White LED devices are voltage sensitive, in practical work is a maximum of 20mA of current, but often in use due to various reasons caused the current increase, if you do not take protective measures, this increase in current over a certain time after the LED will be damaged and amplitude.
LED damage caused by main reasons:
① sudden increase in supply voltage.
② a component or printed circuit lines or other wires short-circuit LED power supply path to form a local circuit, the voltage increased to make this place.
③ an LED causes damage because of their quality and thus the formation of short circuit, the voltage drop to its original passed on to other LED.
④ temperature inside the lamp, so that deterioration of the characteristics of LED.
⑤ inside the lamp into the water, the water is conductive.
⑥ When the assembly did not do the work of anti-static, so that the internal LED has been static electricity damage. Although the applied voltage and current values are normal, but also easily cause LED damage.
So, how can I like the LED circuit protection?
1. Protection circuit with fuse (tube)
As a one-time fuses, and the slow response, poor results, the use of trouble, so not suitable for LED lighting products fuse, because LED lights are now mainly works in the city's glory and the lighting project. It requires protection circuitry to be very harsh LED: When in excess of normal use of the current protection starts immediately, so that access to the power supply LED is off, LED and power supply can be protected, then the whole lamp to automatically restore the normal supply power, does not affect the LED work. Volume of the circuit can not be too much too complicated, the cost is even lower. So with the way the fuse is difficult to implement.
2. 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 was the reverse transient bipolar high-energy shock to the negative 12 power of 10 seconds, the speed of a very short time, high impedance between the poles themselves immediately reduced to low resistance, absorbing up to several kilowatts of power surge , the voltage between the poles of the voltage clamped at a predetermined value, the effective protection of the electronic circuit of precision components. Transient voltage suppression diode with fast response time, transient power, low leakage current, breakdown voltage deviation consistency, easier to control the clamping voltage, no damage to the limit, the advantages of small size.
However, in actual use to meet the requirements found in the voltage to find the value of TVS device is not easy. LED Light bead damage is mainly because the current chip had overheating caused by the Ambassador. TVS can detect over-voltage can not detect over-current. To select the appropriate voltage protection was very difficult to grasp, this device can not produce it would be difficult to use in practice.
3. Select the self-recovery fuse
Resettable fuse, also known as polymer positive temperature thermistor PTC, is a polymer with conductive particles such as composition. After special processing, the conductive particles in the polymer chain in the form conductive path. When the normal operating current through (or components in a normal ambient temperature) is, PTC resettable fuse was low resistance state; when the circuit by abnormal over-current (or the temperature rises), the large current (or the environment temperature ) heat generated by the rapid expansion of the polymer, it cut off the conductive particles composed of conductive pathways, PTC resettable fuse high-impedance state; when the circuit over-current (over-temperature state) disappears, the polymer cooled, the volume back to normal, in which conductive particles constitute a conductive path again, PTC resettable fuse and was the initial low resistance state. In the normal operation of the heat pipe since the insurance recovery is very small, abnormal working conditions in the heat of its high resistance to large, also limits the current through it, and thus play a protective role. In the specific circuit, you can choose:
① shunt protection. LED lamp is generally divided into many branches in series. We can add in front of each branch separately protected components of a PTC. This approach has the advantage of high accuracy, protection and good reliability.
② overall protection. In all preceded beads of light received a PTC component, the entire light protection. The benefits of this approach is simple and does not account for volume. For civilian products, such protection results in actual use, or satisfactory.
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