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Cause Analysis of LED Damage and Introduction of Protection Method of LED Circuit

Article source:admin Popularity:Published time:2019-08-06 19:50

White LEDs are voltage sensitive devices. In actual work, the current is 20 mA, but the current is often increased due to various reasons in use. If no protective measures are taken, the LED will be damaged after the increased current exceeds a certain time and amplitude.

The main causes of LED damage are:
1) Sudden rise in the supply voltage.
2) A short circuit of a component or a printed line or other wire in the line forms a partial short circuit of the LED power supply path, so that the voltage of the LED is increased.
3) A certain LED is damaged due to its own quality, thus forming a short circuit, and its original voltage drop is transferred to other LEDs.
4) The temperature inside the lamp is too high, which deteriorates the characteristics of the LED.
5) The inside of the lamp is filled with water, and the water is electrically conductive.
6) The anti-static work is not done at the time of assembly, so that the inside of the LED has been damaged by static electricity. Despite the application of normal voltage and current values, it is extremely easy to cause damage to the LED.

So, how do I protect the LED circuit?

1. Use a fuse (tube) in the protection circuit
Because the fuse is disposable, and the reaction speed is slow, the effect is poor, and the use is troublesome, so the fuse is not suitable for use in the finished LED lamp. Because LED lights are now mainly in the city's brilliance engineering and lighting projects. It requires LED protection circuits to be very demanding: When the normal use current is exceeded, the protection can be started immediately, so that the LED power supply path is disconnected, so that both the LED and the power supply can be protected. After the whole lamp is normal, it can automatically restore the power supply without affecting the work of the LED. Circuits should not be too complex, not too large, and the cost should be low. So it is very difficult to use fuse.

2. Use transient voltage suppression diode (TVS for short)
The transient voltage suppression diode is a high efficiency protection device in the form of a diode. Its poles when subjected to high transient reverse impact energy can be negative 12th power of 10 seconds speed extremely short time. The high resistance between the two poles is immediately reduced to a low resistance, absorbing up to several kilowatts of surge power. Clamping the voltage between the two poles at a predetermined voltage value effectively protects the precision components in the electronic circuit. The transient voltage suppression diode has the advantages of fast response time, large transient power, low leakage current, good uniformity of breakdown voltage, easy control of clamping voltage, no damage limit, and small volume. However, in actual use, it has been found that it is not easy to find a TVS device that satisfies the required voltage value. The damage of the LED beads is mainly caused by overheating inside the chip due to excessive current. TVS can only detect overvoltages and cannot detect overcurrents. It is difficult to master the proper voltage protection point, and the device cannot be produced and is difficult to use in practice.

3. Select resettable fuse
Resettable fuse, also known as polymer positive temperature thermistor PTC, is composed of a conductive polymer particles. After special processing, the conductive particles form a chain-like conductive path in the polymer. When the normal operating current passes (or the component is at normal ambient temperature), the PTC resettable fuse is in a low resistance state; When an abnormal overcurrent is passed through the circuit (or the ambient temperature rises), the heat generated by the high current (or elevated ambient temperature) causes the polymer to expand rapidly. It will cut off the conductive paths composed of conductive particles, PTC resettable fuse high-impedance state. When the circuit overcurrent (over-temperature state) disappears, the polymer cools, the volume returns to normal, wherein the conductive particles constituting the conductive path again, the PTC resettable fuse has the form of an initial low resistance state. In the normal working state, the self-recovery fuse has little heat, and in the abnormal working state, its heat is very high, which limits the current passing through it, thereby protecting.

In the specific circuit, you can choose:
1) Shunt protection. The general LED light is divided into a number of serial branches. We can add a PTC component in front of each branch for protection. The benefits of this approach are high accuracy and good reliability of protection.
2) Overall protection. A PTC component is attached to the front of all the beads to protect the entire lamp. The benefit of this approach is simple and does not account for size. For civilian products, the results of this protection in actual use are still satisfactory.

Keywords:Protection Method of LED Circu

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