#327
ฝัง
- เผยแพร่เมื่อ 27 ก.ย. 2024
- In video #324 (calibrating a Simpson 260), I used a 50uA Wilson current source/mirror. Several viewers asked for more detail. This video discusses the output impedance of BJT (bipolar junction transistor) current sources / mirrors. It presents the Early Effect and Early Voltage of BJTs, and then shows how the Wilson Current Mirror dramatically improves the output impedance of a BJT current mirror. A Curve Tracer is used to illustrate the transistor properties. Here are helpful links to the videos mentioned in this video, and a link to the notes.
#324: Calibrate the Simpson 260: • #324: How to "calibrat...
#190: Current sources and mirrors: • #190: Back to Basics: ...
Notes:
www.qsl.net/w2a... - วิทยาศาสตร์และเทคโนโลยี
This is magical! It is no wonder the bearded man of Simply Put TH-cam channel says only one person explains clearly and with components values used. And that is Alan Wolfe. I must agree. Most TH-camrs are too much on formula, very few to zero real world examples, too much talk and too less show.
Awesome video, as always. I have to say, I really appreciate the analog “slides” you prepare for all your videos. They are very well structured, clean and easy to follow.
I so love the analog slides! The presence of QR-code (and its content) makes me think how organised Alan (probably) is!
Time to watch this video a second time.. and then, maybe a third one! 😅
This is an awesome circuit. I have replaced a charging resistor in a 555 timer circuit with this current mirror to create a perfect sawtooth signal form my PWM.
Clear, concise and insightful as ever!
The Early Effect is named after James (Jim) M. Early, who did a lot of development work in transistors. Nothing to do with anything being early (or late), it just happened to be his name.
Thanks for that - always good to know.
Good point. In recognition that it's his name, we should use a capital E.
Thera are no magnets in the Hall.
The misconception is close though. Makes more sense than if his name were Late! Your comment is appreciated though, I was wondering why it was called Early.
I was amazed to find that Jim Early described this effect in BJT's in 1952!
J.M. Early, "Effects of space-charge layer widening in junction transistors", Proc. IRE, vol. 40, pp. 1401-1406 (1952).
As usual, Clear, to the point, easy to understand, explained with calm, not tiering, easy to listen up to the end, well illustrated, schematics and hand design.... just 9.9/10 for me Jack ON5OO
If all my professors were as good at explaining concepts as you, my good grades would have been great grades!
Very interesting! Makes me want to build a current source even though I don't have a need for it
Very interesting video. I didn't quite follow the explanation of how the extra transistor prevents the output from loading the matched pair in the current mirror, but the visualization of the Early effect was very clear and the demonstration of the loading really drove the point home. Thanks! I hope you make many more videos about these kinds of electronic building blocks.
The bottom line is that the transistors that determine the current source value (Q1 and Q2) do not see the voltage at the load. The "cascode" transistor Q3 isolates them from the load change, so there's no Early effect in the actual current source devices.
You get a thumbs up just for owning a Tek 576! 👍
Not so hard to own one, if like Alan you've been a TEK application engineer for MANY years!
The 576 was long discontinued by the time I started for Tektronix. I was lucky enough to get this unit from a friend a few years ago that was cleaning out a house and found it.
@@w2aew, wow that was an awesome find, and it is one of the newer ones.
Thanks for the great explanation -as always! I do not recall coming across the term "early effect" in the last 30 years of reading books about electronics! Learnt something new! Thanks!
Another great video. Thank you! I wish you had been one of my professors when I was studying for my EE degree in the early 70’s.
Fascinating, Alan! Thanks for sharing this gem of a circuit! I've never seen it before!
People using fantastic quality vintage test gear deserve a statue.
Please allow me to refine your statement. Gifted, highly trained, eloquent people like AEW using fantastic quality vintage test gear deserve statues. I have a 576 too, but I certainly do not deserve any recognition at all!
Nice video as always. You do a great job of explaining the theory and demonstrating the reality. I was a bit surprised to see Fluke DMM’s, arguably the best in world, instead of Tektronix DMM’s.
Tek no longer makes handheld DMMs, but I do have a few of the older ones. I like the Fluke handhelds better.
w2aew I know Tek also just put their name on some Asian designed test equipment vs what they designed in house. But you can’t go wrong with Fluke DMMs. EEVblog intentionally abused one beyond belief and it just kept working. And they also retain their accuracy remarkably better than just about anything else even when they’re 20+ years old never having been recalibrated. They’re arguably in a class unto themselves.
