DC power + or -?
I have looked at lots of Instructables and websites, but there is a 50/50 split that power flows positive to negative and negative to positive. Which is it? I use both, depending on the circuit I am building it is easier to build one way over the other (NPN and PNP Transistors usually) But I have heard that it used to be thought that positive flowed to negative but I have since heard that the new idea is that it flows negative to positive. I know that everything is supposed to flow from higher concentration (+) to lower (-) but we could have batteries labeled wrong so I don't know. Very confused.
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Electrons flow from the negative to the positive terminals in a DC system. They always have and they always will. It's nothing new.
However, long ago, the crew who determines right from wrong in the electrical world said that "flow" would be recognized as something called "hole flow". This is what "flows" from the positive to negative terminals in conventional electrical current flow.
As to NPN vs PNP, most often, NPN are used for low-side switching whereas PNP are used for switching high-side.. That is, NPN is often more efficient as a sink, and PNP as a source.
In general, speaking as one who has completed the coursework, I'd stick with the convention for "day to day" use, but always remember that electrons actually do flow in the opposite direction from conventional electrical "current". It can help conceptually in certain situations, whereas only thinking by convention can limit your intellectual scope.
However, long ago, the crew who determines right from wrong in the electrical world said that "flow" would be recognized as something called "hole flow". This is what "flows" from the positive to negative terminals in conventional electrical current flow.
As to NPN vs PNP, most often, NPN are used for low-side switching whereas PNP are used for switching high-side.. That is, NPN is often more efficient as a sink, and PNP as a source.
In general, speaking as one who has completed the coursework, I'd stick with the convention for "day to day" use, but always remember that electrons actually do flow in the opposite direction from conventional electrical "current". It can help conceptually in certain situations, whereas only thinking by convention can limit your intellectual scope.
Sep 28, 2009. 5:33 PMXOIIO
says:
It flows from negative to positive. (think an LED, the anode and the cathode)
Sep 28, 2009. 5:44 PMWesley666 (author)
says:
Yes but it goes in the same way which ever way the current is flowing. The arrow is either pointing in the direction it goes or doesn't go. The power could be flowing the other way through the LED (positive to negative) and the negative to positive way only works because the diode is placed in the circuit the same way. This isn't a simple black and white answer. Can you see the electricity flowing - to + through the LED? No, therefore since we can not see it we can't assume it flows that direction. It could flow + to - and still work as long as it is placed in the circuit the same direction. Maybe the diode is made that way, the arrow points the direction the current can flow, and since it is in the circuit the same direction we can think that it flows either way.
The arrow points in the direction of conventional current flow, ie, Hole flow, not electron flow. Electrons flow in the opposite direction from conventional current flow, ie, HOLE flow.
...if you're going to be really picky, in the direction of majority carrier flow, AFAIR.
Sep 28, 2009. 7:00 PMframistan
says:
BOTH answers are correct! Many years ago, in Benjamin Franklins time, they GUESSED WRONG that it flowed from positive to negative. So all schematics and publications show POSITIVE flow. But scientifically, it actually flows from negative to positive. Unless you are a SCIENTIST, you should ignore this fact! On a schematic diagram, we look at a DIODE symbol and it looks like a funnel. The POSITIVE current flows in the direction of the "funnel" or arrow. It was decided many years ago to just IGNORE the mistaken direction of current flow (in the electronics industry) because they didn't want to re-print all the books and schematics ever written. Thats what they told us in electronics classes back in 1979... framistan
Sep 29, 2009. 5:52 AMWesley666 (author)
says:
I can't pick two best answers but yours helped alot too! Thanks so much!
Right. It doesn't actually matter, of course, since Maxwell's equations are symmetric under charge-sign inversion. The electrons (negatively charged) do flow from the "-" label to the "+" label, while the "hole current" (as Seandogue labels it) flows from "+" to "-" as you'd naively expect.
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