Infrared LED is a kind of diode that can emit infrared ray, and is usually used in remote control and other occasions. Commonly used infrared light-emitting diodes are similar in shape to LED, emitting infrared light. The voltage drop of the tube is about 1.4v, and the working current is generally less than 20mA. In order to adapt to different working voltages, the circuit is often connected with a limited current resistor.

The shapes of high brightness LED, infrared LED and photoelectric triode are the same, which is very easy to be confused. Therefore, it is necessary to distinguish them through simple tests. Use a pointer multimeter (1k gear) to connect the black probe to the anode, and the red probe to the cathode (the probe with a clamp should be used) to measure the positive resistance of 20~40k Ω; If the reverse resistance measured by connecting the black probe to the cathode and the red probe to the anode is greater than 500k Ω, it is an infrared LED. Visual inspection is available for transparent resin packaging: the pole with a round shallow disk is the negative pole. If the forward resistance is above 200k Ω (or the pointer moves slightly), the reverse resistance close to ∞ is a common LED. If the black stylus is connected to a short pin and the red stylus is connected to a long pin, the resistance is greater than 200k Ω when the light is blocked, and the resistance changes with the intensity of the light when there is light (the resistance is small when the light is strong). This is a photoelectric triode.

The quality of infrared light emitting diodes can be tested by testing the forward and reverse resistance of ordinary silicon diodes. Measure the forward resistance of the infrared LED and set the multimeter to "R × In 10k "gear, the black probe is connected to the positive pole of the infrared LED, and the red probe is connected to the negative pole. Measure the forward and reverse resistance of the infrared LED. Normally, the forward resistance is about 15~40k Ω (the smaller the value, the better), and the reverse resistance is greater than 500k Ω. If the measured forward and reverse resistance values are close to zero, it means that the infrared LED is damaged by breakdown; If the measured forward and reverse resistance values are infinite, it indicates that the infrared LED is open circuit and damaged; If the measured reverse resistance is far less than 500k Ω, it means that the infrared LED is damaged due to leakage.