This is definitely an effective 4-output stage stabilized DC power supply unit for testing electronic circuits. It delivers very well regulated and stabilised output, that is important for most electronic circuits to provide good results. The circuit gives you an audio-visual indication if there is a short circuit in the PCB under test, so the power supply to the circuit ‘under test’ could be cut-off instantly to protect the important components from damage. The circuit gives you four different regulated DC outputs (12V, 9V, 6V and 5V) and an unregulated 18V DC output, that are selectable by way of rotary switch S2. The selected output is showed on the analogue voltmeter connected to the outputs rails. The circuit works by using a typical 18V-0-18V, 500mA step-down transformer to deliver 18V AC. A rectifier diode comprising diodes D1 and D2 supplies 18V DC, that is smoothed by capacitor C1 and given towards the combination of regulator ICs (IC1 through IC4). The regulator ICs deliver ...