This is the schematic of the 30V/2A power supply I use in my own lab.It may look very complex, but it really isn’t very difficult to understand: it uses only the knowledge we’ve learned in the previous lessons.
The top part looks like the power supply we built in Lesson 7: the transformer L1 transforms the outlet voltage to a safe 30V, which is rectified by bridge rectifier G2 and smoothed by capacitor C5. Transistors T3 and T6 form a darlington transistor. This darlington replaces transistor T1 in Lesson 7. However, the base voltage is not controlled by a simple potmeter, but by an ‘electronic potmeter’ with voltage feedback. The advantage of this feedback is a load-independent output voltage.
Read more original source:
http://www.hobby-electronics.info/go.php?to=11000