PAGE 049 OF 150 · WIRING LEDS
Why Each Parallel LED Needs a Resistor
Slight LED differences cause uneven current sharing.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
The problem
LEDs of the same type still differ slightly in forward voltage. Wired in parallel with one shared resistor, the LED with the lowest voltage takes more current than the others.
What follows
- A difference of just 0.1 V can change the current a lot.
- The hungry LED heats up, its voltage falls further and it takes even more current.
- It may fail, pushing extra current onto the others.
Solution
Give every parallel LED its own resistor. The resistor evens out the differences because it dominates the current calculation.
REMEMBER
In series the same current flows through every LED.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
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