First, the basic concept of LED circuit
LED (Light-EmitTIng-Diode) is a semiconductor that converts electrical energy into visible light. It changes the principle of incandescent tungsten filament illumination and energy-saving lamp trichromatic toner illumination, and uses electric field illumination. According to analysis, the characteristics of LED are very obvious, long life, high luminous efficiency, no radiation and low power consumption. The spectrum of LED is almost entirely concentrated in the visible light band, and its luminous efficiency can reach 80~90%. Comparing LED with ordinary incandescent lamp, spiral energy-saving lamp and T5 trichromatic fluorescent lamp, the result shows that the luminous efficiency of ordinary incandescent lamp is 12lm/ W, the life is less than 2000 hours, the luminous efficiency of the spiral energy-saving lamp is 60lm/W, the life is less than 8000 hours, the T5 fluorescent lamp is 96lm/W, the life is about 10000 hours, and the white LED with the diameter of 5mm is 20~28lm / W, the life can be greater than 100,000 hours. Some people also predict that the future LED life limit will be infinite.
High power means that the luminous rate is large, generally 0.5W, 1W, 3W, 5W or higher. Light intensity and lumens are larger than small power, but the same heat dissipation is also great. Now high power is a single application, plus a large heat sink. The low power is generally around 0.06W. Plugins and piranhas, etc. Now LED flashlight is generally used with low power, the light does not scatter, depending on the angle of illumination of the LED, there are large angles and small angles, small angles are not scattered, large angles are scattered.
Some LEDs cause current increase due to various reasons in use. If no protection measures are taken at this time, the LED will be damaged after the increased current exceeds a certain time and amplitude. So let's take a closer look at the specific causes of LED damage.
Second, the main reasons for LED damage are:
1. A sudden rise in voltage.
2. A short circuit in a component or printed line or other wire forms a partial short circuit in the LED power supply path, causing the voltage in this place to increase.
3. The LED is short-circuited due to its own quality, and its original voltage drop is transferred to other LEDs.
4. The temperature inside is too high, which deteriorates the characteristics of the LED.
5. The water is inside and the water is electrically conductive.
6. When the device is not equipped, the anti-static work is not done, so that the inside of the LED has been damaged by static electricity. Despite the application of normal voltage and current values, it is extremely susceptible to LED damage.
Understand the above factors that cause LED damage. So, how do I protect the LED circuit?
Third, the method of protecting the LED circuit is as follows:
1. Use a fuse (tube) in the LED circuit
Since the fuse is disposable and the reaction speed is slow, the effect is poor, and the use is troublesome, the fuse is not suitable for use in the finished LED lamp, because the LED lamp is now mainly in the glory engineering and lighting engineering of the city. It requires the LED protection circuit to be very demanding: the protection can be started immediately when the current is exceeded, the LED power supply path is disconnected, the LED and the power supply can be protected, and the power can be automatically restored after the entire lamp is normal. Does not affect the LED work. The circuit should not be too complicated, the volume should not be too large, and the cost should be low. Therefore, it is very difficult to implement the fuse.
2. Transient Voltage Suppression Diode (TVS for short)
The transient voltage suppression diode is a high efficiency protection device in the form of a diode. When its two poles are subjected to reverse transient high energy impact, the high resistance between the two poles can be immediately reduced to low resistance at a very short time of 10 minus 12 power seconds, absorbing up to several kilowatts of surge power. The voltage clamp between the two poles is at a predetermined voltage value, which effectively protects the precision components in the electronic circuit. The transient voltage suppression diode has the advantages of fast response time, large transient power, low leakage current, good uniformity of breakdown voltage, easy control of clamp voltage, no damage limit, and small volume.
However, in actual use, it has been found that it is not easy to find a TVS device that satisfies the required voltage value. The damage of the LED beads is mainly caused by overheating inside the chip due to excessive current. TVS can only detect overvoltages and cannot detect overcurrents. It is difficult to master the proper voltage protection point, and the device cannot be produced and is difficult to use in practice.
3. Select self-recovery fuse
The self-recovering fuse is also called a polymer polymer positive temperature thermistor PTC, and is composed of a polymer and conductive particles. After special processing, the conductive particles form a chain-like conductive path in the polymer. When the normal operating current passes (or the component is at normal ambient temperature), the PTC resettable fuse is in a low-resistance state; when there is an abnormal overcurrent in the circuit (or the ambient temperature rises), the large current (or the ambient temperature rises) The generated heat causes the polymer to expand rapidly, which cuts off the conductive path formed by the conductive particles. The PTC self-recovery fuse is in a high-resistance state; when the overcurrent (over-temperature state) disappears in the circuit, the polymer cools and the volume recovers. Normal, in which the conductive particles reconstitute the conductive path, the PTC self-recovery fuse is in an initial low resistance state. In the normal working state, the self-recovery fuse has little heat, and in the abnormal working state, its heat is very high, which limits the current passing through it, thereby protecting.
In the specific circuit, you can choose:
1 branch protection. The general LED light is divided into a number of serial branches. We can add a PTC component in front of each branch to protect them separately. The benefits of this approach are high accuracy and good reliability of protection.
2 overall protection. A PTC component is attached to the front of all the beads to protect the entire lamp. The benefit of this approach is simple and does not account for size. For civilian products, the result of this protection in actual use is still satisfactory.
This article first introduces the basic concept of LED circuit, the cause of LED damage and the sharing of LED circuit protection methods. Firstly, the basic concept of LED circuit is understood and then the cause of LED damage is analyzed. Finally, the protection method of LED circuit is proposed. Sharing the use of fuses and suppression diodes, etc., can achieve the protection of the LED circuit. I hope this article can help you effectively.
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