Electronics > Beginners

Why is this simple Class B amplifier not working?

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colejohnson66:
I'm trying to amplify a voltage from -5~5 V up to -48~48V without using an op amp. The reason being: I need at least amplify a few dozen signals in my project, and the best 100V op amp I could find was the OPA454. However, that is ~$6 a pop in small volume (which is too expensive).

For my requirements, a little distortion is allowed as the voltages don't need to be exact. Also, I am aware of the dead zone, and want to do a Class AB ultimately, but I'd first like to understand how a Class B works. Using LTSpice, I have recreated a schematic I found online (I've attached it here), but when I simulate it, all I get at V(out) is V(in) minus the PN junction drop of ~0.7V. Why?

alsetalokin4017:
Your original schematic does not have a "V3", but your LTSpice sim does. What happens when you lose the V3 from the sim and just connect this to ground as the original schematic shows?

hamster_nz:
Isn't that schematic set up to amplify current, not voltage? (i.e. It is a power output stage)

colejohnson66:
If I connect the collector of Q2 to ground like in the original schematic, V(in) is "clipped" and doesn't go below 0V.

soldar:
You are not going to get +/- 48V out with a single sided 12 V supply.

If you have a single 12V supply the most you can get is +/- 6V if you use a DC blocking capacitor.

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