This power supply is designed for general purpose use. Advantages of the circuit are first the voltage can be adjusted from 0V to greater and second it does not require a double sided secondary winding transformer.
For high voltage outputs you can use L146 or alternatively if you need lower voltage outputs you can use IC 723. Although output current limit is variable, it will be fixed after adjusted. In the table, suitable component values are listed for three different cases (max. outputs: 30V, 40V and 60V).
Regulation voltage for both integrated circuit is at least 2V. R3, R4, R5 and R6 resistors prevent this limitation and keep the output voltage at 0 level with the help of P2 potentiometer. If the input voltage is less than required, this resistors provides sufficient potential between 4 and 5 numbered pins.
When the necessary output voltage is less than the tolerance of the regulator’s minimum value, than potential at 4 and 5 are less. This situation causes the IC balance the output voltage by using 9 numbered pin.
However 9 numbered pin is grounded through R7 and D2, it limits the voltage increase. But current increases too and R7 limits it to 6mA. Current entering to 11 numbered pin and passing through 9 numbered pin causes voltage drop on P1. So Tr3 is got conduction by Tr2.
Visit Here for more.