Generally, the most commonly used 5mm white LED, its normal operating voltage is mostly in the range of 3.0-3.5V, and the normal operating current is 20mA. However, many people mistakenly think that the use of white LEDs will be brighter for overvoltage or overcurrent, but the actual test result is that the luminous flux increases greatly after 15mA, and there is almost no improvement after 20mA, and it increases to 30mA, which is only 5% more than 20mA, but the LED But there is obvious fever. There is also a life test: after working at 20mA for a month, the attenuation is only 5%, and now there is still 95% of the luminous flux. When the 30mA works for 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 has a lifespan of only 600 hours when used under high current. In general, LEDs can be used for more than 50,000 hours, and some manufacturers claim that their LEDs can operate for about 100,000 hours, but this does not guarantee that LED products can also be used for such a long time. Incorrect operation and procedures can easily "destroy" LEDs. LEDs will gradually degrade over time. It is predicted that high-quality LEDs can maintain 60% of the initial light brightness after 50,000 hours of continuous operation. %above. 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.

Is it better to use the parallel connection method or the series connection method?

  LEDs are connected in parallel or in series, which should be determined mainly according to the form and requirements of the power supply box circuit. Parallel or series connection methods have their advantages and disadvantages. The parallel connection method only needs to apply a lower voltage across each LED, but requires the use of ballast resistors or current sources to ensure the same brightness of each LED. If the amount of bias current flowing through each LED is different, their brightness will also be different, resulting in uneven brightness across the light source. However, using ballast resistors or current sources to keep the LEDs at a consistent brightness will shorten battery life. The series connection method can essentially ensure the consistency of the current flowing through each LED, but the power supply voltage is required to be high. When the LEDs are connected in parallel, since the total current of the circuit is the sum of the currents of each LED, the power supply is required to be able to supply a sufficiently large current.

  In addition, in the circuit using the series connection method, when one of the LEDs is disconnected, the entire string of LEDs will not light; but when one of the LEDs is short-circuited, the other LEDs can still be on. In the circuit using the parallel connection method, when one of the LEDs is disconnected, the other LEDs can still be on; but when one of the LEDs is short-circuited, the power supply of the entire circuit will be short-circuited, so that not only the other LEDs cannot work normally, but also It may also damage the power supply. Therefore, in contrast, the circuit of the series connection method is more advantageous.

In practical applications, LED arrays formed in series and parallel are often used, which can overcome or reduce the above-mentioned single LED open circuit or short circuit causing the whole string of LEDs not to light or the influence on the entire circuit and power supply. The so-called series-parallel is to use a small number of LEDs in series and then a ballast resistor to form a branch, and then connect several branches in parallel to form a "branch group". In addition, the series-parallel series form can also be used, that is, on the basis of the formed "branch group", several "branch groups" are connected in series to form the entire lamp circuit. This connection method not only reduces the failure of one LED. In addition, the ballast resistance is divided into zero, and several high-power resistors are turned into dozens of low-power resistors, from centralized installation to distributed installation, which is not only conducive to the heat dissipation of the resistors, but also can make the design of lamps more efficient. compact.