Help Understanding Conventional Vs Electron Current As Relates To Polarized Components

Thread Starter

ArrowJ

Joined Oct 5, 2021
4
Greetings,

I thought I had the concept of conventional vs electron current figured out. I am not good at math, but I understand the formulas works either way if you watch the signs. That all seems fine...until you put a diode etc. in the circuit. Sure, the symbol is drawn the "wrong" way so everyone can play along at home, but if the electrons are actually flowing the opposite direction, and you place a diode in relation to a certain component to say protect it, would the current not actually flow through that component before it was blocked? I am sure I am missing something obvious here, but I cannot figure it out.

Thanks
 

crutschow

Joined Mar 14, 2008
30,116
It makes no difference whether you use conventional or electron flow.

Suppose there is a diode with the cathode connected to the positive electrode of a polarized capacitor.

For current flow, applying a positive voltage to the diode anode causes (theoretical) positive charges to flow through the diode from anode to cathode and adds positive charge the capacitor to generate a positive voltage.

Foe electron flow, applying a positive voltage to the diode anode causes electrons to flow from the cathode to the anode, removing electrons from the capacitor go generate a positive voltage.

So either way the capacitor will get charged to a positive voltage.

And in either case, applying a negative voltage to the diode anode, will cause the diode to block any current flow.

Make sense?
 

nsaspook

Joined Aug 27, 2009
9,991
Greetings,

I thought I had the concept of conventional vs electron current figured out. I am not good at math, but I understand the formulas works either way if you watch the signs. That all seems fine...until you put a diode etc. in the circuit. Sure, the symbol is drawn the "wrong" way so everyone can play along at home, but if the electrons are actually flowing the opposite direction, and you place a diode in relation to a certain component to say protect it, would the current not actually flow through that component before it was blocked? I am sure I am missing something obvious here, but I cannot figure it out.

Thanks
The solution is simple, use conventional current notation and rules. Forget electrons.
 

MisterBill2

Joined Jan 23, 2018
12,424
First, electrons are way to small to see, and in addition they are negative charged. So convention follows the flow of POSITIVE,which is opposite the flow of the electrons. I hope that explanation makes sense, it solved the problem for me, anyway.
 

Ya’akov

Joined Jan 27, 2019
6,033
It might help if you picture conventional current as hole flow, rather than electron flow. Both thing are necessary, there can‘t be one without the other. Choose electrons over holes is arbitrary and Franklin (unknowingly) chose holes.
 

Danko

Joined Nov 22, 2017
1,365
would the current not actually flow through that component before it was blocked? I am sure I am missing something obvious here, but I cannot figure it out.
A diode when functioning in its forward bias condition has its depletion region shrinked to almost nothing. That is, the external supply voltage applied will be used by the device to overcome the barrier potential which gets imposed on it due to the presence of immobile charge carriers in its depletion region. Now, imagine that one reverse biases this voltage by inverting the polarities connected to the terminals of the diode. Ideally, the act of doing so should bring the diode from its ON state to OFF state immediately. That is, the diode which is conducting current in its forward direction is expected to stop conducting instantly.

However, practically, this cannot be experienced as the flow of majority charge carriers through the diode does not cease right at the moment of reversing the bias. They will, in fact, take a finite amount of time before stopping and this time is known as
reverse recovery time of the diode.

1656933177154.png
 

MisterBill2

Joined Jan 23, 2018
12,424
This is why, back in 1965, replacing a 5Y3 rectifyer in a power supply circuit required adding z bjtof additional high frequency filtering to be added. More recent diodes have reduced that recovery time effect somehow.
 

MrAl

Joined Jun 17, 2014
9,169
Greetings,

I thought I had the concept of conventional vs electron current figured out. I am not good at math, but I understand the formulas works either way if you watch the signs. That all seems fine...until you put a diode etc. in the circuit. Sure, the symbol is drawn the "wrong" way so everyone can play along at home, but if the electrons are actually flowing the opposite direction, and you place a diode in relation to a certain component to say protect it, would the current not actually flow through that component before it was blocked? I am sure I am missing something obvious here, but I cannot figure it out.

Thanks
Hi,

It is best to post a schematic of your circuit in question because the question of whether or not a diode protects anything at all depends on what it is being used for, and i cant stress this point enough.

For example, if you want to protect an electrolytic capacitor from being charged in the wrong direction it may help to place a diode in series with it. If you want to protect a power supply from reverse current placing a diode in series with it only works with very passive loads. Connect a battery in reverse polarity and it could blow the power supply out so the diode does no good there.

In general though, you can get an idea how a diode conducts by observing the terminal voltages. To get it to conduct, the anode has to have a voltage that measures more positive than the anode, and there is usually a threshold voltage such as 0.2, 0.4, 0.5, 0.7, etc. If you measure the voltage at each terminal it does not matter what convention you use for the current 'flow' because the conduction does not depend on the current as much as the voltage.

So you can rethink this a little by picturing a diode and either case:
1. The anode more positive that the cathode (conducting).
2. The cathode more positive than the anode (not conducting).

