LM 317 Power Supply


LM317 Power Supply Circuit

The output is adjustable between 1.25 and 13.5 Volts with a maximum current limit of 1.5 Amps. The LM317K regulator is internally protected from current and thermal overloads. A heat sink will be required for most applications however.

lm 317 regulator IC power supply circuit

R1 220 Ω
R2 2 KΩ Variable Resistor
C1 3300 µf 50v
C2 10 µf 25v
C3 1 µf 25v
C4 0.1 µf
D1 100V 5A bridge rectifier
D2 IN 4007
D3 IN 4007
IC1 LM 317
T1 18 VAC 2AMP
F 250mA

The values of R1 and R2 are not critical but R1 should not be larger than 270 ohms. For a fixed voltage output R2 should be selected to give the desired maximum output voltage for a given R1 value. See the calculation on the drawing.

lm-317-ic lm-317-pinout
LM 317 regulator IC LM 317 PinOut

The diodes D2 and D3 in the circuit prevent damage to the regulator during certain adverse conditions such as the output voltage being higher than the input voltage to the regulator or the capacitor across R2 from discharging through the adjustment terminal of the regulator. These conditions will be rare but ten cents worth of protection can save the cost of a new regulator.


An Ammeter could be added to the circuit by placing it between the filter capacitor and the input terminal of the regulator.

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