When use a PNP and when a NPN tramsistor?

[FrED]

Hallo!
I have a question that came to me when i try to design a switch using a relay and a transistor.

I know that there are PNP and NPN transistors. What is the difference they have and why do we have 2 types of transistors? And when do we have to use a NPN and when a PNP?

[Andre]

As long as i know here is no "WHEN".

Basically, the difference between PNP and NON is that PNP gets a + to the collector and needs 0 to the base to become conductive.
NPN gets 0 to the collector and needs + to become conductive.

This is the main difference. So, if you need to switch for example a relay and you have an output that sends 0 when you need to turn it on, then you must use a PNP transistor.

Also, is very usefull in reversing signals (like amplifiers).

There are no more differences between them as long as i know...

[FrED]

so it is a matter of judgment

[kam]

no not exactly. Some times it is mandatory some times not to use PNP or NPN

[FrED]

pffffff

[Supernova]

Man, you have to understand. There is not neutral or ground or something like that in digital electronics. There is only + and - and they are handled the same

So if you have a + signal and you must use a transistor with it, you need a NPN otherwise a PNP...

[FrED]

I think i need to learn some more for transistors 

[Supernova]

Yep, they are very interesting...