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LED lights the latest protection technology(II)

Jun 06, 2017

2. We can choose to restore the fuse. Self-healing fuse, also known as polymer polymer positive temperature thermistor PTC, is composed of polymer and conductive particles. After special processing, conductive particles in the polymer to form a chain conductive path. When the normal operating current passes through (or the component is at normal ambient temperature), the PTC self-recovery fuse is in a low resistance state; when there is an abnormal overcurrent in the circuit (or ambient temperature rises), the high current (or ambient temperature rises) The heat generated by the rapid expansion of the polymer, also cut off the conductive particles formed by the conductive path, PTC self-recovery fuse was high resistance state; when the circuit over-current (over-temperature state) disappeared, the polymer cooling, volume recovery Normal, in which conductive particles and re-constitute the conductive path, PTC self-recovery fuse was the initial low resistance state. In the normal working state from the recovery of the fuse is very small, in the abnormal working state of its high heat resistance is very large, it limits the current through it, which played a protective role. It is small in size, low in cost and can be used repeatedly to achieve automatic protection of automatic start-up; it is solid-state package resistant to impact is not easily damaged; we found in the actual test: because it is a heat-sensitive device, A lot of impact, because the PTC package in the interior of the lamp, the beads must be heated to affect the work of PTC performance. On the already determined lamps can be tested to select PTC, the more reliable way to use it is to keep it away from the heat of the lamp beads.

    In the specific circuit, there are two ways to use when you choose:

1.Shunt protection. General LED lights are divided into many tandem branches. Such as 24V voltage, we are using seven LED light beads in series with a resistor, the current is generally 17 ~ 19mA, according to the need we can choose 7 integer light beads to combine into a whole lamp. We can in front of each branch plus a PTC element were protected. The benefits of this approach are high accuracy and good reliability of protection.

2.The overall protection. In front of all the beads plus a PTC element, the protection of the entire lamp. The benefits of this approach are simple, not the volume. We generally choose this way. In the case of household products, the results of such protection are actually satisfactory.

PTC selection is very particular about, we are through a long time experiment to explore a more accurate corresponding value.

Fourth, LED static protection

All matter consists of atoms, atoms and electrons and protons. When the material gets or loses electrons, it will become negatively charged or positively charged, and these charges accumulate on the surface of the material we call the object to bring static electricity. Charge accumulation is usually caused by the separation of materials from each other, but also by the friction caused by friction called power. There are many factors that affect the accumulation of charge, including contact pressure, friction coefficient and separation speed and so on. Electrostatic charge will accumulate, and if there is no vent channel, this value will eventually be high until the charge generation is stopped, the charge is vented or sufficient strength can reach the surrounding material medium. Dielectric breakdown, the electrostatic charge will soon be balanced, the rapid charge of this charge is called electrostatic discharge. Due to the rapid discharge of the voltage on a very small resistor, the bleed current will be large and may exceed 20 amps. If this discharge is carried out via an electrostatic sensitive element, such a large current will be designed to have only the conduction voltage of more than 3V Current is 20mA LED caused serious damage.

 1. Why should improve the protection of static electricity

Before the 70th generation of this century, many static problems were caused by the lack of static protection awareness, even now there are many people suspected that electrostatic discharge will cause damage to electronic products. This is because most of the electrostatic discharge damage occurs below the human feeling, because the body of the electrostatic discharge of the perceived voltage of about 3KV, and many electronic components in a few hundred volts or even tens of volts will be damaged, usually electronic devices are electrostatic discharge There is no obvious boundary after damage, the components installed on the device after the test, the results of a lot of problems, analysis is also very difficult. Especially the potential damage, even if the use of precision instruments is difficult to measure the performance of a significant change. But in recent years, experiments have confirmed that this potential damage after a certain period of time, the reliability of electronic products decreased significantly. The damage caused by static electricity is absolutely true.

2.Electrostatic damage to electronic products which form?

The basic physical characteristics of static electricity are: attractive or repulsive, with the potential difference between the earth, will produce discharge current. These three features can have three effects on electronic components:

(1) Electrostatic adsorption of dust, reducing the insulation resistance of components (shorten the life).

(2) Electrostatic discharge damage, so that damage to components can not work (completely destroyed).

(3) Electrostatic discharge Electric field or current generated by the heat, so that components damage (potential damage).

(3) The situation is more common, it is difficult to be found in time.

3.What are the characteristics of electrostatic damage to electronic products?

(1)The human body can not directly perceive static electricity unless the occurrence of electrostatic discharge, but the occurrence of electrostatic discharge of the human body does not necessarily have the feeling of electric shock, this is because the human body perceived electrostatic discharge voltage of 2-3 KV, so static with concealment.

(2) potential

Some electronic components by electrostatic damage after the performance did not significantly decline, but repeated cumulative discharge will cause internal injuries and the formation of hidden dangers. So electrostatic damage to the device has the potential.

(3). Randomness

Electrostatic production is also random. Its damage is also random.

(4). Complexity

Electrostatic discharge damage failure analysis work, due to electronic products, fine, fine, small structural features and time-consuming, trouble, cost, require high technology and often need to use high-precision instruments such as scanning electron microscopy. Even so, some electrostatic damage is difficult to distinguish with other causes of damage, people mistakenly take the electrostatic damage failure as other failure. This is often due to early failure or unexplained failure before the damage to the electrostatic discharge is not fully understood, and thus unconsciously conceals the real cause of the failure. So the analysis of electrostatic damage to electronic devices is complex.

4. How to control electrostatic discharge?

From the previous analysis shows that static electricity is due to contact with the object separation, or even no contact with the induction, etc., it can be said: at any time, any place may produce static electricity. To completely eliminate static electricity is almost impossible, but you can take some measures to control static electricity without causing harm.

5.how to control the human body static (human body electrostatic protection)?

The human body is the most common source of electrostatic hazards. For static electricity, the body is a conductor, so you can take the body to the ground measures.

(1). Use anti-static floor / anti-static shoes / socks (static from the foot to the earth)

Through the foot through the anti-static ground, mats, carpets, personnel wear anti-static shoes and socks, forming a combination of grounding.

(2). Wear an antistatic wrist strap and ground (static from the hand to the earth)

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