DC flow of electrons and things like diodes  - Page 1
Forum section: electronics / beginners

author: The_Welding_Library_Guy
author_rank: Contributor
timestamp: February 01, 2019, 09:06:35 pm
content: So, I understand that in DC systems current flows from Neg to Pos but one thing that confuses me is how a circuit like the one below works then? If current flows from neg it shouldn't be able to flow throgh the LED unless is bypasses the breakdown voltage. But even then it shouldn't light the led. Right? I'm sure theirs something simple that i'm missing here so I would be very grateful if anyone could help me understand a bit better.~Thanks

author: Paul Moir
author_rank: Frequent Contributor
timestamp: February 01, 2019, 09:17:27 pm
content: Long ago before anyone knew the charge of an electron, it was assumed that they flowed from positive to negative. Since the symbols and the way of thinking of circuits were defined by this error, it stuck. This is commonly called "conventional current flow". The truth is the electrons go the other way, but for most purposes it's just easier to pretend they flow from positive to negative so the symbols and names make sense.(EDIT: ah, welding: it's pretty obvious which way the electrons are really flowing there.)

author: David Hess
author_rank: Super Contributor
timestamp: February 01, 2019, 09:35:41 pm
content: The *electron* current flows from negative to positive because we initially assumed electrons were positive. The junctions on schematics point along *conventional* current from positive to negative.

author: dmills
author_rank: Super Contributor
timestamp: February 01, 2019, 10:15:24 pm
content: Also while electrons are the charge carriers in METALLIC conductors, this is not true in other types...In molten Salts for example it is the ion that is the charge carrier and electrochemistry was and (to some extent) still is a **Major** user of power, so coming from that direction it is not at all clear that they really got it wrong (Or that it much matters which convention folks use).Current flow in semiconductors is "Complicated".Good textbooks in EE mention the charge on the electron being negative and then (outside the chapter on device physics) never mention it again, because unless you are doing semiconductor physics, particle beam, or plasma engineering it really does not matter.Regards, Dan.

author: Brumby
author_rank: Unknown
timestamp: February 02, 2019, 02:21:24 am
content: Quote from: The_Welding_Library_Guy on February 01, 2019, 09:06:35 pmYes there is. You have mixed the two concepts of "Conventional current flow" and the directly opposite "electron flow". All circuit diagrams are drawn as "Conventional current flow", so looking at them with electron flow in mind will confuse you no end.Basic rule is - never look at a circuit with electron flow in mind - unless you KNOW you need to. (Which is rare.)

author: vk6zgo
author_rank: Super Contributor
timestamp: February 02, 2019, 03:22:21 am
content: Quote from: Brumby on February 02, 2019, 02:21:24 amElectron flow was better known back in the valve (Electron tube) days, because there is no mechanism by which current can flowintoan anode, whereas thermionic emission of Electrons from a heated cathode was a well known effect, even before the first "valve" was builWhen I learnt basic theory, back in the day, we learnt about Electron Flow, then about the historical basis of Conventional Current Flow, & it took the class all of 5 minutes to understand that the various "Right Hand Rules" etc were developed using CCF, & could effortlessly swap between the two ideas.Some EEs (on other fora) get "all bent out of shape" when you mention Electron Flow---it's as if you insulted their mothers!

author: Brumby
author_rank: Unknown
timestamp: February 02, 2019, 04:50:00 am
content: I agree that in the valve era you reallydidneed to know about electron flow - but these days, that's more of a vintage thing - and even CRTs are a thing of the past.That's not to say that understanding the two different views isn't worth the effort - it is - but in day-to-day electronics work, you can work very effectively with just the conventional current perspective.My best advice is - understand what electron flow means ... and then forget about it. If you ever come upon a scenario where such knowledge is required, you will at least be able to identify that and then take steps to augment your understanding appropriately.

author: The_Welding_Library_Guy
author_rank: Contributor
timestamp: February 02, 2019, 10:25:10 pm
content: So to be sure I understand. DC components are labeled backwards to complied with the ideal of conventional current flow essentially? So say I have a 1N4007 dioide in a circuit. I would design the circuit so that the stripe points from positive to negative thinking the stripe represents the blocking side (not sure the accutal erm for this). But in reality the blocking side is the oppoist side that's pointed towards positive?Sent from my VS500PP using Tapatalk

author: Brumby
author_rank: Unknown
timestamp: February 02, 2019, 11:33:19 pm
content: Basically - Yes, you have that correct ... BUT you are still confusing yourself by thinking about electron flow.STOP doing that! ONLY think in terms of conventional current flow and you will understand just about everything without having to go through these mental gymnastics!!!There is a reason that thinkingonlyin terms ofconventional current flowis pretty much universally used ....IT WORKS!The symbols usedwere written forconventional current flow, so trying to apply electron flow thinking is just going to make your life so very, very hard.As I said above,Quote from: Brumby on February 02, 2019, 04:50:00 amYou have the fundamental understanding of the difference between conventional current flow and electron flow. IF you ever NEED to think about electron flow, you can - but don't go looking for those "opportunities".

