It is interesting to observe how amazingly fast technology replaces one another. About thirty years ago, we were quite happy with the electronics we used, simple cars, somewhere uncomfortable and low-speed, modest houses without European-quality repair. But man is so arranged that he constantly strives for something more perfect, and now almost every area of life is subject to constant modernization. This process also affected indication and lighting systems. So, incandescent lamps were replaced by more advanced semiconductor elements - LEDs.
Emitting crystal
The history of the use of semiconductors is older than the use of electronic tubes. A. Popov, who is considered the inventor of radio, was looking for radio waves using a simple semiconductor device. The first Popov diode (detector) was made of a semiconductor crystal fixed in the holder and a pointed spring contact made of tungsten or steel. This contact relied on the area of the semiconductor, and depending on the point of contact it was possible to find the clearest signal of the radio station.
The ability of some crystals to emit light under the influence of current was discovered a little later, by chance, but at first it was not used in practice. Now, LEDs are widely used in special equipment and in everyday life.
What is an LED, what does it look like in a diagram?
An LED is a type of semiconductor element that has the feature of a crystal to emit light under the influence of an electric current passing through it. This effect is not manifested in all semiconductors, but only in those for which energy is released in the light range during the recombination of electrons and holes. An LED, like a regular diode, has a pn junction and transmits current in only one direction.
A feature of the LED as a light-emitting device is that it emits light quanta directly. This distinguishes it from incandescent lamps, where the spiral first heats up to a certain temperature, or halogen lamps with an ionization effect. Loss of energy in LEDs is minimal.
Structurally, the LED includes a substrate with a crystal deposited on it, leads for connection to an electric circuit and a housing, which is also an optical system. The designation of the LED on the circuit has a certain graphic expression, on the electronic board it is indicated by a special encoding.
What is the LED used for, and how is it reflected in its image on the diagram?
The LED emits light, this is its purpose. And in the schematic image, this is clearly indicated by two arrows coming from the element. The use of the device has been very wide:
- Various indication. To signal the inclusion of certain operating modes of electronic devices, individual elements are used. Groups of devices are used in digital displays, where each LED plays the role of a segment of a digit or letter. The symbol of the LED on the diagram included in the group is not set separately for each, but the entire group is displayed in the form of an indicator with a branch and numbering of contacts.
- For domestic, public and industrial lighting.
- As part of screens for street broadcasting, as well as when creating creeping lines.
- In optocouplers. The designation of the LED on the circuit in this case is supplemented by the image of the photodetector element.
- Fiber optic systems. Here, the LEDs act as emitters of a modulated optical wave.
- For backlighting liquid crystal screens.
- Design and entertainment industry.
Features of the designation of the semiconductor in the drawings
Technical norms and rules govern the designation of the LED on the diagram. GOST 2.702-2011 prescribes:
- To depict the LED and other circuit elements using drawing accessories or in electronic form. In this case, the last option should have a resolution of at least 300dpi and contain the file extension tif or bmp.
- The LED has a schematic design in the form of a conventional diode enclosed in a circle. Above the upper right part of the circle are two parallel arrows going from the main element at an angle to the right upwards.
- Near the LED indicate its full alphanumeric index.
- No matter how the LED is located on the circuit, with polarity in one direction or another or at an angle, the direction of the arrows remains unchanged.
- The output coming from the triangle in the diagram symbolizes the anode (+), and from the vertical bar - the cathode (-).
- The LED on the circuit must have its own serial number. Numbering goes from left to right, from top to bottom.
LED - designation polarity
The designation of the LED on the circuit makes it easy to determine its polarity, but in order to determine it with the just purchased element, you need to look at its contacts. The positive terminal of the anode is usually longer than the cathode.
If the LED is mounted on the board, and for some reason it does not have a marking of the elements, then the polarity of the semiconductor can be determined by carefully looking at its case. On the cathode side (negative terminal), there is a notch on the casing of a flat shape. Also, in transparent types of LED housings, its inside is visible. The similarity of the cup in which the semiconductor crystal is located has a direct connection with the cathode.
In the case when it is impossible to determine the polarity by the above methods, but if there is an electronic multimeter, you can use it. They take a conventional diode with a known polarity, put the device on a dialing operation and connect it to a semiconductor. Remember the polarity when the diode conducts current. Connect the LED to the measuring probes. They want him to conduct a current, note his polarity.
LED on the board
When assembling a printed circuit board, radio installers use a diagram and a list of specification items. In accordance with this list, special marking is indicated indicating the type of element and its position number in the diagram. There are international standards for designations on the board, which are widely used in imported equipment.
The designation of the LED on the board is present in the form of a graphic image, letter coding and number. The first reflects mainly the polarity of the semiconductor, the letters indicate the type of device, and the number indicates its serial number in the circuit and list.
The graphic designation of the LED on the circuit board is identical to its image in the drawing, but may not contain a circle around the diode icon. The letter coding is performed in capital Latin letters - LED (imported circuits) and HL (domestic). The number comes after the letters or below. Without a number, it is impossible to determine semiconductor parameters that are not indicated on the board, with rare exceptions.
LED marking
The letter designation of the LED on the circuit (marking) carries all the information about the characteristics of a particular semiconductor device. The marking contains a lot of characters, so it is not put on the device body, but is shown in the circuit or on the packaging of unsoldered elements. The LEDs in the strips are bays in coils, which are marked with marking symbols. Character encoding reflects:
- Series of products.
- LED emission color. Modern light-emitting diodes are white, green, red, blue, orange, yellow.
- Color stream quality. For example, an LED for lighting in a house or on the street, instrument displays, backlights, for image matrices.
- Type of lens. There are light-scattering devices and narrow radiation with dome-shaped, transparent and matte lenses.
- Power of a light stream.
- Power consumption of electricity.
- Manufacturer identification code. It has no practical load.
- Reserve Symbols. Manufacturers leave them for a possible modification of the elements.
There is no specific standard in the labeling of LEDs, so each manufacturer has its own encoding. It is impossible to remember it, but there are not so many serious manufacturers of this product on the market. Among them are companies such as Philips, Cree and Samsung.
Conclusion
In addition to conventional LEDs with pins, there are SMD LEDs with pads. They are small in size. The letter designation of this type of LED on the circuit is identical with LED elements, but on the board it is simplified and usually comes down to indicating the polarity.