diode question

Google "conventional flow vs. electron flow".

The one sentence synopsis:

Ben Franklin was wrong about the directon of current flow, and they had already drawn up all the schematic symbols pointing the "wrong way" by time they figured this out.

-phaeton

It doesn't point; it identifies the anode and cathode.

Don

Sure it points; it points in the direction of conventional current flow. For the OP - we often (very often) refer to currents in the conventional sense (going from positive to negative) even if electron flow is in the opposite direction. Mathematically, looking at a flow of negative charge in one direction (electron flow) and looking at it as a flow of positive charge in the other direction is identical for analysis - just remember to keep the sign of the charge you are dealing with. The fact that positive 'trons don't normally manifest is irrelevant :)

Cheers

PeteS

"randomname" wrote in news: snipped-for-privacy@75g2000cwc.googlegroups.com:

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I'll google it... can't wait to find out who figured it out and how.

thanks

-sam

No it doesn't.

In the direction of conventional current flow.

Graham

Ive always hated this specific topic on the physics of eletricity. the ground (loosley tearmed negative, which isnt technacally right) provides the electrons. The reason a diode works the way it does is because it uses the concept of holes, where electrons COULD be.

Everyone is being picky with your tearmonology of, "diode points from positive to negative". You can REVERSE BIAS a diode, which is the connection you described, or you could FORWARD BIAS, which is the reverse of what you described.

Im talking about the drawing of a diode, which is loosely this:

_|\\|_ |/|

It looks to me that it's pointing to the right, and blocking anything coming in from the left. Like a valve. However in practice it does the opposite.

-sam

On 25 Aug 2006 13:46:54 -0700, in message , "PeteS" scribed:

I believe that what Don means is that the "pointing" of the diode symbol is purely coincidental. I don't know this, but I can make a guess that the graphical interpretation is meant to be of a spreading stream of electrons from the cathode to the anode, in a crude representation of the action in a diode tube.

On 25 Aug 2006 13:14:12 -0700, in message , "randomname" scribed:

I don't believe that the schematic symbol for a semiconductor diode was ever intended to indicate a direction of charge flow, although it is convenient to see it that way. Note that charge flow can be said to be in either direction - positive or negative. "Conventional" charge flow is flow in the positive direction, "electron" charge flow is in the negative direction. Some other miscellaneous pedantry: "current" does not flow, it is flow; and flow of charge should not be confused with movement of electrons.

Good basic stuff:

See lesson 2, "Electric Current"

You're right. Very often people will make their own "rule" for the graphical representation to help them remember what's going on. The only one that always works, because it is correct, is: The Anode is the Arrow.

Newbies often have problems with diodes, because when they build their first project where it matters, a power supply, they expect to see a positive voltage come out of the anode, which is backward. It's so simple, I apologize for saying it, but.... A diode will conduct when its anode is positive with respect to the cathode. If you build a negative PS the AC from the transformer connects to the cathode and you collect the negative pulses from the anode. If you build a positive PS the AC from the xfmr connects to the anode and you collect the positive pulses from the cathode.

In the early days of solid state diodes, they were all point-contact. To us hobbyists of the time, a "crystal diode" was a piece of germanium crystal encased in lead, but with some of the germanium exposed. Then there was the cat-whisker, a small spring-wire, that was used to contact the germanium (making the point contact). The "arrow" of your sketch is the catwhisker and it's pointing to the germanium. The original 1N34 point contact diode had the arrow and bar printed on its white enclosure.

Don

Don

That's actually how I built my diode, too, though I didn't use germanium. I got a piece of galena crystal and poured molten lead around it and used the sharp tip of a needle on a swivel arm to make contact for my AM radio I built. I had tried to use a selenium rectifier, but that was near useless.

Jon

As I think more about it, I think my first one was probably galena, but I don't know that I could tell them apart. My first was probably a Philmore kit. We had a strong local radio station, and I was the first kid in Kennewick to have a radio on his bike.

I didn't see a selenium stack till 1952, I think, while fixing a radio and didn't know what it was. I knew it functioned as a diode with a fairly high forward resistance and the guy at the wholesale house (United Radio, who liked hams, then) filled me in on it. I was always glad to get a bad one - they made good photoelectric cells when you separate the fins. Selenium diodes were only good for the repair shops.

Don

Ya know I tried tracing the curve of a piece of galena. I wrapped a copper wire around a chunk of crystal and tried bobbing another hookup wire on various points. The best I got was some hysteresis and an x^3 looking curve, nothing very rectificationary. Too much current maybe?

Tim

Could be. Try an Ohmmeter. Remember, many Ohmmeters put the + test voltage on the - probe socket.

Don

Some years back, here, this link was posted:

It comes to mind just about now.

Jon

On Sat, 26 Aug 2006 06:36:53 -0500, in message , John Fields scribed:

Still, charge flow and electron flow are not the same thing, although the former depends on the latter. Like ripples depending upon a pond and a falling stone, the stone is not the ripple.