LM317T Resistor Calculator

This LM317T resistance calculator also works for the LM317 and equivalent LM217 voltage regulators. It computes the values of the resistors R1 and R2 required to produce the desired voltage. The absolute maximum input voltage this device can handle is 40 V, and the output range is 1.25 V to 37 V and 1.5 A maximum current. This regulator also requires 3 V headroom, which means that the input voltage must be 3 V higher than the output voltage for sufficient line regulation. A very basic circuit requires the addition of a potential divider (PD) consisting of R1 and R2 for programming the device to produce the desired regulated output voltage.

Calculate R2, given Vout and R1

In this part of the calculator, enter the desired output voltage required (Vout) in volts, and an arbitrary value for R1 in ohms. The default value of R1 is usually around 1 kΩ.

Calculate Vout, given R1 and R2

This will calculate the value of Vout given standard values of R1 and R2. This is useful when you are experimenting with different values of resistors from the E24 Series.

Voltage Regulator Circuits -- Examples

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