PAGE 134 OF 150 · POWER SUPPLIES & BATTERIES
Heat Sinks for Power LEDs
Heat sinks move heat away from the LED chip.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
Why heat sinks
Power LEDs turn a good part of their input into heat at a small chip. A heat sink spreads it into the air so the chip stays cool.
Choosing
A 3 W LED making about 2.1 W of heat, with a 25 degree room and a target of 60 degrees at the board, allows a rise of 35 degrees. The heat sink must be no worse than 35 ÷ 2.1 ≈ 16 degrees C per watt.
- Lower thermal resistance means a better heat sink.
- Use thermal paste or a pad and mount the board flat.
- Place fins vertically with air space around them.
If it is too hot to touch comfortably, add more cooling or reduce current.
REMEMBER
Lower degrees per watt means better cooling.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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