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The corrected
dissipation of the thermal energy, in the active members, is one guarantee
of along and sure operation.
The radiators, also call to you raffreddatori, proteggono the splices
of the semiconductors, assuring their normal behavior .
II concept of thermal resistance covers great importance in the
practical one of the electronics. Because on it it depends the quality of
the operation and the duration in the time of good part of the assemblys
realize to you.
Every phenomenon electrical worker is always accompanied, in smaller or
greater measure, from thermal effects. The light bulb, as an example,
whose task would have to be only that one to make light, when it is
ignited sheet. The transformer, whose main task is that one to lower or to
elevate a tension, is heated. The television set in function emanates
heat. Therefore, these and tantissimi other examples, are to demonstrate
that the conductors electrical workers, to the passage of the current,
increase their temperature, which catch up values more and more elevate to
you with increasing of the intensity of current that crosses them. And if
we want to cite a precise data, we can remember that, when the 6 To for
square millimeter of thread section branch conductor are exceeded, the
temperature of the cable exceeds the 80°C, becoming much dangerous. This
type of production of thermal energy, is caused from hits that the very
small particles of the matter endure in supporting the current flow
electrical worker. In physics it assumes the denomination of "Joule
Effect" and comes taken advantage of in the construction of some devices
you, as as an example stufette for heating and the irons from I iron. But
most times it constitutes a phenomenon negative, to avoid and to fight.
Therefore as it happens in the use of the semiconductors, diode valves,
transistor and integrated circuits, for which it must be taken part in
appropriated way, determine the proportions oculatamente to the values of
tensions and currents and applying to they suitable raffreddatori
elements.
PRACTICAL EXAMPLES
We observe the designs brought back in figure 1.
Fig.
1 - Physical Rappresentazione, on the left, of a transistor and its symbol
electrical worker, to right. The arrows indicate the back of the currents
of collector (Ic) and emittore (). The acronyms signal the noticeable
tensions between collector and base and base and emittore.
On the left the physical outline of a transistor is present, on the
right the graphical symbol. Acronyms and arrows indicate the tensions and
the currents that interest the member in function. On which, therefore,
its degree of heating depends. In fact it is said that the collector
current provokes a loss to them of power, par to the product x the Vce
(tension collector-emittore), that it comes exactly transformed in heat.
And this can be of light entity in the so-called transistors of marks
them, but it can catch up great values much in the power transistors.
Also the current of Ib base (not cited in the outlines of figure 1), is
in a position to provoking losses, for effect Joule, par to the product Ib
x Vbe (tension base-emittore), but draft however of negligible losses.
From figure 1 it is always possible to deduce that the emittore current
corresponds them to the sum of the two currents of collector and base (= +
Ib). And this same observation extends to the Vce tension, that he is
equal to the sum of the two tensions Vcb and Vbe (Vce = Vcb + Vbe).
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