Current Dividers: The Mirror of Voltage Dividers
Current splits across parallel paths — and the formula is the opposite of what you'd expect
If voltage dividers split voltage, current dividers split current. They're the mirror image — and once you see the connection, you'll never confuse them again.
The Big Idea
A current divider has multiple resistors in parallel. Current enters the junction and splits across the available paths. The wider the path (lower resistance), the more current flows through it.
Current divider = current splits across parallel paths. More current flows through the path with less resistance.
Think of a highway splitting into multiple lanes. The widest lane (least resistance) gets the most traffic.
The Formula
For two resistors in parallel:
I₁ = I_total × R₂ / (R₁ + R₂)
I₂ = I_total × R₁ / (R₁ + R₂)
Notice something? It's almost the voltage divider formula — but swapped. In a voltage divider, the bigger resistor gets more voltage. In a current divider, the smaller resistor gets more current.
This makes physical sense: wider pipe (lower resistance) lets more water flow through it.
Why the Formula Is Swapped
Voltage dividers are series circuits (same current, split voltage). Current dividers are parallel circuits (same voltage, split current).
In parallel, both resistors see the same voltage. By Ohm's Law (V = IR), if V is the same, then I = V/R. Lower R → higher I.
Quick check: If R₁ = R₂, each gets half the current. If R₁ is half of R₂, R₁ gets twice the current. Half the resistance = twice the flow.
Voltage vs Current Divider
| Property | Voltage Divider | Current Divider |
|---|---|---|
| Configuration | Series | Parallel |
| Splits | Voltage | Current |
| Bigger R gets | More voltage | Less current |
| Formula | R₂/(R₁+R₂) | R_other/(R₁+R₂) |
Where Current Dividers Show Up
- BJT transistor biasing: Base current is a fraction of emitter current
- Ammeter shunts: A low-value resistor diverts most current away from the meter
- Current mirrors: One current "mirrored" to another branch
- LEDs in parallel: Brightness depends on how current divides
Originally published at https://cliovlsi.github.io/circuit-intuition/articles/current-divider-intuition.html
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