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Topic: Which direction does current flow? (Read 7371 times) previous topic - next topic

Delta_G

In physics class way back in college we handled current either direction.  As long as you had your signs right, it didn't matter.  The result would come out right every time.

But now I am reading a data sheet for a digital switch and it says when current flows into pin Z and out on pin Y there's a concern about Vcc showing up on pin Y if certain conditions are met.  But when current flow into pin Y and out pin Z then there is no concern.

I don't want to have this concern, so which one of those gets + and which gets -?  What's the convention on current flow?  Positive to negative or negative to positive?
|| | ||| | || | ||  ~Woodstock

Please do not PM with technical questions or comments.  Keep Arduino stuff out on the boards where it belongs.

floresta

Quote
Positive to negative or negative to positive?


Yes.

Before a lot was known about electrons it was thought that current flows out of the positive terminal of the battery, through the external circuit components, and back into the negative terminal of the battery.  We now know that electrons are actually flowing in the opposite direction but in general we use the original assumption when we talk about current flow.

As for my 'Yes' answer above ... Inside the battery current is flowing from the negative terminal to the positive terminal so there room for confusion with your question as posed.


Don

Grumpy_Mike

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What's the convention on current flow?  Positive to negative

Positive to negative flow is called conventional current and is what every one in electronics uses.
The other direction is know as electron flow and is used only when you want to consider the actual electrons.

Delta_G

So for the pin it says current is supposed to flow "in" on, that pin is connected to positive and then the other pin goes back to ground.

Right?
|| | ||| | || | ||  ~Woodstock

Please do not PM with technical questions or comments.  Keep Arduino stuff out on the boards where it belongs.

Grumpy_Mike


Delta_G

|| | ||| | || | ||  ~Woodstock

Please do not PM with technical questions or comments.  Keep Arduino stuff out on the boards where it belongs.

jackrae

As you rightly say, it matters not a jot as to which direction you consider it flows since the signs (direction) will balance.  ie the sum of the currents at any point equals zero. However you must stick to a single convention and that generally is from the positive terminal of a current supply source.  The term electron flow is not the same as the term current flow.  Us oldies even had to consider "hole flow" when dealing with transistor theory.

What you need to consider is whether you are considering a current source or a current sink.

A battery is a current source so you can/should consider the current comes OUT of the positive terminal.  However a device such as the arduino which has + and - power supply connections is a current sink.  In this case the curent flows INTO the positive terminal.  BUT, where the arduino has positive and negative output terminals, the current flows OUT  of the + terminal since these terminals are considered as current sources.

All very confusing until you get your head around sources and sinks.

Grumpy_Mike

@jackrae I would disagree with this, sourcing and sinking are terms that refer to if current is controlled next to the ground or next to the supply. Electron flow is never considers in solid state electronics. The legacy of electron flow is however found in the naming of the transistors emitter and collector and the FETs source and drain, but these are just names.

jackrae

Hi Mike
It's your choice - but it works for me
For every answer there is at least one which is equal and opposite (with apologies to Isaac Newton)
Jack

GoForSmoke

Quote
For every answer there is at least one which is equal and opposite (with apologies to Isaac Newton)


And... Just because two people argue doesn't mean that one of them must be right.  ]:D



1) http://gammon.com.au/blink  <-- tasking Arduino 1-2-3
2) http://gammon.com.au/serial <-- techniques howto
3) http://gammon.com.au/interrupts
Your sketch can sense ongoing process events in time.
Your sketch can make events to control it over time.

udoklein

In the end it depends if the current is made of positive or negative charge. All of this and more is very well described in Wikipedia: http://en.wikipedia.org/wiki/Electric_current
Check out my experiments http://blog.blinkenlight.net

Grumpy_Mike


In the end it depends if the current is made of positive or negative charge. All of this and more is very well described in Wikipedia: http://en.wikipedia.org/wiki/Electric_current

No it always flows in the same direction. And by it I mean current.

This is all totally irrelevant to the OP question.

udoklein

Oops, he was asking for the convention --> you are definitely right.
Check out my experiments http://blog.blinkenlight.net

123Splat

It is really, mostly, semantics, BUT,,,
Current does not flow, current IS flow.
Electron current/flow is the observation of the movement of electrons (with negative charge, negative opposes negative, attracts positive) from negative source to positive sink.
Conventional current is the observed flow (or current) of Holes left in the atomic shells of the conductor material by the bumping off of electrons.  The holes represent a positive charge, because of the absense of the electrons, and 'flow' from positive to negative ( positive rejects positive and attracts negative).

Wow, 12 years of college and tech schools did do some good,,,, my brain hurts.

retrolefty

#14
Nov 16, 2011, 09:51 pm Last Edit: Nov 16, 2011, 10:29 pm by retrolefty Reason: 1

Quote
What's the convention on current flow?  Positive to negative

Positive to negative flow is called conventional current and is what every one in electronics uses.
The other direction is know as electron flow and is used only when you want to consider the actual electrons.


I was schooled in the concept that conventional current flow (positive to negative) was defined (incorrectly) by the early pioneers of electricity as they knew that current flowed in one direction only in a DC circuit, but guessed wrong on the actual direction because they knew nothing about atoms and their structure. But the legacy continued to this day in classic electrical engineering. Later as the atom was better understood it was clear that what moves in current flow is electrons from atom to atom via the valence ring and that they move from negative charge to positive.

So colleges continued to teach classic conventional current flow and even 'invented' the 'hole' flow analogy to make their flawed concept work. In my thinking a electron is a physical thing, it has mass and can actually move either by atom to atom or as a stream emitted from a hot emitter. A 'hole' on the other hand is not a physical thing, has no mass and thinking it can 'flow' from atom to atom is rubbish to me. ;)

In U.S. Military electronics training we were taught to use electron flow and that it was negative to positive and to not be confused about all the backward pointing arrows used in semiconductor symbols.

It's always a nice subject to argue about, but like masturbation the end result always leaves one....spent but not completely satisfied.  ;)

Lefty

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