converter - How can I convert a PNP to NPN transistor?

I have a circuit which requires a PNP transistor. I only have an NPN transistor.

Is there a way to convert one to the other given that they have the same characteristics (apart from the npn/pnp part?)

And for others after me... can the reverse also be done? e.g. how does one convert a PNP transistor to its NPN equivalent?

Answer

If it's the only type of transistor in the circuit, the translation is straightforward; build the circuit as designed, reverse the power connections and any other polarised components (diodes, electrolytic caps).

If you need one PNP in a mostly NPN circuit, there is no general solution.

There may be solutions, depending on the configuration of the PNP stage.

For example, if the PNP transistor was being used as an emitter follower, and you have the headroom, you may be able to use an NPN in common emitter, with Rc=Re so that its gain is (approx) 1.

If the PNP transistor was in a complementary power output stage but you can only find low power PNP transistors, I remember seeing an arrangement using a PNP driver transistor and an NPN power transistor to "replace" the non-existent PNP power transistor. Peter Walker did this around 1970 for the Quad 303 power amp (I believe 3 transistors were involved) when there was no PNP version of the famous 2N3055.

And there may be other such substitutions.