Protection methods and techniques of LED lamps
Date: 2015-11-11 09:39:29 Hits: 407

First, why should the LED protect

white LED due to its many advantages, being more and more into people's daily life, its usage is now very great. It is a new device and has its own characteristics. White light LED belongs to voltage sensitive device. When each LED works, the current should not exceed 20mA, and over too many LED will be burned easily. LED if it is used properly, the service life is very long. But in actual use, LED is often easy to break. What is the reason? In fact, it does not take into account the characteristics of LED and add protective circuits to it.

LED is a photoelectric semiconductor device, which is easy to be damaged by static electricity in the process of assembly. This requires electrostatic protection in the assembly process. We found that many manufacturers do not have the concept or do not understand, this is not good.

LED 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. A sudden rise in

two, the cause of

1, the supply voltage of LED damage. There are many reasons for the sudden increase in the voltage of the power supply, such as the quality of the power supply, or the improper use of the user, and so on, which may cause the power supply voltage to rise suddenly.

2 a short circuit of a component or printed line or other wire in a circuit causes a partial short-circuit of the LED supply path to increase the voltage in this region.

3, a LED is damaged due to its own quality, thus forming a short circuit, and its original voltage drop is shifted to other LED.

4, the temperature inside the lamp is too high, make the characteristic of LED go bad.

5, the interior of the lamp is filled with water, and the water is conductive.

6, 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.

these reasons will cause a sharp rise in the current LED, LED chip will soon be burned because of overheating. According to our experience, most of the LED burned is short circuited by both poles, and a few parts are broken. Each LED has a pressure drop of about 3.2V, and if it breaks after it is burned, the string of LED doesn't emit light. If the circuit is shorted, the voltage is transferred to other LED, causing greater currents in other LED, and other LED will burn faster and even critical power supplies. It was a small damage, and it was very easy to cause a big accident. LED generally installed in the high, it is difficult to install, it is more difficult to repair. Therefore, the protection of LED is the actual demand, but it has not been paid attention to, nor is it a problem that many people can not handle. Three, how to

LED to protect

on the protection of LED we first thought is to use the insurance tube, but the insurance tube is disposable, and the reaction speed is too slow, not only the actual use effect is very troublesome, so the insurance tube is not suitable for now LED lamp products, because LED is now the main lamp in the city light engineering and lighting engineering. According to the actual demand, we have done a lot of experiments, and according to the requirements of the project summed up the LED protection circuit to some characteristics, it is very hard to start: protection immediately beyond the normal current, let LED power supply channel was disconnected, the LED and the power supply can be protected, in the the light then automatically resume normal power supply, does not affect the work of LED, the key is because it is civilian products, the circuit can not too complex volume can not be too large, low cost. These requirements are contradictory and restrict each other, and it is difficult to implement them.


should first determine which kind of protection circuit and device.

1, we can choose to use the 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.

but in actual use that is not very ideal. First, it's not easy to find TVS devices that meet the required voltage values. TVS devices are mainly used in lightning protection and lightning protection, as well as over 220V voltage absorption, etc., and the power supply voltage of LED lamps is generally 24V or 12V, the TVS of this voltage is very little, and the test is not good. At the same time, we know that the damage of LED beads is mainly caused by overheating of the current through the ambassador chip. The TVS can detect only the voltage and cannot detect the current. Overvoltage must be the cause of over current, but it is difficult to select the appropriate voltage protection point, this device can not be produced, it will be difficult to use in practice.

2, we can choose the self recovery tube. Self recovery tube, also known as 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 components 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. It has the advantages of small volume, low cost, can be used repeatedly, to realize the automatic start protection automatically exit; it is solid package impact resistance is not easy to be damaged; we found in the actual test: because it is a heat sensitive device, affected by the temperature, the PTC package in the inside of the lamp with the light beads sure to heat it will affect the working performance of PTC. The lamp has been determined through tests to select the PTC, using a more reliable method is to make it far away from the heat of the lamp.

in the specific circuit, there are two options available:

1, shunt protection. General LED lights are split into many serial branches. For example, 24V voltage, we are using 7 LED light beads in series, plus a resistor composition, the current is generally 17~19mA, according to need, we can choose 7 integer multiples of beads to form a whole light. We can add a PTC element in front of each branch to protect it. The advantage of this approach is its high accuracy and good reliability of protection.

