What Are Common Uses of Infrared LED?

Infrared light emitting diode is a kind of diode that can emit infrared light, and is usually used in remote control and other occasions. Commonly used infrared light-emitting diodes are similar in appearance to light-emitting diode LEDs and emit infrared light.

Infrared LED

The duty cycle of some infrared TV remote controllers for color TVs is about 1 / 3-1 / 4; the duty cycle of some infrared remote controllers for electrical appliances is 1/10. Reducing the pulse duty cycle can also greatly increase the emission distance of low-power infrared LEDs. The power of common infrared light-emitting diodes is divided into three categories: low power (1mW-10mW), medium power (20mW-50mW) and high power (50mW-100mW or more). To make the infrared light emitting diode produce modulated light, only a certain frequency pulse voltage needs to be applied to the driving tube.

When infrared light emitting diodes are used to control the controlled devices by emitting infrared rays, the controlled devices have corresponding infrared light-electric conversion elements, such as infrared receiving diodes and phototransistors. In practice, there are paired infrared transmitting and receiving diodes.

The infrared light emitting diode is made of a material with high infrared radiation efficiency (commonly used gallium arsenide GaAs) to make a PN junction, plus a forward bias to inject a current into the PN junction to excite infrared light. The spectral power distribution is a center wavelength of 830-950nm and a half-peak bandwidth of about 40nm. Its biggest advantage is that it can be completely free of red storms (using an infrared tube with a wavelength of 940 to 950 nm) or only weak red storms (red storms have visible red light) and extend the service life. Light is an electromagnetic wave whose wavelength ranges from a few nanometers (1nm = 10-9m) to about 1 millimeter (mm). What the human eye sees is only a part of it. We call it visible light. The wavelength range of visible light is from 380nm to 780nm. The wavelength of visible light is divided into red, orange, yellow, green, cyan, blue, and purple light. It is called ultraviolet light, and the wavelength longer than red light is called infrared light.

Generally used infrared emission tube wavelength: 850nm, 870nm, 880nm, 940nm, 980nm

The relationship between the power and the wavelength of the infrared transmitting tube: 850nm> 880nm> 940nm

Peak wavelength: The energy distribution measured by the luminous body or object on the spectrometer, and the wavelength p corresponding to its peak position.

Radiation intensity (POWER): The unit is mW sr, which indicates the amount of infrared energy radiated by the infrared tube (IRLED).

The radiation intensity (POWER) is directly proportional to the input current (If), and the radiation intensity is inversely proportional to the emission distance. Unit mW sr: Infrared radiation intensity unit, as

There are two ways to transmit and receive infrared light, one is direct radiation and the other is reflection. The direct type refers to the fact that the light emitting tube and the receiving tube are relatively positioned at the two ends of the transmitting and controlled objects, with a certain distance between them. The reflective type is that the light emitting tube and the receiving tube are juxtaposed together. Usually, the receiving tube is always free of light. When the light encounters a reflector, the receiver tube works after receiving the reflected infrared light.

Double-tube infrared transmitting circuit can increase the transmitting power and increase the working distance of infrared emission.

High-brightness LEDs, infrared LEDs, and phototransistors have the same shape, which is easy to get confused, so they need to be distinguished by a simple test. Using a pointer multimeter (1k block) with a black test lead connected to the anode and a red test lead connected to the cathode (a test lead with a clip should be used). The forward resistance was measured at 20 40k; the black test lead connected to the cathode and the red test lead connected to the anode measured a reverse resistance greater than Those above 500k are infrared light emitting diodes. Transparent resin package can be used for visual inspection: the pole with the round shallow plate is the negative electrode. If the forward resistance is above 200k (or the pointer moves slightly) and the reverse resistance is close to , it is an ordinary light-emitting diode. If the black test lead is connected to the short pin and the red test lead is connected to the long pin, the resistance is greater than 200k when the light is blocked, and the resistance value changes with the light intensity when the light is illuminated (the resistance is small when the light is strong). This is a phototransistor.

The quality of the infrared light emitting diode can be tested according to the method of testing the forward and reverse resistance of ordinary silicon diodes. Measure the forward resistance of the infrared light-emitting diode. Put the multimeter in the R × 10k position. The black test lead is connected to the positive pole of the infrared light-emitting diode, and the red test lead is connected to the negative pole. Measure the forward and reverse resistance of the infrared light-emitting diode. Normally, the forward resistance is about 15 ~ 40k (the smaller the value, the better), and the reverse resistance is greater than 500k. If the measured positive and reverse resistance values are close to zero, it indicates that the infrared light emitting diode is damaged internally; if the measured positive and reverse resistance values are infinite, the infrared light emitting diode is open-circuit damaged; if measured, The reverse resistance value is far less than 500k, which indicates that the infrared light emitting diode is damaged by leakage.