Resistive Level Shifter Ratio

R1/R2 = (Vin − Vout) / Vout

Quick answer

This calculator solves R₁/R₂ = (V_in − V_out) / V_out for R1/R2 Ratio. With Input (Higher) Voltage 12 V, Output (Lower) Voltage 26.4 V, the result is -0.5455. It solves in 3 directions, so you can enter the values you have and get the one you need.

Calculator

R1/R2 Ratio
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Formula

R₁/R₂ = (V_in − V_out) / V_out

Description

A resistive voltage divider can shift a higher-voltage logic signal down to a lower-voltage logic level (e.g., 5 V to 3.3 V). The required resistor ratio is determined by the input and output voltages. This is a simple and cost-effective unidirectional level shifting method suitable for low-speed signals. The output impedance of the divider limits the maximum signal frequency due to the capacitive loading of the receiver input. For bidirectional level shifting or high-speed signals, use dedicated level-shifting ICs or MOSFET-based circuits.

Variables

  • R₁/R₂ — Ratio of upper to lower resistor
  • V_in — Input logic high voltage (V)
  • V_out — Desired output logic high voltage (V)

Practical Notes

For 5 V to 3.3 V: ratio = (5−3.3)/3.3 ≈ 0.515. Use R1 = 1 kΩ, R2 = 2 kΩ (ratio = 0.5, Vout = 3.33 V). Keep total resistance low enough (1-10 kΩ) for adequate speed, but high enough to avoid excessive current from the driver. The rise time through the divider is approximately 2.2 × (R1‖R2) × C_load. This method only works for unidirectional high-to-low translation. For low-to-high or bidirectional, use a BSS138 MOSFET level shifter or a dedicated IC like TXB0108.

Symbols and units

Symbol Meaning Default unit Accepted units
ratio R1/R2 Ratio — —
Vin Input (Higher) Voltage V pV, nV, µV, mV, V, kV
Vout Output (Lower) Voltage V pV, nV, µV, mV, V, kV

Step by step

  1. 1. What you know: Input (Higher) Voltage 12 V, Output (Lower) Voltage 26.4 V
  2. 2. The relation: R₁/R₂ = (V_in − V_out) / V_out
  3. 3. Substitute: Vin = 12 V, Vout = 26.4 V
  4. 4. Result: R1/R2 Ratio = -0.5455

Worked examples

Minimum range

Given: Input (Higher) Voltage 0.33 V, Output (Lower) Voltage 0.726 V

Result: R1/R2 Ratio = -0.5455

Low range

Given: Input (Higher) Voltage 3.3 V, Output (Lower) Voltage 7.26 V

Result: R1/R2 Ratio = -0.5455

Typical

Given: Input (Higher) Voltage 12 V, Output (Lower) Voltage 26.4 V

Result: R1/R2 Ratio = -0.5455

High range

Given: Input (Higher) Voltage 0.23 kV, Output (Lower) Voltage 0.506 kV

Result: R1/R2 Ratio = -0.5455

Maximum range

Given: Input (Higher) Voltage 2.3 kV, Output (Lower) Voltage 5.06 kV

Result: R1/R2 Ratio = -0.5455

Solving for each variable

Solve for R1/R2 Ratio

Input (Higher) Voltage 0.33 V, Output (Lower) Voltage 0.726 V → -0.5455

Solve for Input (Higher) Voltage

R1/R2 Ratio 0.025, Output (Lower) Voltage 0.726 V → 0.7441 V

Solve for Output (Lower) Voltage

R1/R2 Ratio 0.025, Input (Higher) Voltage 0.33 V → 0.322 V

How R1/R2 Ratio changes with Input (Higher) Voltage

Input (Higher) Voltage (input) R1/R2 Ratio (result)
1.2 V -0.9545
3 V -0.8864
6 V -0.7727
9 V -0.6591
12 V -0.5455
18 V -0.3182
24 V -0.09091
48 V 0.8182
84 V 2.182
120 V 3.545

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Frequently asked questions

How do you calculate Resistive Level Shifter Ratio?

Use R₁/R₂ = (V_in − V_out) / V_out. With Input (Higher) Voltage 12 V, Output (Lower) Voltage 26.4 V, R1/R2 Ratio works out to -0.5455.

What is the formula for Resistive Level Shifter Ratio?

The formula is R₁/R₂ = (V_in − V_out) / V_out. A resistive voltage divider can shift a higher-voltage logic signal down to a lower-voltage logic level (e.g., 5 V to 3.3 V).

How do you find Input (Higher) Voltage when you know the other values?

Rearrange for Input (Higher) Voltage: with R1/R2 Ratio 0.025, Output (Lower) Voltage 0.726 V, Input (Higher) Voltage is 0.7441 V.

How do you find Output (Lower) Voltage when you know the other values?

Rearrange for Output (Lower) Voltage: with R1/R2 Ratio 0.025, Input (Higher) Voltage 0.33 V, Output (Lower) Voltage is 0.322 V.

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