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Tuesday, July 26, 2016

Which way does current REALLY flow?

I've talked on the podcast about launching a worldwide campaign to require the reversal of ALL those little arrows on the symbols for transistors and diodes.   You see, they are saying that electricity flows from the positive to the negative.  Engineers apparently got that idea from Ben Franklin, and they are sticking with it.  It is time for a change!   Reverse the arrows!  Down with CCF!  Viva Electron Flow!  Let's tell the truth!

This morning Bob Crane W8SX sent me this very interesting article on this topic from Nuts and Volts:

The article describes very well the origins of this controversy. (There were one or two scary moments in which I thought the author was getting ready to tell us that positive ions can move through wires and transistors (NO!) but he pulled back from the brink and clarified that he was talking about ion flow in electro-chemical batteries.  Whew, that was scary!)

But here's a question for the philosophers and historians of electronics:  When physicists decided to label the electron as "negative" this was an arbitrary choice, right?   They could have just as easily decided to call it "positive" with the protons being called "negative" right?  In this case all the arrows in our diagrams would not be in need of reversal, right? 


  1. It's just too late for me, I -know- that electrons go the other way and that in valves they start off from the heated cathode obviously, but I just was brought up with thinking of current going from the positive and following the arrows in transistors. All our equipment uses negative for the chassis and it is simpler to think of the current ending up at the chassis and not originating there. Then when we get into the physics of the semiconductors we discover about holes and the direction that they travel. We can't see the electrons moving in tne wires so in the end it doesn't really matter which way they really go just as long as we stick to one convention.

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  4. AB1YK I always look at the arrows as check valves so they work for me!

  5. OK, so we invert the nomenclature, that would make pro-tons anti-tons, right?

  6. The arrows in semiconductor devices generally point to the N-type material (cathode in a diode, emitter in NPN, base in PNP, channel in a n-channel MOSFET, etc.).

  7. The arrows in semiconductor devices generally point to the N-type material (cathode in a diode, emitter in NPN, base in PNP, channel in a n-channel MOSFET, etc.).

  8. So, electrons flow from negative to postive. But they travel at speed of 80 cm/hr, which is very slow compared to rate at which the electrical energy is transfered.

    The velocity that the energy travels is C, or 3x80^8 M/s in a vacuum. C is always slower depending on the medium that the energy is transfering in whether it's a PCB, or coax, or wire. But my point is that the current that we think about when design and analysing circuits flows at this rate, and not the velocity of the electrons. So to say we should think about electron flow for current is not accurate without this consideration.

    We don't really need to think about the electron flow for most of our work in electronics. But, to understand things like circuit Q, and skin effect you do need to think about it.


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