2012-03-02

Power Supply with Selectable Output

            This simple power supply unit (PSU) uses LM317 IC and can deliver 1.5A current with selectable voltages. Outputs are 1.5V, 3V, 4.5V, 6V, 9V and 12V. The output voltage is controlled only by the resistor combinations. You can use the LM317 calculator to determine these resistor values.
PSU schematic diagram
317 pinout
Part List:
C1 - 2200uF electrolytic capacitor rated 25V
C2, C5 - 100nF Mylar or ceramic capacitor
C3, C5 - 22uF electrolytic capacitor rated 16V
R1, R2, R7 - 120 ohms 1/4W
R3, R4 - 240 ohms 1/4W
R5 - 100 ohms 1/4W
R6 - 20 ohms 1/4W
D1, D2 - 1N4004, 1N4007 or similar silicon diode
317 -  LM317 or similar regulator IC
S1 - rotary switch
DC - see AC to DC converter circuit below
Part List:
Transformer - 220 to 12V center tap rated 15VA minimum
D - Any rectifier diode rated 2A minimum
C - You can omit since we got C1 (2200uF)

Note: I recommend using 220V/15V center tap but excessive heating might occur on when 1.5V is selected and with 1.5A output. The lower the output voltage with higher current, the higher the tendency the LM317 will overheat.

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