Experiment 12 - The Adjustable Voltage Regulator LM317

An example of an adjustable voltage regulator is the LM317. It can generate output voltages from 1,25 V to 37 V.

The output voltage of the LM317 can be adjusted using two resistors R1 and R2.

Circuit diagram measurement of the voltage Vout of the LM317.

Circuit measurement of the voltage Vout of the LM317. (Enlarge)

The output voltage V_out is calculated approximately using the formula...

V_out = 1.25 × (1 + ^R2/_R1) + (0.00005 × R2)

With the two resistors R1 = 220 Ω and R2 = 470 Ω you calculate output voltage V_out...

V_out = 1.25 × (1 + ⁴⁷⁰/₂₂₀) + (0.00005 × 470)

     = 3.9 Volt

In the next experiment, you make the LM317 freely adjustable...