NPN & PNP Sensor adavntages

Hello Guest,

In the early stages of semi-conductor manufacture, the PNP was the only type which could be made, using the single process known at the time.

As development of semi-conductor manufacture improved, it became possible to make the NPN type.

Further developments by major semi-conductor makers, made the NPN slightly easier to make than the PNP, thus the NPN became cheaper.

As improvements became closer together, and the time between a new semi-conductor fabricating factory being built became shorter and shorter, the NPN won the battle, and now has some 90% approx. of the market.

LSI (Large scale Integrated) circuits are also easier to fabricate in NPN, thus are cheaper, as well as being faster.

There are some benefits of using PNP in certain situations, and for those situations, it is OK to spend the extra, to achieve the designed purpose.

High Frequency circuits are almost always NPN technology.

Once a commitment has beenm made by a Maker or user of either PNP or NPN, it becomes more difficult to change, because of both resistance to change (human inertia) and costs of that change.

Kind Regards....

ah, germanium pnps - those were the days.

Hello bhankiii and other interested readers,

I remember using those early PNP transistors, and here is a good early history site, complete with pictures to jog your memories: http://homepages.nildram.co.uk/~wylie/Mullard/Mullard.htm

Kind Regards....

While agreeing with Sparkstation, I also think that human nature plays a part in why PNP is more expensive.

PNP sensors provide a high (positive) signal when it senses and an NPN sensor provides a low signal when it senses.

Which one you use depends on the application but, speaking from a logic point of view, a high signal is "true" while a low signal is "false". Right here you can see a discrepancy. If a sensor is sensing, logic says that the output should be true. If the sensor is sensing and the output is false, you need to use reverse-logic (or negative-logic to be proper about it) to make sense of it.

Now, since people would prefer to have a true output when the sensor is sensing, more PNP-type sensors are purchased than NPN. Law of Supply and Demand kicks in and you have PNP sensors being more expensive than NPN.

Also from a practical standpoint.

NPN proximity sensors are in effect interupting the neutral line, giving rise to situations where the white wire [neutral here in the US] is hot with respect to ground.

the troubleshooting confusion can reach epic proportions when you have both npn & pnp sensors on the same piece of equipment.

Most US equipment uses pnp proxes, whereas Euro equipment npn.

I actually agree with you fully after reading your post, though I had not thought of it quite that way myself.

I was (probably wrongly) of the opinion that it is (for me at least) a tiny bit easier/cheaper to interface an NPN than a PNP (certainly with transistors, I have done little with sensors for some years), being basically a lazy person when designing something.....and thought that the possibly greater sales might cause a more significant drop in price!!! Though I haven't a clue how many are sold of either sort!!

I now prefer your answer......but is it really true?

Hello Andy Germany

<"....but is it really true?....">

se non è vero, è ben trovato

Kind Regards....

I read that as maybe or maybe not......am I near?

Hello Andy Germany

It translates variously as:

If it is not true, it is a very happy invention {Common Saying, quoted by Giordano Bruno in the year 1585 - Dictionary of Quotations, Penguin Edition of 1960 = my reference}

Even if it is not true, it is well conceived {http://www.merriam-webster.com/dictionary/se%20non%20e%20vero,%20e%20ben%20trovato}

If it not true is well found. Even if it's not true, it makes a good story.{http://www.lifeinitaly.com/potpourri/proverbs-3.asp}

Chi pecora si fa, il lupo se la mangia. Non tutti quelli che hanno lettere sono savi.

So now you have it.

Kind Regards....

Excellent way of putting it, sir!

I may have expressed it as a "learned" statement but I did say "I think" at the beginning.

The business with "true" output preference is quite accurate though. I've even seen hardwired safety switches wired as normally-open when they should have been normally-closed. The same preference holds true (there's that word again) with proximity sensors.