Current flow and transistor biasing. - Page 1
Forum section: electronics / beginners

author: medical-nerd
author_rank: Regular Contributor
timestamp: October 06, 2017, 09:20:39 am
content: HiyaI have a very simple question regarding current flow.(I have tried searching the forum but when I click on the second or subsequent pages of a search I get an empty page).I understand the concept that when forward biasing a p-n junction such as the base-emitter junction in a NPN transistor, electrons and holes as majority carriers mean that there is externally a flow of electrons from emitter to base.But historically current flow is from + to - .I have looked at transistor models and descriptions of biasing and both (electron flow and + to - ) are described as current flow depending upon the article.Which version should I use?Cheers

author: danadak
author_rank: Super Contributor
timestamp: October 06, 2017, 10:55:53 am
content: I always thought electron flow was more appropriate, but in somecircles I am in the minority. Choose your poison -https://www.mi.mun.ca/users/cchaulk/eltk1100/ivse/ivse.htmhttp://www.instructables.com/id/Conventional-Current-Vs-Electron-Flow/Regards, Dana.

author: Circlotron
author_rank: Super Contributor
timestamp: October 06, 2017, 11:06:01 am
content: It depends on whether you think your car travels to work, or your work parking space travels to your home.I just think back in the old days they didn't really know which way current flowed so they took a guess and they got it wrong. They are still trying to save face by inventing new theories.

author: medical-nerd
author_rank: Regular Contributor
timestamp: October 06, 2017, 11:46:57 am
content: HiyaI understand the history and that many prefer the + to - flow, what has confused me is that there doesn't seem to be a convention regarding flow in the transistor biasing articles and videos I have read/watched so far.You may be wondering why this is important to me - its because I don't want to copy circuits anymore, I've reached the stage where I want to design them myself and wonder if this is important in circuit simulation - I've never done any and am about to dip my toes in.Or am I just worrying about nothing important?Cheers

author: w2aew
author_rank: Super Contributor
timestamp: October 06, 2017, 02:30:56 pm
content: Quote from: medical-nerd on October 06, 2017, 11:46:57 amIn my 35+ years of experience, the vast majority of articles, texts, videos, references, and professionals use Conventional current flow (opposite of electron flow) when discussing circuit design.

author: rstofer
author_rank: Super Contributor
timestamp: October 06, 2017, 03:48:29 pm
content: I'm with W2AEW, I almost never see electron flow. The US Navy used to use it and may still but they would be in the minority.All through college and throughout my career (and hobby), conventional current flow has worked just fine. Maybe it's just convention but current flow tends to work well with Kirchoff's Laws (writing loop equations). I know we could change the signs and do it the other way but why?One more important point: I can follow the arrowheads through diodes and transistors. Thinking about electron flow against the arrowheads is just awkward.

author: Cerebus
author_rank: Super Contributor
timestamp: October 06, 2017, 04:11:03 pm
content: When you are trying to understand semiconductorphysicsuse electron flow, when you are trying to understandcircuitsand semiconductorcomponentspart in them use conventional current flow.That's the way I think and since I've adopted that approach I haven't got confused between the two, not even once. The only time you really ever need to think about actual electron or hole flow is when you're trying to get a grasp on how the inside of the device works. As soon as you step outside the device and start looking at its interaction with other components then conventional current is the language that everybody uses.

author: medical-nerd
author_rank: Regular Contributor
timestamp: October 06, 2017, 04:19:28 pm
content: Thank you all. I will use conventional current flow + to - .I just need to get the info I've just been working through describing it through electron flow out of my head!! I wish brains had a soft reset function rather than the hard reset of an alcohol binge and bang to head!!You were right Cerebus - the articles were starting by describing physics of semiconductors and followed on from there explaining the circuits using electron flow. I will adopt your approach. It makes it much clearer.Cheers

author: David Hess
author_rank: Super Contributor
timestamp: October 06, 2017, 08:24:46 pm
content: Quote from: Cerebus on October 06, 2017, 04:11:03 pmExactly. And also use the electron flow when dealing with chemistry.I suspect the doublethink of conventional and electron flow is easier for those of us who have done some design or analysis work with vacuum tubes or lack a particle of common sense. The later also allows holdingtea and no tea.

author: rfeecs
author_rank: Frequent Contributor
timestamp: October 06, 2017, 09:30:51 pm
content: Quote from: Cerebus on October 06, 2017, 04:11:03 pmUnless you are trying to understand a PNP transistor or a P channel FET. Then you are going hear a lot about hole flow.Or the J (current density) in semiconductor physics (and in Maxwell's equations) both go in the conventional direction. Electrons have negative charge and flow the opposite direction.

author: CD4007UB
author_rank: Contributor
timestamp: October 06, 2017, 10:28:47 pm
content: These are all good points. But there is more to understanding NPN or PNP transistors than distinguishing conventional current from electron flow.Whatever type of bipolar transistor you have, the forward-biassed base-emitter junction injects 'minority carriers' from the emitter into the base (e.g., electrons into the p-type base for NPN or holes into the n-type base for PNP). Most of the minority carriers diffuse (without recombination) through the thin base to the collector, where they are swept away to produce the collector current. A small increase in the base-emitter voltage then produces a large increase in the emitter current, and hence in the collector current. This allows the transistor to act as an amplifier (e.g., when the collector current flows through a large resistor, producing a large change in the collector voltage of the transistor).So, for an NPN transistor, we concentrate on electron flow, because it's the electrons that are the minority carriers that are injected at the forward-biassed base-emitter PN junction. This is (some of) the important semiconductor physics mentioned by Cerebus.(The base is very lightly doped compared to the emitter, so it does not contain many holes, and to a first approximation we neglect the injection of holes from the base into the emitter.)

