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LM317 / LM338 / LM350 Voltage and Current Regulator Calculator

LM317 / LM338 / LM350 Voltage Regulator Calculator

You can use this Voltage Regulator Calculator to vary the value of the program resistor (R₁) and output set resistor (R₂) and calculate the output voltage for the LM317 / LM338 / LM350 family of three terminal adjustable regulators. This Voltage Regulator Calculator will work for most voltage regulators with a reference voltage (V_REF) of 1.25. Typically, the program resistor (R₁) is 240 ohms for the LM117, LM317, LM138 and LM150 regulators. For the LM338 and LM350 regulators, 120 ohms is typically used for R₁. However, other values such as 150 or 220 ohms can also be used for R₁. Refer to the adjustable regulator data sheets below for more information about these voltage regulators.

Figure 1: Typical LM317 / LM338 / LM350 Voltage Regulator Schematic

To determine the output voltage, enter values for the program (R₁) and set (R₂) resistors and hit the "Calculate" button.

NOTE: this online voltage regulator calculator requires that JavaScript be enabled on your browser.

LM317 / LM338 / LM350 Current Regulator Calculator

You can use this Current Regulator Calculator to vary the value of the program resistor (R₁) and calculate the output current from the LM317 / LM338 / LM350 family of three terminal adjustable regulators. This Current Regulator Calculator will work for adjustable regulators with a reference voltage (V_REF) of 1.25.

Figure 2: Typical LM317 Current Regulator Schematic

To determine the output current from the regulator, enter a value for the program resistor (R₁) in ohms and press the "Calculate" button. This will calculate the Output Current in Amperes and the amount of Power Dissipated across R₁ in Watts.

NOTE: this online current regulator calculator requires that JavaScript be enabled on your browser.

3-Terminal Adjustable Regulator Data Sheets

• LM117 / LM317 1.5A Adjustable Regulator Datasheet - (PDF 464kB)
• LM138 / LM338 5A Adjustable Regulator Datasheet - (PDF 397kB)
• LM150 / LM350 3A Adjustable Regulator Datasheet - (PDF 409kB)

DIY Projects using Voltage and Current Regulators

• Simple Low Resistance Test Jig with LM317 - (external link)
• IRF610 MOSFET / LM317 CCS Class A Headphone Amplifier
• EL84 (6BQ5) Push-Pull Tube Amplifier with LM317 CCS
• KT88 Push-Pull Tube Amplifier with LM317HV CCS
• KT77 Push-Pull Tube Amplifier with LM317HV CCS