author: The_Welding_Library_Guy
author_rank: Contributor
timestamp: February 02, 2019, 11:42:51 pm
content: Yea I understand that. I knew coming in that designing circuits pos to neg works. That's why everything I have ever seen is la yes out that way. I was just try to figure out why my understanding of the what's going on in the conductor didn't match what I was doing in the real world. I was just making sure I understood what I was being told. I know this will most likely never have a practical implementation for me. Was just more of a curiosity~thanks every one for your answers this one had been twisting my mind for a whileSent from my VS500PP using Tapatalk

author: IanB
author_rank: Super Contributor
timestamp: February 03, 2019, 12:02:04 am
content: Quote from: The_Welding_Library_Guy on February 02, 2019, 10:25:10 pmDC components are not labeled backwards, they are labeled properly. Current flows in the direction of the arrow and is blocked the other way. That is why LEDs work, because current flows forward through them in the direction of the arrow, and they have a forward voltage drop which is positive.Quote from: The_Welding_Library_Guy on February 02, 2019, 11:42:51 pmIn the real world, current flows from positive to negative. If you measure it with an ammeter it will show a positive reading when it is flowing from the positive probe to the negative probe. If you pass current through a resistor there will be a positive voltage difference in the direction of current flow.Keep always in mind thatcurrent flows from positive to negative, and circuits are laid out and arranged to reflect that. As long as you remember that and don't confuse yourself with other ideas you will be fine.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 03, 2019, 02:33:11 am
content: Quote from: IanB on February 03, 2019, 12:02:04 amNo, in the real, physical, world Electron Flow is how current works.The existence of vacuum tubes is the most important supporting argument for Electron Flow.Saying "We don't use them anymore, so it doesn't count" is about as effective as sticking your fingers in your ears & saying "La,La,La,La!"Yes, Conventional Current Flow is a useful concept, & works almost everywhere, but it is a historical accident, & can't be twisted into anything else,.In an effort to justify CCF some people (notably EEs) insist that you would have to multiply everything by minus 1 if using Electron Flow.This seems to be rooted in an archaic concept that "positive is 'higher' in potential than negative" which is in reality, utter balderdash.Electron Flow causes exactly the same polarity voltage drops across resistors as CCF.This is the beauty of the thing--- we use CCF happy in the knowledge that things like "Right Hand rules" work, & we don't have to invent "Left Hand rules" -- for most everything else, the two ideas are interchangeable.If your advice is to use CCF for its convenience, & don't go down the path of having to make mental conversions every time, I would agree, but denying the existence of the real mechanism of current flow in conductors because it is "confusing" is pretty much saying that people don't have the intellectual capacity to understand two different ways of viewing things.I, & my contemporaries had no problem with the two concepts, so why are younger people likely to become confused?

author: MrAl
author_rank: Super Contributor
timestamp: February 03, 2019, 02:58:51 am
content: Quote from: The_Welding_Library_Guy on February 01, 2019, 09:06:35 pmHi,You can view the circuit in two ways, using conventional current or the drift flow of electrons.The components we often see have their arrows pointing in the direction that conventional current would flow if it could flow.You can usually just forget about 'electron' flow.An interesting fact. If you view a wire as a tube of electrons and narrow that down to just one electron width, if you leave out one electron and watch the electrons move from right to left, you will find that the 'hole' moves from left to right!Look for a video on the web.

author: IanB
author_rank: Super Contributor
timestamp: February 03, 2019, 03:09:22 am
content: Quote from: vk6zgo on February 03, 2019, 02:33:11 amYour advice is exactly why the OP is confused. If you want to spread confusion, this is the way to proceed.And in fact, considering electron flow is not the right way to reason about current. The correct way is to consider current flow to be an accounting problem, where we account for charge transfer. For example, if I lend you $100, is that positive or negative? You might think it is positive in that your cash balance went up by $100, but it is also a negative as you have now acquired a debt. You have to consider that you owe me $100 so that counts as −$100 in your net worth.The same it is with current. Current simply causes charge to be transferred from A to B. If A is down 100 coulombs then B is up 100 coulombs. It really doesn't matter whether it is electrons or pixies that transfer the charge. The accounting is the same. Increased charges are positive and decreased charges are negative.

author: Brumby
author_rank: Unknown
timestamp: February 03, 2019, 04:53:25 am
content: Quote from: IanB on February 03, 2019, 03:09:22 amI have to agree.You can be very successful with contemporary electronics - design, construction, testing and repair - without ever knowing about electron flow, especially where thermionic devices are not involved.

author: james_s
author_rank: Super Contributor
timestamp: February 03, 2019, 04:55:38 am
content: Just pretend that electricity flows from positive to negative, then all the schematic symbols will make sense. It doesn't matter what the electrons are actually doing, you can't see the electrons anyway. All schematic symbols are drawn assuming positive to negative flow.

author: Brumby
author_rank: Unknown
timestamp: February 03, 2019, 04:59:43 am
content: Quote from: vk6zgo on February 03, 2019, 02:33:11 amWhile technically correct, this is essentially irrelevant - especially when there is someone who is trying to wrap their head around some basic concepts.Let them learn to do things with "conventional current" thinking. This will give them a solid foundation on practical knowledge that will yield a wealth of understanding that will serve them well for decades to come.If they never work with thermionic devices or semiconductor wafer design, they could easily run a career without knowing how to think in terms of electron flow.