A transistor with a height of 0.4 cm and a diameter of 0.6 cm is mounted on a circuit board. The transistor is cooled by air flowing over it with an average heat transfer coefficient of 30?W/m2•K. If the air temperature is 55°C and the transistor case temperature is not to exceed 70°C, determine the amount of power this transistor can dissipate safely. Disregard any heat transfer from the transistor base.
What will be an ideal response?
A transistor mounted on a circuit board is cooled by air flowing over it. The transistor case temperature is not to exceed 70*C when the air temperature is 55*C. The amount of power this transistor can dissipate safely is to be determined.
Assumptions 1 Steady operating conditions exist. 2 Heat transfer by radiation is disregarded. 3 The convection heat transfer coefficient is constant and uniform over the surface. 4 Heat transfer from the base of the transistor is negligible.
Analysis Disregarding the base area, the total heat transfer area of the transistor is
Then the rate of heat transfer from the power transistor at specified conditions is
Therefore, the amount of power this transistor can dissipate safely is 0.047 W.
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