The current in the out has instability plays between 10A and 16A
The circuit is also usable as a 3
...30 V (and not 0
...30 V!) 20 A supply I think too.
(to make a 0... xx V supply also a negative voltage is needed ...)
The instability is caused (maybe) by the too big value of the cap C2 (play with smaller values like 500pF, see the datasheets), and ..
I think in this case it's not a good idea the using a big diode seriell with the current limiting resistor R17. This diode's forward voltage has a long time temp drift and this can be caused instability too. Use a well valued pure resistor instead!
There is a big danger: without any output load (or with a small load) the DC input voltage (getting from the 28v AC input) maybe (sure!) exceeded the 40 V limit of the IC. Use a simple Zener circuit to solve it! Study the example apps in datasheets!
For current adjustment to reach 20A you will only need to change the value of R11 a little. Instead of 5K6 you can put 6K8 and can control 20A.
I don't agree! It (the changing of the value of the R11) is unnecessary in this case, with the pot R15 you can set any current limit (to 1000 A :-). The R11's value determined the min.
settable current limit value only).
For some big output current (and for a low output ripple if needed) increase the values of the filter caps C4 and C5 (to 100 000 uF... or more)!
Only according to my opinion...