An electronic device, such as a power transistor mounted on a finned heat sink, can be modeled as a spatially isothermal object with internal heat generation and an external convection resistance.

(a) Consider such a system of mass M, specific heat c, and surface area AS' which is initially in equilibrium with the environment at T_∞. Suddenly, the electronic device is energized such that a constant heat generation E_g (W) occurs. Show that the temperature response of the device is where

0 = T – T(∞) and T(∞) is the steady-state temperature corresponding to t → ∞; θ_i = T_i - T (∞); T_j = initial temperature of device; R = thermal resistance I/hA_s; and C = thermal capacitance Mc.

(b) An electronic device, which generates 60 W of heat, is mounted on an aluminum heat sink weighing 0.31 kg and reaches a temperature of 100°C in ambient air at 20°C under steady-state conditions. If the device is initially at 20°C, what temperature will it reach 5 min after the power is switched on?

exp- , RC