The biggest characteristic of led lamp beads is that it has unidirectional conductivity, that is, when a forward voltage is applied, the diode will turn on and the diode will emit light, and when you apply a reverse voltage, it will cut off, that is, it will not Light up and glow. The basic principle is that when a forward bias voltage is applied, the potential barrier drops, and the majority carriers in the P and N regions diffuse to each other. The electron mobility is much greater than the hole mobility, and a large number of electrons will diffuse to the P area, which constitutes the injection of minority carriers in the P area. The electrons recombine with the holes in the valence band, and the energy obtained during the recombination is released in the form of light energy. By making full use of this principle, we can detect the quality of LED lamp beads.
1. Incoming materials, first observe the appearance of the lamp beads for defects, such as breakage, degumming, soldering, and check whether the component pins have been cut for the plug-in. Any abnormalities must be ruled out.
2. Distinguish the cathode and anode of the lamp beads. For SMD lamp beads, the large pad is the negative electrode and the small pad is the positive electrode. For the plug-in DIP lamp beads, the long leg is the positive electrode and the short leg is the negative electrode.
3. Prepare a multimeter and adjust the gear to transistor gear or diode symbol when there is also a buzzer in place, because the voltage is about 3v at this time, which is convenient for testing. Use the multimeter red pen to contact the anode contact body of the lamp bead, and use the multimeter black pen to contact the cathode contact body. Observe whether the light is on.
4. If the led light is on during the test, it means that the lamp bead is basically functional. If the led light is off, exchange the red and black test leads and test again. In order to avoid the cathode and anode of some lamp beads are opposite to the general ones, we call it reverse polarity package. Sometimes you need to consult the LED lamp bead manufacturer.
5. The basic judgment of the color temperature of the lamp bead is that when it is off, the color of the lamp bead is getting darker and darker in order, indicating that its color temperature is getting smaller and smaller. For example, dark yellow has a color temperature of 2800-3200k, and light colors have a high color temperature, above 6000k. The lamp bead lights up to observe the color of the lamp bead. Whether the brightness is appropriate. Choose lamp beads with suitable color temperature.
Note: Generally, LED lamp beads have a voltage range, and the forward voltage drop is 2.7-3.6V. Please do not add voltage higher than this value to both ends of the lamp beads. Too low voltage lamp beads will not light up, too high voltage will burn out the led lamp beads. If possible, use a special instrument-integrating sphere test is the most accurate.
Led lamp bead repair? When we use LED, we must first look at which kind of lamp bead and see the basic parameters. The driving current of 3528 lamp bead should not exceed the maximum current required by the specification, preferably not more than 20mA. The recommended driving current of 2835 lamp bead is 45-50mA. Between; 1w lamp beads, current at 150ma. Each LED will have a different VF value. Therefore, in actual circuit application, it is best to design lamps with similar VF values in series on a circuit to facilitate matching resistors with different resistance values to achieve the purpose of constant current; pay attention to the LED poles. Do not connect it wrongly. Generally, the longer end of the lamp pin is the positive pole, and the shorter one is the negative pole. If the two lamp pins are the same length, carefully identify the mark.
Plug-in led lamp bead repair, directly remove it with a soldering iron, pay attention to the polarity on the pad, and replace it directly, because this kind of led lamp bead is very cheap. For smd patch led lamp beads (3528, 2835, 3014), this type of volume is relatively small, and it is generally replaced by blowing and heating. For high-power 1w-3wled lamp beads, because the pins are relatively long, you can also use a soldering iron to burn the feet in exchange. Recommend led fluorescent lamp
