SAFE THERMAL OPERATION OF POWER TRANSISTORS UNDER PULSED EXCITATION
A method by which the circuit designer may determine if a specified maximum internal temperature of a transistor will be exceeded, or if a transistor will enter thermal runaway for a given set of operating conditions is described. The method is derived by applying the theory of solid-state heat flow to simplified thermal models of power transistors. Laplace transforms are used to solve the differential equations of heat flow. Stability is analyzed by considering a linear approximation to the variation of heat dissipated with temperature. For safe thermal operation, the allowable input power to a transistor as determined by maximum permissible temperature alome must be derated. The derating factor is proportional to collector voltages, saturation current at ambient temperature, thermal resistance from collector junction to ambient, and circuit stability factor. The temperature at which thermal runaway occurs varies as the logarithm of the reciprocal of these same quantities. These conditions may be used as a criterion for safe thermal operation for low frequency and switching applications. (auth)
- Research Organization:
- New Mexico. Univ., Albuquerque. Engineering Experiment Station
- DOE Contract Number:
- AT(29-1)-789
- NSA Number:
- NSA-14-001648
- OSTI ID:
- 4237313
- Report Number(s):
- UNM-TR-EE-18; SCDC-910
- Country of Publication:
- United States
- Language:
- English
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