LED string / array calculator
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Circuit values
LED string results
Total forward drop
Vf × LEDs in series
Series resistor (per string)
(V − series drop) ÷ If
Resistor power (per string)
If²·R — pick a part rated at ~2×
Total supply current
If × parallel strings
Total power
Vsupply × total current
About the model
Each LED in series adds its forward voltage, so the string drop is Vf × N and the series resistor sees the supply voltage minus that drop. Parallel strings share the supply current — the supply must deliver If × (number of strings). A separate resistor per string is safer than one shared resistor, because a shared resistor cannot balance small Vf differences between strings.
This assumes a constant Vf. Real LEDs shift forward voltage with temperature and batch, so use the datasheet curve for a production design and rate the resistor at roughly 2× its dissipation.
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