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This is adjustable elctronic fuse that can be used to protect power supplies from short circuits or can be also used to limit the current usage. It can be adjusted for currents from 100mA up to 4.3A.

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

This is an easy to make power supply which has stable, clean and regulator 0-28V 6/8 Amp output voltage. By using two 2N3055 transistors we become more then 2 times the amount of amps then the power supply delivers, making it real though to brake ;). Although you could use this design to deliver 20 amps (with almost no modifications and with a proper transformer and a huge heat sink with a fan), I did not needed such much power. Make sure you mount them on a huge heat sink, as the 2N3055 transistors can get very hot at full load.

This is High current and Adjustable Volt 0 to 30V 20A. It easy circuit and nice circuit, Because use IC LM338 and IC 741. Volt Output adj by VR1-1K. IC LM338 to hold heat-sink. Transformer is 20A up.

After many years of employing this ugly and clumsy bench power supply, I decided it was time to build something better, smaller and nice looking. It began as a variable power supply based on an LM338 5A voltage regulator and external power adapter. LM338's Data Sheet has several very helpful application notes and circuits. I chose one that illustrated variable output and included protection diodes. Diodes are included to protect the regulator from damage in case the input is accidentally shorted to ground. This is a distinct possibility if using jumpers to attach it to the power supply. Also the output of station supply may be shorted if some other device fails. Without the diodes, if this happens, the capacitors will dump their charge back through the regulator. Since the current spike may be many amps, the regulator may fail. The diodes steer the current around the regulator and into ground, thereby protecting it from damage. With adequate input the LM338 makes a fabulous variable power supply. This small supply is user friendly and fits nicely on my cluttered bench.

This is a 1.2 - 12 V, max 1A power supply with a low voltage indicator LED. The indicator part incluedes three diodes and one LED. For example you are charging a battery, you can observe the charge status at that moment. Another advantage of this circuit, when the drawn current exceeds 1A (practically 0.85A), the current protector in LM317 intervens and LED indicator warns you about the very low output voltage. Be careful while choosing the transformer. Most of the products are specified as 10VA but their outputs are not as said. Another good property of this circuit is the mains noise does not pass to the DC part.

This is very simple 1.2 - 36V adjustable bench power supply with 5A of output current. Max input voltage is 37V and output is adjustable via potentiometer between 1.2 up to 36 volts. TIP147 PNP darlington transistor boosts the current of LM317 from 100mA to 5A. LM317 is the most useful and inexpensive adjustable regulator and for this circuit you can also use LM317L that can give 100mA, that's enough for transistor bias. D1 and D2 are protection diodes because when you turn the circuit off the output capacitors are discharging and can damage the transistor or regulator.

This is a LM338 based power supply which is not complicated and easy to build. I am using the supply for a long time, have no problem yet. Only current adjust is missing but I overcome this situation by using an LCD panel ampermeter. There is no PCB for the circuit. I took a 3x16 copper plate and strip the unused areas by a knife. If you want you can use analog meters instead of LCD panels.

This is a basic universal variable Power Supply voltage regulator circuit using an LM317, 3-terminal regulator in a TO-220package. The Universal Power Supply output voltage can be set to anywhere in the range 1.5V to 30V by selecting two resistances. By using a potentiometer, R2, as one of the resistors you can dial up the output voltage wanted. Either AC or DC input can be supplied to the PCB via a socket or terminal block. Connection can be either way around. This is because we have provided a bridge rectifier on board. The input DC voltage to the regulator must be at least 2.5V above the required output voltage. An off/on switch is provided. For many applications (say 12V at 60mA) a heat sink will not be necessary. The LM317 will provide slightly higher output voltages than 30 volts. However, for most hobbyists over 30V will not be needed. So to make a small PCB we have used some electrolytic capacitors rated to 35 volts. To be safe for continuous operation the maximun input DC voltage to the regulator should not be over 33V. With a 2.5V to 3.0V drop across the regulator this will give a regulated output of 30V. You can draw up to 1.5A from the LM317. If you need higher then use an LM338T rated to 5A.

Here is a simple and economical 10A variable power supply with 1.2-30V. LM317 have been used to drive 3 NPN TIP41C transistors (or three 2N3055). Nothing to say about the project, it is really simple. The main supply must be connected to a rectified source (transformer + 20-30A bridge rectifier). For Q1,2 and 3 can be used any power TO220 transistor (TIP132C,TIP41C etc) or three external 2N3055 transistors.