Why does NPN exist?

[NetNathan]

I like PNP (source) way better. It just seems more natural and correct to be controlling the +DC voltage than the -DC. It is a real pain when specifying components and making sure you are not getting NPN (sink). I think this is especially important when the -DC is grounded also, as control issues could be caused.
With AC voltage you never really switch the neutral, so why with DC?

 

[JaxGTO]

When I used to work in the Explosive Areas we used NPN. Only because it is less likely to cause a spark if you short out the sourcing input. If you short it you just get an input. Same with sinking outputs.

 

[strantor]

I think like many aspects of control systems, there is a mix of different ways of doing things that results from one country's standards becoming mixed in with another country's. Or standardizing on something early in the game and holding onto it because it's so prevalent, even though better options exist.

I think the "high side switching" scheme comes from AC control systems where there it really makes no difference between switching L or N, but we standardized on switching L. Then DC controls and transistors come along and it actually does make a difference. Low- side switching is easier with DC. PNP/P-MOS transistors require extra charge pump components to elevate the gate voltage above source voltage, where NPN/N-MOS transistors don't. The price difference today is negligible to the point most manufacturers just sell NPN or PNP for the same price, but probably back in the day it was cheaper to go NPN.

 

[JesperMP]

+1 that NPN was a tad less expensive in the past.
That was the explanation when I studied electrics in late 80's. Even then it was becoming abnormal with NPN.

 

[parky]

NPN is often used in electronics slightly more so than PNP, so it is historical before PLC's were really a thing, also there is some reason for using sink rather than source as spikes tend to be positive therefore unlikely to cause false triggering of PLC inputs the switching point lets say is 70% of the supply voltage if for example a PNP source then as most spikes are positive it will be sitting at 24V, so a spike of 10v above 24 will not be seen as a input change i.e. assume the switching point is 8v for a sink, but a source will be sitting at 0V, a spike of 10-12v may trigger the input. TBH I have only come across false triggering on one system in over 40 years of PLC programing, changed the one input card to sink &it cured the problem.

 

[ndzied1]

I like PNP (source) way better. It just seems more natural

I would think if someone worked where NPN was the standard it would seem more natural to them and PNP would seem “weird”

 

[exabmorgan]

I actually enjoy the interactions I have with people that don't read datasheets very carefully and message me about their problems with Outputs.


They want to know why they are 'broken'. I get to say 'how are you measuring it' (I even have the tone of voice down so I sound less judgemental). They yell 'Voltage, I don't see Voltage'
-I get to burst their bubble : "You were never supposed to". Then a light lesson on NPN vs PNP.


It all pays the same, being on a thread or call like that is easy and the user gets an education. All problems are solved at 5pm.

 

[durallymax]

Study semi-conductor physics and history, it'll make a little more sense then. NPN early on was much easier and cheaper. These days largely irrelevant.

I still run into stuff daily using NPN (Very common on a number of VFDs to be configured that way from factory, but I'm often using Asian brands so that would explain a lot of it). I could care less which it is, it's just a circuit. But PNP is fewer late night calls.

 

[Puddle]

Keyence sensors tend to default to NPN. Annoyingly, this is done in the initial setup and can't be changed after that so if missed, it has to be factory reset.

Much prefer PNP, it's just a more logical approach for me.

 

[I_Automation]

I work on a lot of equipment built in Europe and have talked to engineers over there. Germany, Italy, France & others.



The common reply they give is "NPN devices and inputs respond faster than PNP"


When I ask how 0.01ms is going to effect a PLC with a scan time of 0.15 seconds they can't say.

 

[parky]

The original NPN (way before PLC's) was used as a complementary pair (NPN & PNP) i.e. push pull for power amplifiers, these consume no power when no signal is present & give higher power output,digital IC's before mosfet also used complementary output stages so there are probably two of the many reasons they exist, it has nothing to do with PLC's but sensor manufacturers often use NPN output stages as it makes them simpler & probably cheaper (well in the early days).

 

[geniusintraining]

Only because it is less likely to cause a spark if you short out the sourcing input....

Never thought of that but good reason, worked a lot with high VOCs areas and never much thought about it

 

[IO_Rack]

The original NPN (way before PLC's) was used as a complementary pair (NPN & PNP) i.e. push pull for power amplifiers, these consume no power when no signal is present & give higher power output,digital IC's before mosfet also used complementary output stages so there are probably two of the many reasons they exist, it has nothing to do with PLC's but sensor manufacturers often use NPN output stages as it makes them simpler & probably cheaper (well in the early days).

I think this is probably the best answer for the original poster. I will add that open collector is more flexible to integrate in the electronics world.

I do believe that having both standards in the same building presents some confusion. Being presumptuous, I would have to say most maintenance people wire and replace devices based on point to point (or terminal to terminal).

To me, a complete circuit is a complete circuit. It doesn't matter where you switch it.

 

[NetNathan]

When you are troubleshooting the connection , that is one issue.
My biggest issue is with specifying and ordering components for the system. I have to always make sure I am ordering PNP (Source) and NOT NPN (Sink).