The conventional designation of the LED in the diagram

It is interesting to observe, with what astonishing speed one another technology is replaced. About thirty years ago we were quite pleased with the electronics we used, simple cars, somewhere uncomfortable and low-speed, modest houses without European-quality repair. But this is how a person works that constantly strives for something more perfect, and now almost every sphere of life is subject to constant modernization. This process was also touched by the systems of indication and illumination. So, in place of incandescent bulbs came more advanced semiconductor elements - LEDs.

Radiant crystal

The history of the use of semiconductors is older than the beginning of the use of electronic type lamps. Popov AS, who is considered the inventor of radio, searched for the presence of radio waves with the help of a simple semiconductor device. The first Popov diode (detector) was made of a semiconductor crystal fixed in the holder, and a spring tapered 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 most clear signal of the radio station.

The ability of some crystals to emit light under the action of a current was discovered a little later, accidentally, but at first it was not used in practice. Now LEDs are widely used in special equipment, and in everyday life.

What is the LED, what does it look like on the diagram?

A light-emitting diode is a kind of semiconductor element, which has the feature of a crystal to emit light under the action of an electric current passing through it. This effect is manifested not in all semiconductors, but only in those in which in the process of recombination of electrons and holes energy release occurs in the light range. The LED, like a conventional 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 directly separates the quanta of light. This distinguishes it from incandescent lamps, where first the helix is heated up to a certain temperature, or halogen lamps with the ionization effect. The energy losses in LEDs are minimal.

Structurally, the composition of the LED includes a substrate with a crystal applied to it, leads for connection to an electrical circuit and a housing that is also an optical system. The designation of a light-emitting diode on the circuit has a certain graphic expression, on an electronic board it is designated by the special coding.

What is the purpose of the LED, and how is it reflected in its image on the diagram?

The LED emits light, this is its purpose. And in the schematic image it is clearly indicated by two arrows coming from the element. The device has received a very wide application:

• Different indication. To signal the inclusion of certain operating modes of electronic devices use separate elements. Device groups are used in digital displays, where each LED plays the role of a segment of a digit or letter. The conventional designation of the LED on the circuit in the group is not set separately for each, and the whole group is displayed as an indicator with a branch and numbering of contacts.
• For household, public and industrial lighting.
• In the composition of screens for street broadcasting, as well as when creating running lines.
• In optocouplers. The designation of the LED on the circuit is then supplemented with the image of the photodetector element.
• Fiber-optic systems. Here, the LEDs act as emitters of a modulated optical wave.
• For illuminating the screens on liquid crystals.
• Design and entertainment industry.

Features of semiconductor designation in the drawings

Technical norms and rules regulate the designation of the LED in the diagram. GOST 2.702-2011 prescribes:

• Display the LED and other elements of the circuit with the help of drawing accessories or in electronic form. In this case, the last version should have a resolution of at least 300dpi and contain a file extension tif or bmp.
• The LED has a schematic version in the form of a conventional diode enclosed in a circle. Above the right upper part of the circle there 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 on the circuit is located, with the polarity in one direction or the other, or at an angle, the direction of the arrows remains unchanged.
• The output from the triangle symbolizes the anode (+) on the diagram, and the cathode (-) from the vertical line.
• The LED on the diagram must have its own serial number. Numbering goes from left to right, from top to bottom.

LED - polarity of the designation

The designation of the LED in the diagram makes it easy to determine its polarity, but to determine it from the newly purchased element, you need to look at its contacts. The positive terminal of the anode usually has a longer length than the cathode.

If the LED is installed on the board, and for some reason it does not have an element labeling, the polarity of the semiconductor can be determined by looking closely at its housing. On the side of the cathode (negative terminal) on the body is a notch of a flat shape. Also, the transparent types of LED enclosures are visible inside. The similarity of the cup in which the semiconductor crystal is located has a direct connection to the cathode.

In the event that it is impossible to determine the polarity by the above methods, but there is an electronic multimeter in the presence, you can use it. Take a conventional diode with a known polarity, put the device on a vertex operation and connect it to a semiconductor. Remember the polarity when the diode conducts a current. Connect the LED to the test probes. They want it to conduct a current, mark its polarity.

LED on board

When assembling a printed circuit board, radio monitors use a circuit and a list of elements of the specification. In accordance with this list, a special marking is made indicating the type of the element and its position number on the diagram. There are international standards for designation on the board, which are universally used in imported equipment.

The designation of the LED on the board is present in the form of a graphic image, letter code and number. The first displays mainly the polarity of the semiconductor, the letters indicate the type of device, and the number - on its ordinal number in the scheme and list.

The graphic designation of the LED on the circuit board is identical to its image in the drawing, but it may not contain a circle around the diode icon. The alphabetic encoding is executed in capital Latin letters - LED (imported schemes) and HL (domestic). The number goes after the letters or below. Without a number, it is impossible to determine the parameters of the semiconductor, which the board does not indicate with a rare exception.

Marking of LEDs

The letter designation of the LED in the diagram (marking) carries all information about the characteristics of a particular semiconductor device. The marking contains a lot of symbols, so it is not placed on the body of the device, but is brought in the circuit or on the package of un-decapitated elements. LEDs in the ribbons go in coils in coils on which marking symbols are placed. The character encoding reflects:

• A series of products.
• The color of the LED radiation. Modern light-emitting diodes come in white, green, red, blue, orange, yellow.
• The quality of the color flow. For example, the LED for lighting in the home or on the street, the indication of devices, lighting, for image matrices.
• Type of lens. There are light scattering devices and narrow-beam radiation with domed, transparent and opaque lenses.
• Luminous flux power.
• Power consumption.
• Manufacturer identification code. Has no practical load.
• Symbols of reserve. Manufacturers leave them for possible modification of the elements.

There is no definite standard in the labeling of LEDs, so each manufacturer has its own coding. Remember it is impossible, but serious manufacturers of this product on the market is not so much. Among them, there are companies such as Philips, Cree and Samsung.

Conclusion

In addition to conventional LEDs with leads, there are SMD-LEDs with contact pads. They are small in size. The letter designation of this type of LED in the diagram is identical with the LED elements, but on the board it is simplified and usually reduces to indicating the polarity.