Detailed explanation of common problems of LED light-emitting diodes

LED light-emitting diode

First, is the LED adopting the connection method or the serial connection method?

LEDs are connected in series or in series, and should be determined mainly according to the form and requirements of the power box circuit. Parallel or series connections each have their advantages and disadvantages. The parallel method only needs to apply a lower voltage across each LED, but a ballast resistor or current source is needed to ensure that the brightness of each LED is consistent. If the magnitude of the bias current flowing through each LED is different, their brightness is also different, resulting in uneven brightness of the entire light source. However, using ballast resistors or current sources to ensure consistent LED brightness will shorten battery life. The series connection method is very good in ensuring the consistency of the current flowing through each LED, but the power supply voltage is required to be high. When the LED adopts the parallel connection method, since the total current of the circuit is the sum of the respective LED currents, the power supply is required to supply a sufficiently large current. In addition, with the circuit connected in series, when one of the LEDs is open, the entire string of LEDs is not bright; but when one of the LEDs is short-circuited, the other LEDs are still bright. With the circuit of the parallel connection method, when one of the LEDs is open, the other LEDs can be bright; but when one of the LEDs is short-circuited, the power of the entire circuit will be short-circuited, so that not only other LEDs can not work normally, and It is also possible to damage the power supply. Therefore, the circuit connected in series is more advantageous.

Second, why not use white LEDs for overvoltage or overcurrent?
Generally, the most commonly used 5mm white LED has a normal operating voltage of 3.0-3.5V and a normal operating current of 20mA. However, many people mistakenly believe that the use of white LEDs for over-voltage or over-current will be brighter, and the actual test result is that the luminous flux is very strong after 15mA. After 20mA, there is almost no growth, increasing to 30mA, only 5% more than 20mA, but LED There is obvious fever. There is also a life test: 20mA works for one month, the attenuation is only 5%, and now there is 95% of the luminous flux. When 30mA is working until 19 days, the luminous flux is only 50%. It can be considered that a white LED that can work for 100,000 hours under normal conditions is used at high currents and has a lifetime of only 600 hours! In general, LEDs can be used for more than 50,000 hours, and some manufacturers claim that Its LED can operate for about 100,000 hours, but this does not guarantee that LED products can be used for so long. The wrong operation and process can easily “destroy” the LED, and the LED will gradually degrade over time. It is predicted that the high-quality LED can maintain the initial brightness after 60 hours of continuous operation. %the above. In order to extend the life of the LED, it is necessary to reduce or completely dissipate the heat generated by the LED chip. Thermal energy is the main reason why LEDs stop functioning.

3. Why is the color of the light emitted by the white LED always blue or yellowish?
This is due to the fact that white LEDs are originally covered with a phosphor of the conversion material on a 1nGaN-based material that emits blue light. This material emits yellow light when excited by blue light. A mixture of blue light and yellow light is thus obtained, which is white light to the naked eye. Looking at the emission spectrum of the white LED, it has two peaks, so the LED that actually emits white light does not exist. Such devices are difficult to manufacture because LEDs are characterized by emitting only one wavelength of single-color light, while true white light requires multi-color spectral synthesis. Due to the technological relationship, including LEDs imported from more than ten yuan, there is also this problem. There are color casts on the edge of the spot, just how much.