But indeed the inductor is not at the right place ....It can't be in the primary because any asymetry of the secundary current will apply a dyssimetrical voltage on the primary of the transformer....And asymetrical current occur during transients, when load vary rapidly....
This is why this power supply is basically unstable and the pre-regulator has a tendency to oscillate like a hell, saturate the transformer, consume a primary current of 30 to 50A and blow up the fuses and circuit breakers.
With the years, it gets worse because the capacitor C27 loses its value and then there is no way to prevent it from oscillating
Wat would be the solution of this problem ?
There are two solutions:
- to place the inductance not in serie with primary of the transformer, but in serie with the secundary of the transformer.
- no need of inductance if you use a transformer with high short circuit impedance like MOT.
R108 is a little fussy, if you trim with the output unloaded it starts dropping the output voltage well before you reach zero current. The practical lower limit for R2 will be a few tens of mA.
Current limitation of this power supply is very basic and not intended to work as a precision current source.
It only use a single diferential amplifier and gain is very low.
But it is very stable for this reason and can be very fast ....
The greatest problem of this power supply (0-20V and 0-7V) are the shunt resistors: they are made with thin wires and prone to failure.