Gain in a common collector amplifier (9-Transistors)

Let's derive the gain in a common collector amplifier. The gain is usually 1, so the common collector amplifier is used as a buffer. Let's do a full derivation with examples.
Aaron Danner is a professor in the Department of Electrical and Computer Engineering at the National University of Singapore.
danner.group
Video filmed and edited by Cheryl Lim.
@randomcheryl

[@MapleKlister]

Thank you so much for these videos! I knew all this stuff 40-plus years ago, when I got my AAS in electronics, but have forgotten most of it. Your efforts here are very much appreciated!

[@rubhern8187]

Thanks Dr Aaron Danner. Very well explained and illustrated. You give and demystify circuits in a very logical manner from principal to end. Reaching this far now I can say I have managed to tackle ac and dc signals going through a circuit.🎉🎉🎉

[@pilobond]

Thank you for all these amazing videos. I am an ex-EE (undergrad) but now a physician. I am a ham radio operator and do electronics as hobby now. You mention in this video that you want Rin to be as large as possible. However, in RF, people often try to "match" the impedance, often at 50 ohm. I understand that this maximizes the power transfer. But wouldn't it still be advantageous to keep Rin as high as possible and then obviously impedance match on the output side? Or I wonder if this is because at RF, it's hard to keep the Rin high (due to parasitics and etc.) so they just assume Rin is somewhat fixed and then work on the matching circuit??

[@abh361]

what an explanation please do more 🥰

[@henrysiegertsz8204]

Common collector amplifiers have a Voltage gain of 1, but it has a current gain limited to the current gain factor (hfe) and collector resistor current limiting.

[@JonDeth]

*TY, this was incredibly well done and helpful.* I am playing catch up as well as review, and you reminded me that the voltage divider for bias is seen as a parallel resistance and I immediately remembered why. I'm finishing up some common emitter designs and had forgotten this for my RC filters. I was within range, but this helped me pinpoint designs as well as explained why a particular cap seemed to have cleaned up my output signal so well, and another was significantly reduced in bass. I needed a major reduction due to excess, but my figure was showing me 95 Hz when it's in fact, much higher than that! By sound, 95 Hz didn't seem reasonable, so I checked.

[@tomlovie]

If the capacitors are polarized, what is the correct polarity?

[@h49suthar]

If you consider electrolytic polorize capacitor, they have Negative mark on one side.

[@tomlovie]

@@h49sutharexactly - which side should be connected to positive and negative?

[@thebrokenengineer]

@@tomlovieThink about this for a moment, where is the voltage "most positive"? It is at the point of the voltage divider, in his example there is a swing seen at the base of between 5.05 and 4.95 volts. On the other size we have a swing between .05 and -.05 volts. So far so good, now can you see where the positive terminal of the capacitor is? Feel free to answer but this should be obvious. As a side note, while a polarized capacitor (like an electrolytic or tantalum) could be used they generally are not for radio frequencies due to parasitics associated with these type of caps. Ceramics are a better choice here and as an added bonus these little things are NOT polarized so the problem goes away.

[@tomlovie]

@@thebrokenengineerthanks for explaining this, I appreciate it.

[@andrejtih7373]

спасибо!!!)

[@INDIANchhanel-ii7zz]

Sir how to make crytal oscillator using crytal oscillator and switching transistor ( found in old crt TV's supply or npn transistors) or bjt transistor

[@SouravTechLabs]

Use pierce oscillator configuration?