![]() The unfortunate side effect of the way LEDs are made to do what they do, is that they are quite fragile electrically. In a through-hole device, the die is mounted to the ‘anvil’, the larger hand of the electrical connection, while the fine wire goes to the ‘post’, and the two together make up the ‘leadframe’ which is surrounded by a variety of resin package types. ![]() In an SMD, this is attached to one of the device pins, while the other pin is attached to the conductive mounting. The other face is the radiant surface where the light comes from, and has a tiny fine wire attached. One face of this is mounted directly to a metal frame for physical support and electrical connection, usually formed into a reflective cavity for through-hole devices and sometimes for Surface Mount Devices (SMDs). Notwithstanding the white version, LEDs are produced with a small ‘die’ of semiconductor material. White LEDs are still made with a phosphor coating, but now the combination of phosphor and its own doping chemicals means that all sorts of whites can be produced, from a nearly-red warm white, through pure white and sunlight, to a very blue white. Material science has come a long way, but the principle remains the same. Early versions of this emitted a very blue light, as the phosphor coating emitted a yellow light and so some blue light was allowed to be emitted to make the total light appear white. White LEDs generally use a phosphor coating on a blue or UltraViolet (UV) LED, with the high-energy blue or UV light stimulating phosphorescent light emission. The other main exception is the emission of white light. We found examples of this from research laboratory situations, but none we found were commercial productions. A rare one is some PN junctions constructed in such a way that more than one wavelength is produced. There are exceptions to this general rule. The reality is that it emits a narrow spectrum of light with a dominant peak wavelength. This means that one PN junction can only emit one colour of light. The wavelength (which is what gets interpreted by the brain as colour) of the emitted light depends on the substrate and doping chemicals. The important point is that if the substrate and doping chemicals are chosen carefully, light is emitted while current flows through the PN junction. The exact way this occurs through energy bands and charge carriers like electrons and holes is an interesting topic, but contributes little to what needs to be understood for this article. ![]() Most semiconductor devices we use in electronics are made this way and are formed from PN junctions: Transistors, signal diodes, rectifier diodes, and any devices based on them. While early lab developments in semiconductors used separate materials joined at a point or face to create the PN junction (the area where P and N type materials meet), most production methods add chemicals to one semiconductor crystal substrate to create the PN junction. Despite the fact that silicon is the more familiar semiconductor material to us, LEDs are usually made from gallium arsenide (GaAs), gallium arsenide phosphide (GaAsP) and indium arsenide (InAs), with less common materials also around. The result is a region of P-type material and a region of N-type material, depending on how the material is doped. Some of the material will be treated with doping chemicals, creating an area with an absence of electrons. Light Emitting Diodes are a semiconductor device in which a material that can be both insulator and conductor depending on the circumstances is treated to control its behaviour. To understand RGB LEDs effectively, it helps to revisit regular LEDs. We aim to take the mystery out by discussing the difference between analog and digital RGB LEDs, and the most common types within those categories. ![]() For those approaching Making from a non-electronic background, Red/Green/Blue (RGB) LEDs can seem mystifying. While many makers are intimately familiar with RGB LEDs, others are new to the field of Making or are experienced Makers who have simply not used RGB LEDs before. We look at both analog and digital RGB LEDs, the differences between them, and how to use them.
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