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How to Judge the Positive and Negative Poles of SMD LEDs

SMD diodes are also known as crystal diodes. In addition, there are also early vacuum pump electronic device diodes; it is an electronic component with unilateral conduction current. There is a PN junction and 2 wire terminals inside the semiconductor material diode. These electronic components have the conductivity of unilateral current according to the direction of the additional current. Generally speaking, calcination of p-type semiconductor and n-type semiconductor produce a chip crystal diode which is a p-n junction page. On both sides of its operating interface, Space charge layers appears, forming an electrostatic field. When the operating voltage is added to zero, the amount of the creeping current is the same as that caused by the construction of the electrostatic field due to the difference in the content of free electrons on both sides of the p-n junction.

Features of SMD LEDs

①The mechanism of lighting is that it is cold lighting, not through heating or charging and discharging, so the service life of components is about 50~100 times longer than that of tungsten bulbs, about 100,000 hours.

②Without the warm-up time, the lighting response time is faster than ordinary bulbs (about 3 ~ 400ns).

③ High efficiency of photoelectric conversion, low power consumption, saving about 1/3 ~ 1/20 of the energy consumption compared with lamps.

④Good shock resistance, improved reliability, and low-cost system software operation.

⑤Easy to small and medium-sized, thin, lightweight, no shape restrictions, very easy to make a variety of applications.


  1. Cleaning, no need to use unknown organic chemical liquid to clean the SMD LED: Unknown chemical liquid will destroy the SMD LED. When cleaning is necessary, immerse the SMD LED in ethanol for less than 1 minute at all normal room temperature and of course dry for 15 minutes before starting the application.
  2. Anti-humidity and cold, in order to prevent the equipment from absorbing moisture during transportation and storage, we package the outer packaging of the SMD LED in a waterproof aluminum packaging bag, and we equipped with a moisture-proof agent and an environmental humidity card. The moisture-proof agent plays a key role in the operation. The environmental humidity in the packaging bag, we mainly use the environmental humidity card to monitor the environmental humidity in the packaging bag.
  3. Store at a standard temperature <40°C after the storage bag is sealed.

SMD LEDs Advantages

The SMD LEDs is attached to the surface of the PCB circuit board, suitable for SMT production and processing, and can be reflowed in a soldering oven. The SMD LED very well solves the problems of chromaticity, angle, flatness, stability, consistency, etc. It has the advantages of strong anti-seismic working ability, low spot welding failure rate, and good high frequency characteristics. It indicates that we must supplement the reflective layer with less epoxy resin.

According to the removal of the heavy carbon steel raw material feet, the specification becomes smaller, and we can reduce the net weight of the product by half at will, and the volume and net weight are only 1% of the traditional plug-in components. /10 up and down, after the use of patch packaging, we can reduce the volume of electronic equipment by 40% to 60%, reduce the net weight by 60% to 80%, and finally the application is becoming more and more extreme.

We made the packaging of the in-line LED using glue. The operation process of gluing is to first introduce liquid epoxy resin glue into the LED forming cavity, then insert the arc-welded LED bracket, put it into the drying box to let the epoxy resin glue dry and solidify, and then remove the LED from the mold core. Get out and form. Because the production technology is relatively simple and low-cost, it has a high market share.

SMD LEDs positive and negative resolution method

  1. Look at the sign

Large-sized LEDs have some markings around the pole piece pins, such as rounded corners, painted colors, or different pin sizes. Generally, those with markings have small pins and the short side is the negative pole (ie negative level). Small-sized 0805 and 0603 packages have a “T” shape at the bottom or the side of the inverted triangle symbol “T” with a horizontal side is positive; negative grade.

  1. Measure with a multimeter

When checking the positive and negative of the SMD LEDs, we must use the “R*10k” gear to check. During the inspection, connect the two wires of the two DC ammeters and the light-emitting diodes to each other. If we offset the watch rod more than half, there is a light spot in the LED. Which means that we connect the SMD LEDs in the forward direction.

At this time, we connect the positive level to the black pen, and the negative level to the red DC ammeter. Then exchange the two DC ammeters and connect them to each other with the light-emitting diodes (connection in the opposite direction), and the stem of the meter does not move. If the lever does not move or stops after shifting, it means you damage the SMD LEDs.

However, it is not easy for beginners to use a digital multimeter at all. At this time, there is one thing that everyone basically understands. The LEDs with higher output power are all divided into positive and negative. Each pole means one end, and there is an extra pin at one end. If you pay attention, you will find that there is a small round hole on this pin. One end with a small round hole is a positive level, and the other end is a negative level.

  1. Observe the electric level in the tube

Look at the electrical levels inside the pipes, the smaller ones are positive, and the larger ones that look like a bowl are negative.

  1. Look at the missing corners

We often use 5050 SMD LEDs in the field of LED energy-saving lamps. This type of SMD LEDs is rectangular, and one of the four bevels has a small missing corner. The end with the small missing corner is the Negative level and positive level at the other end.

  1. Look at the foot position

The pin position of the LED is generally longer for the positive stage, and the pin position for the negative stage is shorter.

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