Aaaah, it's driving me mad - Page 1
Forum section: electronics / beginners

author: adras
author_rank: Regular Contributor
timestamp: September 30, 2024, 01:25:41 am
content: I have an electron source, a container with a capacity of 1000 electrons(MINUS). I also have another container which lacks exactly 1000 electrons(PLUS). Normally we call something like this a battery.When I connect both terminals together using a wire, current flows from minus to plus.Now let's create a simple mosfet curcuit. I assume that it's better to place the load before the gate, than after the source.This creates two circuits (simplifying to the mosfet being always turned on, leaving only two connections at the mosfet):1. Plus, Load, Mosfet, Minus2. Plus, Mosfet, Load, MinusNow in general in electronics we say current flows from positive. This means, for circuit no.1 the voltage after the load is lower, thereby reducing the current, and the mosfet has to switch a lower load. This makes sense to me.However, physics basically say the following:I have my container, MINUS, the electrons go through the mosfet, and after that are facing the resistance of the load, and then resulting in a lower voltage. On the other hand, this is curcuit no.1, and it means a ton of current flow through the mosfet before the voltage is reduced by the load.The other way: I have my container, MINUS, the electrons flow through the load, resulting in a lower voltage, and the mosfet has to switch that. This would be circuit no. 2This is incredibly confusing, since there are many contradictions. It took me two attempts to get it right. There is a contradiction in between the way we design curcuits and the way current actually flows/where the load actually is.It took me years to find an example like this. Please don't reply with a generic answer like, current flows from plus to minus. It doesn't. An electric field propagates, and it has a source(MINUS) and a destination(PLUS).

author: Andy Chee
author_rank: Super Contributor
timestamp: September 30, 2024, 01:51:19 am
content: The only way to avoid confusion, is to stick with the conventions used in the discipline you are working in.If you are working in chemistry or physics, then it is universally accepted that electrons flow from negative to positive.If you are working in electronics, then it is universally accepted that current flows from positive to negative.For an explanation of why the difference exists, it is in the history of the discovery of electricity.In summary, when electricity was first discovered they had no idea that electrons existed. But in order to perform mathematics for electricity you need to define a direction, so they just arbitrarily decided that current flows from positive to negative. Remember: they do not know about electrons yet.Over 100 years later they discovered electrons, and realised it was the wrong direction. But it's too late to change everything after 100 years!

author: Nominal Animal
author_rank: Super Contributor
timestamp: September 30, 2024, 04:20:18 am
content: I resolved the confusion for myself by applying solid state physics, and thinking in terms of charge carriers.The flow of positive charges indicates the direction of the conventional electric current. The flow of negative charges is the opposite direction.(Electric current itself can be defined as the rate of charge flowing through some surface, say a cross section. Voltage between two points describes the amount of energy one would need to 'spend' per positive unit charge to move the charges from one point to the other. It is all symmetric, too: no need to worry overmuch whatcauseswhat, because they tend to cause each other.)In metal conductors and in vacuum, electrons carry negative charge.In electrolytes, positive and negative ions carry corresponding charge.In semiconductors, electrons carry negative charge, and electron vacancies or "holes" carry positive charge. In n-type semiconductors, most of the charge carriers are electrons; in p-type, most are "holes". In all ways that matter, although an electron "hole" is not a real particle, it can be treated as such. (It is the lattice structure around the "hole" that provides the properties and reacts to e.g. electric and magnetic fields, and it does so in a manner that is equivalent to the "hole" quasiparticle reacting to them and the lattice to the quasiparticle.)To determine which way the charges flow in practice, check what carries the current, and what causes the charge imbalance in the first place. That should be enough to let you work it out, because chemical or electromagnetic energy is needed to create new charge carriers, and they recombine back to neutral whenever possible. If the charge carriers have positive charge, that is also the direction of the conventional electric current. If the charge carriers have negative charge, the conventional electric current is in the opposite direction.I like this, because I don't need to memorize anything. I only need to understand; and have some way to check the details (like exactly what kind of ions carry the charges in an electrolytic, for example) whenever needed. Simple logic handles the rest – and I can do simple logic.

author: Xena E
author_rank: Frequent Contributor
timestamp: September 30, 2024, 05:57:53 am
content: Ignoring the analogy for the source of potential difference and the incorrect terminology for the mosfet, (I think you mean source and drain for the circuit under consideration ?)Basicallyyou can consider what you describe as a battery, switch and load in series, then whatever 'way round' you consider the electricity 'flowing' the current at any point in the circuit will be the same: the switch will alow the electrical flow to commence and the load will govern at what current.The order and direction that electrical charge arrives at any point in a completed circuit is immaterialIt's time to hit the books and brush up on fundamentals.

