Working principle, identification and application of infrared light-emitting diodes
Infrared light emitting diodes (IR LEDs) and infrared light receiving diodes are collectively referred to as IR LED pairs. The shape of an IR LED pair is similar to that of a regular circular LED. For those who are not familiar with IR LED pairs, it can be difficult to distinguish between the IR LED emitter and the IR LED receiver. The following methods can be used to distinguish between the two:
1. Use a multimeter to measure and identify
The resistance between the poles of the IR LED pair can be measured with a multimeter to determine whether it is an IR LED.
Method 1: With the IR LED pair in a condition where the end is not exposed to light, switch the meter leads to measure the forward resistance and reverse resistance. The IR LED emitter has a smaller forward resistance and larger reverse resistance. When the black lead is connected to the positive pole (long pin), the smaller resistance (1k-20k) is the IR LED emitter. If both the forward and reverse resistances are large, it is the IR LED receiver.
Method 2: When the black lead is connected to the negative pole (short pin), the larger resistance is the IR LED emitter, and the smaller resistance that changes with the strength of the light is the IR LED receiver.
2. Test the IR LED by powering it on
An LED and a resistor can be connected in series with the IR LED pair being tested to display the working status of the IR LED.
Point the remote control (DVD remote control, etc.) at the IR LED pair being tested and press any button on the remote control. If the LED lights up, it is the IR LED receiver. If it does not light up, it is the IR LED emitter.
The working voltage and current of the IR LED in the transmitter circuit can be measured to determine its performance. The voltage at both ends of the LED is usually zero when static (i.e., no button is pressed).
When dynamic (i.e., when a button is pressed), it will jump to a smaller voltage value. Depending on the encoding method of the remote control system, the structure of the driving circuit, and the voltage of the power supply, this voltage value is usually between 0.1V and 0.85V.
If the value is not within this range or differs too much, it can be determined that the IR LED is not working properly. If the driving amplifier circuit is normal, it is often due to the IR LED being damaged.
The IR LED should be kept clean and intact, especially the spherical emitting part at the front end, which should not be contaminated by dirt or damaged by friction.
Otherwise, the infrared light emitted from the core will produce reflection and scattering, directly affecting the propagation of infrared light. This may result in reduced sensitivity of the remote control and shortened control distance. In severe cases, it may cause malfunction or even failure of the remote control.
All parameters of the IR LED must not exceed their limit values during operation. Therefore, when selecting a replacement, attention should be paid to the model and parameters of the LED. The current limiting resistor of the IR LED should not be changed arbitrarily.
Because the wavelength of infrared light is quite wide, IR LEDs must be used in pairs with IR receiving diodes to avoid affecting the sensitivity of the remote control or causing loss of control. Therefore, when selecting a replacement, attention should be paid to the wavelength parameters of the infrared light signal it emits.
The packaging material of the IR LED has a low hardness and poor high-temperature resistance. To avoid damage, the solder joint should be far away from the root of the pin, and the soldering temperature should not be too high. The soldering time should not be too long. It is best to use metal tweezers to clamp the root of the pin to help dissipate heat.
The bending and fixing of the pins should be completed before soldering, and the body and pins should not be subjected to any force during the soldering process. As IR LEDs are increasingly used in various products, their applications are becoming more and more widespread.
Watt Smith
Collaborator & Editor
Hello! My name is Watt Smith working on Chipdatas. I write and share relevant articles on electronic components category.
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