Breakdown Voltage in NPN Transistors: Analysis and Examples

This lecture discusses the breakdown voltage in NPN bipolar transistors, focusing on the avalanche effect in both common base and common emitter configurations. The instructor begins by introducing the concept of breakdown voltage, assuming a transistor gain of 255 and a multiplication factor of 4. The analysis starts with the common base mode, where the collector current is examined as a function of the collector-base voltage while keeping the emitter current constant. The lecture then transitions to the common emitter mode, where the collector current is again analyzed, but this time as a function of the collector-emitter voltage with a fixed base current. The instructor explains the conditions under which the collector current diverges, emphasizing the relationship between the breakdown voltage and the diode's characteristics. The lecture concludes with a summary of the findings, highlighting the differences in breakdown voltage behavior between the two configurations, specifically noting that the breakdown voltage for the common emitter configuration is 10 volts, which is 1.5 times the breakdown voltage of the diode.