Forum Diagram

This power supply is meant as an auxiliary or as a permanent power supply for all common circuits based on a stabilized DC voltage between 3 and 30V provided that the consumption does not exceed 3A. Of course this power supply unit can also be used for other purposes. Be replacing the trimmer by a potentiometer, it may even be used as an adjustable power supply unit. A good quality heatsink must be used.
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Parts list:
R1 = 8.2K
R2 = 2.2K
R3 = 680R
R4 = 1K
R5 = 82K
R6 = 0.18R/5W
C1 = 470p
C2 = 100nF-63V
C3 = 100nF-63V
C4 = 100uF-63V
C5 = 10KuF-60V
D1-D6 = 6.6A
Q1 = MJ3001 (Darligton)
IC1 = UA723D

Specifications:
* Overload protected
* Sshort-circuit stable
* Output current: max. 3A
* Output ripple voltage: 0.5mV
* Output voltage: adjustable from 3 to 30V, stabilized
* Input voltage: 9 to 30V AC (depending on the desired output voltage)

Source: http://www.extremecircuits.net/2010/02/3-30v-3a-adjustable-regulated-dc-power.html