author: magic
author_rank: Super Contributor
timestamp: September 30, 2024, 06:06:00 am
content: Could you at least start with posting unambiguous schematics of the hypothetical circuits you are considering?Quote from: Xena E on September 30, 2024, 05:57:53 amSounds like a good plan. It's hard to even understand what the question is about.(I doubt that it has anything to do with internal operation of semiconductors, for the record).

author: iMo
author_rank: Super Contributor
timestamp: September 30, 2024, 08:32:18 am
content: The OP describes a mosfet switching a load wired in 1. drain, or 2. in source. He/she is trying to understand the way how to interpret notion of the current flowing through the mosfet and through the load and the voltage on the mosfet and on the load from the perspective of physical and agreed "electron's flow" in both examples.I would add to his/her confusion that "the speed of electrons" in metals or semiconductors (as in the above examples) is only a couple of millimeters per second..

author: magic
author_rank: Super Contributor
timestamp: September 30, 2024, 10:10:06 am
content: And I was under impression that it was something about whether the MOSFET switches low or high voltage and whether load current is low or high, which obviously makes no sense because both cases are identical.That's why I asked for details. We could sit here, speculate and debate alldayweek long, and nothing will come out of it.Oh, and by the way, it's definitely not a battery but a capacitor.

author: Xena E
author_rank: Frequent Contributor
timestamp: September 30, 2024, 10:46:34 am
content: Quote from: iMo on September 30, 2024, 08:32:18 amThey actually said:QuoteThey also said:QuoteWhich shows a complete misunderstanding of the subject.Also:Quote from: magic on September 30, 2024, 10:10:06 amI agree, we should be fair to the op to explain themselves better.X

author: adras
author_rank: Regular Contributor
timestamp: September 30, 2024, 11:47:05 am
content: Maybe I have a better chance this way.+ Pole, R1, R2, R3, - Pole.Suppose + and - has a voltage of 5V. What do you see when measuring - pole and R3? You're supposed to see 5V minus R3, but that's not the case, you measure this, when you connect to R1 and +. But when you measure at the back of the circuit, you measure the voltage after R2 and R3, not the one of R1 alone.My issue is just this. All makes sense if current flows from positive to negative, but according to physics it flows from negative to positive. And at this point, none of the knowledge I learned in any book makes any sense anymore.

author: PGPG
author_rank: Frequent Contributor
timestamp: September 30, 2024, 01:09:19 pm
content: Quote from: Andy Chee on September 30, 2024, 01:51:19 amElectronics would be easier if we were made of antimatterBeing new here I am surprised anyone can have a confusion with it. Who cares in what direction electrons travel. Why bother with it? When you think of current you think of current and not electrons.Perhaps my luck was that when I (at 10 years old) was learning the absolute basics of electronics, just like people when they defined the direction of current flow, I had no idea about the existence of electrons. Later when I heard about electrons I just took the information that they flow in opposite direction than current, and nothing more comes out of it.I found at net first electronic book I have read:https://archive.org/details/abc-radioamatora-c.-klimczewski-wyd-1953/ABC_Radioamatora_C_Klimczewski_wyd_1953_pdf_compressed/mode/1upThere are more pictures than text so not knowing the language you can imagine at how simple (understandable for a child) examples everything is explained. For example a filter is a hole in the fence through which the skinny ones (waves) can squeeze through but the fat ones cannot. Based only on this book I have build my first detector radio receiver.Quote from: adras on September 30, 2024, 01:25:41 amForget (as total as you are able to) about electrostatic when you try to understand electronic. The best would be like you have never heard a word about electrostatic.In electronic negative or positive charge can't be collected in any single element. Any single electronic element always have no electrostatic charge. Your two containers in electronic have to be one element so even one has -1000 and the other +1000 they both being one element have no charge (if measured relative external world). Even in electrostatic having such two containers you can one load with -1000 and second with +800 in electronic it is not possible. Such element having these two containers inside it have to have at any time moment at them exactly opposite charge.Quote from: adras on September 30, 2024, 01:25:41 amIn your model when half of electrons will move to the opposite container a potential (between containers) will be 2 times lower, but when from 1.5V battery you took half of its capacity you still have around 1.5V at it. So no. What you describe we not call battery. What you describe you can call Leyden bottle (in electronic it is capacitor).Quote from: adras on September 30, 2024, 01:25:41 amThis sentence is true or false depending on what circuit part current you have in your mind, what we can only guess.If you think (as I suppose) about current in the wire you used to connect terminals than this sentence is false - current in this wire flows from plus to minus.But if you think (what I don't suppose) about the current in your element consisting of your two containers than this sentence is true - in this capacitor current flows from minus to plus.In electronic current always flows in closed circle. As at each connection (in electronic net) along that circle there are different potentials and current in whole circle flows in the same direction than in some part of circuit current have to flow from plus to minus and in other parts from minus to plus.Things begin to complicate when we came to AC (alternating current) when you can have phase shift between voltage and current. If shift is 90° then at the moment when voltage is 0 current has its maximum and when voltage is maximum current is 0.Quote from: adras on September 30, 2024, 01:25:41 amThis sentence I completely don't understand. Gate is used to control MOSFET.Imagine a crane whose hook is raised by a motor that is turned on by a button. What you said is a consideration of whether to place the load in front of the button or suspend it under the hook.

