PAGE 043 OF 150 · POWERING LEDS
What Happens Without a Resistor
Current rises unchecked and the LED can burn out in moments.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
What goes wrong
With no limiting resistor, the only things restricting current are the supply's own capability and the LED's small internal resistance.
Results
- On a bench supply or mains adaptor, the LED can pass far more than its rating and fail in an instant.
- On a weak coin cell it may survive briefly, because the cell cannot deliver much current.
- Even if it survives, the LED may be dim later because the chip is damaged.
Rule
Never connect an LED directly to a supply unless a driver or resistor sets the current.
REMEMBER
The resistor sets the current, so the resistor sets the safety.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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