Thanks. Great to see this demonstrated in real time. I know the principle but its hard to grasp in my head. Seeing it like this helped so much.
I really like your videos where you explore circuits like this.
This guy is incredible! I do learn a lot with his explanation.
Thank you once again for an excellent tutorial. Very well paced as always.
Once again, you have an excellent video, best I've seen on the "early voltage" analysis! Really enjoy your works!
Thanks, learned something again.
Clear and very pedagogic, so much appreciated. Thank you!
Very informative - i only knew the theorie but not the practice
At 6 minutes you say that, in Q1, the Vbe is a product of collector current. That's the reverse of the usual cause and effect. I'd like to hear a little more about that.
Спасибо!, отлично объяснили.
Thank you!, well explained.
It's great that you do these educational videos man. But I also think you should know that Fine Tune CB will use your name and videos about this stuff (because he has) to troll and push his snake oil on CB users. He has a post that claims you said that digital oscilloscopes are garbage. (You didn't say that but it doesn't stop him from linking your videos at a certain time and making it seem like you did)
Love the videos man. I don't have a clue but one day I might. Thanks.
Thank you for this beautiful explanation.
Helpful video. I liked it
I learned a lot from this video. Thank you!
Excellent tutorial.
very nicely explained thanks
wonderful video
Great video!
Thank you
This is like before the Op Amp, old school.
We STILL use these circuits in the discrete world.
Though you have explained the Early effect well, you could have elaborated a little more on the how exactly is the "balancing act" performed, that is, how exactly and why does the 3rd transistor improve the circuit so drastically. I will look at your other current mirror videos to see if I have missed something.
Excellent explanation.
Excellent as always, Alan! Thanks!
Nice video sir. Thanks.
nice demo
Very cool circuit. THANX
Informative and really well explained , as usual . Thanks
Eleven hundred likes in less than a day! This is impressive Sir
Awesome Content
Excellent as always.
Cheers,
Nice, as usual.
There is no need to say anything like always your videos are so useful. Dou you try making a time measurement circuit by charging a capacitor with this constant current source in a video. If it occurs aI will be very happy. Regards.
There are a lot of subtle things to be careful of when doing that. One is the output impedance of the source as described here. Another is that many capacitor types will change capacitance with bias voltage. Best to use highly stable film caps for this. Not ceramic or electrolytic.
@@w2aew You are right I will try it, thanks a lot again.
Thank you!
As always your content is fantastic ... Thank You for sharing.. Cheers :)
Waiting for the next video. 😍
*SUPER*
When in doubt, cascode it out!
Thanks
Excellent ! Thx
Can you elaborate a bit more and a bit slower on the last configuration with the third transistor? This is a very interesting configuration that i would to understand better
Hi sir, can you make the video on how the poly phase filter works?
You should do a video lesson about optocouplers to remove noise and hissing in circuits and lower the signal to noise ratio. I'm not sure what CTR Current Transfer Ratio means because the Optocouplers datasheets specs will list the CRT like 5mA which if the input of the optocouple has 100mA the output of the optocouplers max output current is 5mA? I don't understand what is the differences between electrons compared to photons because if you have 100mA of current/electrons and the 100mA of electrons converts to 100mA of photons? What I'm saying that pound for pound when concerting current/electrons into photos its not going to be a 1:1 conversion
The higher the VCE voltage drop across the transistors will decrease the base width modulation. I'm confused why transistors even have a Base width modulation as well as what is adjusting the base width modulation of a transistor? The SLOPE of the line is the BETA and Output Collector impedance. I'm not sure why the collectors output impedance would changes its Z impedance based on the base current/base voltage. The BETA is the gain of the transistor which Beta is just extra electrons
Is there an IC that stuffs these 3 transistors, into a TO92 package, or multiple of them onto a single chip?
I've been using the regular "Widlar" design, to supply 3mA to color changing led, independent of the supply voltage (4V~15v).
Widlar circuit is enough for what I'm doing, but it was nice to see how little Wilson design varies!
LM334
@@robegatt I've used them.
They're expensive compared to GP transistors, when you want to control dozens of LEDs, with each LED having it's own CC source.
@@piconano the good old dilemma: integrated or discrete with all the "salad" around them?
A great teacher in a great lab, as I already wrote. This time at 00:21 you show your pcb including a smaller board with little copper squares for a prototype in a Manhattan style... Who sells those boards with the copper foil already cut in small squares? And what is its name?
