Yours are the best electronics instructional videos on the internet. If I magically had access to these videos back when I was a kid I'd be a retired physicist by now with a 60 year hobby in amateur radio. But better late than never. You're filling in many of the gaps in my Swiss cheese of electronics knowledge. Thank you.

When I left college as an electronic engineer I built thyristors and breakover diodes in a semiconductor plant. Your videos and explanations are reminiscent of the Forrest Mims books back in the day. Excellent and well put together videos!

It still nice to see the old analog Simpson meter. Still in use . Good video well explained!

The best explanation about electronics I've seen. Wished I had a teacher like you. I wish all the success you deserve.

This channel is fantastic! The explanations of important fundamentals are clear and the practical applications are always mentioned. I follow along and experiment with each topic covered. Thank you so much for your effort and I wish you all the best!

The HP RPN calculator is a really nice touch. I am still using my trusty HP35s.

Valued info! Thanks! I love how the majority of your projects involve less than a $5 of a handful of parts.

I've been a student of EE for 25 years and your style is the most impressive I've seen so far! I love the simply laid out notes and common themes. I'm on the binge and I want a vid specifically detailing the inside of an opamp from you. All the others I watch aren't cutting it!

Professor, so much thankful for your videos. I never never have had the opportunity of learning with such a perfectly explanations. THANKS.

I recently retired and now have time to learn about electronics. You are a good teacher, and I appreciate your videos. Thanks for all your hard work. 73!

Love this video, looking to understand transistors since ~1 year and making slooooowly progress.

Best practical electronics & education channel out there. Hands down.

Cheers Alan, simple, straightforward, and very useful! Back to my bench!

I really like your back to basics videos, I always learn something new. Very well done too!

One of the best channels to refresh and learn electronics ... As always , Excellent work W2

Brilliant. Thanks for explaining these mysterious little circuit blocks!! Now I see how they help increase the gain in audio stuff.

Your VOM is in parallel with the current source and this causes a reading error. I guess it is a 20kohm/V meter, so in the 10V range it has an impedance to 200k, that matches the impedance you calculated.

Time really flies when watching your videos. Thanks for the great explanation.

As usual, clear and informative video. Thank you.

Really clearly explained, again! Thank you, love to see this continue on into a diff amp too.

Fantastic presentation Allen. I really enjoy your presentations and get allot of inside from them.

Another really great back to basics video, thanks! Also liked the HP 15C calculator.

Gosh I wish you were my electronics teacher on my graduation. Thank you for the excellent videos.

Thanks for the video. (My Fluke 87vMax multimeter is back for a safety recall, if I ever see my meter again, if they repair it. Check yours?) This setup gave me some issues because I was down to my intrepid Cen-Tech P37772 meter with the patent infringment yellow bumper, and worn selector switch, which also doesn't do microamps. So I needed to scale the current up the setup. I also used two power supplies to keep my bias divider in one place, but that might be cheating. What I found: I was displeased with the linearity (low input-impedence) Why I found it: likely because I was against the compliance voltage for my altered setup. What made recovered the fun: I replaced R2, with a diode, which brought up the bias voltage, and linearized the setup better. Also, placing 1 though 5 LEDs in the current source with very little change in apparent brightness made it fun, once again, all the way past 12 volts. They didn't smoke at 15. What opportunity I found: By watching the LED brightness when changing the voltage, I could see the limits of the voltage compliance. Oddly, the 2n222 handled the current quite well. Apparently, some have a max continous current of 600mA, others 800mA (likely with some kind of clip-on heatsink.) What opportunity I missed: while I practiced calculating the input impedance a few the circuit, I should have for this setup, but didn't. Thanks, again for the videos.

Thanks for another great, thorough explanation.

Thank you hit the nail on the head I was looking for something on current I like the way you present your vid's.

really love these back to basics videos.

Nicely explained, although I'll have to replay it a few times for my mind to take it all in!

Thanks Alan - a good tutorial on a subject I'm a bit fuzzy on. I'm going to have to watch this again. Cheers!!

Another good (and useful) video Alan. Thank you for prparing it.

I very much enjoyed this. These have always been a little fuzzy for me but this cleared it up nicely.

Chapeau Maestro! Very clear and well explained...

Great video. Earlier today I built most of the circuits you showed, my favorite was the voltage divider biased BJT with two diodes in place of R2 in the divider. This circuit was remarkably stable, even when I changed the supply voltage or dropped in transistors with different betas. One configuration I tested, a 500 uA sink, showed less than 10 uA change with a 100% swing on the supply voltage. Remarkable.

