Hi, I am working on single transistor amplifications and last day in the lab I worked with the BC237 audio bjt. I've done some calculations and measurements and then wanted to try all process samely by reversing the transistor. I.e. operating it in the reverse active mode. Well interestingly the gain have increased some how... ... Is this normal? Well as far as I know if not necessary one should avoid the reverse active mode because the doping levels of the base emitter etc. are completely different. Is there somthng different about these audio transistors? What do you think?

Appreciating any contibutions to this discussion. thnx

 

If you connect a typical transistor so that the emitter terminal is in place of the collector, and vice versa, you would indeed expect lower current gain relative to normal operation. For many silicon planar transistors, the maximum working voltage would also be much less in the inverted mode. Their base-emitter reverse breakdown voltages may be just a few volts.

Transistors may be damaged by operation in the reverse mode, particularly if the base-emitter breakdown voltage is exceeded. This can reduce the current gain subsequently measured in the normal direction. Some types of transistor are very sensitive to damage of this kind.

Perhaps the gain in your circuit appears larger with the transistor inverted due to some difficulty with biasing: could you please post a schematic?

 

European BCxxx transistors have the emitter and collector pins opposite to American 2Nxxxx transistors in the TO-92 plastic package.