Abstract

This paper shows a numerical polynomial approximation to the issue of how junction transistors "BJT" and field effect transistors "FET" can work in safe or unsafe conditions in explosive atmospheres.  We have analyzed the most widely used transistors with thermal imaging, working in a controlled environment, to characterize their thermal behavior. With this characterization, we can predict their possibility to ignite a classified location (explosive atmosphere) fundamentally by mean of thermal-conduction and reaching the minimum activation energy of the combustible vapor, dust or flying. We have bring these transistors to their nominal rated values specified by their currents and working voltages, and we found that the effect of heat dissipation on the base-emitter junction of a transistor BJT is really non linear and much greater than on the threshold voltage of polarization of the FET due to the inherent loses to obtain the nominal voltage of the diode that forms the base-emitter junction. We have found experimentally that it is very easy to obtain a thermal difference of more than 200 °C in overheating of a common BJT compared to a MOSFET with a similar load in fixed polarization. We found temperatures over 300ºC in BJTs in common operating ranges, when the accepted “safe” temperature is supposed to be no more than 200ºC in any case. This issue is addressed with performance-based analysis, focused on temperature, and it suggest that equipment with BJT technologies should not be implemented in some areas of hazardous or explosive locations; so MOSFET technologies are preferable.