Heatsinks

Heatsinks

Heatsinks rely on ...

  • Conduction: Use a good conductor of heat. This will be metal. Aluminium or more rarely copper is used.
     
  • Convection: To maximise convection, have a large surface area often with fins.
     
  • Radiation: Matt black colouration to maximises heat radiation.
    A large surface area also help with heat radiation.
     
  • Good thermal contact: Use silicone grease or another thermal contact compound. This improves the heat flow from the component into the heatsink.
     
  • Large thermal capacity: Heatsinks are heavy. This allows the heatsink to soak up sudden short bursts of heat.
     
  • Forced convection: Heatsinks can be fan assisted (Computer processor cooling). For serious heavy duty applications like industrial power switching, large motor control or high power radio transmitting they can be water or oil cooled.
     
  • Heatsinks are often manufactured as part of the equipment case.

 

DC Power = Volts x Amps

  • P = V I

AC Power = Volts(rms) x Amps(rms)

 

The heat (in Watts) generated in a component can be calculated using the formula above.

  • Heatsinks are rated in Degrees per Watt or oC/W
     
  • Temperature_Rise = Power_Dissipated x Heatsink_Rating

This heatsink rating number tells you how much the heatsink temperature will rise when one watt of heat is dissipated. Bigger heatsinks get rid of waste heat more easily so their temperature rises less.

Source/Emitter Follower Dissipation Example ...

Heatsink Calculations

A MOSFET/transistor is attached to a heatsink. The heatsink is rated at 10 oC/W, The potential difference across the device is 5 Volts. The device current is 0.5 Amps. How much will the heatsink warm up above room temperature?

P = V I

P = 5 x 0.5

P = 2.5 Watts

Temperature_Rise = Power x Heatsink_Rating

Temperature_Rise = 2.5 x 10

Temperature_Rise = 25oC