How much do you know about LED junction temperature?

Some people say that the LED can reach 50000 hours, the light fade is controlled within 30%, but the power supply can not reach 50000 hours, so the overall light fixture can not reach 50,000 hours. How can this problem be explained?

A: The ICs, resistors, transistors, and diodes in the power supply can reach 50,000 hours. Electrolysis alone must be highly valued in the design. There are two key parameters in the technical indicators of electrolysis: use time and temperature. When the environmental temperature of electrolysis is reduced by 10 degrees, the use time can be doubled. Electrolysis should be selected to be more than 120 degrees Celsius. Secondly, when electrolysis is designed, the electrolysis capacity should be enlarged without affecting the performance of the circuit. The indicator of the use time is how many hours after the capacity is reduced by 80%, but it is not broken. At this time, the electrolytic capacity parameter will change, but it is not completely broken and cannot be used. So after rigorous consideration, the design of the power supply can reach 50,000 hours, to ensure that the entire lamp life of up to 50,000 hours, and the light fade control within 30%.

All LED lamps have this fatal flaw, and so far, no one has proposed a good solution. All engaged in LED power supply, or engaged in LED finished lamps and lanterns, all avoid this issue, pretend Do not know, but the actual mass production, this problem is endless, of course, there are more people who do not understand, completely do not understand what is going on.

Phenomenon Description: The most common problem is to do a project, a few hundred lamps, often for no reason without damage, common like a street mounted LED street light, sometimes not bright, often bad, repaired and broken, broken and then repair There are LED fluorescent lamps, many use non-isolated power supply, often found in mass production are destroyed, the root cause is here. Are caused by the surge voltage, surge voltage generated many reasons, the common is an outdoor lightning strike, or Is a large load on, off, voltage clutter and the like. According to the written method, is a very high voltage, often up to thousands of volts, instantly added to the input power supply, and then from the input power supply to the output end.

The PWM adjustment of the switching power supply requires several clock cycles, and if the input voltage momentarily changes (up to thousands of volts) and the time is very short (tens, hundreds of ms), then the switching power supply has no time to adjust. At this time, the performance is the instantaneous high-voltage transmission to the output, especially the current LED fluorescent lamp step-down circuit, because the load is in the 300V high-voltage circuit, 300V high voltage instantly becomes larger, this high voltage is added to the output The isolated power supply will be better, but many can't escape.

Some people say that the use of TVS, choke, X capacitors, in fact, is not very useful. Because the LED working under normal current is very sensitive to voltage changes. LED works at stable current, such as straw lamp, working at 20MA, stable When the voltage is about 3.1V and the voltage applied across the two ends increases by 0.1V, the current at both ends does not increase by a few percent, but it may increase by several tens of percent. It is not increased by 0.5%. Ten, but a few hundred percent increase, that is, several times, although the above several components can play a role, but the TVS filtered voltage is still more than 400V, this voltage will still make the output current fierce Increase, when the output is equivalent to a short circuit, the performance of non-isolated power supply is instantly destroyed constant current ring, or even switch, directly led to the entire LED annihilated, the phenomenon of isolated power supply is to destroy the switch tube, resulting in the light is not bright. This is the root cause. This is determined by the LED characteristics. Many constant-voltage power supplies, such as 12V common constant-voltage power supplies, often have low damage rates when used with some other loads. However, when the same power supply is used for three strings, several strings and re-pointing LEDs are often found. A lot of blowouts are caused here because of the LED's load characteristics, which are more likely to damage itself and damage the power supply.

What is the junction temperature?

The junction temperature is the temperature at which each diode connects to the base when the LED is operating. Keeping the junction temperature at a minimum level increases the attenuation of LED light. Junction temperature is the key to evaluate the quality of LED products. Low junction temperature can prolong the service life of LEDs.

How to manage the control junction temperature?

San Xun LED lamps use aluminum heat sinks for the lamp housing. This unique design minimizes the junction temperature as much as possible.

How do LED lights differ from traditional light sources such as incandescent, fluorescent, and xenon lamps?

Unlike other light sources, LEDs convert invisible electricity directly into visible light and generate no heat or other forms of radiation, such as ultraviolet light. Traditional light sources even radiate 360 ​​degrees or more. The LED's light radiation range is a fixed arc. The use of LEDs is an advantage when some facilities and lighting designs need to be fixed and pose challenges to many light sources today.

LED advantages and application of LED technology in the general lighting challenges?

LED has the advantages of high efficiency and durability. These advantages allow us to save energy, save money, keep our costs under control, and extend lamp life. Since the LED's light radiation range is a fixed arc shape, there is no light loss caused by absorption by the lighting device or light pollution caused by the light radiation angle. On the other hand, when this LED is used in the lighting industry, it poses a challenge to its fixed arc radiation angle. Well-designed luminaires use LEDs as light sources to ensure that light is evenly distributed over the illuminated area.

What are the advantages of using a LED light source for environmental protection?

LED-based lighting fixtures with mercury or harmful gases can achieve the longest service life and minimize waste. In addition, they are made from completely recyclable materials, so their pollution to the environment is minimal. When they are applied to the facilities, LED lights can be eliminated when they are specially designed to turn darkness into daytime and reduce the negative impact of street lights on people.

