Talk:Diode

Unheadered stuff

Does anyone know which type of symbol (DIN 6779 / ISO / IEC / ...) the displayed symbol in the article is? it would be nice to add the comment there...

_i_
 ^
/ \
---
 |

---

Does anyone know how a diode prevents current from flowing in one direction but permits it in the other?

For the case of a semiconductor-based diode see the discussion of a p-n junction on the semiconductor page. Someone might want to adapt this for the Diode main page. -- Matt Stoker

In a vacuum diode, the materials of the anode and cathode have different attraction to keep their electrons, the cathode may be pointed to concentrate the electric field and the cathode is usually heated to "boil" off electons. The anode is called the "plate" because it is flat to spread out the field so it is not anywhere strong enough to pull out electrons. Sorry not to include links. I can help find more detail if needed. David R. Ingham 04:44, 7 January 2006 (UTC)

---

Does the use of galena as a detector (referred to in semiconductor devices) predate the vacuum tube rectifier? - David M

The crystal in a crystal radio is a naturally occurring mineral, used as a detector before practical vacuum-tube electronics. (I believe it has a point contact that is at least analogous to the point-contact diode of about 1950 that is the start of the Bell Labs drive toward commercial semiconductor electronics.) If the crystal of the crystal radio is galena, then the answer to your question is yes. --Jerzy 15:34, 2003 Nov 19 (UTC)

---

I thought I'd just explain why I changed "current" to "charge". Current doesn't really flow from A to B, but charge does. Just like "water flow rate" doesn't flow anywhere, but the water itself does. --User:Dgrant

Arguable. The current revision "they allow an electric current in one direction" doesn't make sense to me. It seems to be missing a verb. "...current to occur..." sounds better to my ear, but can we just call "current flows" common usage? -- Tim Starling

Yes, you are right. "to occur" or "to exist" would be the purest form in my opinion, but we can leave it the way it is. It's quite interesting I was able to find a fair share of both usages on Google. No doubt "current flowing" is probably more common. --Dave

It was I who changed "charge" back to "current", but in the light of the comments above, I decided that my version was no more or less correct than the previous one. Now, in an effort to please everybody, I have expanded the definition to mention both charge and current.

I think that the question of whether current "flows" or just "is" is merely a question of style. At worst, I think that "current flows" is harmlessly redundant. -- Heron

True. I think I can agree with "harmlessly redundant". I like the first paragraph now, how it uses singular form "diode" and "it" instead of "diodes" and "they".

The phrase "current flows" is harmless only if you already understand electrical physics. For newbies the phrase creates a serious misconception: the wrong idea that "current" is a substance, a substance which can "flow." This error grows to full-blown proportions in textbooks aimed at kids in grade school. Authors of these textbooks don't discuss the flow of charges within wires, instead they explain that "current electricity" flows in wires. An easy way to pop these bubbles of misconceptions is to ruthlessly remove all apparently harmless miswording such as "current flows." Instead say "charges flow" or "electrons flow" or "electric currents appear," etc. --Wjbeaty 21:07, Apr 14, 2005 (UTC)

I agree. Unfortunately, there are many examples of the 'sloppy' use of terminology that, IMHO, hinder the learning process. I recently began teaching an introductory class in electrical engineering. In preparing for this class, I came to realize how careless I had become with the terminology of my field. In the end, my own understanding of the material improved once I began to critically evaluate how I used terms such as current. Alfred Centauri 14:17, 27 May 2005 (UTC)

Diode vs rectifier

As this is the general 'diode' article, it seems to me that the section on rectification schemes can be moved into rectifier, and the discussion of p-n diode characteristics can be cut down and handled on p-n junction instead. Any thoughts? - mako 05:45, 10 July 2005 (UTC)

Yes, I agree this article is getting confused between rectifier and diode descriptions. After all, many diodes are not in fact used as rectifiers at all. Rectifiers should IMHO be moved to the rectifier article. Alan

Good point. Let's split them completely. - Omegatron 05:04, July 31, 2005 (UTC)

Gas discharge diode

I had not heard of this device before. Does it exist? Can anyone refer to an example part or manufacturer or example of useage?? Al

I'm pretty sure it exists; I'll look it up when I have time. BTW, thanks for your contribs. Do consider signing up for an account. - mako 21:41, 31 July 2005 (UTC)

No evidence on these devices has yet come to light so i have moved the para here for consultation. What think you O? Light current 01:27, 6 August 2005 (UTC)

Gas Discharge Diode : There are two electrodes, not touching, in some kind of gas. One electrode is very sharp. The other has a smoothly curved finish. If a strong negative potential is applied to the sharp electrode, the electric field near the sharp edge or point is enough to cause an electrical discharge in the gas, free carriers are created, and a low resistance path appears. If the reverse potential is applied, the electrical field strength around the smooth electrode is not enough to start a discharge. (The discharge can only start easily at the negative end because electrons are much more mobile than positive ions.) These are sometimes used for high-voltage high-current rectification in power supply applications.

