I admire your willingness to teach but need to point out that a true constant current circuit will deliver the same current not just into a varying load but also from variances in Vcc. What you have is a current sink. If you vary Vcc even fractionally, the collector current (the load current) will shift accordingly. It's no longer constant. If you further expand your equation for Vb it approximates Vb = Vcc*(R2/(R2+R1)). This you can then substitute for Vb in your equation. If Vcc changes then Vb changes and so IL changes. Your circuit requires Vcc to be rock solid regulated for constant current to be realised. Not viable for loads that run directly off a battery for instance where terminal voltage falls over time as load is applied.

@petarmiletic997

4 жыл бұрын

Replace R2 with 2 diodes in series and you get constant current, Ic=Vdiode/Re

@boblewis5558

4 жыл бұрын

Not completely true, as using two diodes in the bias chain solves the vcc problem for any reasonable deviations. See my comment above.

@treelibrarian7618

4 жыл бұрын

I knew we had a problem as soon as he said Re was to "reduce thermal runaway" ... my favourite CC is similar but 2 transistors - replace R2 with a second npn (T2) with its base to the emitter of T1, emitter to ground, and collector to the base of T1. Vre is now 0.61V whatever else goes on, as long as enough current is coming down R1 to power the original transistor. Thermal changes in T1 are irrelevant. Can sink constant current down to less than 1V from ground (which is often important). Since transistors, resistors and diodes all cost the same these days (1p), there's no cost penalty and R1 value is now arbitrary, so when there's a charge for each extra value in the pick-and-place machine you can substitute a value already used elsewhere... win win win. Turn the whole thing upside down with pnp's for a CC source instead of sink. Re sets the current, rather than having anything to do with thermal runaway.

@boblewis5558

4 жыл бұрын

@@treelibrarian7618 yup! Same principle as signal diodes, but even better overall and as you say bugger all difference in cost and same component count.

@treelibrarian7618

4 жыл бұрын

@Kevin Counihan , I just can't imagine what that extra resistor would protect against. If T1 is already short, worse things are already happening - does it matter what happens to another 1¢ component? otherwise, sounds like wise practice to use it for testbench supply, though one CC would be enough? fun fact: T1 can also be a MOSFET and then higher currents can be controlled easily.

Great video. If you wanted to make this circuit a variable current source, all you need to do is replace R1 and R2 with a potentiometer with the wiper blade going to the base of the transistor. To vary the current, just turn the knob of the potentiometer increasing or decreasing the current to whatever value you want. I would start with a 100K potentiometer first and see how it behaves. Other potentiometers are also possible.

Great tutorial on constructing a constant current source. Theory then hands on labs are the only way to learn electronics. Thanks Paul and happy birthday.

Now this is the content I'm looking for. Happy Birthday and keep up the good work.

That helped to take some of the mystery out of CCS for me. Thanks!

"Thank You", thank you very much for the diagram and formulas. That was REALLY great 😋😎😋

Very usefull and helpfull video, thanks :). And Happy Birthday Paul with your 50th!!! anniversary!!!!!!!!!

Another great video this is a circuit we all should all know deep down. Now I actually understand the math part of it. Thanks Paul you rock and have a great birthday 🎂.

Happy Birthday buddy and many thanks for these videos. They are both interesting and educational. Please keep them coming as they brighten my day when I see a new video from you. Many thanks and have fun, Joe

Happy Birthday Paul! Thanks for yet another very helpful video!

Your instructions are brilliant

Cool, been looking for just this circuit for use when playing with various high output LED's from China!

You really have this down. I can't seem to just dream stuff up like you. I feel I need to google circuits. It's best to understand it. Thanks

Awesome circuit and well explained, thank you! I am trying to design my own current source to use in a zero temperature coefficient application. I was using the LM334 with a diode (opposite tempcos) but the LM334 is too large for my board. Hoping to try this design out - thanks again!

Great explanation

Happy Birthday Paul and thanks for your work

Gold! Thank you very much

Thanks Paul. Happy Birthday!

Awesome video. You do a great job explaining things. Happy birthday!

Thank you very much helped me those equations!

Congratulations for sharing (from Belgium.👏 👌 👏)

Great explanation!!

Awesome. Thank you

Great video! And happy birthday Paul! :)

Great clip, many thks.

Definitely save this one to my saved file. (Subscribed)

thank you the tutorial is useful

Really liked this video. Classic circuits are just what I need to know, please do more. I’m going to build this circuit and have a play. Thanks 🙏 🏴󠁧󠁢󠁥󠁮󠁧󠁿

@ArnaudMEURET

4 жыл бұрын

Make sure to check out the comments here when you come across its various shortcomings

@lookupverazhou8599

7 ай бұрын

Except the current's not constant. I just made this. Current doesn't stay the same when varying the load.

I liked it, I gave it a thumbs up but I'm totally lost! Lol good thing we have replay! 😎 Happy birthday 🎉

just saw this video, so happy belated birthday to ya Paul! sorry im a lil late to the party haha. excellent example of a CC source, wonderfully simple.

