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 Post subject: Diode confusion please help
PostPosted: Oct Wed 16, 2019 2:26 pm 
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Hi All
I am in the process of installing a full wave rectifier in my IG-42 Generator. Please read the attachments and tell me why current flows from the anode to the cathode in a diode but the opposite in a tube.
Thanks


Attachments:
Full-Wave Bridge Rectifiers.docx [89.25 KiB]
Downloaded 31 times
All About Diodes.docx [107.62 KiB]
Downloaded 35 times
full wave IG-42.PNG
full wave IG-42.PNG [ 95.91 KiB | Viewed 1957 times ]

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 Post subject: Re: Diode confusion please help
PostPosted: Oct Wed 16, 2019 2:33 pm 
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"conventional" current flow is + to - That means Anode to Cathode (Plate to Cathode in a tube)

PS: conventional current inside a power source is - to +

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 Post subject: Re: Diode confusion please help
PostPosted: Oct Wed 16, 2019 3:18 pm 
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I agree, current flow has been a source of confusion for years in all aspects of DC circuits, including automotive. Lots of articles about it and the historical confusion are out there.

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 Post subject: Re: Diode confusion please help
PostPosted: Oct Wed 16, 2019 3:45 pm 
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Page 80, Slurzberg and Osterheld, Electrical Esssentials of Radio, 1944.
Attachment:
Slurzberg_Essentials_Current.jpg
Slurzberg_Essentials_Current.jpg [ 286.53 KiB | Viewed 1929 times ]

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 Post subject: Re: Diode confusion please help
PostPosted: Oct Wed 16, 2019 3:59 pm 
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If you'd like a bit more stress on your brain, consider this: The classic analogy to water flow implies that you can put electrons into one end of a wire, and the same ones will eventually come out the other end. Is this, in fact, the way it works?

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 Post subject: Re: Diode confusion please help
PostPosted: Oct Wed 16, 2019 4:07 pm 
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Consider a cathode ray tube, where the electron is generated at the cathode (small end of tube) and is accelerated to the display end phosphor (big end of tube) which is highly and shockingly positive relative to the cathode. That's how I always considered electron flow. Now current flow ( or holes), well that's a whole weird strange consideration.

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 Post subject: Re: Diode confusion please help
PostPosted: Oct Wed 16, 2019 4:12 pm 
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The minimum brain stress might be to think of charge flow. Electron flow is the movement of negative charges. "Conventional" current flow is the movement of positive charges.

The textbooks also present things in terms of propagation of electric fields.

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 Post subject: Re: Diode confusion please help
PostPosted: Oct Wed 16, 2019 4:31 pm 
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Cadmandu asks ?
Quote:
tell me why current flows from the anode to the cathode in a diode but the opposite in a tube.
Thanks

See the attached diagrams (one rather crude ) and note cathode and anode positions are the same for tube and diodes.


Attachments:
TubeVersesDiode .png
TubeVersesDiode .png [ 34.12 KiB | Viewed 1916 times ]
DiodeVersesTube.png
DiodeVersesTube.png [ 28.26 KiB | Viewed 1916 times ]

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 Post subject: Re: Diode confusion please help
PostPosted: Oct Wed 16, 2019 8:53 pm 
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Wow that is strange that current flows in the opposite direction of the electrons. I thought that current was a measurement of electron flow.
In that diagram of the IG-42 upgrade with the blue diodes is the negative output of the bridge actually grounded by the function switch in standby mode.


Attachments:
ig 42 ps clean.PNG
ig 42 ps clean.PNG [ 19.75 KiB | Viewed 1868 times ]
Heathkit IG-42 Laboratory Signal Generator_0000.jpg
Heathkit IG-42 Laboratory Signal Generator_0000.jpg [ 553.79 KiB | Viewed 1868 times ]

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 Post subject: Re: Diode confusion please help
PostPosted: Oct Wed 16, 2019 9:01 pm 
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This is maybe splitting semantic hairs, but current is simply the propagation of charge, field, or whatever parameter we want to use. The direction is an arbitrary convention. The other nit is that nothing really " flows"..... eg an electron going into one end of a wire will not likely appear at the other end.

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 Post subject: Re: Diode confusion please help
PostPosted: Oct Thu 17, 2019 12:36 am 
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There really isn't anything inconsistent about it at all. Inside a rectifier tube or a diode, electrons leave from the cathode and arrive at the anode. So if you connect the anode to something which draws electrons off, say a power transformer winding, and you connect a load to the cathode, it will pull electrons from the load and make it positive. Even though the electrons went the other way, the load is now more positive so one can say positive current flowed into it. As long as you keep your point of view consistent, problems work out the same either way.

In semiconductors both electrons and "holes" (places in the molecular structure where electrons should be) move. In gasses and solutions, both electrons and positive ions flow. So it is most helpful to learn how to visualize both kinds of flow.

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 Post subject: Re: Diode confusion please help
PostPosted: Oct Thu 17, 2019 1:54 am 
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"Conventional" current flow (positive to negative) was invented by Ben Franklin long before anyone knew what electricity was. He thought it was a fluid. Then, later, it was found that electrons moved from negative to positive. This became important when vacuum tubes were invented. So engineers defined "electron" current as negative to positive while physicists continued to use conventional current. Then transistors came along and charges could move either way, or even both ways at once. (This also happens in liquids and gasses but nobody worried about it until the transistor age.) So engineers went back to conventional current. That removed a bunch of negative signs from various equations. So now, almost everyone agrees that current flows from positive to negative regardless of the way the charge carriers are moving. But old books and some old timers still use electron current.