...and finally I understand current sources. Awesome video. Thank you :)

the slope of the IV characteristics is 1/R @ 6 min. So for a ideal constant current source, output impedance is infinite (1/infinite is 0 which means flat line).

WOW! Amazing video! thank you very much for the detailed explanation and for showing the actual use of a current generator. A question I've been asking myself for a long time was "what are current sources used for?"

Wow!! Great explanation

Excellent, i can see that I was the last person to comment. I'm understanding more now and noticed the ring of two as an example of a current source. It would be great to see you do a video on that.

another extremely informative video. thank you

Thanks,very very nice and simple tutorial, i hope you go forwards and waiting for more basics videos

Thanks Alan! You're the man!

Thank you for that awesome video. I love these back to basics videos. You have mentioned that the gain of an amplifier could be massively increased with a current source. It would be great if you could do a video about that topic to show how that works.

very clear explanation, thank you

It's a wonderfull video. I hope to see another video about current mirrors using Mosfet, wilson,wildar, wildson modificate, active cascode.... thanks for yours videos

Well done, excellent video!

calmly taught, thank you.

I'm enjoying your show - especially the b.e.e. stuff.

This is very helpful for some working I'm doing on pulse magnet motors and what to do with the excess energy output.

Great video about current soutces.

This is really good stuff, thanks!

Great video. Just correction on current changed is in milliamp, but Allen kept say Microamp.

Thank you very much for this video.

Thanks for the video, it is very helpful.

Fantastic video! Thanks

Thanks for the tutorial.

Very cool videos, thanks man.

great video thank you

Great Video, Good Presentation.

Great lesson on current sources for tabletop circuits. My area of application is industrial and automotive where temperatures change from -20C to 70C at best. My designs have to cope with -40C to 80C. These basic current controllers won’t be useable without temperature compensation. Just consider the 0.6v Vbe reference voltage these circuits use, over a small 50C temperature range the voltage will change by 2mV per degree, that’s 100mV change for a 600mV reference! Even the self heating can render the current out of range. Throw in todays trend to run everything from a single battery or a USB voltage and you suddenly have a much more interesting design. I consider any circuit design to be incomplete if it doesn’t have some temperature compensation or a good reason not to use it. I’m sure you have a few design options for temperature correction, perhaps an update video one day.

Excellent!

Current sources are very useful. THANKS

Absolutely awesome!!!

Simply awsome video. Im getting there :-) Thanks for great stuff :-)

Very nice video!

So awesome! Thank you!

really awsome video.

awesome, thanks alot for this video

Super video. Thank you.

Brilliant video with much for me to learn...including from the comments! I'm working through building these circuits to solidify my learning but am not sure how to set up a floating power supply. Would you be able to provide a brief explanation on how you set that up please?

awesome vid ! 🔥

Thank you for the pdf love your vid's.

Is there a way to temperature compensate a current mirror used as to measure high side current? The current mirror I am using had a pnp and npn matched pair. The issue i see is the offset and slope changes as a function of temperature. Is there a way to compensate it?

Thank you very much

Thank a lot, very interesting.

Just been building your second "sink" circuit - 0.6V across a 120 ohm emitter Resistor with a view to create a 5mA constant sink. That particular circuit was in an exam paper , GCE A level - June 1981 AEB Electronic Systems Paper 1. Testing the sink current in an actual circuit I'm getting about 10mA. The paper also asks for graphs of collector current and output voltage when you charge a 1000uF capacitor.

So, without the VOM it is actually a higher impedance. Great! It would be nice to see the same video with the VOM in parallel to the voltage source.

thank you for the great video

Nice video - I always forget how useful these are outside of ICs. Have you done a video on the "long tailed pair" before? Would make a good follow up ,,,

When looking at a schematic of a passive network or active network, how can you tell if the passive network or active circuit is a current source or voltage source? Can passive LCR or LR or LC networks be a current source or voltage source how can you tell?

gran video como todos los que usted hace mister gracias.

Could you possibly consider a video on different types of oscillator.Specifically why most designs don't oscillate as expected,or work every time in a simulation program but when constructed never do ?

Thank you.

You do an incredible job of walking a dumbo like me through this subject. One question........ you said a couple of times that the constant current source can improve the gain of a transistor, the reason isn’t so obvious to me.

