6A/0-28V variable power supply circuit diagram

The figure below is a schematic diagram of a variable power supply with a current output of 6A or 8A and an output voltage of 0~28V.

Component list:

Circuit description:

This is an easy-to-make power supply with a reliable, clear, and regulated 0 to 28 volt 6/8 amp output voltage. By using two 2N3055 transistors you will get twice the amount of current.

Although the 7815 power conditioner may trip during short circuits, overloads, and overheating, the fuse in the main part of the transformer and fuse F2 on the output side will protect your power supply. The rectified voltage measured on C1 is: 30 volts x SQR2 = 30 x 1.41 = 42.30 volts. Therefore, all capacitors should be rated for 50 volts. NOTE: If 1 of the transistors should blow, the output voltage will be 42 volts.

P1 allows you to "regulate" the output voltage between 0 and 28 volts. The minimum voltage for the LM317 is 1.2 volts. To make the output voltage zero I placed 3 diodes D7, D8 and D9 around the output with the LM317 towards the base with the 2N3055 transistor. The optimal output voltage of LM317 is 30 volts, but using diodes D7, D8 and D9, the output voltage is about 30v – (3x0.6v) = 28.2v.

Use the P3 to adjust your built-in voltmeter, of course a fine digital voltmeter is a better solution.

P2 will give you the best available current control limit in output +Vcc. When using a 100 ohm/1 watt varistor, the current is limited to approximately 100 ohms/1 watt. 3 amps @ 47 ohms and +-1 amps @ 100 ohms.