7 High current variable power supply (1.2V to 30V at 5A)

We are going to design a simple, very cheap, high power, variable power supply unit (PSU) with current control or protection. Diagram below is our design basis. We have three main parts, the voltage regulator, current amplifier, and current controller. Voltage regulator is the one that controls the variable voltage output, which in our case LM317 IC. Current amplifier is an add-on circuit component that boosts the output current. Current controller is the circuitry that protects the entire power supply unit from short circuits and overloading. You can use either ordinary fuse or current limiter circuit as your current controller.
PSU design
Power supply unit below is rated 150W and has an output current of 5A. Output voltage can be varied from 1.2V up to 30V DC, thus very suitable as power source of your electronic projects, devices, battery chargers and others.
High power PSU schematic diagram
Circuit Operation:
DC input is a 35VDC using AC-DC converter below. R1, Q1, and Q2 limits the maximum to 5A (read more on how current limiter works). Q3 and R3 is the current booster that increases the current capacity of LM317 regulator. R4 is the potentiometer that controls the output voltage from 1.2V to 30V (see LM317 calculator to know how these output voltages are arrived).
Part List:
R1 - 0.15 ohms resistor 10W
R2 - 1.8 kilo-ohms 1W
R3 -  4.7 ohms 1/2W
R4 - 5 kilo-ohms potentiometer
R5 - 220 ohms 1/4W
Q1 - 2N4403 or any general purpose PNP transistor
Q2 - IRF4905 power FET or similar power PMOS
Q3 - MJE2955t or similar PNP power transistor
C1 - 220uF electrolytic capacitor rated 50V
C2 - 22uF electrolytic capacitor rated 50V
LM317 - regulator IC
DC input - regulated 35V DC (see AC-DC converter circuit below)

Part list diagrams: click to enlarge
LM317 pin
IFR4905 pins
MJE2955t pins
 The DC input
AC-DC converter
Converter Part List:
X'former - 220V/27V-0V-27V center tap transformer min 180VA
D - rectifier diode min 6A current rating
C - 1000uF electrolytic cap 50V (higher capacitance the better)
Fuse - 1A @ 220V

Similar variable PSU projects:
1. Simple variable PSU - (+1.2V to +28V at 1.5A) positive output
2. Negative variable PSU – (-1.2V to -28V at 1.5A) negative output
3. Dual variable PSU – two outputs positive and negative @ 1.5A, from 0V to 28V