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How to quickly detect the quality of light-emitting diodes?

baijiahao | 17/07/2021

Diode is one of the most commonly used electronic components. Its biggest feature is unidirectional conduction, that is, current can only flow from one direction of the diode. The function of the diode is a rectifier circuit, a detection circuit, a voltage stabilizing circuit, and various modulation circuits. , Are mainly composed of diodes, and their principles are very simple. It is precisely because of the invention of diodes and other components that our colorful world of electronic information was born. Some novices do not know how to correctly detect the quality of light-emitting diodes, maybe they will understand after reading this article.

Identification of light-emitting diode: Light-emitting diode is a device with positive and negative poles. Of the two pins, the longer one is the positive pole and the shorter one is the negative pole. For transparent or semi-transparent plastic-encapsulated light-emitting diodes, the shape of its internal electrodes can be observed. The internal electrode of the positive electrode is smaller and the internal electrode of the negative electrode is larger.

The parameters of the light-emitting diode: the maximum working current IFM refers to the maximum forward current allowed by the long-term normal operation of the light-emitting diode.

Maximum reverse voltage URM: refers to the maximum reverse voltage that a light-emitting diode can withstand without being broken down.

The role of light-emitting diodes: light-emitting diodes are widely used in lighting, display, indication, remote control, and communications.

Features of light-emitting diodes:

1. Large voltage adjustment range: LED uses a low-voltage power supply, and the power supply voltage is between 3-24V DC, depending on the product. There are also a few DC36V, DC40V, etc., so it is a safer power supply than using a high-voltage power supply, especially suitable In public places.

2. High efficiency: Compared with incandescent lamps with the same light efficiency, the energy consumption is reduced by about 80%, and energy-saving lamps are reduced by about 40%.

3. Strong applicability: The volume is small, and each unit LED chip is 3-5mm square, so it can be prepared into various shapes of devices, and it is suitable for variable environments.

4. High stability: 100,000 hours, the light decay is 50% of the initial.

5. Response time: The response time of the incandescent lamp is millisecond, and the response time of the LED lamp is nanosecond.

6. Environmental pollution: no harmful metal mercury, etc.

Detection principle: According to the unidirectional conductivity of the diode, a diode with good performance has a small forward resistance and a large reverse resistance; the greater the difference between these two values, the better. If the phase is similar, the performance of the diode is not good or has been damaged.

How to judge the quality of light-emitting diodes:

First, the multimeter selects the diode file.

When observing, the long legs are positive. When measuring with a meter, if the meter has a reading, the end of the red test lead is the anode of the diode at this time, and the light-emitting diode will glow;

If there is no reading, turn the test leads around and measure again. If there is no reading in the two measurements, it means that the light-emitting diode has been damaged.

If not, test it again in reverse. If there is no indication in the two measurements, it means that the Zener diode has been damaged. If there is a reading, it is normal.

If the resistance value measured twice is very small, it means that the diode has broken down; if the resistance value measured twice is very big, it means that the diode has been disconnected: the resistance value of the two measurements is not much different, indicating that the diode performance is not good. In these cases, the diode cannot be used. It must be pointed out that because the volt-ampere characteristic of the diode is non-linear, when the resistance of the diode is measured with the different resistance files of the multimeter, different resistance values ​​will be obtained; in actual use, the current flowing through the diode will be larger, so the diode exhibits The resistance value will be smaller.

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