# Diode arrow

Discussion in 'General Electronics Chat' started by qitara, Mar 15, 2014.

1. ### qitara Thread Starter Member

Jan 18, 2013
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Hi

Does a diode arrow point in the conventional current flow or the electron flow ?

2. ### DerStrom8 Well-Known Member

Feb 20, 2011
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Conventional current flow, so positive is at the back of the arrow and negative is at the front.

3. ### WBahn Moderator

Mar 31, 2012
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One way to visualize this (though it is getting harder for students to relate to today) is to think of the diode as representing a "cathode ray tube". The vertical line is the "cathode plate" and the triangle represents the spray of cathode rays coming off the cathode, starting at the center and spreading out. Since we know that "cathode rays" are actually electrons, that means that the "spray" is actually electrons, and thus the "arrow", which is pointing in the other direction, is in the direction of conventional current flow.

This little device is useful in general for keeping the concepts of "anode" and "cathode" straight.

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4. ### spinnaker AAC Fanatic!

Oct 29, 2009
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This is all assuming your students know what a CRT is. Yes we still have them ins scopes but how soon will they disappear entirely?

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5. ### WBahn Moderator

Mar 31, 2012
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Which is why it is getting harder for students to relate to today.

6. ### MrChips Moderator

Oct 2, 2009
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If you always think of conventional current flow you will never have a problem relating to electronic circuits.

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7. ### qitara Thread Starter Member

Jan 18, 2013
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is there any parts out there that uses the electron flow instead of the conventional flow ?

8. ### MrChips Moderator

Oct 2, 2009
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What do you mean by "parts"? The vast majority of electronic devices use electron flow.
However, direction of charge flow is a relative concept created by human minds. It doesn't matter which convention you choose as long as you are consistent.

It is like asking "is the north pole up or down?".

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9. ### #12 Expert

Nov 30, 2010
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Right. The plusatrons know exactly when to jump off the phosphor and run to the cathode.

Here's another way to look at it: Always think in terms of electron flow and you'll never go wrong.

Point is, always think in one way or the other until you get experienced enough to think equally well in either direction. Just be consistent and you'll get by with conventional flow with only a few exceptions. After you do that for a few years, you will be able to think in either direction.

Jul 18, 2013
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Unfortunately the standard check valve symbol used for a diode, is based on Ben Franklin's assumption that electron flow was from +ve to -ve.
Hence it being technically backwards facing.
Anyone that came through the tube era often intuitively tends to think in electron flow (cathode to anode).
Max.

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11. ### MrChips Moderator

Oct 2, 2009
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I must be an exception. I came through the vacuum tube/valve era and conventional current flow works for me.

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Jul 18, 2013
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I can think in both, but I suspect if you come across a tube circuit you think in terms of electron flow, no?
Max.

13. ### qitara Thread Starter Member

Jan 18, 2013
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so if i comprehend, is the Franklin assumption of the electron flow from
+ve to -ve the standard used every where in circuit/electric diagrams ?

14. ### #12 Expert

Nov 30, 2010
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I can live with that. Conventional flow makes the math easier with the positive on the top of the page and not having to deal with all those "-" signs. It's intuitive compared to electron flow.

My first 40 hour job was vacuum tube TV repair, and I used conventional flow most of the time, but I found myself reverting to electron flow when I would get in a pinch about, "What's this circuit doing?". Eventually, I became comfortable in either method. I use conventional flow right up to the moment I get lost. Then I switch to my old standby, "electrons can not lie". How does this voltage tripler work? I track the electrons. How does a car battery run the starter motor? I use conventional flow.

Just be consistent on any particular job. After a few years, you will be comfortable thinking in either direction.

15. ### DerStrom8 Well-Known Member

Feb 20, 2011
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What drives me crazy is students at the uni who have access to the school's digital scopes, and they have no idea how to adjust them manually. Everyone just hit's that stupid "auto-scale" button and wonders why it doesn't work when the trigger is off. I always try to encourage them to adjust the knobs by hand and change the scales to make it look the way they want it to. I can't stand it when students insist on using the auto-scale button instead of learning how the scopes actually work.

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16. ### #12 Expert

Nov 30, 2010
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It's the, "point and click" generation.

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Jul 18, 2013
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Pretty much standard thinking and this method is known as the conventional flow.
A CRT was mentioned, I have a problem visualizing the screen electrons all moving back to the filament/cathode!.
Max.

18. ### MrChips Moderator

Oct 2, 2009
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Don't need to.

How does one figure out how to apply a negative bias to the grid? I raise the potential of the cathode by adding a resistor from cathode to ground.

Where do electrons come into the picture?

19. ### #12 Expert

Nov 30, 2010
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I thought I covered that in post #9. The plusatrons know exactly when and where to jump off the CRT phosphor and run to the cathode. In mere amplifier tubes, they swarm around the plate, often getting too eager and causing secondary emission when they get excited about waiting for their turn to jump to the cathode.

20. ### THE_RB AAC Fanatic!

Feb 11, 2008
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OR, you teach them that the arrow looks like a letter "A", for "Anode".

They actually remember that.

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