# 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?

• It may be possible to use one for the other in a given circuit with a small design change, but what you're asking is not possible, there is no conversion to make a NPN into a PNP. Commented Dec 16, 2012 at 11:09
• Could you post the schematics of the circuit you're dealing with? Or at least, what's the load that is supposed to be switched be the PNP transistor? Commented Dec 16, 2012 at 11:15
• So get some PNP already. Transistors are cheap and available. Get a handful of 2N4401 (NPN) and 2N4403 (PNP). These will be good for a lot of hobby projects and are quite cheap if you buy 100 or so at a time. That should last a while. Commented Dec 16, 2012 at 14:36
• What you are wanting to do is not possible - BUT as others have said, if you provide the cct diagram people can help with ways to use an NPN transistor BUT otherwise you are wasting your time and that of other people. Commented Dec 16, 2012 at 14:48
• @RussellMcMahon My actual question was really specific so I asked it in a more general way first because this answer might help more people than just me. I'll do a follow up question which is much more specific
Commented Dec 16, 2012 at 17:02

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.

If you have the exact NPN equivalent you only need to mount the circuit as it is drawn, so that the base, collector and emitter terminals of the NPN are connected where base, collector and emitter of the PNP should go, and then reverse the power supply polarity. This trick works in most cases, but it depends on the circuit we are speaking about. The exact same thing works if you want to use a PNP instead of a NPN. Remember that all the transistors in the circuit should be changed with theyr complementary, so if you have PNP's and NPN's in your circuit there's no way out, you need both types of transistors.

• What if you can't change the other transistors? Is there a way to use a PNP where a NPN is needed?