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f-alpha.net » Electronics » Integrated Circuits » Voltage Regulator » Let's go... » Experiment 12 - Adjustable VR

Experiment 12 - The Adjustable Voltage Regulator LM317

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

Attention!

The connectors of the LM317 are different from those of the voltage regulators 78xx and LM2940!

Circuit diagram measurement of the voltage Vout of the LM317.

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

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

Vout = 1.25 × (1 + R2/R1) + (0.00005 × R2)

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

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

     = 3.9 Volt

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

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