Estimating Transistor Heat Transfer Equation and Calculator

Heat Transfer Engineering
Engineering Physics

Estimating Junction Heat Transfer and Temperature of a Transistor Equation and Calculator

Transistor Junction

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Preview: Estimating Junction Heat Transfer and Temperature of a Transistor

Transistor Junction


Q = Heat Dissipation (W)
ΔT = Change in temperature (°C)
R = Junction thermal resisitance (°C/W)


The temperature of the case of a power transistor that is dissipating 3 W is measured to be 50°C. If the junction-to-case resistance of this transistor is specified by the manufacturer to be 15°C/W, determine the temperature at the junction of the transistor. The case temperature of a power transistor and the junction-tocase resistance are given. The junction temperature is to be determined. Assume Steady operating conditions exist.

Analysis The schematic of the transistor is given above, then the junction temperature becomes:

Junction Case Calculation

Therefore, the temperature of the transistor junction will be 95°C when its case is at 50°C.

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