Building Steps
Here the step-by-step procedure to build the triple output DC power supply:
1. Collect all the electronic components displayed in the circuit diagram.
2. Connect switch S1, fuse, transformer and mains cord to the assembled PCB as well as the box.
3. Keep the multimeter in DC voltage range (more than 25V DC) and measure the DC voltage across capacitors C1 and C7 (1000 µF, 35V). This voltage should be around 18V×1.41=25 to 26V DC. Check both positive and negative voltages with respect to ground.
4. It is advisable to use three-wire mains cable and plug. If you are using any metallic box, earthing wire/pin of the mains plug should be soldered to the body of the metallic box using an earthing tag.
5. If the 18V-0-18V transformer is replaced with 15V-0-15V transformer , the output voltage of the variable supply using LM317 will be correspondingly lower.
6. If proper voltages are available, go to step 7. Otherwise, check the connections.
7. Connect variable regulator LM317 to the circuit and check 1.25V to 20V output by varying the 2.2-kilo-ohm linear potentiometers.
8. Now connect ICs 7812, 7912, 7805 and 7905 to the circuit and check their output voltage.
9. Connect terminals, potensiometer, switches and indicator LED on the front panel of the box and complete the connections. Close the box by using screws.
