PNP or NPN Transistors

Roff · Jan 22, 2008

I turned the diagram upside down, as you suggested. It doesn't change anything.

3v0 · Jan 22, 2008

Roff said:
I turned the diagram upside down, as you suggested. It doesn't change anything.

My use of source and sink are as shown by Roff. It is the only way I have ever seen the terms used.

Roff · Jan 22, 2008

3v0 said:
My use of source and sink are as shown by Roff. It is the only way I have ever seen the terms used.

I was beginning to think that Nigel and I were the only ones on this forum with an opinion on this subject.

Nigel Goodwin · Jan 22, 2008

Roff said:
I'm not concerned about conventional flow. I just wanted to be sure we were on the same page. And I still want to see a schematic of how you expect to get a PNP common emitter stage to sink current.

OK, here's your diagram, labelled correctly.

Roff · Jan 22, 2008

Nigel Goodwin said:
OK, here's your diagram, labelled correctly.

You have current flowing from negative to positive in the battery. How does that work?
Also, transistor current flows in the direction of the emitter arrow. You have it flowing in the opposite direction.

picbits · Jan 22, 2008

I use PNP for high side driving and NPN for low side driving.

Same with MOSFETs - P Channel for a high side driver and N channel for a low side driver.

Although on the odd occasion I've used a bootstrapping boost converter thingy for driving N channel FETs configured as high side drivers.

Nigel Goodwin · Jan 22, 2008

Roff said:
You have current flowing from negative to positive in the battery. How does that work?
Also, transistor current flows in the direction of the emitter arrow. You have it flowing in the opposite direction.

Like I said before, you're thinking conventional current flow - think electron current flow instead.

Sinking and sourcing is about low side or high side switching, polarity makes no difference.

Funny NYPD · Jan 22, 2008

NPN and PNP all depends on your application, they both got a reason to exist.

picbits · Jan 22, 2008

Funnily enough I was thinking about this the other day.

I was always "brought up" with NPN transistors - I had a bit of a morbid fear of using PNP (30 years of electronics !!) but recently I've had to use them and they're not as scarey as I thought they would be lol.,

Roff · Jan 22, 2008

Nigel Goodwin said:
Like I said before, you're thinking conventional current flow - think electron current flow instead.

Sinking and sourcing is about low side or high side switching, polarity makes no difference.

So we weren't on the same page after all. Nevertheless, you can't make a common emitter PNP source electrons, or sink conventional current. Same for NPN, only opposite.
For common collector, the opposite holds true.
Sinking is defined as conventional current into a port, or electron flow out of a port.

Nigel Goodwin · Jan 22, 2008

picbits said:
Funnily enough I was thinking about this the other day.

I was always "brought up" with NPN transistors - I had a bit of a morbid fear of using PNP (30 years of electronics !!) but recently I've had to use them and they're not as scarey as I thought they would be lol.,

It's probably down to age?, which is why I'm surprised at Roff? - I started off with valves, negative chassis, conventional current flow, then it changed to germanium transistors, usually PNP with positive chassis and electron current flow. When silicon appeared it flipped back to negative chassis and conventional flow again.

It makes NO difference, it's just a question of a reference point, that's all.

What I have found confusing over the years (and probably why I understand the chassis concept so well?) is circuits that are drawn 'upside down', where you measure from the top rail on the circuit diagram. Some of the early transistor stuff was like this, with +ve at the top (as with valves) but using upside down PNP transistors. Not a lot was ever done like this, but it really makes you have to think how something works.

Perhaps it's the way we read?, from top to bottom, so we like current (of whatever type) to flow from top to bottom?.

Roff · Jan 22, 2008

Nigel Goodwin said:
It's probably down to age?, which is why I'm surprised at Roff? - I started off with valves, negative chassis, conventional current flow, then it changed to germanium transistors, usually PNP with positive chassis and electron current flow. When silicon appeared it flipped back to negative chassis and conventional flow again.

It makes NO difference, it's just a question of a reference point, that's all.

