White LED belongs to the voltage sensitive device, in the actual work is based on 20mA's current limit, but often due to various reasons in the use of the resulting current increases, if no protective measures are taken, the current increases more than LED will be damaged after a certain time and amplitude.
The main causes of LED damage are:
A sudden rise in the voltage of the supply.
A short circuit of a LED supply path is formed by a short circuit of a component or printed line or other wire in the circuit, which increases the voltage in this region.
A LED is damaged due to its own quality, thus forming a short circuit, and its original voltage drop is passed on to other LED.
The temperature in the lamp is too high to deteriorate the characteristics of the LED.
The interior of the lamp is filled with water and the water is electrically conductive.
In the assembly, did not do anti-static work, so that the internal LED has been damaged by static electricity. Although the normal voltage and current value are applied, it is also easy to cause damage to LED.
So, how do I do LED circuit protection?
1. the fuse circuit is used in the protection circuit
Because the fuse is one-time, and the reaction speed is slow, the effect is bad, and the use of trouble, so fuse is not suitable for LED lamp finished product, because the LED lamp is now mainly in the city's glorious project and lighting project. It requires LED protection circuit to be very harsh: can immediately start protection beyond the normal current, let LED power supply channel was disconnected, the LED and the power supply can be protected, in the light then automatically resume normal power supply, does not affect the work of LED. The circuit can not be too complicated, the volume can not be too large, and the cost is lower. So it's difficult to use fuse.
2. use transient voltage suppressor diode (referred to as TVS)
Transient voltage suppressor diode is a diode form of high efficiency protection device. When it's poles by the reverse transient high energy shock, with 10 minus 12 seconds short time speed, high resistance between the poles themselves immediately reduced to low resistance, absorption up to several kilowatts of power surge, the voltage clamp between two poles at a predetermined voltage value, a effectively protecting precision components in electronic circuit. Transient voltage suppressor diodes have the advantages of fast response time, large transient power, low leakage current, good consistency of breakdown voltage, easy control of clamping voltage, no damage limit, small size and so on.
However, in practical use, it is difficult to find TVS devices that meet the required voltage values. The damage to the LED light bulb is mainly caused by overheating of the current through the ambassador chip. The TVS can detect only the voltage and cannot detect the current. It is difficult to select the appropriate voltage protection point, and this device can not be produced, and it is difficult to use in practice.
3. select self recovery fuse
Self recovery fuse, also known as polymer polymer positive temperature thermistor PTC, is composed of polymers and conductive particles. After special processing, the conductive particles form a chain conducting pathway in the polymer. When the working current through (or component under normal ambient temperature), the PTC self recovery fuse a low resistance state; when the circuit has abnormal current through (or ambient temperature), high current (or ambient temperature) heat generated by the rapid expansion of the polymer, it cuts off a conductive path a conductive particle, PTC self recovery fuse in a high impedance state; when the current in the circuit (over temperature) disappeared after the polymer cooling volume returned to normal, the conductive particles again form a conductive pathway, PTC self recovery safety wire and a low resistance state initial. In normal working condition, the heat of the self recovering pipe is very small. In abnormal working condition, the heating is very high, the resistance is great, and the current passing through it is limited, so that it plays a protective role. In the specific circuit, you can choose:
Shunt protection. General LED lights are split into many serial branches. We can add a PTC component in front of each branch to protect it separately. The advantage of this approach is its high accuracy and good reliability of protection.
Overall protection. Add a PTC component to all the front of the bead to protect the whole light. The advantage of this approach is simplicity, not volume. For civil products, the results of this kind of protection in actual use are satisfactory.