ECE3400 Lecture 27: BJT Push-Pull Amplifiers and VBE Multipliers (Analog Electronics, Georgia Tech)
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- Опубліковано 5 лип 2024
- Reference: leachlegacy.ece.gatech.edu/ec...
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0:00 -- Introduction
1:12 -- Push-pull output stages
2:53 -- Crossover distortion
5:08 -- An impractical solution
6:09 -- VBE multipliers
9:44 -- Bias current calculation
10:57 -- Design example
12:01 -- Bias adjustment
13:23 -- Leach Low-TIM Amplifier
14:03 -- 1176 Limiting Amplifier
14:41 -- Tube power amplifiers
This is easily the best video on Push-Pull Amplifiers I've found on UA-cam. The thing the other videos were missing was the straight forward math and examples to re-enforce the explanation. Fantastic video, thank you!
This is one of the best lectures I have ever came across, this is some really awesome job ! Thank you
Thank you for your kind words!
Congrats!!! Your Tutorials are in my POV, the best you can get: very interesting content, very easy to follow ( even from a non native English speaking perspective) good pace, easy/comprehensive balanced explanations, good and clean visuals, no annoying background noises... welll...what else to say: Thank you, and please keep on!!
GA Tech alumnus here. I attended several of Marshall Leach's lectures.
Nice job professor, Now a days a very few teach analog electronics.
Nice work, professor. I am a practicing EE, but not specializing in transistor amps. I have to troubleshoot and repair my vintage Marantz amp. This brings it all back. Thank you!
Awesome stuff. I repair professional audio power amplifiers and this helps a lot. Thank you. 😊
Thanks, Prof. Aaron 👍
You are welcome!
Outstanding
brilliant
Thanks!
@@Lantertronics it so amazing to see how someone can master a subject, I'm still at the stage where this stuff is so overwelming and feels like magic. Maybe one day the math will make sense haha. Thanks for making your videos they are quite inspirational
That gyraf site is 🔥
True!
What happened to lectures 20 to 25?
They are not in the ECE3400 playlist.
They don't exist in a refined video form -- maybe in the future if/when I get time, so I wanted to leave space for them in the numbering sequence.
Why do some class AB amplifier have bias currents up to 1000mA or even higher when you just need 50mA to make the crossover line straight?
These are Class AB amplifiers, but they differ in their depth of Class A operation. There is a myth that Class A operation provides better sound quality. In fact, deep Class A operation results in higher power losses, and on top of that, it sometimes degrades the performance of power transistors, as their gain drops at higher currents.
Deep Class A is sometimes used in Class AB amplifiers, in which transistors in the power amplifier output operate in a common-emitter arrangement, that is, the signal is received from the collectors or drains. These are rail-to-rail amplifiers, which actually work better at higher resting currents. This is because these amplifiers are less resistant to load, and raising the resting current partially offsets this problem.
Amplifier outputs with transistors in a common emitter arrangement are also often found in high-speed ICs that have rail-to-rail output. Manufacturers of such circuits, however, state that achieving the full voltage range of operation is possible only with very small loads - for example, 10 k ohms. If you increase the load, for example, to 1 k ohms, the circuit will work, but the allowable amplitude of the output signal will be greatly reduced.
In conclusion, we can say that sometimes this increased resting current is a marketing gimmick, and sometimes it is necessary to achieve the intended output parameters of the amplifier.
@@GluonToo I agree
the That2180 and some SSI and Alfa ic's have "multipliers" inside, they are hidden, secret.
always wondered about that, this was the first time i heard a explanation about it and still ...
13:24 holy cow!
now that's what i call over complicated, lol
what kind of voltage regulators would that circuit have (back than)?
Check out Marshall's writeup on the Low TIM amplifier: leachlegacy.ece.gatech.edu/papers/lowtim/feb76feb77articles.pdf
The multipliers you are referring to in the THAT and SSI chips are very different than the VBE multiplier discussed here.
@@Lantertronics thank you, but: Connect to the campus VPN and then retry
@@Lantertronics Thanks.
i have introduced it in to the simulator.
at first it clipped massively to the power rails, then i realized i put the power on the wrong side of the circuit, now it doesn't do anything. here is the file for the falstad simulator, was quite a massive job.
"/2fl8prex" just paste this behind a Falstad simulator "shared" link.
@@AnalogDude_ That's very strange, it should be public. Just try googling "low Tim amplifier"
Why are there diodes???
In the case of the first amplifier, diodes D3-D6 increase the voltage drop and allow reducing the resistance of R25. In addition, they respond to the temperature of the interior of the amplifier, not just the power output heat sink itself. If the interior temperature increases, the current of transistor Q7 also increases, that is, the voltage CE deposited on it decreases. Therefore, eventually the bias of the power transistors also decreases.
In the second case, the diodes spread the voltages that control the bases of transistors Q8 and Q9 by about 1.4 volts, so that both transistors remain on all the time and have bias.