Hi prasimix,
I have some remarks
I lookt a your last schematic and i see a
phase lag carnival...Just for the CV mode, working backwards...
IRFP250, gate capacitors, Q2 and R33 of 2k2, better to use a 5 a 10mA current source here or lower R33 to at least 1K
There is enough current available for charge op the gate capacitors, but not to discharge them.
R23 + C9
Extra gain of Q3
C12
R7 + C1
R21 + C11
R36 + C15
C3
R15 + C6
R14 + C15
C4 + R12
Hallelujah
Do you think you can win this fight, to get a stable power supply?
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Some 2 cents of opinion
Make the pass transitor as fast as you can, thus current source, or lower R33.
My best performance setup was a Sziklai Darlinton, 2SA1943 and a 2SC2911.
Always use a capacitor direct on the output therminals, rule of thumb, 50uF/Amp
The better yuor design is, the lower the capacitor value can be.
In your design you put two opamps in series and a extra gain stage Q3, all inside 1 loop...
Almost impossible to get it stable unther "normal" use for a lab power supply.
Probably your current limit is too slow to protect your power fet.
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Just some pictures to make some info more clear.
First some measurements i have done to get the best Ri of my design.
On the top its 1 Ohm, bottum is 1m-Ohm.
The green line is the output filtering impedance
A = Tip142
B = FET PSMN034
C = 1 Compound Darlington
D = Green line impedance output network
F = Dubble Compound Darlington, YESSS! about 17m-Ohm Ri at 100Khz.
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This is a picture that shows current through the Darlington with a fast control loop.
It takes about 10uSec to come back to the set current of 5 Amps.
I dit not like that, so i placed a extra current limiting transistor around the darlington pair.
And this is how it lookt afterward...
Only a peak of 7 Amps, and FAST!
I use normaly about 5 Amps Max/Darlington, this from a 10 Amp design power supply
The extra current limithing circuit looks like this:
I hope you can use some of my remarks :-)
Kind regarts,
Blackdog