0-28V 20A Power Supply (LM317, 2N3055)

S2 switches between +- 3 Amps and full output current The relay is used to switch
off the power supply voltage when the mains (S1) are/is switched off. So no delay
do to the discharge of C2, and so preventing output voltages from not return to zero
 immediately. A MB2504 is used as it is a 25 ampere rectifier bridge which also
should be cooled. Or you could use eight BYW29 8 amp diodes (TO220 pinning)
 mounted on a heat sink. Mount a little heatsink on the LM317 IC Remember to
 isolate the 2N3055 transistors from the chassis/radiator! Use a radiator (heat sink)
of appropriate size and surface area; insulating and heat-conducting spacer or at
least a thin mica; hot adhesive and thermal paste.
* 2 x 15 volt 20+- amps
* D1...D4= Bridge rectifier MB2504 (25 amps cooled) or eight BYW29 8 amp diodes
 (TO220 pinning cooled) or 8 x MR750 (MR7510) diodes (MR750 = 6 Ampere diode)
 or 16 x 1N5401 (1N5408) diodes.
* F1 = 2 Amp
* F2 = 25 amp
* R1 2k2 2,5 Watt
* R2 240 ohm
* R3,R4,R5,R6 0.1 ohm 10 watt
* R7 6k8
* R8 10k
* R9 47 Ohm 1 watt
* S2 mini switch
* R10 8k2
* C1,C7,C9 47nF
* C2 four times 4700uF/50v or one 22000uF/50v
* C3,C5 10uF/50v
* C4,C6,C9 100nF
* C8 330uF/50v
* C10 1uF/16v
* D5 1N4151
* D6 1N5401
* D10 MR750
* D11 LED
* D7, D8, D9 1N4001
* IC1 LM317
* Two 2N3055 transistors
* P1 5k
* P3 10k trimmer
* relay = 30 volts AC, 2x10 amp switching