Great video!, Thanks a lot! I really enjoy your videos. Can i ask you a question? In the video at 7:44, what do you mean by "floating power supply"?

It's interesting to see that the output impedance of the 2N2222A of 190K across the range 2V to 10V when sinking around 0.5mA as calculated at 11:34 is almost the same as the output impedance of 192K across the range 5V to 10V, which is given by 5V/(419-396)μA. That's useful because some devices have a "knee" at lower collector voltages where the incremental output impedance drops off. It's also worth noting that the 2N2222A datasheet gives a wide range of output impedances at Ic=1mA and Vce=10V of between 30K and 200K. At Ic=10mA, Vce=10V, that falls to between 5K and 40K, meaning that the 2N2222A is not so useful as a constant current supply at higher currents.

Thank you

11:33 .... re: Using the current sink as a load for an amplifier. Dumb question: Is this a good strategy for a LNA block that must amplify very low-V (uV) raw sensor output (assuming the opamp ckt is well designed for noise)?

I love these fundamental electronics videos. Can I ask you how to match transistors used in a current mirror? Is it ok to compare the measured Hfe? Or are there other parameters needed.. (like thermal coefficients..) ? Thanks in advance.

Would it be possible to demonstrate dependent voltage/current sources? Also, are you planning on doing a BJT differential amplifier with a current source?

Thanks for the video, helped a lot! I just came across another current source configuration called the "wilson current mirror". Could you do video about this one and explain why you would pick a wilson current mirror over the basic two transistor current mirror configuration :-)

When engineers say an Op amp is a LOWER Characteristic op amp, what do they mean by "lower characteristic? In OP AMP schematics they often use transistor or FET current sources and current mirrors and differential , Common mode rejection. If you look at common Op Amp schematics for common part number some use differential inputs using transistors while others use FETs inputs plus it looks like they are configured in a current source, current mirror, differential configuration for inputs#1 and inputs#2. If the circuit designed is for an op amp LF348 and LF347 which is JFET inputs, you can't use a replacement like an LM741, TLO84, LM324 because those op amps aren't JFET inputs which I'm not sure why it wont work in circuits as an cross reference part. It would be nice if you made a video lesson about common OP amp part number schematics to go over the FET/transistor configurations inside the op amps of the current sources, current mirrors, etc

Precesion current source based on simple zener? You can make much better using combination of the Widlar mirror and peaking current source. 2 BJT + 3 resistors, no zener, great stabililty, etc.

Thanks شكرا

W2aew, Current source circuits were mostly used for headphone amplifiers cause there was no standard output impedance for headphones? A Constant current source amplifier circuit "can drive any load" impedance that is why they used them for headphones?

@ 12:00 mark, I am interested to know why using the current sink with an impedance of 190k is an advantage over simply using a 190k resistor in the amplifier application you mention.

@w2aew for the first example of the "source" PNP, does Re become a fixed voltage? I assume Ve is Vb - .6., and does the fixed voltage change with resistance change of the Re? I'm trying to experiment with a 10k and 1k..

Hi Pro. At 9:28, is the BJT in saturation or linear region? Why there is a 1.0K resistor at emitter? Thank you for these knowledgeable videos.

Do you have a video you'd recommend for the variable, floating power supply? I'm confused by how its set up. 1) I normally see supplies hooked up with the negative to the ground. 2) It seems to be putting its positive out on the +10V rail. In my mind that would cause a short between the variable supply's voltage (assuming its any value other than 10V) and the 10V rail. But this must not be the case here. Thanks for any insight

I came across your video while searching for a solution to my problem. I built a circuit exactly like what you have on top right hand side of frame, you're pointing at it at 4:53 I've selected 5V as supply voltage. The resistor is 50 Ohms. I plan on charging a 20Ah NiMH cell connected to the output (via a schottky diode to prevent back flow when the source is off). It provides about 310mA, but quickly runs up and gets into a thermal run away. The current increases until the output transistor is destroyed. I've tried with 2x 2N2222, then went beefy, and used 2x TIP42C NPN transistors. Same effect. Both transistors are matched. Tried a resistor as load instead of battery. Same result. Then I installed a heat sink on the output transistor, and it works fine now! Why is this happening on only 300mA draw? How can I stabilize it? Would a MOSFET with its negative temp coefficient stop the thermal runaway? Do they even make current mirrors using MOSFETs?

hi Alan great video but i have a question. i didn't get why you put a 470 ohm resistance in parallel with supply. will you please shed some light on that