Pretty much what the question says. Is it just a fancy name for any npn and pnp bjt?

 

They are two transistors that have close to identical properties, except for being opposite in polarity.

 

Ditto, it just means that the transistor is a close match to one of the opposite polarity. Probably as much a marketing tool as anything else, to sell two transistors instead of risking that the designer looks for a complementary one from another supplier.

 

In some designs it is useful to have NPN and PNP transistors that are well matched to each other with regard to a number of the parameters. Using them allows the designer to squeeze some of the cost and complexity out of a design while maintaining adequate performance. The designer could always search data sheets to find a suitably matched transistor, but having the manufacture offer one up usually saves a bunch of time and effort -- and the designer's time and effort also represent costs to the project.

 

A typical example of where complementary matched transistors might be used is in a linear push-pull power output stage.

 

It used to be that manufacturers would put the two devices on the same substrate. That way, thermal effects would occur equally on both transistors, thus minimizing the need for separate compensation circuits. I don't know if this is done any more.

 

It used to be that manufacturers would put the two devices on the same substrate. That way, thermal effects would occur equally on both transistors, thus minimizing the need for separate compensation circuits. I don't know if this is done any more.

Not at the TO-220 or TO-3 level. Too much heat to get rid of. You can still get them in TO-5 size or plastic DIP.

 

Not at the TO-220 or TO-3 level. Too much heat to get rid of. You can still get them in TO-5 size or plastic DIP.

There aren't many complementary pairs at that level.

 

Amplifiers that use complementary TRANSISTOR pairs are long gone. Sure you can find some old Sansui or Phase Linear amps that used them, but they are going on 40 plus years old.

 

While I've never done much with complementary pairs of discrete transistors, I believe the TO-3 cased 2N3055 has a complementary PNP in the MJ2955. I think (but don't know) that this is the same as the 2N2955.