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Analog challenge:High power/high speed amplifier for physics experiment

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Mazo:
Hello everybody,
I am tasked with designing an amplifier for physics experiment and I would be very glad to hear all opinons and receive help  :-+
Summarised the device should fit in the following.

Powered by 30-100V(+- so 60-200V)
Output current up to 4-5A
Output voltage swing->Not of high importance,anything reasonble will suffice
Gain-everything above 20dB(voltage gain) is acceptable.
Now the hard part-it should do all that @0Hz-1MHz output frequency(pure sine).
Some gain droop is acceptable.
Harmonic distortion should be low(say below a few %)
Operating into an coil placed on a wildely varying magnetic materials so the load impedance is inductive...ish.(Load isolation resistor?)
The expected load indutance range is ~20-200uH

All requirements aren't set in stone so feel free to deviate a little.

What have I thought about for the moment:
GaN based class D amplifier switching at ~2.5-3MHz and a very good output filter-Hard to implement(I have zero experience with GaN) and blows the budget as the device should be relatively low cost-ish(think a few hundred EUR(USD))
Classical voltage feedback discrete amplifier as in a audio amplifier-out of the question as required GBWP is in the order of 10-100MHz :phew:
Open loop amplifier(Harold Black doesn't like this  :D ) -Hard to get linearity out of?
Current feedback topology of some kind using either discrete only devices or a "boosted" op-amp:
What I think is the best version for now:

The output is the big "+" at the middle the op-amp is the LT1818 and the trannies are non standard LTspice models,otherwise I would have provided the sim.(It is slow as hell anyway)
Any values you see are gut sense based for now ;D

Any ideas and suggestions are welcome.
P.S All parts even obsolete are ok(if one can still find them) since it is a one-off.

Wimberleytech:
What output voltage swing are you expecting?  <nevermind...I see you want rail-rail>>

BTW, 4-way connections are a bad drafting practice.

Kleinstein:
The requirements don't look that unusual. So rather similar to a slightly faster Hifi amplifier.
The only unusual part would be the variable power supply and the idea to get close to the rails. This would normally be things not important for a one off. Who cares about a few 10 W of extra heat in such a case.
4-5 A is not such a high current.

My suggestion would be a more or less normal class AB amplifier, just with slightly fast transistors. No need to go exotic, just the regular better audio ones.

An inductive load is not a problem for voltage driving. The tricky part would be of the coil/ load shows self resonance.
An inductive load may only need a little bit more care with the SOA - here it helps the current is not that high.

pwlps:
Your specs look similar to those of MRI gradient amplifiers. Googling for "MRI gradient amplifier" I see many papers, you might find some inspiration there.

duak:
I expect the output stage will have thermal runaway issues.  The idle current in the output stage is a function of the quiescent current  of U11 and the temperatures & VBEs of Q13, Q16, Q6 to Q10 and Q1 to Q5.  Forward biased diodes in series with R15 & R16 as well as R13 & R14 would help but may require rethinking their values.  I might consider temperature compensated current sinks/sources to replace these resistors. 

R1 to R10 may also be a bit low to help current sharing among the devices in the output stage.

Q13 & Q16 have to stand off almost the full supply rail to common voltage and thus dissipate extra power for no reason.  I would reduce their VCEs to a much lower value.  Perhaps use the cascode CB base bias voltage?

In the end, the slew rate of the output stage is established by how much current can be quickly driven into and taken out of the bases of the output devices.  The driver stage may need voltages outside of the rails or to accept a lower output voltage swing to speed up the turning off of the output devices.  It may be possible to use peaking capacitors, inductors or even T-coils to help.

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