Components have ratings

Ratings can be Voltage, Current or Power (Volts, Amps or Watts

If a Current of Power rating is exceeded the component overheats and burns out. (Boom)

The component fails because it gets too hot. (Ouch)

We can increase the Power or Current we put through a component by keeping its temperature down. (Great)

• The inside of components needs to stay below a critical temperature – say 200 degrees.

• When the component operates heat is generated.

• To get the heat to flow out of the component the inside needs to be warmer than the outside.

Heat leaves because the component is hot

There are three ways to loose heat:

Conduction (When a component touches something) HEAT FLOWS THROUGH THE COMPONENT LEGS INTO THE BOARD. HEAT ALSO FLOWS INTO HEAT SINKS.

Convection (When air flows over the component or heatsink)

HEAT FLOWS INTO THE AIR FROM THE COMPONENT OR HEATSINK

Radiation (When the component emits

infra red radiation)

Heat is radiated out – black helps

Heat is convected away – surface area and forced flow helps.

Heat is conducted away – good conductors and surface area help

What does this mean for components?

They are usually made black to radiate the most heat.

The surface area of some components needs to be increased so there is more area to loose heat. The best way to do this is with fins.

Natural convection is when currents of air are created from hot objects. The flow is usually slow.

To really speed up heat flow air can be forced over components with a fan, like in a computer box, and over the CPU of many computers which have fans.

FINS ARE NORMALLY VERTICAL SO HOT AIR RISES THROUGH THEM !!

• The amount of heat flow depends on the temperature difference and the resistance to heat flow.

• As the power generated increases the temperature difference must also increase.

• To keep the maximum internal temperature below 200 degrees we can either reduce the resistance or cool the surroundings.

We reduce the resistance by the use of heat sinks, fins, themal paste etc.