Oh, and I totaly support that
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Originally I was going to use a single polarity supply to the transistors. That's why the coupling caps needed to be incorporated. However, I decided to use dual polarity and a Darlington-pair CLASS AB amplifier. This way I won't need the coupling capacitors since the output voltage rail will be around 0V lvl (assuming components are properly matched and heatsinked). However, I still don't see how feeding a portion of the output back to the op-amp will work because the 0V DC lvl will not provide sufficient biasing current. I tested the 120V boost circuit found in this guide:
https://www.electro-tech-online.com/custompdfs/2008/09/AN-272-3.pdf
Feeding the output back into the input on an inverting amplifier creates negative feedback which results in a predictable gain, increased bandwidth and reduced noise.
It did not work in MULTISIM. All I get is DC rail of 0V at the output (just as I thought would happen).
Which circuit did you build?
I assume you're talking about figure 6?
I don't see why it shouldn't work.
Have you used the correct component values and not done anything daft like not connecting all 0V nodes or using a single 120V supply rather than a positive and negative 120V supply or forgetting the positive and negative 15V supply?
P.S. I need to boost a 2.5Vp sinewave signal to 115V rms. Oh and no, I don't want to incorporate a step-up transformer into the design...
The circuit will give a gain of -Rf/Rin = -100k/10k = -10 that's right the formula is the same as the usual inverting op-amp formula.
The booster circuit is quite easy to understand.
Q1 and Q2 form a common base amplifier with a low input impedance.
Q3 and Q4 form a common emitter amplifier with a high gain and higher input impedance.
Q5 and the diodes forms a current regulator that biases Q6 (a high gain common emitter amplifier).
Q7 and Q8 form an emitter follower with a high input impedance and very low putput impedance.
The buffer is placed in the useual feedback loop.
The booster is an inverting amplifier so the usual input connections are reversed.
The 20pF and 100pF capacitors added to the feedback loop act as a phase shift compensation network which prevents oscillation.
To increase the output current:
Q7 and Q8 need to be darlington transistors.
The 100R resistors need to be reduced to 4R7.
Two more diodes need to be added to Q7 and Q8's bases.
The supply voltage to the circuit needs to be a minimum of 170V to get 115VAC RMS on the output.
It's possible to power this circuit from a single power supply, but the input volatage needs to be 340V to get 115VAC RMS on the output.
Is 1.2A the peak current or RMS current?
If it's the latter, then you'll need to increase the suppy to >175V.