Regulator Feedback Divider

Vout = Vref · (1 + R1/R2)

Quick answer

This calculator solves Vout = Vref × (1 + R1/R2) for Output Voltage. With Reference Voltage 26.4 V, Top Resistor 10 kΩ, Bottom Resistor 22 kΩ, the result is 38.4 V. It solves in 4 directions, so you can enter the values you have and get the one you need.

Calculator

Output Voltage (V)
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Formula

Vout = Vref × (1 + R1/R2)

Description

Almost every adjustable regulator—LDO or switcher—sets its output by comparing a divided-down sample of the output against an internal reference. The feedback divider R1 (top, output to FB) and R2 (FB to ground) program the output voltage. This formula gives the output for a chosen divider, or the resistor needed for a target output.

Variables

  • Vout — Regulated output voltage (V)
  • Vref — Internal reference voltage (V)
  • R1 — Resistor from output to feedback (Ω)
  • R2 — Resistor from feedback to ground (Ω)

Practical Notes

Keep divider current well above the FB pin bias current (e.g. R2 ≤ 10–100 kΩ) for accuracy, but not so low it wastes power. Add feedforward capacitance across R1 for better transient response.

Symbols and units

Symbol Meaning Default unit Accepted units
Vout Output Voltage V pV, nV, µV, mV, V, kV
Vref Reference Voltage V pV, nV, µV, mV, V, kV
R1 Top Resistor kΩ mΩ, Ω, kΩ, MΩ
R2 Bottom Resistor kΩ mΩ, Ω, kΩ, MΩ

Step by step

  1. 1. What you know: Reference Voltage 26.4 V, Top Resistor 10 kΩ, Bottom Resistor 22 kΩ
  2. 2. The relation: Vout = Vref × (1 + R1/R2)
  3. 3. Substitute: Vref = 26.4 V, R1 = 10 kΩ, R2 = 22 kΩ
  4. 4. Result: Output Voltage = 38.4 V

Related quantities from the same inputs

  • P = V² / R = 69.7 mW
  • I = V / R = 2.64 mA

Worked examples

Minimum range

Given: Reference Voltage 0.726 V, Top Resistor 100 Ω, Bottom Resistor 0.22 kΩ

Result: Output Voltage = 1.056 V

Low range

Given: Reference Voltage 7.26 V, Top Resistor 1 kΩ, Bottom Resistor 2.2 kΩ

Result: Output Voltage = 10.56 V

Typical

Given: Reference Voltage 26.4 V, Top Resistor 10 kΩ, Bottom Resistor 22 kΩ

Result: Output Voltage = 38.4 V

High range

Given: Reference Voltage 0.506 kV, Top Resistor 100 kΩ, Bottom Resistor 0.22 MΩ

Result: Output Voltage = 0.736 kV

Maximum range

Given: Reference Voltage 5.06 kV, Top Resistor 1 MΩ, Bottom Resistor 2.2 MΩ

Result: Output Voltage = 7.36 kV

Solving for each variable

Solve for Output Voltage

Reference Voltage 0.726 V, Top Resistor 100 Ω, Bottom Resistor 0.22 kΩ → 1.056 V

Solve for Reference Voltage

Output Voltage 0.33 V, Top Resistor 100 Ω, Bottom Resistor 0.22 kΩ → 0.2269 V

Solve for Top Resistor

Output Voltage 3.3 V, Reference Voltage 1.55 V, Bottom Resistor 0.47 kΩ → 0.5306 kΩ

Solve for Bottom Resistor

Output Voltage 3.3 V, Reference Voltage 1.55 V, Top Resistor 1 kΩ → 0.8857 kΩ

How Output Voltage changes with Reference Voltage

Reference Voltage (input) Output Voltage (result)
2.64 V 3.84 V
6.6 V 9.6 V
13.2 V 19.2 V
19.8 V 28.8 V
26.4 V 38.4 V
39.6 V 57.6 V
52.8 V 76.8 V
105.6 V 153.6 V
0.1848 kV 0.2688 kV
0.264 kV 0.384 kV

The same result in other units

Unit Value
mV 38400
V 38.4
kV 0.0384

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Frequently asked questions

How do you calculate Regulator Feedback Divider?

Use Vout = Vref × (1 + R1/R2). With Reference Voltage 26.4 V, Top Resistor 10 kΩ, Bottom Resistor 22 kΩ, Output Voltage works out to 38.4 V.

What is the formula for Regulator Feedback Divider?

The formula is Vout = Vref × (1 + R1/R2). Almost every adjustable regulator—LDO or switcher—sets its output by comparing a divided-down sample of the output against an internal reference.

How do you find Reference Voltage when you know the other values?

Rearrange for Reference Voltage: with Output Voltage 0.33 V, Top Resistor 100 Ω, Bottom Resistor 0.22 kΩ, Reference Voltage is 0.2269 V.

How do you find Top Resistor when you know the other values?

Rearrange for Top Resistor: with Output Voltage 3.3 V, Reference Voltage 1.55 V, Bottom Resistor 0.47 kΩ, Top Resistor is 0.5306 kΩ.

What units does Regulator Feedback Divider use?

Output Voltage is shown in mV, V, kV. Values are held in SI base units internally, so you can mix prefixes without converting by hand.

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