Ah, sorry, I should've followed up immediately. According to Electronics by Millman and Seely (1951), there's a whole slew of gas-filled tubes, with various internal structures. I'll have to think about where to put them, though, as some aren't really diodes. (As for the paragraph above, I'm not sure about this "very sharp" electrode etc. business; it'd be enough to say that the tubes operate based on breakdown/ionization. It also seems it's a cold cathode tube. I doubt such things are used anymore, as a significant reverse voltage would also cause conduction.) - mako 05:06, 6 August 2005 (UTC)

No V-I curves...?

There are no V-I curves for the different diodes. Perhaps one for the "normal" or rectifier P-N diode and one for the zener/avalanche diodes would be helpful. If there's consensus, I will create the images and insert them into the articles - unless the images have already been created and excluded for some reason. Rohitbd 12:59, 27 September 2005 (UTC)

I made one to show negative resistance, which is used in Gunn diode and Tunnel diode. You could base new ones off of that? Also you should always check Commons before making a new image (I don't do this often enough.) I don't see any images for this on Commons, though. — Omegatron 13:43, 27 September 2005 (UTC)

I have created the V-I characteristics image of a rectifier diode as below. Please let me know if it is ok. Thank you. Rohitbd 18:25, 27 September 2005 (UTC)

I-V characteristics of a P-N junction diode (not to scale).

Looks good, though some numbers for current would provide useful context. Maybe a title too - "Typical semiconductor diode I-V characteristic", perhaps. - mako 19:50, 27 September 2005 (UTC)

We could indicate current values, but IMHO that will lead non-technical readers into believing that the values shown are the factual ones - which is not the case. Currents vary from device to device. The forward turn-on voltage, however, is true for almost all Si/Ge devices and IMO can be included as a fact. PS: I have slightly changed the V-I curve in the reverse bias region. I believe this to be the correct one for a rectifier - the previous one was perhaps more zener-like. Rohitbd 11:07, 28 September 2005 (UTC)

A non-technical reader may also assume that the chart is to scale; I just think some context is useful. Perhaps then a note in the caption about typical currents would be appropriate. Also, I have never heard these referred to as "V-I" characteristics. The ordering is always Y-axis, X-axis. Is this opposite (to me) convention common in your experience? - mako 22:00, 28 September 2005 (UTC)

Ok...but I do not know (rather remember) what typical current values to use. Maybe you can provide me with some (leakage current, reverse current...?). And "V-I" is perhaps my own "quirk"...maybe I memorised it that way all along - I shall use whatever is the accepted convention - good that I did not add this directly into the image. Rohitbd 07:40, 29 September 2005 (UTC)

Looking at the datasheet for a 1N4001, the quoted reverse current is 30 uA. There's no forward leakage parameter; not really a factor when rectifying I suppose. I guess I would say typical current in the off region is on the order of microamps. - mako 00:21, 30 September 2005 (UTC)

Added the relevant intormation into the image. Please check if everything is in order and I will link it into the article. Rohitbd 09:48, 30 September 2005 (UTC)

Since no one has objected, I have added the image to the article. Rohitbd 10:08, 5 October 2005 (UTC)

types of diodes

i love how the list of diode types is in a completely random order. the descriptions are fine, but it's impossible to quickly find the desired entry. typical "missing the forest for the trees" behavior from wikipedians.

I don't understand the paragraph concerning gold-dopped diodes: gold is supposed to make the diodes operating faster, but the paragraphs ends on the topic of main rectification (i.e very slow operation). Also, it is said that gold-dopped diodes can operate at "signal" speed. Does that mean "high frequency signal"?CyrilB 13:24, 6 March 2006 (UTC)

Thermionic or gaseous state

Is it planed or hoped that gasious state devices will be described here. David R. Ingham 04:46, 7 January 2006 (UTC)

Shockley's Diode Equation

I've heard something about the equation not taking into account "photon recycling effects", which cause the equation to be very inaccurate in the case of photovoltaics. I think this would be significant enough to note on the page. Fresheneesz 21:18, 23 February 2006 (UTC)