What I have found confusing over the years (and probably why I understand the chassis concept so well?) is circuits that are drawn 'upside down', where you measure from the top rail on the circuit diagram. Some of the early transistor stuff was like this, with +ve at the top (as with valves) but using upside down PNP transistors. Not a lot was ever done like this, but it really makes you have to think how something works.

Perhaps it's the way we read?, from top to bottom, so we like current (of whatever type) to flow from top to bottom?.

But what about me surprises you?

Nigel Goodwin · Jan 22, 2008

Roff said:
So we weren't on the same page after all. Nevertheless, you can't make a common emitter PNP source electrons, or sink conventional current. Same for NPN, only opposite.
For common collector, the opposite holds true.
Sinking is defined as conventional current into a port, or electron flow out of a port.

Never heard anything like that?, a quick google finds the complete opposite.

https://encyclopedia.thefreedictionary.com/Current+sources+and+sinks

Your way is a very poor way to try and understand how circuits work!, limiting yourself so much.

picbits · Jan 22, 2008

Actually I can probably blame MR R A Penfold for using mainly NPN transistors in the first (and only for many years) electronics book I owned.

My Grandparents bought it for me many eons ago and I've still got it now.

Nigel Goodwin · Jan 22, 2008

Roff said:
But what about me surprises you?

Just that I thought you came from an era where you would have no problem understanding the concepts of current and electron flow - from back in the valve/tube days.

I've no idea of your age, but I've always presumed you are from that era - perhaps because of your 'US of A' avatar which you mentioned came from an old show (which I'd never heard of).

Roff · Jan 22, 2008

Nigel Goodwin said:
Just that I thought you came from an era where you would have no problem understanding the concepts of current and electron flow - from back in the valve/tube days.

I've no idea of your age, but I've always presumed you are from that era - perhaps because of your 'US of A' avatar which you mentioned came from an old show (which I'd never heard of).

I have no problem understanding the concepts of current and electron flow. I just generally think in terms of conventional flow. With tubes (which I haven't worked with since I was a pup, but I think about them occasionally ), I generally think conventional current flow, except when I think about the workings inside the shell. Did I say something that made you think I have trouble with that concept? I thought you were nuts there for a little while, and I'm still not sure you use the commonly accepted definitions of source and sink.
I had looked at that link you posted, and thought about referring you to it. It says:

A source or a sink is defined by which compartment is viewable by the observer.

A source is:

A flow of positive charges from the "invisible" to the "visible" compartment (i.e. "toward the eye"), or...

A flow of negative charges from the visible to the invisible (away from the eye).

A sink is:

A flow of positive charges "away from the eye", or...

A flow of negative charges "toward the eye".

Note the phrases I have highlighted in red. "A flow of positive charges" is conventional current flow.
In the source definition, the "invisible" would be like a PNP with the emitter at the positive rail. The "visible" would be a resistive load to the negative rail. Either rail could be referred to as ground or earth.

Roff · Jan 22, 2008

is a discussion of logic gates, with sourcing and sinking described in terms of electron flow. It supports what I have been saying.

Oh, and I'm 66.

3v0 · Jan 22, 2008

Wikipedia says this:

There is no actual physical difference between a current source and a current sink. Whether you call the flow of current a source or a sink depends entirely on your point of reference

I set the point of reference when I said you use a NPN to sink...

So what is the flap about Nigel ?

weegee · Jan 22, 2008

picbits said:
Funnily enough I was thinking about this the other day.

I was always "brought up" with NPN transistors - I had a bit of a morbid fear of using PNP (30 years of electronics !!) but recently I've had to use them and they're not as scarey as I thought they would be lol.,

This is exactly my point!!

well done that man

I was wanting to know why this was, as i found myself designing for npn instintivly, even though i have loads of pnp and npn here, so cost ect dosn't come into it. I also don't do anything over 40mhz so i imagine the switching speed isn't affecting me too much.

Roff · Jan 22, 2008

3v0 said:
Wikipedia says this:

I set the point of reference when I said you use a NPN to sink...

So what is the flap about Nigel ?

Which is consistent with what I'm saying.
As far as I can tell, Nigel believes that a sink is an electron sink, and a source is an electron source. The industry standard is just the opposite.

PNP or NPN Transistors

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