It doesn't really cause any problem which is used as long as it is consistent. Confusion arises in a few books and articles where the author switches back and forth without warning.

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 Post subject: Re: Diode confusion please help
PostPosted: Oct Thu 17, 2019 2:38 am 
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I don't believe engineers worked with electron flow. In college we were taught the math and the conventional current flow. As an aside, it was acknowledged that those in electronics without higher education often used electron flow.

It has caused confusion and anger. It doesn't matter what you call it as long as you recognize the mechanism and can write the equations.

Yes Ben Franklin picked a direction which ended up opposite to what actually occurred. His random decision caused electronic charge to be negative. So while electrons flow in one direction, that's negative current and it's considered correct to draw current flow arrows in the opposite direction.

Upon entering college, this caused me a moment of confusion but then I joined the club and haven't looked back. Of course, when charges flow they aren't always electrons. Sometimes positive ions, sometimes protons, and so on. And in semiconductors there are holes, which are electrons missing and equivalent to positive charge.


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 Post subject: Re: Diode confusion please help
PostPosted: Oct Thu 17, 2019 2:48 am 
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???I can't tell if you are joking.....

I never saw anyone denigrated because they believed in electron flow vs. "conventional" current. And I never saw anger---maybe occasional mild confusion.

Other boring details:
Positive ions or protons do not flow---if anything flows, it is electrons---or maybe the holes that are left behind.

But nothing really "flows"---current is the propagation of changes in field strength---OR, if you prefer--changes in **The Force**

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 Post subject: Re: Diode confusion please help
PostPosted: Oct Thu 17, 2019 3:23 am 
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Positive charges and ions don’t “flow?” I suppose you are too young to remember ion traps on picture tubes, ionic bombardment in other kinds of tubes, or electrolytic capacitors, where a certain percentage of the conductivity comes from positive ions in the electrolyte?

And half of semiconductor theory is about holes where an electron should be in the crystalline structure but isn’t due to an impurity deliberately introduced into the crystal. They act as if they are positive charges.

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 Post subject: Re: Diode confusion please help
PostPosted: Oct Thu 17, 2019 6:33 am 
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Brother, this discussion sure causes problems.

Of course positive charges "flow"...especially in a solution of ions or in other chemical processes...not to mention particle accelerators (that's supposed to be funny...)

Of course electrons "flow"...it is the movement of electrons in the outer shell of conductive materials that result in conductivity...

So, here we are discussing diodes, semi-conductors, and vacuum tubes all of which "flow" somewhat differently.

I just had to deal with the fact that "flow" in vacuum tubes is sometimes dealt with opposite to diodes by some descriptors.

Just like the positive pole of a battery is the cathode....confusing when you think of a vacuum tube.

It makes my head hurt.


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 Post subject: Re: Diode confusion please help
PostPosted: Oct Thu 17, 2019 9:27 am 
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Sorry for adding to the confusion.....:)

In some of my comments, I was thinking only about "flow" in wires. How about the question whether you can put in an electron at one end of a wire and expect to see the same electron come out the other end? Based on my limited knowledge, this doesn't happen and therefore the water flow analogy breaks down.
But--if the above is true--is there then a paradox in that current flow through a vacuum does appear to be be more like water flow?

A big part of my struggle is that I learned electricity and electronics long before I really started to understand the physics.

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 Post subject: Re: Diode confusion please help
PostPosted: Oct Thu 17, 2019 9:37 am 
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This is really great stuff you guys are brilliant. How about the old Mercury tubes that ionize and cause electon flow

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 Post subject: Re: Diode confusion please help
PostPosted: Oct Thu 17, 2019 12:55 pm 
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"brilliant"??---not here
Always remember the definition of "Expert"------"a drip under pressure"

One thing everyone **might** agree with is that conduction requires free electrons---more precisely, electrons that are in the "conduction band" of the atomic structure.

When you "ionize" a gas--eg Mercury vapor, you get a mix of electrons and positively-charged ions. I'm not sure I understand all the differences between conduction in the ionized vapor---compared to liquid Mercury.
Further, is it not possible to ionize the gaseous phase of a material that is not otherwise conductive?

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 Post subject: Re: Diode confusion please help
PostPosted: Oct Thu 17, 2019 2:32 pm 
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Me? I am just short of stupid. Folks like Bob, Barry, and the others have forgotten more than I will ever know!

I came to electronics just a couple of years ago, even though I was well trained in science,

My father, who was a really smart guy and a mechanical engineer, used to tell me that electricity was witchcraft.

What I try to do now is just grasp enough of the basics to help me solve these problems.

I just chimed in on this topic because i have had to reach some peace as a newcomer to this topic. It is one of the harder things for me to come to grips with as I learn to to trace current flow through a circuit. For some reason, it is easier for me to follow electrons in circuits and positive charges in batteries and ionic mixtures. But, then, I was great at physical chemistry and much poorer at conventional physics.

I have a Great Courses on physics that I will watch when I retire!

Steve


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