V. THERMAL CONSIDERATIONS
One of the key layout considerations in a power supply is removing the heat from components. Historically, that meant figuring out which components generated significant heat and mounting them to a heatsink. But as the power supply becomes integrated with the system,mounting components to a heatsink is becoming less attractive and there is a move to have the PWB act as the heatsink.
There are a number of ways to move heat including conduction, convection and radiation and the power supply design uses all three. For electrical engineers, it is useful to translate thecooling process into an electrical circuit analogy.
Heat can be thought of as a current source,temperature as a voltage, and conduction, convection and radiation paths can be thought of as resistances. Fig. 18 shows the electrical analog of a semiconductor dissipating heat and its cooling path. The heat, which is treated as a current source, flows from the semiconductor die through the package to an interface and then into a heatsink. Traditionally, this was a fairly easy circuit to analyze. The heat could be calculated, the semiconductor manufacturer provided the thermal resistance of the package (in ºC/W), there was characterization data on the package to heatsink interface available and the heatsink manufacturer provided its thermal resistance. So the engineer simply needs to multiply power times the sum of the thermal resistances to calculate temperature rise above ambient.作者: 哈哈哈哈 时间: 2011-5-1 08:34 标题: PCB散热