I was thinking of using a pre-biased transistor in a design for the first time and started looking at datasheets to make sure I understood how they'd work in my situation. Much to my surprise the On Semiconductor MMUN2113LT1G datasheet has the transistor drawn upside down of the way I'm used to seeing them, and has the emitter labelled as ground. In my application, I would've intended to collect emitter to 5VDC supply voltage, base to the output of a push-pull comparator whose output I need to reverse, and collector to a separate downstream circuit's input.

If I ignore the orientation and the "ground" label, everything else looks acceptable for my needs, but the ground label surprised me. Why is it labelled that way? Does it need to be connected to ground for any reason?

 

Unusual, yes, but there's no law to say that ground has to be the more negative rail of a supply.
In the age of vintage motor cars and germanium transistors it was common to have a positive-ground system.

 

If I ignore the orientation and the "ground" label, everything else looks acceptable for my needs, but the ground label surprised me. Why is it labelled that way? Does it need to be connected to ground for any reason?

It's probably labelled that way due to lack of imagination on the part of the dude (or dudette) who wrote the data sheet. Just connect the emitter to Vcc and you should be good to go.

 

Unusual, yes, but there's no law to say that ground has to be the more negative rail of a supply.
In the age of vintage motor cars and germanium transistors it was common to have a positive-ground system.

Yeah, I knew there wasn't anything wrong with hooking emitter up to ground - I just wanted to make sure it wasn't somehow mandatory for reasons I couldn't understand. Sounds like all is well.

Thanks!

 

It's probably labelled that way due to lack of imagination on the part of the dude (or dudette) who wrote the data sheet. Just connect the emitter to Vcc and you should be good to go.

Excellent! That's what I was hoping. Just needed confirmation. The datasheet tripped me out. Thanks!

 

Why input, output and ground would even be labelled is rather baffling.

I quite like those transistors, since they save parts and even at moderate volume it can cost a lot more to put a part like a resistor on a board than the cost of the part. It depends a great deal on the pick & place equipment your assembly house has. Some assembly houses have to be pressed rather hard to get them to confess some of the details.

One thing I usually do is to go over a design to see if I can reduce the variety of parts, which saves money all along the way with ordering, handling, inventory, slots & setup in p&p machines, etc. In non-critical locations you can sometimes do things like say "Oh, that's the only 15 k resistor on the board, I can easily change it to 10 k or a 22 k." Sometimes if you only need one or two signal type diodes and are also using small transistors you can use a transistor junction instead of a diode and get the diodes off the parts list. Never forget DeMorgan's theorem if you are using "random logic."

There are some spiffy dual transistors in tiny 6-pin packages.

 

When I first started using transistors they were mostly germanium PNP so after being used to using valves it was a bit strange having the common (ground.) rail a positive and the power supply negative. When silicon transistors came out they were mostly NPN so ground went back to being th negative.

Les.

 

As most here know by now, I personally dislike the term 'Ground' to describe power common, it is a bit of a misnomer IMO.
.Max.

 

As most here know by now, I personally dislike the term 'Ground' to describe power common, it is a bit of a misnomer IMO.
.Max.

I think of Reinhold Niebuhr every time I see you state that dislike...

God grant me the serenity to accept the things I cannot change; courage to change the things I can; and wisdom to know the difference.​

 

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; and wisdom to know the difference.​

You're supposed to get that with old age, but I'm not so sure about that........?
King Canute had the same problem
Max.