Characteristics and Applications of Infrared Light Emitting Diodes

Infrared remote controls have been widely used in televisions, audio systems, and various household appliances. The control distance of the remote control can generally reach 6-8 meters, making it very convenient to use. Due to the large usage of infrared remote control, its infrared transmission and reception circuits are equipped with complete supporting components, which are not only cost-effective but also reliable, and the circuit is extremely simple. Electronic enthusiasts can easily assemble remote controllers for various purposes using these devices, which are not only practical but also increase their interest in production.

The characteristics of infrared light-emitting diodes are that infrared light is invisible and cannot be detected by the human eye. In electronic technology, infrared light-emitting diodes (also known as infrared emitting diodes) are used to generate infrared radiation

Its appearance is similar to that of a light-emitting diode (LED). The transistor BG acts as a switch. When a driving signal is applied to the base, the BG transistor saturates and conducts, and the infrared light-emitting transistor D also conducts in the forward direction, emitting infrared light (near-infrared light of about 0.93 μ m)

When using a circuit to emit infrared radiation to control the corresponding controlled device, the distance controlled is proportional to the emission power of D. In order to increase the control distance of infrared radiation, the infrared light-emitting diode D should operate in a pulsed state, that is, the operating current is pulsating. Because the effective transmission distance of pulsating light (modulated light) is proportional to the peak current of the pulse, simply increasing the peak current Ip as much as possible can increase the emission distance of infrared light. The method to increase Ip is to reduce the pulse duty cycle, that is, to compress the pulse width τ, as shown in Figure 10. Some TV infrared remote controllers have an infrared light-emitting tube working pulse duty cycle of about 1/4 to 1/3; Some electrical products have infrared remote controls with a duty cycle of 1/10. Reducing the pulse duty cycle can also greatly increase the emission distance of low-power infrared light-emitting diodes. The common infrared light-emitting diodes are divided into three categories of power: low power (1mW~10mW), medium power (20mW~50mW), and high power (50mW~100mW or more). When using infrared light-emitting diodes with different powers, corresponding power driver tubes should be configured. As shown in the figure, to generate modulated light from the infrared light-emitting diode, simply apply a pulse voltage of a certain frequency to the driving tube

When using infrared light-emitting diodes to emit infrared radiation to control a controlled device, there are corresponding infrared to electrical conversion components in the controlled device, such as infrared receiving diodes, phototransistors, etc

There are two ways to emit and receive infrared radiation, one is direct radiation and the other is reflection. Direct type refers to the placement of the light-emitting tube and the receiving tube at opposite ends of the emitting and controlled objects, with a certain distance in between; Reflective refers to the situation where the light-emitting tube and the receiving tube are placed side by side, and the receiving tube is always without light. It only works when the infrared light emitted by the light-emitting tube encounters a reflector, and the receiving tube receives the reflected infrared light.