npn vs. pnp outputs

[jcraft]

I was just wondering what the advantages or diadvantages of each are. Mainly in regards to industrial sensors and controls. Not sure when you would use one over the other. Thanks.

 

[sreid]

It mostly depends on the tradition of the industry. PNP comes from the relay logic tradition where relays switch the plus voltage to a common ground. NPN comes from the electronics industry where it made much more sense to switch loads to ground (NPN transistors).

 

[Skogsgurra]

Yes, that is true. Historically.

These days the PNP is more or less standard in process control. The reasons: A cable shorted to ground does not activate anything - it would in an NPN system. Some guys also think it is easier to fault-find. But I am not so sure about that. Mostly a question of what you are used to.



Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...