A 160-W silicon power transistor operated with a heat sink (θS A=1.5^∘ C / W) has θJ C=0.5^∘ C /

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A 160-W silicon power transistor operated with a heat sink...

A $160-\mathrm{W}$ silicon power transistor operated with a heat sink $\left(\theta_{S A}=1.5^{\circ} \mathrm{C} / \mathrm{W}\right)$ has $\theta_{J C}=0.5^{\circ} \mathrm{C} / \mathrm{W}$ and a mounting insulation of $\theta_{C S}=0.8^{\circ} \mathrm{C} / \mathrm{W}$. What maximum power can be handled by the transistor at an ambient temperature of $80^{\circ} \mathrm{C}$ ? (The junction temperature should not exceed $200^{\circ} \mathrm{C}$.)

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Key Concepts

Thermal Resistance Network

This concept involves the modeling of the various thermal resistances between different components or interfaces in a system. In devices like power transistors, the thermal path is usually modeled with multiple serial thermal resistances, such as junction-to-case, case-to-heatsink, and heatsink-to-ambient resistances. This model is analogous to electrical resistance networks and is used to calculate temperature gradients resulting from power dissipation.

Junction Temperature

This term refers to the temperature at the semiconductor junction within a device. It is a critical parameter because exceeding the maximum junction temperature can lead to failure of the device. Calculating the junction temperature involves adding the temperature rises across each thermal resistance from the junction to the ambient environment, taking into account the power dissipated.

Power Dissipation Calculation

This concept involves determining the maximum power a device can safely dissipate without exceeding its maximum allowable junction temperature. It is derived by balancing the power input and the temperature rises within the thermal resistance network. Specifically, given the ambient temperature, allowable temperature rise, and total thermal resistance, one can compute the maximum power that can be handled.

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