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Voltage boosting an opamp

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David Hess:
f5r5e5d, that is like an oscilloscope z-axis or horizontal amplifier.  The major difference is that they use a common emitter output configuration;  the inversion allows a small amount of AC coupling between the output of the error amplifier and the current source to produce a symmetrical transient response.

But an error amplifier using an operational amplifier is too slow to require or output cascodes or coupling to the current source making for a less complex circuit.

Yansi:
Just a quick reply, the rest later:

Simple SE is a powerwaster. If I need to deliver up to 10mA, it has to run with 10 or more mA of the CCS. I like the previous solution more, due to not wasting power continuously. 1W is not a significant problem, but well... why? If it can be solved by adding a trannie or two. Even if they will be unbiased, the resulting crossover distortion is not a problem for my application, as I need mostly DC operation. I'd like to try lowering the idle consumption of the whole device, as it already is wasting a lot power in other power supplies.

About the load Z spec: As I mentioned earlier. See how I did the feedback loop for it to be stable at any C load. (or I think it will be stable). Couldn't find a better image: http://i.cmpnet.com/eetimes/news/08/09/1540chart_pg48.gif
But like that. I think it should make it stable into any sensible capacitive loading, isn't it? But I might be wrong.

Also, as it will be used as a general purpose control voltage supply, one can connect anything to it, so specifying the load is not that easy here.

BTW, what purpose does the R6 C2 serve in your schematic? Such small capacitance value there.

f5r5e5d:
moving the goal post?

you said you needed 1 ma, I give a circuit showing how to do that - with to-92 Q no heat sink


I wanted to show simple, don't think you can get much simpler than just 2 output Q without wasting even more power in bigger negative V with a pull down R

the folded cascode drive removes the sign inversion of the output stage allowing both loops negative feedback to sum at the op amp inverting input

Zero999:
I redesigned it, disregarding all the other schematics posted here. I believe this is the most basic approach.

It should be stable, without any additional compensation capacitor because op-amp has a gain of 10 and the booster gain stage has a gain of just under 3.2, thanks R4 & R5.

It can sink 10mA but only source around 1mA. If it doesn't need to sink so much current, then Q2 & D1 can be removed. If it needs to source more current, then an additional transistor is required.

R6 could be replaced with a current sink which would improve both the linearity and reduce the current consumption when the output voltage is higher.

Zero999:

--- Quote from: Yansi on January 02, 2017, 02:52:31 am ---Just a quick reply, the rest later:

Simple SE is a powerwaster. If I need to deliver up to 10mA, it has to run with 10 or more mA of the CCS. I like the previous solution more, due to not wasting power continuously. 1W is not a significant problem, but well... why? If it can be solved by adding a trannie or two. Even if they will be unbiased, the resulting crossover distortion is not a problem for my application, as I need mostly DC operation. I'd like to try lowering the idle consumption of the whole device, as it already is wasting a lot power in other power supplies.

About the load Z spec: As I mentioned earlier. See how I did the feedback loop for it to be stable at any C load. (or I think it will be stable). Couldn't find a better image: http://i.cmpnet.com/eetimes/news/08/09/1540chart_pg48.gif
But like that. I think it should make it stable into any sensible capacitive loading, isn't it? But I might be wrong.

Also, as it will be used as a general purpose control voltage supply, one can connect anything to it, so specifying the load is not that easy here.

BTW, what purpose does the R6 C2 serve in your schematic? Such small capacitance value there.

--- End quote ---


This will source more than 10mA and sink 10mA.

I've implemented the current sink to reduce the power consumption.

It will have crossover distortion though, which can be removed, at the expense of more components and power consumption.

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