PAGE 041 OF 150 · POWERING LEDS
Constant-Current Drivers
A driver holds current steady as voltage changes.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
What a driver does
A constant current driver holds LED current steady regardless of changes in supply voltage or LED forward voltage. It is the right choice for power LEDs.
Types
- Linear drivers regulate by burning off excess voltage as heat. They are simple and quiet.
- Switching drivers, such as buck converters, are more efficient and suit higher power.
Simple example
An LM317 regulator with a resistor between its output and adjust pins behaves as a current source. R = 1.25 ÷ I, so for 350 mA R = 3.6 ohms, dissipating about 0.44 W.
Always check the driver's voltage and current range against the LED.
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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