author: rfeecs
author_rank: Frequent Contributor
timestamp: October 06, 2017, 11:49:41 pm
content: I made the mistake of breaking out the first few words of Cerebus's post and ignoring the rest. To be clear, I agree with this 100 percent:Quote from: Cerebus on October 06, 2017, 04:11:03 pmI was also pointing out that even semiconductor physicists use conventional current flow.My high school electronics teacher, on the other hand, was an ex Navy technician. He used a text book that defined current as electron flow. At the same time, in physics class we used conventional current flow. I don't recall being too confused about it. Later everything was conventional current flow, so I stuck with that and never looked back.

author: Brumby
author_rank: Unknown
timestamp: October 07, 2017, 12:05:12 am
content: I have always said that, by all means, learn about electron flow (in fact, I would recommend it) - and then promptly forget about it.In circuit design, analysis and discussion it is conventional current flow that is used by the vast majority ... but if youdohappen to come across references that indicate (or state) electron flow is being used, your memory will kick in and you won't get completely lost.

author: bson
author_rank: Unknown
timestamp: October 07, 2017, 12:29:28 am
content: When talking about EE models current flows from + to -. When talking about physics, charge moves from - to +.It's important to understand that current isn't a movement of electrons, but of charge. It's perfectly possible for holes to move also without any significant electron movement. This is particularly the case with semiconductors.

author: rfeecs
author_rank: Frequent Contributor
timestamp: October 07, 2017, 01:05:17 am
content: Quote from: bson on October 07, 2017, 12:29:28 amYou mean an electron moves from - to +?What I remember from physics is if point A is higher potential than point B, then there is an electric field from point A to point B (+ to -), and a charge q will experience of force from A to B (+ to -). So if q is positive, then it moves from + to -. If the charge q is negative (like an electron), it moves from - to +.

author: Brumby
author_rank: Unknown
timestamp: October 07, 2017, 02:47:21 am
content: The point is - you do notneedto be so specific in describing charge or current in a discussion at the electronics design and analysis level.Doing so will only complicate matters in a way that is completely unnecessary. I am not saying it is invalid - far from it - just that it isunnecessary... and you will expend an inordinate amount of energy doing so, withnorealbenefit.As I said before - understand about electron flow and then forget about it.You will be hard pressed to find ANY discussion, design or other processes whereconventionalcurrent flow will not be more than adequate.The purpose of any concept is to encapsulate the physical reality in a sufficientlypracticalmodel so that it can be used in practical situations. Conventional current flow does this - and does it so well, that even when electrons were found to flow the other way ... conventional current flow still flourished.If you still find this hard to accept, then I would point you to the quantum world, where even the specific nature of the electron isn't as clean cut as you would like.The precise nature of our universe is so bizarre that we cannot understand every detail in every situation. For a start, we don't know everything - but even the things wedoknow are so complex, we would have trouble trying to work with just a fraction of that knowledge.The solution is to define a model - a simple set of elements which defines a practical description that allows us to actually do something in our macroscopic world. The conventional current model does this - and does it very well for designing electronic circuits.

author: Circlotron
author_rank: Super Contributor
timestamp: October 07, 2017, 08:08:51 am
content: Quote from: Brumby on October 07, 2017, 02:47:21 amAre you saying that women have conventional current flow?

author: Brumby
author_rank: Unknown
timestamp: October 07, 2017, 08:47:25 am
content: Not touching that one with a barge pole ofinfinitelength.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: October 07, 2017, 08:49:35 am
content: The crazy thing is that for half a century of valve (vacuum tube) electronics we had the correct notation. Nobody talked about a hot cathode sucking positronic rays or summat out of the anode. They would have been laughed out of the place if they had. Then, with transistors, it was madewrongagain. Yet, nobody laughed. Or even objected.Sometimes, human behaviour is indeed incomprehensible.Come back flat-earthers, you are not alone in your attachment to disproved concepts.

author: Brumby
author_rank: Unknown
timestamp: October 07, 2017, 09:00:59 am
content: Did theynevertalk in terms of conventional current flow with valve circuits?

author: whalphen
author_rank: Regular Contributor
timestamp: October 25, 2017, 05:21:24 pm
content: I think Franklin did us a favor! Charge and electrons are not the same thing. Charge is a property of a charge carrier. Electrons happen to be negative charge carriers. If we talk about the direction of current, we could be talking about negative charge carriers or positive charge carriers. If we're talking about positive charge carriers (which we sometimes use), they move from positive to negative. If we're talking about negative charge carriers (which are more common in electronics), then the direction of flow of the charge carriers goes from negative to positive.Just as in mathematics, positive is the default and negative is designated with a special symbol (the negative sign), I think it's appropriate to talk in terms of positive charge carriers and conventional current by default. Just know that when we use typical conductors the charge carrier is not positive, it's negative, so we have to remember that those negative charge carriers are flowing in a direction opposite to that of a positive charge carrier.Who knows what the future brings? We use positive charge carriers in semiconductors. We may some day use positive charge carriers more extensively in yet-to-be-discovered technologies. So it's appropriate that we talk about current flow in terms of positive charge carriers flowing from positive to negative. And, if we use negative charge carriers such as electrons, we have to use a negative sign to designate that. Remember that electrons are not nature's only charge carrier. They just happen to be the one more commonly used in electronics at this point in time.

author: bd139
author_rank: Super Contributor
timestamp: October 25, 2017, 06:44:53 pm
content: Just a note: I’ve seen electron flow used and taught in Europe a lot. Philips used it in a lot of their service literature as well.