CIRCUIT BUILD 04 · LEDs & Resistors

Building a Parallel LED Circuit

Why each LED branch in a parallel circuit needs its own resistor, even though they all share the same supply.

You'll need: a DC supply, two or more LEDs, one resistor per LED, and a breadboard.

Wiring LEDs in parallel means each one connects directly across the same two supply rails, independent of the others. Unlike a series chain, every LED here sees the full supply voltage, and — critically — each branch needs its own resistor. LEDs aren't perfectly identical; tiny manufacturing differences mean one LED will always conduct slightly more easily than another. Share a single resistor across parallel LEDs and that slightly-easier LED hogs almost all the current, glowing bright while the others stay dim or dark, and the current through it can rise until it fails.

Size each branch's resistor exactly as you did for a single LED (Lesson cb-02) — the parallel branches don't affect each other's math at all, since each one is really its own independent series loop sharing the same two rails.

This is the standard way to drive several LEDs from one supply — a small "status panel" with three or four independent indicator LEDs is just this pattern repeated.

Two independent branches Same two supply rails, but each LED branch carries its own resistor — never share one resistor across parallel LEDs.

BUILD TIP

In a parallel LED circuit, every branch needs its own resistor — sharing one resistor across parallel LEDs lets small manufacturing differences starve some LEDs and overdrive others.

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