The Shockley equation is derived with the assumptions that the only processes giving rise to current are drift, diffiusion, and thermal R-G. It ignores photocurrent and R-G center processes. That's why it's often called the ideal diode equation; R-G center current in the depletion region, series resistance at high forward bias, and reverse breakdown processes are all unaccounted for if you rely only on the Shockley equation. -- uberpenguin @ 2006-06-25 13:36Z

First Diodes

I always thought the first diodes were point contact diodes, used in crystal sets, but the article claims the first diodes were thermionic. Any references to back the article's claim? Also, my understanding is that the symbol for a diode is actually a drawing of a point contact diode. It has nothign to do with arrows and the direction of current flow. The symbol is polarised as it is because the 'whisker' of a point contact diode is the anode and the flat plate is the cathode. The "arrow" in the diode symbol is really a sharpened needle (whisker) on a flat plate.John Dalton 11:27, 15 March 2006 (UTC)

I agree that the article needs clarifying. I will try to work on it a little. Maybe the confusion is that the first thing called a "diode" was a thermionic tube. Crystals predated vacuum tubes but they were called rectifiers. Today it would be called a Schottky barrier diode. Snafflekid 19:46, 15 March 2006 (UTC)

From the rectifier article: "the difference between the term diode and the term rectifier is merely one of usage, e.g. the term rectifier describes a diode that is being used to convert AC to DC.". The rectifer article goes on to describe the *process* of rectification with passing reference to "point contact rectifiers or crystal detectors". As a *device* crystal diodes/rectifiers seem to have "fallen through the cracks" in that the device itself is outside the scope of the rectifier article and not considered to be a diode in the diode article. Perhaps we are a victim of changing terminology? Crystal (point contact) diodes were originally named by the function they performed. At some point as rectifiers found wider application (possibly corresponding with the invention of the themionic diode??) the name of the function (rectification) and device (diode) seem to have been separated. Possibly this is why themionic diode have gottten the label of "first diodes", as they appeared around the same time as the word "diode" found wider usage? Need to find references to back up this theory!John Dalton 20:25, 15 March 2006 (UTC)

I've added a section on crystal diodes. The article is now internally inconsistent as both thermionic diodes are crystal diodes are claiming to be the first. If I get the time I'll try to fix it, but fel free to jump in before me.John Dalton 21:03, 15 March 2006 (UTC)

The saga continues. I'm not so sure crystal diodes were used before thermionic diodes now. The principle of crystal diodes was discovered in 1874. The principle of thermionic diodes was discovered in 1873. A Thermionic device was patented in 1883, but developed no further. The first practical thermionic diode was patented in 1904. Crystal diodes were in use before then. Maybe I'll just add a 'history' section to the article.John Dalton 21:24, 15 March 2006 (UTC)

Radio demodulation

By my understanding, crystal radios got their name from the crystal in the rectifier, not the quartz crystal in the earphone.John Dalton

I didn't see any reference to a needle and a razor blade?

Question

Would anyone know the reasoning behind placing a diode across the controls of a DC low voltage relay?

It's a protection diode. When you switch off the relay coil, the collapsing magnetic field creates a voltage (the back-EMF) much larger than that used to energise it, and of the opposite polarity. This voltage can sometimes be enough to destroy the transistor that controls the relay. The diode soaks up the back-EMF without interfering with the normal operation of the relay. --Heron 20:53, 18 April 2006 (UTC)

Not fast enough... I put my explanation, though it is not as good!

The magnetic coil of a relay is an inductor, so it is not possible to instantaneously interrupt the current in it. If you try to do so, using a switch or a transistor, the inductor will generate high voltages that can damage or destroy your switch. Placing a diode across the coil provides an alternative circuit to the current (until the inductor is completely discharged), so there is no overvoltage. -- CyrilB 20:58, 18 April 2006 (UTC)

I'm considering rewording the "Overvoltage protection" section and possibly renaming it to something more appropriate as i think it might be missleading, especialy to an amature. the section should realy refrerence inductance with perhaps a wikilink to inductors. i would appreciate peoples thoughts before i change the section.

Radiation Detector

(mostly as a reminder to myself) the section on radiation detection needs clean-up and correction. Unfortunately also the semiconductor detector article is not good, so I can't copy from there. Sergio Ballestrero 23:10, 3 May 2006 (UTC)

Picture Links

I made the titles of the schematic diagrams into links to their respective articles.--24.16.148.75 23:24, 30 June 2006 (UTC)

Manatom

I have removed the obscure line:

                                   Engr.Louriel R. Manatom

I have no idea why it was there; if somebody has an explanation, he's free to offer it. John Reid 07:36, 16 October 2006 (UTC)