And already here you will notice that we never had to know what current convention we would be using later.

In electronics it never seems to matter until we get into chemistry, then it may matter. It matters when we have to know what the electrons themselves are doing. This means it could also matter on a physics test, and there are also cases where there are no 'holes'.
 

Thread Starter

ArrowJ

Joined Oct 5, 2021
4
It makes no difference whether you use conventional or electron flow.

Suppose there is a diode with the cathode connected to the positive electrode of a polarized capacitor.

...

And in either case, applying a negative voltage to the diode anode, will cause the diode to block any current flow.

Make sense?
First, please accept my apology for not posting a schematic. I did think about it, but I do not know how to use schematics yet, nor the tools to create them. I am still working my way through the first volume of the text book on this website.

I really appreciate this answer. It was extremely helpful in wrapping my mind around this. Thank you so much!
 

DickCappels

Joined Aug 21, 2008
8,831
It might help if you picture conventional current as hole flow, rather than electron flow. Both thing are necessary, there can‘t be one without the other. Choose electrons over holes is arbitrary and Franklin (unknowingly) chose holes.
Hole flow works fine for me when it comes to "conventional" circuits, but try to imagine hole flow inside a cathode ray tube where holes are selectively sucked off the back of the screen into the electron gun...
 

Ya’akov

Joined Jan 27, 2019
6,033
Hole flow works fine for me when it comes to "conventional" circuits, but try to imagine hole flow inside a cathode ray tube where holes are selectively sucked off the back of the screen into the electron gun...
I find that analogies in electricity always have a starkly delimited domain of validity. It's netlike there are blurry edges where they begin to break down, it's plain discontinuity, they just work for a particular facet and fail everywhere else.

I don't think this reduces the utility. They aren't intended to explain everything but to make different parts accessible and provide and effective way of visualizing things to learn or apply them. To understand things fully you have to resort to Maxwell which does successfully integrate everything.
 

MrAl

Joined Jun 17, 2014
9,169
Hole flow works fine for me when it comes to "conventional" circuits, but try to imagine hole flow inside a cathode ray tube where holes are selectively sucked off the back of the screen into the electron gun...
Ha ha, yes i was thinking the same thing. Holes do not always accompany electrons.
Also, what we call "current flow" may be restricted also. The interesting thing is everything else seems to work the same, but "hole flow" is probably restricted to only solid state physics.

There is a view in pure philosophy that says that if you can not separate something from it's surroundings without destroying it's properties, then it is not real. We believe we can take an electron out of a wire and it's still an electron, but can we really take a hole out of a wire and still call it a 'hole'. I think that the hole goes away if it does not have any electrons around it. If we consider the hole to be a mass of electrons with maybe one less than somewhere else, i think it's really the same story. There may be different views on this though.
 

nsaspook

Joined Aug 27, 2009
9,991
Analogies are fine but as usual things are more complex than they seem at first glance.

With a CRT that electron KE from motion is useful but remember that pure KE is no longer electrical energy. Some electrical energy was transformed during the acceleration from an electric field into the energy of moving mass with a charge. it's very small charged rock aimed at other small charged rocks.


https://sciencedemonstrations.fas.harvard.edu/presentations/crt-paddle-wheel
https://fathomingphysics.nsw.edu.au..._VCalisa_Phys_Teach_vol_52_iss_3_142_2014.pdf
 
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MisterBill2

Joined Jan 23, 2018
12,424
How about considering the totally correct reality is that "electron flow is the flow of NEGATIVE CHARGE, and that therefore in the opposite direction we have the flow of POSITIVE CHARGE, which is what remains when the negative stuff leaves? This is not an analogy, and so it does not break down. And given that all of the articles are much to small to see, and magicly flow through solid metal conductors, it should satisfy all.
 

BobTPH

Joined Jun 5, 2013
5,248
When learning basic electronics it is best not to think about charge carriers. Think of current as some magic stuff that flows from positive to negative. Think of resistors as restricting that flow. Think of capacitors as saving it for later, and inductors as trying to keep it going, resisting change.
 

BobaMosfet

Joined Jul 1, 2009
2,002
Greetings,

I thought I had the concept of conventional vs electron current figured out. I am not good at math, but I understand the formulas works either way if you watch the signs. That all seems fine...until you put a diode etc. in the circuit. Sure, the symbol is drawn the "wrong" way so everyone can play along at home, but if the electrons are actually flowing the opposite direction, and you place a diode in relation to a certain component to say protect it, would the current not actually flow through that component before it was blocked? I am sure I am missing something obvious here, but I cannot figure it out.

Thanks
Check your diode datasheet and curves for more understanding of the humble diode.
 
Last edited:

MrAl

Joined Jun 17, 2014
9,169
When learning basic electronics it is best not to think about charge carriers. Think of current as some magic stuff that flows from positive to negative. Think of resistors as restricting that flow. Think of capacitors as saving it for later, and inductors as trying to keep it going, resisting change.
Hi,

That's a cute way of looking at it :)
 
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