So in working on my foxhole radio - I realized I needed to look at diodes a bit more as I was making essentially a DIY diode with the pencil and razor blade. And in looking at diodes, I realized that something just didn’t add up. And perhaps by the end of this post still won’t add up.
I’m going to further preface this by saying I think having two different theories is dumb and stupid. Especially when people are trying to learn this stuff for the first time!
So video below shows what I understand:
The question is if current/electrons go from the negative side of the battery to the positive side of the battery, how do diodes only allow current to go from anode to cathode (or P to N)?
Alright, so after digging around /way/ too much, it seems that there are TWO different types of theories - the right one and the wrong one that people keep around because it’s been around for a long time. I seem to be referencing both with my question. Let’s start with the wrong one:
Conventional Flow Theory
The idea was that charge flowed from something with positive charge to something with negative charge (though negative charge is due to having more electrons). And because we associate “positive” with “surplus” and “negative” with “deficiency,” engineers decided to retain the old concept of electricity with “positive” referring to a surplus of charge, and label charge flow (current) accordingly.
Electron Flow Theory
This is clearly not how batteries work. So another theory called the Electron Flow Theory came about to show how electrons actually moved - which was from negative to positive (as the electrons moved from the negative to the positive pole):
Ahh…much better. But then we have the diode issue - below is what we would expect of a normal diode set up:
So when the + end of the battery is attached to the anode, and the - end of the battery is connected to the cathode, we get current capable of lighting up a bulb!
If we label this according to conventional flow notation - everything makes sense - current goes from the surplus side to the deficient side of things and current goes through the diode as expected.
But! If we use electron flow notation - the way electrons actually “move” around in a circuit we get the following. And it looks completely backwards to how we’d expect current to move in a circuit with a diode:
How has it been explained away?
So some people say, just deal with it or that’s just how people notate it. But if the electron theory shows current flowing in the very direction that a diode’s supposed to block it, how can /anyone/ ignore it?! And with almost everything else we talk about where/how the electrons move through a component…but somehow the definition of a current changes for diodes? *confused* Here are some explanations others have given:
- In a semiconductor it is sometimes useful to think of the current as due to the flow of positive “holes” (the mobile positive charge carriers that are places where the semiconductor crystal is missing a valence electron).
- In semiconductors, when we say current flows from + to -, we don’t mean the electron flow, we mean the hole flow. We know positive charges come from protons and negative charges come from electrons. But we also know that protons do not flow since the proton is stuck in the nucleus, therefore positive charges do not physically flow. Electrons on the other hand, do flow since they can jump from atom to atom so negative charges can flow. But when the negative charge jumps, it leaves behind a “hole” of positive charge that originates from the proton in the nucleus which no longer has its charge canceled to zero because the electron isn’t there anymore. As the electrons move in one direction and leave behind holes, it will appear as though the holes flow in the opposite direction. This hole flow is conventional current. So it’s hole flow for entire circuits and not electron flow?
- Current is positive charge. So even if protons don’t move, the fact that electrons are moving from the negative to positive end of a diode means that a positive charge is “moving” from the positive to negative end of a diode.
- The latest explanation is that direction is less important than how they are placed in the circuit - that is relative to the polarity of the power source. So if they are placed in a configuration that allows current flow through them, so be it. But if the polarity reverses, it’ll block current. So if you have an ac current, it will seem as if the diode is blocking current from one “direction” but not the other. Thanks to @whixr for his help :p