Why LED life is measured with light decay?

LED lamps have a much longer life than incandescent and fluorescent or xenon lamps. LED lights generally have a lifetime of 50,000 hours to 100,000 hours. With the passage of time, the luminous flux of LED lamps with long use time will become smaller and will not be completely abandoned. This reduction in luminous flux is called "light decay," and the available time (working time) of an LED lamp is calculated using light decay.

The evaluation of the service life of LED lamps on an industry standard is an evaluation point when the LED light source reaches a light decay of 30%. 100,000 hours is not equal to the lifetime of a lamp. The service life of an LED light source is rated to be discarded when the light decay reaches 30%. More than 10 hours of LED light will still work, but the luminous flux will be reduced.

Why does the white light LED need to perform spectrophotometric separation? The white light LED lamp must undergo spectrophotometric separation before leaving the factory (some LEDs that have not been spectrophotometrically separated will emit pure white, some bluish, and some yellow). The color instrument is expensive, and the general small plant does not have such a device. Therefore, the white light produced generally receives the spectrophotometric separation of the major manufacturers. Since it is not the product of its own factory, the spectrophotometric separation will not be so careful. Some small plants simply do not split light. They generally pull customers at low prices. Therefore, when buying a white LED, don't blindly try to make it cheap. Be sure to purchase the LED light emitting tube single particle lamp or module of the same manufacturer, same batch, and the same color to create the same batch of light characters.

What are the differences between track lights, two lines, three lines, and three circuits?

The track slot is not the same, the function is not the same. For example, the three-loop track slot can separate the track lights in the track. He can divide the track lamps into several groups to control the lamps in the track. The two lines will not work. The three lines are more. The ground line.

What is the humidity of the working environment of our LED lamps?

Can work under 90% humidity.

What is the difference between light source power, optical radiation power, and total power?

Total power = light source power + power drive loss power Light source power = optical radiation power (light energy) + heat power (heat energy)

Power efficiency = light source power / total power The power represented by the number in our product code is the light source power.

What are the causes of LED junction temperature?

When the LED is working, the following five conditions can cause the junction temperature to rise differently:

a. Bad electrode structure of the device, the material of the window layer substrate or the junction region, and the conductive silver paste all have a certain resistance value. These resistors are added together to form the series resistance of the LED device. When current flows through the P-N junction, these resistors will also flow through them, which will cause Joule heating, resulting in increased chip temperature or junction temperature.

b. Since the P-N junction cannot be perfectly perfect, the efficiency of the element injection will not reach 100%. That is to say, in addition to the charge (hole) injected into the N area by the P area during LED operation, the N area will also be Injecting a charge (electron) into the P zone, in general, the latter type of charge does not generate a photoelectric effect, and is consumed in the form of heat. Even if the useful part of the charge is injected, it will not all become light, and some of it will be combined with impurities or defects in the junction region and eventually become hot.

c. Practice has proved that the limitation of the light output efficiency is the main reason that causes the LED junction temperature to rise. At present, advanced material growth and component manufacturing processes have enabled most of the LED's input electrical energy to be converted into light radiant energy. However, since the LED chip material has a much larger refractive index than the surrounding media, the resulting internal Most of the photons (>90%) cannot overflow the interface smoothly, but generate total reflections at the chip and dielectric interface, return to the interior of the chip and eventually absorbed by the chip material or substrate through multiple internal reflections, and change in the form of lattice vibrations. Heat, causing the junction temperature to rise.

d. Obviously, the heat dissipation ability of LED components is another critical condition that determines the junction temperature. When the heat dissipation capability is strong, the junction temperature drops. Conversely, when the heat dissipation capability is poor, the junction temperature will rise. Because the epoxy adhesive is a low thermal conductivity material, the heat generated at the P-N junction is difficult to dissipate upward into the environment through the transparent epoxy. Most of the heat passes through the substrate, the silver paste, the tube shell, and the epoxy adhesive layer. PCB and heat sink diverge downward. Obviously, the thermal conductivity of related materials will directly affect the heat dissipation efficiency of the components. A common type of LED has a total thermal resistance of 300 to 600°C/w from the P-N junction region to the ambient temperature. For a power LED component having a good structure, the total thermal resistance is about 15 to 30°C. /w. The huge difference in thermal resistance shows that ordinary LED devices can only work normally under very small input power conditions, while the power dissipation of power devices can be as large as watts or even higher.

What are the ways to reduce the LED junction temperature?

a, reduce the thermal resistance of the LED itself;

b. Good secondary heat dissipation mechanism;

c. Reduce the thermal resistance between the LED and the secondary cooling mechanism mounting interface;

d, control rated input power;

e. Lowering the ambient temperature The input power of the LED is the sole source of the thermal effect of the component. A portion of the energy is converted to radiant energy, and the rest of the energy eventually becomes hot, raising the temperature of the component. Obviously, one of the main methods to reduce the temperature rise effect of LED is to try to improve the electro-optical conversion efficiency (also called external quantum efficiency) of the device, so that as much input power as possible is converted into light energy. Another important approach is to improve the components. The heat loss ability causes the heat generated by the junction temperature to be emitted to the surrounding environment through various methods.