White light LED is a voltage-sensitive device. In actual work, the current is 20mA as the upper limit, but the current will often increase due to various reasons in use. If no protective measures are taken, this increased current The LED will be damaged after a certain time and range.

The main reasons for LED damage are:

     ① Sudden increase in power supply voltage.
     ② The short circuit of a certain component or printed line or other wires in the circuit forms a local short circuit of the LED power supply path, which increases the voltage in this place.
     ③A certain LED is short-circuited due to its own quality damage, and its original voltage drop is transferred to other LEDs.
     ④ The temperature inside the lamp is too high, which makes the characteristics of the LED deteriorate.
     ⑤ Water enters the lamp, and the water is conductive.
     ⑥The anti-static work was not done well during assembly, so that the inside of the LED has been damaged by static electricity. Although the normal voltage and current values are applied, it is very easy to cause damage to the LED.
     So, how should I protect the LED circuit?

1. Use a fuse in the protection circuit

Because the fuse is disposable, the response 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 the LED lamp is now mainly used in the city's glorious project and lighting project. It requires the LED protection circuit to be very harsh: the protection can be activated immediately when the normal current is exceeded, the power supply path of the LED is disconnected, so that the LED and the power supply can be protected, and the power supply can be automatically restored after the entire lamp is normal. Does not affect the LED work. The circuit cannot be too complicated, not too big, and the cost is low. Therefore, it is very difficult to implement using a fuse.

2. Use transient voltage suppression diodes (TVS for short)

Transient voltage suppression diode is a high-efficiency protection device in the form of a diode. When its two poles are subjected to a reverse transient high-energy impact, it can immediately reduce the high resistance between its two poles to a low resistance at a speed of 10 minus 12 seconds in a very short time, and absorb up to several kilowatts of surge power , The voltage between the two poles is clamped to a predetermined voltage value, which effectively protects the precision components in the electronic circuit. Transient voltage suppression diodes have the advantages of fast response time, large transient power, low leakage current, good uniformity of breakdown voltage deviation, easier control of the clamping voltage, no damage limit, and small size. However, it is not easy to find TVS devices that meet the required voltage value in actual use. The damage of the LED light bead is mainly caused by the overheating inside the chip due to excessive current. TVS can only detect overvoltage but not overcurrent. It is difficult to choose a suitable voltage protection point, and this kind of device cannot be produced and is difficult to use in practice.

3. Choose a self-recovery fuse

Self-recovery 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-like conductive path in the polymer. When the normal working current passes (or the component is at normal ambient temperature), the PTC resettable fuse is in a low resistance state; when there is an abnormal overcurrent in the circuit (or the ambient temperature rises), the large current (or the ambient temperature rises) The heat generated quickly expands the polymer, which cuts off the conductive path formed by the conductive particles. The PTC resettable fuse is in a high resistance state; when the overcurrent (over-temperature state) in the circuit disappears, the polymer cools and the volume recovers Normally, the conductive particles re-constitute the conductive path, and the PTC resettable fuse is in the initial low resistance state. In the normal working state, the self-recoverable fuse has very little heat, and in the abnormal working state, its heat is very high and the resistance value is large, which limits the current passing through it, thereby playing a protective role.