White LED lamp beads are voltage-sensitive devices, 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 The current exceeds the certain time and amplitude after the LED lamp beads will be damaged.

LED lamp beads cause damage to the main reasons are:

① sudden increase in power supply voltage.

② part of the line or printed wiring or other short-circuit and the formation of LED lamp beads power supply local short circuit, so that the local voltage increases.

③ a LED lamp beads because of their own quality damage and thus the formation of short circuit, it is the original voltage drop passed on to other LED lamp beads.

④ the temperature inside the lamp is too high, so that the characteristics of LED lamp beads deteriorate.

⑤ inside the water into the water, the water is conductive.

⑥ in the assembly did not do the anti-static work, so that the internal LED lamp beads have been static damage. Although the application of the normal voltage and current value, but also easily lead to damage the LED lamp beads.

So, how can I carry out the protection of LED lamp beads circuit?

1. Protection circuit using fuse (tube)

As the fuse is a one-time, and the reaction is slow, the effect is poor, the use of trouble, so the fuse is not suitable for LED lamp products, because the LED lights are now mainly in the city of glorious engineering and lighting works. It requires LED lamp protection circuit to be very harsh: beyond the normal use of current can immediately start the protection, so that the LED power supply path was disconnected, so that LED and power can be protected in the normal light after the normal recovery Power supply, does not affect the LED work. The circuit can not be too complicated volume can not be too much, the cost is even lower. So the use of the fuse to achieve it is very difficult.

2. Using a transient voltage suppression diode (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 their 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, transient power, low leakage current, good consistency of breakdown voltage, easy control of clamping voltage, no damage limit, small size and so on.

However, it is not easy to find a TVS device that meets the required voltage value in actual use. The damage to the LED beads is mainly due to the overcurrent of the chip. TVS can only detect overvoltages can not detect overcurrent. To choose the appropriate voltage protection point is difficult to grasp, this device can not produce it is difficult to use in practice.

3. Select the self-healing fuse

Self-healing fuses, also known as polymer polymer temperature thermistor PTC, is composed of polymer and conductive particles. After special processing, the conductive particles in the polymer to form a chain conductive path. When the normal operating current passes (or the component is at normal ambient temperature), the PTC self-recovery fuse is in a low- impedance state; when there is an abnormal overcurrent in the circuit (or ambient temperature rises), the high current (or ambient temperature rises) The heat generated by the rapid expansion of the polymer, also cut off the conductive particles formed by the conductive path, PTC self-recovery fuse was high resistance state; when the circuit over- current (over-temperature state) disappeared, the polymer cooling, volume recovery Normal, where the conductive particles and re-constitute the conductive path, PTC self-recovery fuse was the initial low resistance state. In the normal working state from the recovery of the fuse is very small, in the abnormal working state of its high heat resistance is great, it limits the current through it, which played a protective role. In the specific circuit, you can choose:

① Shunt protection. General LED lights are divided into many tandem branches. We can in front of each branch plus a PTC components were protected. The benefits of this approach are high accuracy and good reliability of protection.

② overall protection. In front of all the beads plus a PTC component, the protection of the entire lamp. The benefits of this approach are simple, not the volume. For civilian products, the results of this protection in practical use are satisfactory.