2, overall protection. Add a PTC element to all the front of the bead to protect the whole light. The advantage of this approach is simplicity, not volume. We usually choose this way. As far as household products are concerned, the result of this kind of protection in actual use is satisfactory. The choice of

PTC is very particular, we are through a long time of experiments to find out the more accurate corresponding value. Electrostatic protection

four, LED

all matter is made of atoms, electrons and protons in atoms. When matter gets or loses electrons, it will become negatively charged or positively charged. These charges accumulate on the surface of the material and we call it electrostatic. Charge accumulation is usually caused by the separation of materials from each other, or by friction, called frictional electrification. There are many factors that affect the accumulation of charge, including contact pressure, friction coefficient, separation rate, and so on. The electrostatic charge accumulation, if there is no discharge channel, this value will eventually reach very high, until the cause effect, stop the charge charge is discharged or attained sufficient strength can penetrate the surrounding material medium so far. When the dielectric is broken down, the electrostatic charge is quickly balanced. The rapid neutralization of the charge is called electrostatic discharge. Due to the rapid discharge voltage at very little resistance on the discharge current will be great, probably more than 20 amperes, if the discharge by electrostatic sensitive components, so large current of the design will be only the turn-on voltage is 3V and current is 20mA LED causing serious injury.

1, why should improve the electrostatic protection awareness

in this century 70 generations ago, a lot of electrostatic problems are caused because people do not have electrostatic protection consciousness, even if there are a lot of people suspected of electrostatic discharge can cause damage to the electronic products. This is because most of the electrostatic discharge damage occurs in people's feeling, because of the perception of human body electrostatic discharge voltage is about 3KV, and many electronic components in hundreds of volts or even tens of volts can be damaged, usually electronic devices are no clear boundaries of electrostatic discharge damage after the component is mounted on the device after the test results there are a lot of problems, analysis is quite difficult. Especially for potential damage, it is difficult to measure the performance of the instrument even if it is made of a precision instrument. But in recent years, experiments have proved that the reliability of electronic products has dropped significantly after a certain period of time. The damage caused by static is absolutely true.

2, what are the forms of electronic products of electrostatic damage? Basic physical properties of

: electrostatic attraction or repulsion, and the earth there is a potential difference, will produce the discharge current. These three characteristics can have three effects on electronic components:

(1). Electrostatic dust components reduce insulation resistance (shorten life).

(2). The electrostatic discharge damage to the damaged element can not work (destroyed).

(3). The electrostatic discharge electric field or current heat generated by the element that injured (potential damage). The

(3) which is more common, it is very difficult to be found in a timely manner.

3, what are the characteristics of electronic products of electrostatic damage?

(1).

concealment of the human body can not directly perceived unless there is electrostatic electrostatic discharge, but also the human body electrostatic discharge must not have the feeling of a shock, this is because the electrostatic discharge voltage of human perception is 2-3

KV, so the electrostatic is hidden.

(2). The potential of

some electronic components from electrostatic properties after injury was not significantly reduced, but the number of cumulative discharge will cause injuries to the device and the formation of hidden dangers. Therefore, electrostatic damage to the device is potential.

(3).

random generation of static electricity is random. Its damage is also stochastic.

(4). The failure analysis work complexity

electrostatic discharge damage, due to electronic products, fine micro structure characteristics and time-consuming, tedious and expensive, high technical requirements and often requires the use of scanning electron microscope and high precision instrument. Even so, some electrostatic damage phenomenon is difficult to distinguish from other causes of damage, so that people mistakenly mistook the electrostatic damage for other failures. This is often attributed to early failure or unknown failure, and thus unconsciously masked, prior to an incomplete understanding of ESD damage

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