PNP transistors

[andrebc]

Does anybody know what PNP Q3 was used instead of a NPN bjt? I just don’t know when to decide which one to use. In other words what are the applications of PNP transistors? Please send your feeback.

 

[crutschow]

A PNP is used instead of an NPN where you want a transistor to operate with the opposite bias (PNPs operate with negative collector-to-emitter bias, NPNs with positive collector-to-emitter bias). In the circuit you posted, the PNP is used to simplify the interconnection of the two stages, since it eliminates an interstage coupling capacitor and some bias resistors. Notice how the PNP is upside down as compared to the NPN so the collector is biased more negative than the emitter.

NPNs are used more often then PNPs because, for the same general transistor die size and design, the NPNs have higher gain and frequency response.