2024-08-06

White LED lamp bead damage causes and protection methods

White LED lamp bead is a voltage sensitive device, in actual work is the current of 20mA as the upper limit, but often due to various reasons in use caused by the current increase, if you do not take protective measures, this increase in the current exceeds a certain time and amplitude after the LED lamp bead will be damaged.

The main reasons for the damage of LED lamp beads are:

① Sudden increase of supply voltage.
② The short circuit of a component or printed line or other wire in the line forms a local short circuit of the LED lamp bead power supply path, so that the voltage in this place increases.
③A LED lamp bead is damaged for its own quality reasons and thus forms a short circuit, and its original voltage drop is transferred to other LED lamp beads.
④ The temperature in the lamp is too high, which makes the characteristics of the LED lamp beads worse.There is water inside the lamp, and the water is conductive.In the assembly time did not do a good job of anti-static work, so that the internal LED lamp beads have been damaged by static electricity. Although the normal voltage and current values are applied, it is also very easy to cause damage to the LED lamp beads.

So, how to protect the LED lamp bead circuit?

1. Fuse (tube) is used in the protection circuit

Because the fuse is disposable, and the reaction speed is slow, the effect is poor, and the use of trouble, the fuse is not suitable for LED lights in the finished product, because LED lights are now mainly in the city's luster engineering and lighting engineering. It requires the LED lamp bead protection circuit to be very harsh: it can start protection immediately when it exceeds the normal use of current, so that the power supply path of the LED is disconnected, so that the LED and power can be protected, and the power can be automatically restored after the whole lamp is normal, without affecting the LED work. The circuit should not be too complex, the volume should not be too large, and the cost should be low. So it's very difficult to do that with fuses.

2, use transient voltage suppression diode (TVS)

Transient voltage suppression diode is a kind of high performance protection device in the form of diode. When its poles are affected by the reverse transient high energy impact, it can reduce the high resistance between its poles to low resistance at a very short time speed of 10 to the minus 12 seconds, absorb up to several kilowatts of surge power, clamp the voltage between the poles in a predetermined voltage value, and effectively protect the precision components in the electronic circuit. Transient voltage suppression diode has the advantages of fast response time, large transient power, low leakage current, good consistency of breakdown voltage deviation, easy control of clamp voltage, no damage limit, small size and so on. However, in actual use, it is not easy to find TVS devices that meet the required voltage values. The damage of LED light beads is mainly caused by the overheating of the internal chip. TVS can only detect overvoltage but not overcurrent. To choose the right voltage protection point is difficult to master, this device can not be produced and it is difficult to use in practice.

3. Select a self-restoring fuse

Self-restoring fuse, also known as polymer positive temperature thermistor PTC, is composed of polymer and conductive particles. After special processing, the conductive particles form a chain conductive path in the polymer. When the normal working current passes through (or the component is at the normal ambient temperature), the PTC self-restoring fuse is in a low resistance state; When there is an abnormal overcurrent in the circuit (or the ambient temperature rises), the heat generated by the large current (or the ambient temperature rises) makes the polymer expand rapidly, which cuts off the conductive path composed of conductive particles, and the PTC self-restoring fuse shows a high resistance state; When the overcurrent (overtemperature state) in the circuit disappears, the polymer cools, the volume returns to normal, in which the conductive particles re-constitute the conductive path, and the PTC self-restoring fuse shows the initial low resistance state. In the normal working state, the heat of the self-restoring fuse is very small, and in the abnormal working state, its high heat resistance is very large, which limits the current through it, thus playing a protective role. In the specific circuit, you can choose:

① Branch protection. General LED lights are divided into many serial branches. We can add a PTC component in front of each branch for protection. The advantages of this method are high accuracy and good reliability of protection.
② Overall protection. A PTC component is attached to the front of all the light beads to protect the whole lamp. The advantage of this method is that it is simple and does not take up volume. For civilian products, the results of this protection in actual use are satisfactory.

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