power dissipation and cooling needs

[mrkozmic]

Are there any basic rules for at what power dissipation heatsinks are required for processors? Is it likely that at 1, 2, 4 or 8W of power dissipation a heatsink is required?

 

[neetinsingh]

hi

visit following link u will find answer of ur questions.........

http://www.heatsink-guide.com/peltier.htm


bye

neetinsingh

 

[rkodaira]

In general semiconductors devices dissipates heat and if they need or not a heatsink attached to them depends on some factors.
First: check in the datasheet what is the maximum temperature allowed for the junction.
Second: check what are the thermal resistances from the junction to case and case to ambient. These figures have the unit K/W (kelvin per watt) or C/W (celsius degrees per watt).
Third: calculate what is the maximum power to be dissipated by the device.

For example: a fictitious device has the maximum junction temperature of 150 celsius degrees. The ambient temperature is 25 celsius degress. Checking the datasheet, the thermal resistance junction-case is 1 K/W and the thermal resistance case-ambient is 3 K/W. The device will dissipate 80W. So the expected temperature in the junction can be calculated:

80W x (1K/W + 3K/W) + 25 C = 240 + 25 = 265 C (it will burn or melt the device), so you need a heatsink of at least:

(150 - 25) / 80W - 1K/W = 1.5625 - 1 = 0.5625 K/W (thermal resistance of heatsink).

In the other hand: if this device will dissipate only 10W, without heatsink the temperature in the junction will be:

10W x (1K/W + 3K/W) + 25 C = 40 + 25 = 65 C what is perfectly reasonable.

When you use a heatsink, you should consider also the thermal resistance of the contact between the case and the heatsink surface. As it is not perfect and there are some air gaps (air is bad thermal conductor) we use a thermal compound grease to fill the gaps and improve the heat conduction.