They're called MePads, and are available from QRPme.com.
www.qrpme.com/?p=product&id=MeSl
@@w2aew Thanks a lot! It's a great source for me. I did not know it. 73s.
Hi! Sir, I'd love watching you on odysee.com as well. They claim you can have your videos copied over automatically, and that there's no censorship... Thanks for these cool videos!
I always like your videos! That was really good. I imagine its quite stable in relation to junction temperatures too?
It is!
I have seen current mirrors in audio amplifiers but I don't think that I have seen this being used before! Would this work well in an audio circuit? If so, an implementation circuit would be much appreciated! It's actually been quite a while since I've last looked at an audio circuit with a current mirror in it, I think that it's time again to revisit this to bring it out of memory storage status LoL...
I love your videos and have seen most of them at least once. Thank you for some good youtube content!
Question: if you remove Q2 and replace it with a node, and then place a resistor (call it Rs) between that node and the 12v source, you would get a pretty good current source where you can control the current with I=.7/Rs. I've verified that the output impedance for this current is also very high. With this being a two transistor solution rather than a three transistor solution, do you know why you would use one design over the other.
I really like these circuit analysis videos. Please keep producing them!
The two transistor version wouldn't be as stable with temperature changes.
@@w2aew ah interesting, ill go play with that a little.
Good lesson, thanks for explanation of "early effect" and how to work around it with the additional transistor added.
Great video!
How important is the hfe matching with these transistors in such a mirror as well as thermal runaway?
Q1 and Q2 should be as closely matched as possible, for the sake of current accuracy. Q3 can be anything. You might even use a larger transistor for Q3, because it will have higher voltage across it, and will tend to dissipate more heat than Q1 and Q2, which will never have anymore than 1 volt across them at the same current. Keeping Q1 and Q2 the same temperature will help, to keep the difference in current between the reference and the output from changing very much. The output transistor can be whatever temperature it wants to be, since it's effectively being driven in cascode.
@@vincentrobinette1507 Thanks! I guess Q3 still does need enough hfe to provide the current?
Or in other words, if you want to mirror something like 100mA, you don't want to drive like 1mA or so?
Darlington would probably work in that case.
@@vincentrobinette1507 Also I think this could be a (MOS)FET as well maybe?
@@p_mouse8676 You're exactly right, you will lose the beta of Q3. If you don't want to lose that, a Darlington pair will reduce that to the beta of the drive transistor multiplied by the beta of the power transistor. All that means, is that 1.4 volts appears across Q1. If you use a Sziklai pair, (PNP transistor driving an NPN transistor) you can keep the voltage across Q1 the normal ~.7 volts. It doesn't matter much, the important thing is to keep the voltage across Q1 as consistent as possible, to keep the output current as constant as possible. I would imagine, you could even use a MOSFET, which would allow ~3.5 volts across Q1, with no beta loss whatsoever. the problem with that is the gate threshold voltage varies with temperature, which would create current drift caused by varying the voltage across the reference resistor. (R1)
@@vincentrobinette1507 Thank you so much, makes a lot of sense now! :)
Thanks !!
Excellent. Could you put this current mirror at the top of a differential-amplifier or would the change in the feedback voltage side effect the base of the Cascode? (You can tell that I don't know what I'm talking about). Thanks for the great videos. I'm very new to electronics and finding them excellent.
Putting a current mirror as the load on a differential amplifier is a very common thing to do inside of op amp themselves. Gives a tremendous amount of voltage gain due to the extremely high output impedance of the current source.
@@w2aew Thank you...
I have seen this many times in audio amplifier inputs and I mean the current mirror but never seen the 'Early' effect compensated for, forgive this question but could you explain please ?...cheers. oh yeah Fab vid !! :)
The explanation starts at about 6:10. Bottom line - the transistors that "set" the current do not experience any C-E voltage change with the load applied, thus no change in current due to the Early effect. The "output" transistor that is providing the current to the load is simply passing the constant current through it - it isn't part of *setting* the current value.
Hello Sir? Park kyu-ho from South Korea. My homebrew AM Radio occurs Freuancy Drift problems.
Simple AM Radio. I want to know that the temperature of RED OSC Coil(alike 7mm IFT).
I put up MONO capacitor in LC OSC curcuit. I have no any N150, N200, N250 capacitors.
So is the output impedance improvement essentially the beta of Q3 times the previous impedance?