Nice video. Please do more videos in this series of 'circuits you should know'!

Happy Birthday Paul.

Happy Bday Paul, and enjoy the day cheers.

Happy belated birthday and thank you for the tip. That may come in handy down the road.

Good stuff, thanks. And as many who commented before me have said, happy birthday sir! Also, by the bits of all this I am grasping, if you were to put a potentiometer in r2, that would give you the same scenario as the current adjustment potentiometer on a benchtop power supply? Thanks for the stimulation of mental growth in me and my kids as well.

Happy Birthday Paul! 5.0 is a nice one...

The actual Engineering Starts from here, A big Respect from me sir . From India

Great explaining as always. It clears some doubts. But I kind of expecting to see some more. By the way. Hope you enjoyed your birthday. God bless.

Very understandable

Très bien merci 👍

Happy Birthday and thanks!

Belated birthday wishes :). Thanks for this vid!

That was great! thanks for the video! HAPPY BIRTHDAY!!!! :)

Great videos!

@learnelectronics

2 жыл бұрын

Glad you think so!

Happy birthday from Thailand, Paul!

You are moving up in the world as you were just in my recommended videos.

@learnelectronics

5 жыл бұрын

Awesome, I didn't know KZread even knew who I was.

Very good video again !!!! Happy Birthday and have a great day !!!!!

Belated birthday wishes Paul ..you're the best!

Nice for a laser, etc,etc,. Thank You so much.:)

Than you sir,you are my hero!

Happy Birthday Paul. Enjoy your day. 👍

Let my start by saying Happy Birthday But I will not give your a passing grade for that constant current source. Replace R2 with a red LED or two diodes would help because it will reduce its dependency on input voltage, but a even better solution is a JFET, it is a constant current source sometimes without external components, sometimes you need a single resistor. None of the above is perfect, you need something with a stable reference and more gain to be closer to perfect. In one of my designs I needed a a led (Opto coupler) to work from as low possible voltage to as high as possible voltage, a JFET did that nicely, my final design is rated from 4V to 25V and includes a polarity protection diode, a opto coupler, a red LED and a JFET with resistor to limit current. Low limit is due to voltage drops in the different part, high limit is due to the JFET.

Thank you and happy birthday

excellent! new patrion. thank you and happy bday!

@learnelectronics

5 жыл бұрын

Thank you

nice tutorial

Happy birthday Paul...Enjoy.🎈

Super... Simple!!!!

I thought I had left my multimeter on.

@learnelectronics

5 жыл бұрын

Lol it was mine

@gartmorn

5 жыл бұрын

My poor dog is so jumpy and she noticed your meter was on Paul!

@mikehermesmeglio

5 жыл бұрын

I thought it sounded like the sleep function on a Hakko soldering iron

@chloejackson-reynolds418

5 жыл бұрын

@@mikehermesmeglio They go to sleep?

@mikehermesmeglio

5 жыл бұрын

@@chloejackson-reynolds418 Yes. They have a sleep function to reduce tip temperature and then eventually it will shut off completely if it's not being used.

thanks for sharing sir ! and Happy Belated Birthday :)

Thannks for shareing

man you are awesome if my electronics doctor would explain like you do,i would have been much better thanks

Happy birthday then and enjoy cup cake. Thanks for the circuit

amigo me agradas 👍👍😁 . gracias por tu conocimiento

Happy birthday and may God you, Paul

👍👍 nice i got it

This guy is great

thanks Paul I love it when i learn something new great show and sorry its late i give you a great big HAPPY BIRTHDAY

@learnelectronics

5 жыл бұрын

Thanks

Happy birthday! Have a good one! Really useful video! I have a doubt, though, could I use this sort of circuit to test a lithium ion/lipo battery discharging? Or would that be overkill for this?

Another cool demonstration would be to vary the load and measure the load current! This proves that it's constant current!

HAPPY BIRTHDAY TO YOU!

Happy Birthday! I think you should do a series of transistor current sources and sinks, like you did with oscillators. After the cupcake, of course.

Happy CupCake Day to you Paul... 🧁 And, YAY, I get to play some more with my newly arrived Resistor board thingy, thanks Prof... 👍🏻 🤪 🐍

Happy belated Birthday, just catching up now. Have a great week.

i am amazed that you know the transistor beta to an accuracy of three significant figures and are confident enough to be able to base your calculations and design on it

@kreynolds1123

5 жыл бұрын

He did say its his "absolute favorite" transistor. :D

@sadie6391

5 жыл бұрын

@@kreynolds1123 it'd be my fave too if beta only varied one part in a thousand over the full operating range and manufacturing spread :)

Thanks Paul. Your video was great. I’m looking forward to more like this as I start back into the electronics field/industry.

Happy Birthday!!!!

I promise to support you, as "best" I can 😋😎😋

First of all WISH YOU HAPPY BIRTHDAY TO YOU SIR. classically explained. 🎂🎂 🌹🌹🎂🎂.

