White LED because there are many advantages, are more and more into people's daily life, its use is now becoming very great. It is a new device that has its own use on the features. White LED is a voltage-sensitive device. Each LED work when the current should not exceed 20mA, more than too much LED will be easily burned. If the LED is normal use, its life is very long. But people in the actual use of LED is often easy to bad, what reason? In fact, is not taking into account the use of LED features and add protection circuit.
LED is a photoelectric semiconductor device, in the assembly process is easy to be static injury. This requires electrostatic protection during assembly. We found that many manufacturers do not have this concept or do not understand, this is not enough.
LED in the actual work is 20mA current for the upper limit, but often due to various reasons in the use of the current increase, if not take protective measures, this increase in current over a certain time and amplitude after the LED It will be damaged.
2. Cause of LED damage
(1). Sudden increase in supply voltage. So the power supply voltage suddenly rose a lot of reasons, such as the quality of power problems, or improper use of the user, etc. may cause the power supply voltage suddenly increased.
(2). A short circuit of a component or printed line or other wire in the line forms a local short circuit of the LED power supply path, which increases the voltage in this area.
(3). An LED because of its own quality damage and thus short-circuit, its original voltage drop on the other LED passed on.
(4). The temperature inside the lamp is too high, so that the characteristics of LED deterioration.
(5). The interior of the lamp enters the water and the water is conductive.
(6). In the assembly time did not do anti-static work, so that the internal LED has been static damage. Although the application of the normal voltage and current values, but also easily lead to damage to the LED.
These reasons will cause a significant increase in LED current significantly, and soon the LED chip will be burned because of overheating. According to our experience, most of the LED burned after the two-pole short circuit, a small part of the open circuit. Each LED about 3.2V or so the pressure drop, it burned after the explosion if this string of LED will not light up. If the short circuit of this voltage to the other LED, resulting in other LED current, the other LED will be burned faster, and even critical power. Originally small damage is very easy to cause a major accident. LED is generally installed in the high, the installation is not easy, it is more difficult to repair. So the protection of LED is the actual demand, but there is no attention, but also a lot of people no way to deal with the dilemma.
How to protect the LED
The protection of the LED we first thought is to use the fuse, but the fuse is a one-time, and the reaction speed is too slow, both the actual effect is also very troublesome, so the fuse is not suitable for the current LED lights finished, Because the LED lights are now mainly in the city's glorious works and lighting works. In response to this practical needs, we have done a lot of experiments, and according to the requirements of the project summed up the LED protection circuit to have the characteristics of it is very harsh: beyond the normal use of current can immediately start the protection, so that LED power supply path It is broken, so that LED and power can be protected in the normal light after the normal power supply can be restored, does not affect the LED work, the key is because it is a civilian product, the added circuit can not be too complex volume can not be too much, The cost is low. These requirements are contradictory, mutual constraints, it is difficult to achieve.
First, you should determine which protection circuit and protection device is selected.
1. We can choose to use the transient voltage suppression diode (referred to as TVS). Transient voltage suppression diodes are a high-performance protection device in the form of diodes. When its poles are subjected to a reverse transient high-energy impact, the high resistance between the two poles can be reduced to a low resistance at a rate of 10 times the negative time of 10 times the square, absorbing up to several kilowatts of surge power , The voltage between the two poles in a predetermined voltage value, the effective protection of the electronic circuit in the precision components. Transient voltage suppression diode has the advantages of fast response time, high transient power, low leakage current, good consistency of breakdown voltage, easy control of clamping voltage, no damage limit, small size and so on.
But found in actual use is not very satisfactory. It is not easy to find a TVS device that meets the required voltage. TVS devices are mainly used in lightning protection and lightning protection, and more than 220V over-voltage absorption, etc., and LED lamp power supply voltage is generally 24V or 12V, this voltage value of TVS finished very little, the test is not good. At the same time we know: LED light bead damage is mainly because the current is too large to make the chip caused by overheating. TVS can only detect overvoltages can not detect overcurrent. Overvoltage is certainly the cause of overcurrent, but it is difficult to choose the appropriate voltage protection point, this device can not be produced is difficult to use in practice.