explained. Wish I had seen that when I was doing HNC electronics many years ago as that was the best transistor circuit operation explanation I've seen. Thanks for posting it
I like your explanation.
You are always describing the bias point in terms of Vbe and this results in a very clear differentiation between the different classes of amplifiers.
The general definition of bias point as the DC collector-emitter voltage (Vce) and the collector current (Ic) when no input signal is applied is more difficult to understand.
The bias point is simply the static DC voltages and currents that exist in the circuit, not including any small-signal application. I'm glad you found my explanation helpful.
The Vb you set is a valid bias point as long as the transistor still follows the linear relationship: Ic=Beta*Ib.
You explained everything in terms of static Vb and Vc voltages without looking at the static Ib and Ic currents and this makes it unconventional in my opinion, but useful and very practical.
At 10:58 he says "remove the transistor from the circuit" but he meant the resistor
Excellent tutorial !
The best way to watch these if you're learning like I am is to follow along with your own breadboard. Except I've watched this a couple of times already to make sure I didn't miss anything.
Wow. It just doesn't get any better than this! Thank you Alan.
I've finally found someone who makes sense and is easy to listen to. Thanks for your videos,i'm a subsciber now.
+Brett Reed Thank you! Tell your friends!
I've been looking at some other videos on BJT behaviour. This is a fabulous step-by-step tutorial. The scope shots at the end brought it home for me. I'm looking forward to wiring this up and playing with it.
73 AI7GU
Seriously one of the best explanations I have heard so far.
I wanted say this dude is the best. easily understood down to business thank you.
Learned alot from this video. Great to have that visualized on the scope. Thanks for posting this sir
Outstanding tutorial. It would be interesting to see a demonstration of the band-pass filter setup that you described being used with the class C amp to restore the full sine wave. Thanks for posting this!
I got my bachelors in EE but I never had a better teacher than you. You are very clear and to the point. I'm an RF antenna engineer looking to develop my amplifier skills. If you see this, do you have a masters? How much experience do you have? It sounds like you've been in industry for a long time and are very knowledgable about many different aspects of EE.
excellent tutorial, I really learned alot from this tutorial, especially with the DC waveforms watching the base voltage versus the collector voltage, going from cutoff through the active region and into saturation, that visual demonstration clarifies what is written about this subject in the textbooks.
Thanks for your tutorials.
Thank you very much for taking the time to make this tutorial, now I really understand how the transistor works as an amplifier.
After watching your videos I find myself wanting to buy things like waveform generators and scopes and building some simple circuits. Your explanations are very clear, Thank you.
+Gua Var asked why the emitter resistor. That resistor, along with the bias voltage at the base (set by the two base resistors) sets the emitter and thus collector current. The emitter current will be (Vb-0.6)/Re - that is, the emitter voltage is 0.6V (approx) below the base voltage, and the emitter current just follows Ohm's law. The collector current will be at most a few percent less than the emitter current (see alpha). Knowing the collector current you can choose an appropriate collector resistance - too low and you have low output voltage, too high and you go out of the active region, starting on positive signal peaks.
Thx Alan, now every thing is clear. By the way, you channel is my best in electronics engineering on youtube.
Thanks for the fine tutorial. It's just what I needed to be able to bias a replacement
driver transistor on my Atlas 210X. I will have to experiment a bit to determine what
class of amplifier is needed.
Thanks a lot Alan for yet another crystal clear tutorial, you are a gifted teacher.
Hard to believe I passed my associates degree in Electronics engineering twenty years ago. Come here for refreshing my memory. What is troubling me now is, if CB is amplitude modulated how are there side bands? Frequency modulation produces side bands as a function of it's design but AM modulation should be on top of the carrier. These wonderful inconsistencies of my knowledge base come out when Young people ask me questions
Any type of modulation of a carrier increases the BW of the signal. The BW increase beyond the carrier are the presence of the modulation sidebands. AM is no different. AM if formed by multiplying a sinusoid (carrier) by the baseband signals (one or more sinusoids). In the simplest form (single tone baseband), this is essentially multiplying sin(w1*t) by sin(w2*t). The trigonometry tells us that when you multiple two sinusoids together, you get energy at w1+w2 and w1-w2 - the upper and lower sidebands. By adding a DC offset to the baseband signal, you also preserve energy at the carrier (w1).
Than Youu! Great way of explaining things! Back when I was a student, I was strugling on how we decide on resistors values....
Oh dear! You saved my life with this wonderful video
Damn, dude, you give GOOD mentoring!
You truly make it easy to see the relationships between the various transistor terminal volts, amps, and resistances.
Good on you!
I will keep following your vids!
Cheers,
Dave
All of your videos, including this one, are fantastic! I hope to find (if you already did one) a MOSFET "back to the basic" video! Thanks for all of your work
+theawt I do have one on the basics of JFETS and MOSFETS:
ua-cam.com/video/oambDFa0Pr8/v-deo.html
Thanks man!
Priceless!!
WOW just looking for some RF biasing info and found this guy, i will be watching more im sure, still finding new ways to use my old Tektronix 7923A Oscope, Thanks for these videos and 73s
I hope you enjoy more of my videos.
Well done!
Many beginers have trouble understanding the way resistors value are chosen. Even for a simple C-E amplifier.
I you have the time you could make a video. Set the requirements and design a simple ac CE amp. Crunching numbers for the resistors and everything.