Check with a multimeter. Using a pointer multimeter with a ×10kΩ stop can roughly judge the quality of the LED. Normally, the forward resistance value of the diode is dozens to 200kΩ, and the value of the reverse resistance is ∝. If the forward resistance value is 0 or ∞ and the reverse resistance value is small or 0, it is easy to damage. This detection method cannot actually see the luminescence of the luminescent tube, because the ×10kΩ block cannot provide a large forward current to the LED. If there are two pointer multimeters (preferably the same model), you can better check the light emitting diode. Use a wire to connect the \"\" terminal of one multimeter to the\" - \"terminal of the other meter. The remaining \"-\" pen is connected to the positive electrode (P region) of the luminescent tube under test, and the remaining \"\" pen is connected to the negative electrode (N region) of the luminescent tube under test. Both multimeters are in gear x 10 Kω. Normally, when it's switched on, it lights up normally. If the brightness is very low, or even does not emit light, you can dial the two multimeters to ×1mΩ if, if it is still very dark, or even does not emit light, it indicates that the LED performance is poor or damaged. It should be noted that the two multimeters cannot be placed in ×1mΩ at the beginning of measurement, so as not to cause too much current and damage the LED.
(2) Measurement of external power supply. The optical and electrical characteristics of LED can be measured more accurately with 3V voltage regulator or two serial dry batteries and multimeters (either pointer or digital). This can be done by connecting the circuit as shown in Figure 10. If the measured VF is between 1.4 and 3V, and the luminous brightness is normal, it can indicate that the luminous is normal. If VF=0 or VF≈3V is measured and does not emit light, it indicates that the luminescent tube is broken. Detection of infrared light-emitting diodes, due to infrared light-emitting diodes, it emits 1 to 3μm of infrared light, which can not be seen by the naked eye. Usually, a single infrared light-emitting diode emits only a few mW of power, and different models of infrared LED luminous intensity Angle distribution is not the same. The forward voltage drop of infrared LED is generally 1.3-2.5V. Because the infrared light emitted by it is invisible to the human eye, the detection method using the visible light LED can only determine whether the positive and reverse electrical characteristics of its PN junction are normal, but can not determine whether its luminescence is normal. To this end, it is best to prepare a photosensitive device (such as 2CR, 2DR type silicon photocell) as a receiver. Use a multimeter to measure the voltage change at both ends of the battery. To judge the infrared LED plus appropriate
1. Identify the positive and negative electrodes of the diode, one end of the white line is the negative electrode, and the other end is the positive electrode.
2. Switch the knob on the multimeter to the on\/off position, and insert the red and black pen into the correct position of the multimeter.
3. Connect the red watch pen to the positive diode and the black watch pen to the negative electrode. Then observe the reading, and if it overflows (that is, shows 1), the diode has failed. If there is a reading, then exchange the pen, if there is a reading and not overflow, the diode is bad.
4. If it is a light-emitting diode, if the diode is normal, you can see a faint light, and the long foot is a positive pole.