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Voltage Divider Calculator

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Overview

A voltage divider is one of the most fundamental circuits in electronics. Two resistors in series split a supply voltage (Vin) into a smaller output voltage (Vout) tapped between them.

This MicroSim has two modes:

Mode Description
Find Vout Set Vin, R1, R2 → see the resulting output voltage
Find R2 for target Set Vin, R1, and your desired Vout → get the required R2 value

The Voltage Divider Formula

\[V_{out} = V_{in} \times \frac{R_2}{R_1 + R_2}\]

In "Find R2" (inverse) mode the formula is rearranged:

\[R_2 = R_1 \times \frac{V_{out}}{V_{in} - V_{out}}\]

Controls

Control Range Notes
Vin 1 – 24 V Supply voltage
R1 100 Ω – 100 kΩ Log scale
R2 100 Ω – 100 kΩ Log scale; active in Find Vout mode
Target Vout 0.1 V – 0.99 Vin Active in Find R2 mode

R1 and R2 use a logarithmic scale so small values (hundreds of ohms) and large values (tens of kilohms) are equally accessible on the slider.

Learning Objectives

After using this simulation, students will be able to:

  • Implement a voltage divider to produce a target output voltage (Bloom L3 — Apply)
  • Explain how changing R1 or R2 affects the voltage ratio
  • Recognise practical constraints (minimum and maximum resistance values)
  • Calculate current draw and power dissipation for a divider design

Key Observations

  1. Ratio, not absolute values: Vout depends only on the ratio R2/(R1+R2). Doubling both resistors keeps Vout the same but halves the current.
  2. Loading effect: This simulation shows the unloaded divider. A load in parallel with R2 will pull Vout down.
  3. Power trade-off: Lower resistances give a stiffer divider (better load regulation) but waste more power.
  4. Impractical R2 warning: If the required R2 falls below 10 Ω or above 10 MΩ, the simulation flags it as impractical.

Lesson Plan

Duration: 20 minutes
Bloom Level: Apply (L3)

Phase Activity
Warm-up (3 min) Predict: "If R1 = R2, what is Vout/Vin?"
Explore (7 min) Use Find Vout mode — vary R1 and R2, observe the voltage bar
Apply (7 min) Switch to Find R2 mode — design a 3.3 V divider from 5 V, then a 1.8 V divider
Reflect (3 min) Compare current and power for two designs that both produce 6 V from 12 V

References