This is a basic universal variable Power Supply voltage regulator circuit using an LM317, 3-terminal regulator in a TO-220package. This small supply is user friendly and fits nicely on my cluttered bench. With adequate input the LM338 makes a fabulous variable power supply. The diodes steer the current around the regulator and into ground, thereby protecting it from damage. Since the current spike may be many amps, the regulator may fail. Without the diodes, if this happens, the capacitors will dump their charge back through the regulator. ![]() Also the output of station supply may be shorted if some other device fails. This is a distinct possibility if using jumpers to attach it to the power supply. Diodes are included to protect the regulator from damage in case the input is accidentally shorted to ground. I chose one that illustrated variable output and included protection diodes. LM338's Data Sheet has several very helpful application notes and circuits. It began as a variable power supply based on an LM338 5A voltage regulator and external power adapter. Or 8 x MR750 (MR7510) diodes (MR750 = 6 Ampere diode) or 16 x 1N5401 (1N5408) diodes.Ĭ2 four times 4700uF/50v or one 22000uF/50vĪfter many years of employing this ugly and clumsy bench power supply, I decided it was time to build something better, smaller and nice looking. Or eight BYW29 8 amp diodes (TO220 pinning cooled) 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.ĭ1.D4= Bridge rectifier MB2504 (25 amps cooled) Or you could use eight BYW29 8 amp diodes (TO220 pinning) mounted on a heat sink. So no delay do to the discharge of C2, and so preventing output voltages from not return to zero immediately.Ī MB2504 is used as it is a 25 ampere rectifier bridge which also should be cooled. The relay is used to switch off the power supply voltage when the mains (S1) are/is switched off. The 2N3055 pass transistor must be mounted on an adequate heatsink.S2 switches between +- 3 Amps and full output current A 1 kOhm output resistor provides stability for the power supply under no - load conditions. A 100uF electrolytic capacitor is used for ripple voltage reduction at the output. Since desired output of the supply is 1 Ampere, maximum current limit is set to 1,5 Ampere by resistor Rsc whose value is 0,422 Ohm. A 100-pF capacitor from pin 13 to pin 4 furnishes gain compensation for the amplifier.īase drive to the 2N3055 pass transistor is furnishes by pin of the uA723. ![]() For fine trimming the output voltage, a potentiometer can be installed between R1 and R2. The reference terminal at pin 6 is tied directly to pin 5, the non inverting input of the error amplifier. The output through R1 and R2, providing about 7 V with respect to ground at pin 4. This applied to pin 11 and 12 of the IC uA723/LM723, as well as to the collector of the 2N3055 series pass transistor. Then receives +20 Volts DC from rectifier / filter section. The supply receive from 220 /120/110 Volt AC, then lowered by the transformer.
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