In my experience, the LT1468 is as care-free as it is performant. I never experienced instabilities with this OPA.Was that just on its own, with nothing but the usual resistors in the feedback loop? My concern isn't the op-amp in isolation, but according to the other schematics posted in this thread, it will have a pass transistor on the output, inside the feedback loop. The extra delay due to a transistor, especially a big slow Darlington pair, can cause oscillation, with a fast op-amp. It's possible to avoid this by slowing the op-amp down, with a capacitor between the inverting input and output, but why not just use a slower op-amp in the first place?
As of why the CV opamp needs to be fast, it needs not to introduce much phase lag as it is driven by CC opamps. So, CV opamps needs to be much fast than CC opamps.
Stability is checked in ltspice. In fact, it was the biggest challenge for me. Output stage is a plain push-pull stage with just two transistors, no darlington. This is why I also have to limit maximum output current. I hope I can get 1A, but we'll see. I understand with higher frequencies bjt gain drops. Assuming hfe is 100, getting 1A output requires 10mA drive current from the opamp. Is this too much for lt1468? Typical output current claimed to be 22mA, but, as I understand, higher output current slows opamp down.
I'll make the circuit on a perfboard and report results here.
As of why the CV opamp needs to be fast, it needs not to introduce much phase lag as it is driven by CC opamps. So, CV opamps needs to be much fast than CC opamps.
As of why the CV opamp needs to be fast, it needs not to introduce much phase lag as it is driven by CC opamps. So, CV opamps needs to be much fast than CC opamps.Output of your CV opamp swings 1:1 with output of your supply. You may look not only for a gain bandwidth product, but also for a slew rate.
22V/µs is not that fast for 90MHz opamp.
TL082 with GBP of 4MHz has for instance 13V/µs slew rate and this is one of the reasons, why it is quite popular in lab power supplies.
For me bandwidth is a small-signal parameter, and slew rate is a large-signal parameter. I'm fairly sure I need bandwidth for my application.
You have a LT-Spice simulation, so it should be quite easy to check the actual slew rate and evaluate how close it gets to max. values from the datasheet.
consider the LM195/395, whose integral protection makes them safe to operate in parallel arrangements.
Actually, I evaluated slew rate of tl071 and tl051, check this thread: https://www.eevblog.com/forum/projects/adding-offset-to-comparator-lm311-doesnt-work-the-way-i-expect/msg3365146/#msg3365146 . The results make me thinking that choosing the best opamp requires a lot of practical knowledge, some of it is, probably, not in datasheets. Like, slew rate vs input overdrive.
Or output impedance vs load vs frequency.
changing the circuit has more benefit than using a faster operational amplifier
It is a pity that precision differential pairs are only available in a practical sense as part of operational amplifiers because they are very useful for high performance regulators.
consider the LM195/395, whose integral protection makes them safe to operate in parallel arrangements.
I think they are just darlingtons with ballast resistor bult-in (+some protection circuitry). Do you think they will bring any advantage over a discrete version? (except for less board space). They also have 2V saturation, which is... kinda expected for three transistor, but a lot for my application.
It is a pity that precision differential pairs are only available in a practical sense as part of operational amplifiers because they are very useful for high performance regulators.
Are there op-amps with sink only outputs, or at least a much weaker pull-up, than sink, which work up to 30V? I had a quick look and couldn't find any. There are comparators of course, such as the LM393, but they're uncompensated and difficult to stabilise. It would be nice to be able to connect the outputs together in OR configuration, without diodes.