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LM317 voltage regulator circuit

Short answer

The LM317 is a 3-terminal adjustable positive regulator. Vout = 1.25(1+R2/R1) with R1=240 Ω and R2 a potentiometer. Place 0.1 µF input bypass and 1 µF output capacitors. Input voltage must be at least 3 V above Vout. The IC provides internal current limiting and thermal shutdown.

Draw a voltage regulator circuit using IC LM317.

            +--------------+
 Vin o--+---| IN       OUT |---+------+--o Vout
        |   |    LM317     |   |      |
      [C1]  |     ADJ      | [R1]   [C2]
        |   +------+-------+   |      |
       GND         +-----------+     GND
                   |
                 [R2] (pot)
                   |
                  GND
  • LM317 is a three-terminal adjustable positive voltage regulator (IN, OUT, ADJ), giving 1.25 V to 37 V at up to 1.5 A.
  • It maintains Vref = 1.25 V between OUT and ADJ. The current Vref/R1 flows through R2, so

Vout = 1.25 (1 + R2/R1) + Iadj R2, with Iadj ≈ 50 µA.

  • R1 = 240 Ω (120 to 240 Ω) and R2 is a potentiometer. Changing R2 changes Vout.
  • C1 (0.1 µF) is the input bypass capacitor and C2 (1 µF) the output capacitor. Vin must be at least 3 V above Vout.
  • The IC has internal current limiting and thermal shutdown.

✓ Answer checked by Claude Opus 5.5 (high effort)

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