LED Quality Checking

White LED is voltage-sensitive device, in the practical work is based on a maximum of 20mA of current, but often as a result of the use of a variety of reasons caused by the current increase, if we do not take protective measures, which increased the current more than a certain amount of time and extent of damage after the LED will be.



LED damage caused by the reasons are:



① the sudden increase in supply voltage.



② line in a component or printed lines or other wires to form the short-circuit LED power supply of the local short-circuit pathway to increased voltage of this place.



③ an LED because the quality of their own and therefore the reasons for the formation of short-circuit damage, which the original voltage drop on the LED's passed on to the other.



④ lamp temperature is too high, so that deterioration of the characteristics of LED.



⑤ internal lamp into the water, water is conductive.



⑥ in the assembly did not do a good job in the work of anti-static, so that the internal LED of the injury has been static. Although it is normal for the imposition of voltage and current values, is also vulnerable to damage caused by the LED.



Well, I like how to carry out the LED circuit protection?



1. To protect the use of fuse circuit (tube)



As the fuse is a one-time, and the slow response, poor results, the use of trouble, so not suitable for LED lights fuse finished, because LED lights are now mainly in the city's glorious works and lighting works. It calls for LED protection circuit must be very harsh: the use of current in excess of normal can immediately start to protect, so that the power LED was disconnected path, so that the power LED and can be protected throughout the lamp automatically after the restoration of normal for electricity, does not affect the LED work. Circuit can not be too complex can not be too much volume, the cost is even lower. Therefore, the way the use of fuses is very difficult to achieve.



2. The use of transient voltage suppression diode (referred to as TVS)



Transient voltage suppression diode is a form of high-performance diode protection device. When it is subject to reverse the polarization of the transient high-energy shocks to the negative 12 power of 10 seconds the speed of a very short time, so that their high resistance between the bipolar immediately reduced to low resistance to absorb the surge of up to several kW power the clamping voltage between the two poles in a predetermined voltage value, the effective protection of the electronic circuit components of precision. Transient voltage suppression diode has a fast response time, transient power, and low leakage current, breakdown voltage deviation of consistency, and easier to control the clamping voltage, no damage to the limit, the advantages of small size.



However, in actual use was found to meet the requirements to find the value of the TVS device voltage is not easy. LED Light bead damage is mainly due to the current Ambassador of the chip have been caused by internal overheating. TVS can not only detect over-voltage over-current detection. Please select the appropriate voltage protection points, it is difficult to master, this device will not be able to produce it difficult to use in practice.



3. Resettable Fuses



Resettable Fuses polymers, also known as positive temperature thermistor PTC, is a polymer with conductive particles, etc.. After special processing, the conductive particles in the polymer chain in the conductive path constituted. When the normal operating current through (or components in a normal ambient temperature) when, PTC Resettable Fuses were low resistance state; when the circuit through the abnormal over-current (or the environment temperature), the large current (or the environment temperature ) so the heat generated by the rapid expansion of the polymer, it is cut off by the composition of conductive particles of conductive pathways, PTC Resettable Fuses were high impedance state; when the circuit over-current (over-temperature state) after the disappearance of polymer cooling, the volume of return to normal, in which conductive particles constitute a conductive path again, PTC Resettable Fuses also showed the initial low resistance state. Work in the normal state since the restoration of insurance of the heat pipe is very small, the work in the abnormal state of its high heat resistance on a lot, it limits the current through it, thus playing a protective effect. In the specific circuit, you can choose:



① shunt protection. LED lamp is generally divided into many series slip. We can slip in each of the previous component, respectively, plus a PTC protection. In this way the advantage of high accuracy, good reliability of the protection.



② the overall protection. Beads in front of all the light of a PTC increase access components, the protection of the entire lamp. The benefits of this approach is simple, does not account for the volume. For civilian products, such protection in the actual use or the results satisfactory.