author: PGPG
author_rank: Frequent Contributor
timestamp: September 30, 2024, 01:48:10 pm
content: Quote from: adras on September 30, 2024, 11:47:05 amTry to be more precise.If you write that (+) and (-) has a voltage of 5V that means that they both (each of them) have 5V relative to some common reference potential. So between (+) and (-) you have 0V.In such case at each resistor ends you will have the same potential of 5V.You probably wanted to write that voltage between (+) and (-) is 5V.Quote from: adras on September 30, 2024, 11:47:05 amWhat does it mean?To measure R3 you need ohmmeter.To measure voltage you need to specify two nets (connection points) between which you want to measure it. R3 is not specifying net but element.Quote from: adras on September 30, 2024, 11:47:05 amIf R has 100Ω than you ask how many it is 5V - 100Ω. I think no one knows.Quote from: adras on September 30, 2024, 11:47:05 amWhat is 'this'?How you connect to R1 (R1 has two ends you can connect to. Be more precise).If you want to speak about measuring voltage between both ends of R1 you can write of 'measuring voltage at R1'.I don't know what you want to say. Do you want to say that to measure voltage at R3 you have to measure voltage at R1?Quote from: adras on September 30, 2024, 11:47:05 amYou've outdone yourself here. I can't even imagine what you were trying to say.Quote from: adras on September 30, 2024, 11:47:05 amCurrent flows in opposite direction than electrons.You must have had a really stupid physics teacher.It happens. My brother, while studying at the academy, argued with a doctor of physics who insisted that in an oblique throw the tangential velocity to the direction of motion is constant. It had to rely on the professor's intervention so that the doctor understood how it was.

author: radiolistener
author_rank: Super Contributor
timestamp: September 30, 2024, 02:14:24 pm
content: Quote from: adras on September 30, 2024, 01:25:41 amIn electronics, the direction of current is defined as the movement of positive charges. When negative charges, such as electrons, move from the negative to the positive terminal, this means that positive charges are moving in the opposite direction relative to the negative ones. Therefore, the accepted direction of current in electronics is correct.The movement of electrons is characteristic of current in metals, where electrons serve as the charge carriers. However, this does not mean that current always involves the movement of electrons. In electrolytes, current can consist of the movement of both negative charges (anions) and positive charges (cations). Therefore, current can result from the motion of different types of charges depending on the medium

author: Andy Chee
author_rank: Super Contributor
timestamp: September 30, 2024, 02:20:52 pm
content: Quote from: adras on September 30, 2024, 11:47:05 amYou appear to have difficulty in communicating your idea to us.I would suggest you include some pictures/diagrams/schematics with labelled points of interest.Do not use generic pictures. You need to communicate your idea, not some random image from the internet.

author: Xena E
author_rank: Frequent Contributor
timestamp: September 30, 2024, 02:59:40 pm
content: Quote from: Andy Chee on September 30, 2024, 02:20:52 pmHere's an exercise for @ adras.In the diagram, what is the voltage across:R1, (points A and B)?R2, (points B and C)?R3, (points C and D)?Lastly what is the current in the circuit?

author: djsb
author_rank: Super Contributor
timestamp: September 30, 2024, 03:48:36 pm
content: And also which way does the CONVENTIONAL current flow (ignore the electron current for all PRACTICAL purposes)?

author: coromonadalix
author_rank: Super Contributor
timestamp: September 30, 2024, 04:17:26 pm
content: CONVENTIONAL current flow ---- search for this and google will give you tons of answers

author: TimFox
author_rank: Super Contributor
timestamp: September 30, 2024, 06:10:32 pm
content: My mnemonic for conventional current flow in a circuit drawing:Showing the direction of conventional current as an arrow in parallel with the conductor/resistor/whatever: positive current in that direction induces a voltage from a positive end (feather end of arrow) to the negative end (pointy end of arrow).

author: bson
author_rank: Unknown
timestamp: September 30, 2024, 06:18:31 pm
content: Quote from: Nominal Animal on September 30, 2024, 04:20:18 amAn analogy I like to use is air bubbles in water. Sure, they are an absence of water, which defines them, but they are definitely a distinct "thing" with their own name. Holes are positive charge carriers in a sea of electrons the way air bubbles move through water. (Well, not exactly, but no analogy should be taken too far.)