#356: Back to Basics: the Emitter Follower, or Common-Collector Amplifier

Sir, your video's are outstanding, I know of no one who can explain difficult subjects (for me they are) so well. Your drawings are so helpful! Thank you for taking the time making these video's...

45 years since I did this at collage. So nice to be refreashed. I now understand better than I did back then, Thanks.

Eternal life to this man, if you were on the Titanic the entire crew would agree to give you a boat just for you.

"Basic" turns into "Simple" (kindof) once a good teacher such as you explains it. Thanks for sharing and the good paper- and camerawork

Great video Alan, I’d have gone the EE route if you were one of my early teachers. Really enjoying finally understanding a lot of details my young mind didn’t get, now years later making sense through your videos.

When I was teaching at a local university I did a session "proving" that an emitter follower could have a gain greater than one. Use an audio frequency that can be measured by your standard VOM of the day (20,000 ohm/volt). Measure the base signal, then move the meter prob to measure the emitter signal. Voila, the emitter is greater than the base. This is an "illusion of measurement" When you read the HIGH impedance base, you load it more than you would when you move the probe and read the LOW impedance emitter. This is a well-known phenomenon in the industry but it's a wonderment to a new student.

The way you explained in/out impedances was so delicious I could almost eat it. Well done. With love and respect from Shiraz.

I'm 75 and enjoy some of your videos. Always informative. I was first licensed amateur about 65 in hi school, Navy ET-R from 68-74 (maintained GCA RADAR and TACAN) and have been in and out of electronics since, but I'm way way behind on modern stuff.

Another superb video, Alan - thanks! I think it'll become one of your classics. That question about clipping, from The Art of Electronics, has caused a lot of head-scratching. Much better to see it solved as you've done here, by equipping people with the background, than by addressing just the question in isolation.

I’ve been watching you since my 2nd year of electronics engineering and now as a young professional with 2 years of experience I still watch your videos to remind myself what I’ve learned. Analog is my passion but unfortunately high speed digital and power is my day-to-day. Thank you for doing this for all of us. Ipsa scientia potestas est

The hand drawn diagrams are clear and well done. They really help clarify what you are talking about and make it much easier to reproduce for older simple minded low time hobbyists like myself 👍

Man, missed these back to basics videos. Thanks!

The Emitter-Follower is a simple circuit for running low impedance instruments from a weak signal. Thank you very much.

Alan, deep gratitude for your hard work to teach we knuckleheads. I was stumped re: how to get the signal output from my LimeSDR to drive a pallet MRFX1K80H until I stumbled upon your material and a few other generous folks. Hope you have a good field day. 73's W6MGV.

amazing solved my lots of questions, thanks again you are the best teacher i have ever seen. Thanks from bottom of my heart.

Probably your best video till now. Really appreciate your in depth explanations. Especially I finally understood your definition of impedance. Great with the math and circuit explanations. Thanks a lot! :) I hope you continue soon.

When I started I had troubles understanding this because on a scope you see the base voltage versus emitter voltage (or in other cases the collector voltage). The theory also talks about a voltage follower if they talk about a follower. While it is a current driven component. Building things to experiment did not clear up things. For me all became clear when my mentor asked during my first serious repair (old scope) 'what is the voltage over that resistor' . Why ? I asked, 'so you know the current' he told me and looking at current gave me so much more insight and information. The problem it is that you need expensive probes if there are no resistors. Measuring current is often not easy. When I got a Tek 6042 current probe I started to look at the current much more often. Nowadays I repair "unrepairable" electronics for a living and it makes things so much more easy if I look at current. I have a nice collection of rather special current probes for that (for most flux gate and hall based, to I can use them to 'see' current in traces ). Using them is often not easy but it can tels a lot. For instance, if you measure 0 volt this can be a short with some current or just no voltage because there is no current. Looking at the current can make repairing a lot more easy. I am talking by the probes that can measure current in traces. The normal "around a wire" probe needs more work. What I sometimes did was lifting a pin and adding a piece of wire in series to connect the probe or cut a trace and solder a wire over it to connect the 6042 probe. Btw, a thermal camera can also be a great way to see current, because everything that conducts has resistance and warms up. It is very cool to watch traces and components on a cold PCB during start up. You see the smallest differences in temp. In a Fluke scope meter I could see the power asic come to life first and also the problem, one of the pins being short. And this before things start to smoke :-)

With every video I'm impressed that you always maintain such a precise language and use the proper terminology and it's still easy to follow (probably rather because of that). Hats off! I'm an EE myself (power systems though, not that experienced with analog circuits) and would love to see a video (series) of a slightly more complex analog circuit - e. g. a hifi amplifier or a higher voltage cascode amplifier - and follow your thoughts from start to end: How do you analyze the problem (starting with the requirements), how do you come up with a circuit (what are the methods to come up with a good design), the math, (maybe a simulation?), and finally a prototype/measurements/refinements. I know it's a bit much to ask, but I think I might not be the only one that would really appreciate something like this. Again, thank you for sharing your knowledge!

Oohhh, sooo goood! Thank you, Alan. I will have to watch it, several times, to extract all the goodness. Cool!

Damn Alan, I forgot how high the level is on your lectures on such "simple" topics. I need to learn more. I now realized how much I missed the series