The adjustable voltage regulator LM317
can supply 1.5 A at an output voltage of 1.2 V ... 37 V. In contrast to the fixed voltage regulators
of the 78xx family, where the reference voltage U r is related to ground, U r
at the LM317 to the output voltage U out . This offers the possibility, with only three connectors
and set the output voltage using two resistors (see circuit below). Since U r
for the LM317 always 1.25 V, applies to the output voltage U out = 1.25 * (1 + R2 / R1)
R1 should have a value of 240 ohms. The marked diode 1N4001 protects the regulator if the
The output voltage should be higher than the input voltage (for example, when switching off when the
Output side "thick" cones in the circuit). The DIode can also be omitted.
Only two external resistors are required to adjust the output voltage. Click on the button
Radiobutton can be between calculation of the output voltage (input R1 and R2) or the resistor
R2 (input R1 and output voltage) can be selected.
Alternatively, the normally-ground reference pin of a fixed-voltage regulator can also be switched over
a voltage divider "lifted" and thus also with a fixed voltage regulator different voltages than
the printed ones are generated. To avoid oscillations, a capacitor can be connected parallel to R2
(also with the LM317). Please also take into account the occurring power loss (cooling)
of the voltage regulator.