This 0- to 12-Vdc variable power supply uses an IC voltage
regulator and a heavy-duty transformer to provide a reliable dc power
supply. Looking at the schematic shown, you can sec that transformer Tl
has a 120-V primary and a 28-V secondary. Filtered dc is fed to the
input (pin 2) of the LM317T voltage regulator, IC, which keeps the
voltage at its output constant (pin 3) regardless (within limitations)
of the input voltage.
Pin 1 of the LM317T is the adjustment pin. Varying the voltage on pin 1 (via PI) varies the output voltage. Diodes D5 through D7 and LEDs LI through L3 give an approximate indication of the output voltage. Each LED/diode path has a limiting resistor to limit the current to a level that is safe for the LED.
Build a 0 To 12V, 1A Variable Power Supply Circuit Diagram
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