Common Collector Amplifier - Theory and Basics (1/2)

[@HitAndMissLab]

I can't believe how much undersubscribed is this channel, taking into the account highest possible standard of content it provides.

[@planker]

Excellent. Really good information, bottom line, it's a current amp with good output impedance. My brain smiles, thanks.

[@lad4694]

FesZ with spectacular video timing as always

[@Mike-H_UK]

Another interesting video. While agreeing with everything that you say, my recent experiences with emitter followers is less rewarding. When driving even a fairly low capacitance load, the base transit time effect (finite Ft) translates this into a negative input impedance and high frequency oscillation instability at a much higher frequency (200-300MHz) than what the circuit was ever intended for (30MHz). I eventually got the circuit to work with good decoupling and several cascaded high loss ferrite beads in the base, but it had turned into a bit of a monster by the end!

[@SheikhN-bible-syndrome]

Same I can't get the distortion down luckily it's mostly the kind of distortion that "sounds good" but still I want to have a clean signal going to my speaker

[@wombatau]

I like the lighting in this one

[@newmonengineering]

Great job as usual!! I appreciate the time and effort you are putting into these videos. I look forward to the entire series on it. After going through bjt do you plan to do a mosfet one?

[@FesZElectronics]

Honestly, I'm not sure; there is not that big of a difference in the general performance between the 2 types of transistor. I'll have to look into this in a bit more detail.

[@gkdresden]

Another interesting thing is the push pull common emitter output stage because of its rail to rail operating advantages. It is probably worth a video to this type of output stage. It is especially useful for relatively low supply voltages, but I have used it in an amplifier with a +/- 12 V power supply to get 14 W of output power without higher harmonic distortion instead of 11 W.

[@M0NTVHomebrewing]

Brilliant! Thank you very much!

[@ferrabras]

It would be nice to say how the selection of resistors (impendances) and operation point (current) affects the noise figure of the cicuit. It took me a while to understand it.

[@cmuller1441]

At 12:00 why has the source been changed to Rser=3k ???

[@FesZElectronics]

When measuring output impedance, it is also impacted by input impedance; I changed the input to 3K to be closer to a real life use case.

[@p.k.420]

Thank you sir😊

[@DERKONIG12345]

This type is also called emitter follower...

[@pluscrafter7117]

Why is in the formula to demermine the input and output impedance not dependent of the inpedance of the input and output decoupling capacitors?

[@FesZElectronics]

It makes the assumption that the decoupling capacitor (or the AC signal coupling capacitors) are ideal

[@ferrabras]

It's valid to calculate at the band pass range. You can also use the capacitor impedance, and have to include "parasitic" capacitances of the transistor.

[@SheikhN-bible-syndrome]

I've got a lot of 2sc5198 power transistors but I can't find any videos of someone making a power amplifier using several large transistors is all I find are these small power amplifier designs

[@toruscore]

Hey, thanks for this video, I've been thinking about emitter followers for RF buffers recently. I had an idea re voltage swing but found no material or discussion of it: Why not put an inductor at the emitter. I get nice voltage swing, and even symmetric below the negative rail. Have you thought about this? Is it a dumb idea? Simulations look ok so far. Cheers

[@FesZElectronics]

I think the problem with this has to do with the initial dc biasing; having a resistor is helpful to ensure stability over gain variations; you can of course use an inductor, but you need to make sure the average collector current does not vary with temperature. In a similar fashion in common emitter amplifiers, an emitter resistor is used for biasing, but for high frequency operation, this resistor is shunted using a capacitor.

[@toruscore]

Yes, that makes sense. In fact, for my preliminary test setup, I put a small shunted resistor between the inductor and emitter. I haven't done the calculation whether this would in principle be enough to be safe from temperature runaway before one loses more voltage drop than one has gained before... Maybe if the bias base current is provided using some Z diode to get more voltage drop :)

[@Mike-H_UK]

I tried this idea a year so ago. One major difficulty with an RF amplifier is getting enough inductance with a self-resonant frequency considerably higher than the maximum frequency of use.

[@JohnWick-pw1jt]

Common emitter

[@tarikcamacho]

I wish I could hear you better but your vocalization is so bad for a no-native english speaker. I see the content is good but I can´t understand what you are saying. Pity!