Electronics have always been a bit of a weak spot with me. When I was a wee blogger, I had a "Science Fair 150 in 1 Electronic Project Kit (Cat No. 28-248)." Ok, technically I still have it, rescued from my parent's basement a few years ago. Basically, it consists of a board with a number of installed circuit elements-- capacitors, resistors, etc., plus some outputs (a light bulb, a rudimentary LED number display, a speaker, etc). There's an included booklet that tells you how to hook various things up to other various things in order to get various results-- flashing lights, musical tones, timers, and so on. I eagerly followed the instructions, and got the effects, but had no real idea of what was going on-- I just followed the directions like a recipe.
So now, today, [mumblety] years later, I'm setting out to rectify the situation. (Get it? Rectify? That's an electrical engineering joke!) So here, more or less, is how a diode works.
A diode, according to the dictionary, is "an electronic device that has two electrodes or terminals and is used especially as a rectifier." Not very helpful, actually. Electrodes/terminals I know, those are the "ends" of a circuit element, that can be attached to other elements. A rectifier (see, I told you it was an EE joke), as it turns out, is "a device for converting alternating current into direct current." Ok, that makes more sense to me. So a diode is an electronic device that has two ends and is usually used to turn AC into DC (generally not the other way around). But how?
A diode is, somewhat simplified, a chunk made up of two types of material with a wire sticking out of each bit. The two sections have specific electrical properties such that the boundary between them allows current to flow only in one direction (at least theoretically). The details on how that works rapidly get very technical, so I'll leave it there, at least for now. The point is that alternating current builds up on one side of the diode, like waves crashing upon a semiconductor levee (this is getting unexpectedly poetic), and when the waves get large enough, the "water" begins to flow down the other side, away from the barrier.
This has some useful effects, besides the simple rectification property. The threshold at which the diode allows current to start flowing (the "height of the levee," as it were) is dependent on temperature, so a diode can be used as a simple temperature sensor-- if current is flowing, it must be at least X degrees (where X depends on the type of diode). They can also temper current surges, like tiny little surge protectors. And finally, there's the ubiquitous LED, or Light Emitting Diode, poised to be not just Das Blinkenlight on your device, but also a replacement for your household bulbs. This is starting to get awfully long, so I think I'll stop here, and cover LEDs more specifically tomorrow.
And of course the original diodes were tubes, which worked somewhat differently (I knew how once -- mumblety years squared) from the semiconductor variety.
ReplyDeleteThe details are different, but the basic principle is the same-- there's a junction that allows the flow of current in only one direction (something about being able to jump a gap in a vacuum from a charged cathode to an anode but not the other way around).
DeleteSo that's where that kit went!
ReplyDelete