An electronic device, such as a power transistor mountedon

Chapter 5, Problem 5.20

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An electronic device, such as a power transistor mountedon a finned heat sink, can be modeled as a spatiallyisothermal object with internal heat generation and anexternal convection resistance.(a) Consider such a system of mass M, specific heat c,and surface area As, which is initially in equilib- rium with the environment at T?. Suddenly, theelectronic device is energized such that a constantheat generation (W) occurs. Show that the tem-perature response of the device iswhere ??T?T(?) and T(?) is the steady-statetemperature corresponding to tl?; ?i?Ti?T(?);Ti?initial temperature of device; R?thermalresistance ; and C?thermal capacitance Mc.(b) An electronic device, which generates 60 W ofheat, is mounted on an aluminum heat sink weigh-ing 0.31 kg and reaches a temperature of 100C inambient air at 20C under steady-state conditions.If the device is initially at 20C, what temperaturewill it reach 5 min after the power is switched on?