PCB Tools

Trace width for a given current, and the series resistor for an LED. Two calcs you reach for on every board.

Trace width — IPC-2221

Current (A)

Temp rise (°C)

Copper weight

Layer

Minimum trace width

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IPC-2221 derating. Internal traces need ~2× the width of external for the same current. Add margin for long runs and reliability.

LED series resistor

Supply voltage (V)

LED forward voltage (V)

LED current (mA)

Resistor

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Power dissipated

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Use rating

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Common LED Vf: red ~1.8–2.2, yellow/green ~2.0–2.4, blue/white ~3.0–3.4. Pick the nearest standard resistor at or above the calculated value.