This circuit is a circuit diagram of a variable power supply. Variable power supply circuit is a simple but reliable one based on an integrated voltage regulator from the eldest LM723. R2 set the output voltage. The maximum flow is determined by the value of R3, the excessive current in the circuit protection senses R3 and LM723 voltage output stage begins to close off this fast voltage approaches 0.65 V. In this way the current through R3 can never exceed 0.65/R3, even if output is shorted. C3 and C4, both ceramic, should be placed as close as possible to the integrated circuit, because the LM723 can be vulnerable to unwanted oscillations. The following is a schematic drawing:
The LM723 works with the input DC voltage V and IC 9,5-40 itself can be the source of about 150 mA if the output voltage is not more than 6-7 V below the input. When the external pass transistor is used (in the usual emitter-follower mode), the base-emitter of T1 is a significant resistance and the output stage of integrated circuits is relatively light load. All the current drawn by the load through a T1 and it decreases the amount of power that is proportional to the current and the difference between input and output DC voltage.