Is beta/2 * output impédance of third transistor. Jean-Louis
Nice video as always. But I have a question, in the final circuit still the VEC of Q3 is changing from almost 0V to almost 10V but how come this time we dont see the Early effect? My own answer which I am not 100% sure about is that this time the VBE of Q3 also varies and does not remain constant (Base of Q3 also changes) in such a way that it compensates for the Early effect (by actually changing the base current of Q3) while in the first circuit the VBE of Q2 (output transistor) was absolutely constant so we could see the effect of Early voltage
The Early effect is taking place in Q3 for sure, but is masked by the fact that the current available to it via Q2 is fixed. The feedback around Q1 causes the Q3 base to be adjusted accordingly.
Genius. But, what is your tablet? I’ve been looking for it. The paper white is great. The graph paper is great.
What the hell is it?
It is from www.remarkable.com
If the current source really had infinite output impedance, how would any current be flowing in the load? How does that make it an ideal source of current ?:/
Infinite output impedance simple means that the value of the current doesn't change when the voltage at it's output changes.
@@w2aew Thx! I guess i thought of 'impedance' not simply as a relationship between deltas. My mistake :)
what is the use case of such circuit ?
Current sources have a lot of uses: often used to bias differential amplifiers (emitter or source-coupled pairs), as well as an active load inside of operational amplifiers as well as other apps within ICs. Also used to bias diodes such as LEDs, and used to create linear voltage ramps when used in conjunction with capacitors, etc. Lots of uses.
Hello tell me how you got this on cro
It is not an oscilloscope, it is a Curve Tracer. en.wikipedia.org/wiki/Semiconductor_curve_tracer
Fantastic! After 4 years in University and trying to understand from different textbooks, I still was wondering what the Early effect was, all this time! You have a talent to get the salient points across that one might miss in a dry lecture environment with uncharismatic and dare I say unentused professors. Super video ! Much RESPECT.
You're the only person I give thumbs up before watching the video.
In the start commercial the 👍is pressed, because you know it is interesting!
Last time I was this Early, I got mistaken for a triode.
Bjr Monsieur.
Je suis Français et j'ai regardé l'ensemble de vos Vidéos.
Je vous remercie pour toutes les informations que vous m'avez communiqué.
Je parle juste en mon nom, car je connais pas l'avis de l'ensemble de votre communauté.
En France, nous avons beaucoup moins de matériels d'occasion Qu aux États-Unis Unis. Vous avez beaucoup de chances.
Toutes mes sincères salutations et félicitations pour votre travail.
Bye-bye thierry
Very clearly stated and easy to understand! Thanks!
two transistors and three transistors both are excellent current monitor, Thanks man Thanks
Great video! I was just looking for something like this on your channel yesterday :)
Good demo, but wouldn't a better explanation be as follows: 6:30
"Q3 acts as an emitter follower, and copies the voltage on R1 onto the collector of Q2. The V_CE of Q2 is therefore held at a constant potential-difference (as opposed to a variable potential-difference in the previous two-transistor case), allowing Q2 to mirror Q1's current unhindered by base modulation. Any variability of the potentiometer is compensated by Q3, thereby exposing Q2 to a constant power-load".
Great explanation as always and very inspiring as I plan to soon do some electronics theory/project videos. Really like your format and knowledge :)
As always, clear explanation :)
Hi, very informative video. I have similar doubt while making the current source. I'm using a FET and op-amp for feedback method to generate a constant current source. It's showing the same problem with different load. Can you suggest how to rectify that? It will be very helpful for me.
Difficult to comment without seeing your circuit
Great video
Can you do a video on the OTA amplifier? Please
That looks like a very good current source. Thanks.
amazing stability there. Excellent. Thank you for sharing :)
My #1 favorite subscription on TH-cam.!Great job on all your videos, Alan. I enjoy what you put out immensely!
Thanks. I liked your explanation ,now I get it.
Thanks Alan! This is another wonderfully simple explanation, that beats anything usually written on paper. You have "that gift" for communicating with an heterogeneous audience.
Excellent explanation. Note that the Wilson current source can also be viewed as a Cascode type of circuit (or Pentode/Tetrode circuit for tubes) where the second transistor (or tube grid) shields the primary transistor (or tube grid) from load voltage changes. Many thanks for this.
That's right!
🙏🙏🙏❤️🙏🙏🙏
Merci.
Nice.
I love all your videos! You are an outstanding teacher.