Therefore, thermal grease is applied to the various mating surfaces to remove/replace as much air as possible between the mating surfaces and thereby optimize the flow of heat out of the component and into the heat sink. If this happens, heat gets trapped and accumulates within the component, and the component can be damaged or destroyed as a consequence of excessive heat buildup. If air is trapped between a component and its heat sink, the air acts as a thermal insulator and limits the flow of heat from the component into the heat sink. (NB: A specially-engineered material called thermal grease (a.k.a., thermal compound, thermal paste, heat sink compound) is used in some heat sink applications when attaching a heat sink to an electronic component. In this way a single block of metal can be used as the heat sink for multiple electronic components, and if necessary (for operator / equipment safety reasons) the metal heat sink can be electrically bonded to ground potential.) For example, try an Internet search using "TO-3 insulator kit". (NB: When attaching a metal heat sink to a component, quite often an electrical insulator of some sort is installed between the component's metal pad and the metal heat sink, and special fastening hardware is used, to ensure the heat sink is galvanically isolated from the voltage on the component's metal pad. a) What is the junction-to-case thermal resistance. Bonding the semiconductor die directly to the metal can in this manner optimizes the flow of heat from the semiconductor die-which dissipates power and produces heat-to "the outside world" through the metal can.įor what it's worth, many electronic component case styles bond the silicon die to a metal pad to facilitate heat flow out of the die-e.g., TO-220, TO-262, leadless chip carrier, just to name a few-and quite often that metal tab has voltage on it. The maximum rated power refers to the transistor case at 25C. The collector is mounted/bonded directly onto the metal can, and this is why the collector voltage is present on the metal can. The collector is the gray colored substrate material (look at the edges of the square shape, and in the "trough" that snakes back-and-forth between the base and emitter, which are on top). Scroll down the page to the figure titled 2N3055 transistor internals it shows how this particular power NPN transistor is mounted inside a TO-3 case. If you can access the website Wikipedia, see the article titled 2N3055.
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