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Voltage Regulator Resistor Divider Calculator
This calculator helps determine resistor divider values for adjustable voltage regulators. It can calculate output voltage from R1 and R2, or calculate the required R2 value from a target output voltage. It is useful for LM317-style regulators, adjustable LDOs, and feedback-divider based DC-DC converters.
Input Parameters
Results
For adjustable regulators, R1 is typically connected from output to adjust/feedback, and R2 is connected from adjust/feedback to ground.
Equations Used
Output Voltage:
Vout = Vref × (1 + R2 / R1) + Iadj × R2
Required R2:
R2 = (Vout - Vref) / (Vref / R1 + Iadj)
Where:
Vout = regulator output voltage
Vref = regulator reference voltage
R1 = resistor from output to adjust or feedback pin
R2 = resistor from adjust or feedback pin to ground
Iadj = adjust pin current
Frequently Asked Questions (FAQ)
Q1: What does this calculator do?
It calculates the output voltage of an adjustable regulator from R1 and R2, or calculates the required R2 value from a target output voltage.
Q2: What are R1 and R2 in a voltage regulator divider?
R1 is usually connected from the output to the adjust or feedback pin. R2 is usually connected from the adjust or feedback pin to ground.
Q3: Why does Iadj matter?
Iadj is the adjust pin current. In some regulators it slightly increases the output voltage, especially when R2 is large.
Q4: Can this be used for DC-DC converters?
Yes. Many adjustable buck, boost, and LDO regulators use a similar feedback divider formula. Set Vref according to the regulator datasheet.
Q5: What R1 value should I use?
Common LM317 designs often use 240Ω for R1. For switching regulators, use the datasheet recommendation to balance feedback current, noise immunity, and power loss.
Q6: Why check resistor power?
The divider resistors dissipate power continuously. Power calculation helps select resistor ratings with proper safety margin.
