Mission and purpose of a heat sinkThe electric power loss (Ploss) is located at the junction of semiconductor devices and resistors to heat (Q) and causes a temperature increase. The temperature of the barrier layer (θJ) must not exceed a maximum value to ensure a stable operation, and to avoid the destruction of the semiconductor. This maximum allowable junction temperature can be taken from the data sheets of semiconductor manufacturers. Can not be sufficiently aware of the semiconductor body to the surrounding medium, usually air, the heat dissipated, so the component must be mounted on a heatsink. The effective surface area for heat dissipation housing is thus increased. This leads to higher reliability and lifetime of the semiconductor or the entire circuit. A heat sink is made of highly thermally conductive materials, generally of an aluminum alloy with an adjusted and appropriate for the application geometrical structure and surface characteristics.
Materials used are:
- AlMgSiO, 5 F22 for aluminum extrusions
- AlSi8Cu3 for aluminum die castings
- Al99, 9 hh aluminum strip material
Operation of a heat sink, heat and Konvektionsarten
The heat transfer from the heat source (eg junction of the semiconductor) over the heat sink to the surrounding medium is composed of:
- the heat transfer from the heat source to the heat sink
- the heat conduction within the cooling body to the heat sink surface
- the transfer of heat from the surface by free or forced convection to the surrounding medium
- the heat radiation depending on surface characteristics
The thermal resistance and the thermal equivalent circuit
The heat resistance is defined as the ratio of temperature rise at a power supplied and used as a measure for the heat-dispensing capacity of the heat sinks and comparability. The lower the thermal resistance, the lower the expected temperature increase and the more "better" is a heatsink. The thermal resistance is expressed in K / W (Kelvin / Watt). Heat sink and semiconductor form a functional unit that can be prepared analogously to the Ohm's law in electrical engineering as a thermal equivalent circuit:
Structure in the following areas:
- Supply of the power loss (Ploss) is reacted in the heat flow (Q)
- Heat conduction from the barrier layer on the mounting surface of the component
- Heat output of the heat sink to the surrounding medium
Calculation of the required thermal resistance for a given power dissipation and the allowable temperature gradient
Best uses for LED's are low wattage.2012-12-31 13:57:45 by MisterGreenJeans
They are semiconductors and have trouble dispersing with excess heat whan working with equivilent of 100 w incandescent light. Getting rid of heat requires large aluminum finned heat sinks that add unnecessarily to the cost IMHO. Kinda like going backwards.
Why concentrate 100 watts of LED's in a small package then put them behind a diffuser (light fixture) anyway?
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