Happy Birthday!

Hi, I really like your videos. Could you do a series of classic circuits like this?

@learnelectronics

5 жыл бұрын

Yes

Sir, I wish to congratulate you on making this video where you explain " A constant current source". Many people do not know the difference between a " Voltage source" and a "Current source". First, let us assume that the collector current characteristics with a varying collector voltage of a BJT are "horizontal straight lines" for given base current. Your circuit, though so simple, gives the right idea about the fact that the current source is at the collector of the BJT while a voltage source is at the emitter of the BJT. As I said it is not a perfect current source nor a perfect voltage source and since my daughter is in education teaching the basic electronics, I often discuss with her how to demonstrate the action of a voltage source and a current source. This is what I do. I use the circuit that you showed and put a DC small motor, first connected at the collector and then the same motor connected at the emitter replacing the 'Re' in your circuit. When the motor is placed at the collector as a load, there is a constant current in it so the motor provides a CONSTANT TORQUE. The manner and the noise the motor makes when it speeds up is that the motor takes a lot of time to speed up and the sound is gentle and slowly rising. Even if you stop the motor shaft with your fingers no damage is made as there is a constant current in the motor due to constant base current. If the little DC motor is now placed at the emitter instead of Re, then at that point the transistor is a VOLTAGE source and so the motor will have a variable current, very high to start with as there is no back emf from the motor. At the start, the motor will accelerate very very fast and reaches a constant speed. This is because the voltage source connected to a small DC motor is a SPEED CONTROL SYSTEM and not a CURRENT CONTROL SYSTEM. I am now a very old engineer and you know when I was very young I formulated this " model" for the manner in which a current flows out of a current generator. Since you were in the Navy I am sure that you will appreciate my analogy. * Assume a kettle of water being boiled with a flame underneath it. The rate at which the vapor evaporates is only due to the flame size. The vapor normally stays above the surface of the water and if we want the vapor to reach further up we must put a vacuum cleaner to such it up. The base-emitter junction in a BJT is the flame power that evaporates the electrons and the collector voltage is the vacuum cleaner which will suck the steam through the insulator represented by collector base material which is a reverse diode!! Sometimes I describe the base-emitter junction as doing the same job as a catapult on an aircraft carrier. The catapult shoots the planes forward one by one and the aircraft as they are launched ARE NOT ALLOWED TO TOUCH EACH OTHER. This is the manner in which electrons are shot forward into the collector insulating material, individually like machine gun bullets where THEY DO NOT TOUCH EACH OTHER and in between there is the high insulating collector material AND THIS IS THE REASON WHY A CURRENT GENERATOR/ SOURCE HAS A HIGH OUTPUT IMPEDANCE. The collector voltage in an NPN BJT is only acting as a vacuum cleaner to such up the CONSTANT NUMBER OF ELECTRONS LAUNCHED BY THE BASE EMITTER JUNCTION. It is very important to know that while traveling through the insulating material that makes up the base-collector path ( reverse diode) the electrons leave an insulating space between them to form the high output impedance of the current source. It is the emitter-base junction that the decides the number of electrons launched to the collector insulator path and not the collector voltage. I have a good mechanical analogy of what makes a voltage source with its VERY LOW OUTPUT IMPEDANCE as when we take the output from the emitter as in the case of your circuit. But I shall explain that some other time. Congratulations on our presentation. You have brought back many good memories of my youth, and that was a very very long time ago when even the transistor was not yet invented......... I grew up with glass tubes and glass valves where the insulation between the grid and the anode was a perfect vacuum or an insulator which in the BJT they try to obtain it through using the high impedance of a reverse biased diode...............it was easier to learn about the dynamics of electrons traveling through insulators when handling glass tubes in 1940!

Happy birthday!

Nice

Happy belated day of spawning. Thanks for the brush up vid bud.

Shazam, thank you very much. Have a wonderful belated birthday!

This is really taking the long way around, you know. It's a lot easier to understand if you point out that setting the voltage at the base also sets the voltage at the emitter - when operating in the linear region of the device.. That emitter voltage then determines the current through the emitter resistor . . . which in turn, "is essentially" the collector current and does not vary with the collector resistor.

Happy birthday 👍

Happy birthday Bud

Very interesting circuit to me and as always you explained it very well. Thank you! Could you tell me where or Howe to get this resistor board? Boris🇨🇭

Happy Birthday ;)

Happy birthday brother

Happy birthday🎂 to u sir🎉🎉🎉

A constant current source requires a way to MEASURE the current flowing through it.

Thanks, I be actually learned something here!

Beautifuly explained Thank you More like this 👍

@eladioh3858

5 жыл бұрын

Happy birthday

My problem is Re and the power dissipated gets high if you want a 10A 12V constant current source. Is there a better way when you’re getting into higher currents? The application for the circuit is to charge a super capacitor bank without melting wires or blowing fuses.

Happy birthday! ( A couple years and a few days late! :) )

Happy Birthday.

I'm sorry to hear that.

happy Birthday :)