Electrolytic capacitor is really leading to the short life of the LED lamp culprit?

It is often said that the main reason for the short life of the LED lamp is the short life of the power supply, and the short life of the power supply is due to the short life of the electrolytic capacitor. There is some truth to these claims. Because the market is flooded with a large number of poor electrolytic capacitor short life, and now in the fight price, so some manufacturers to use regardless of the quality of these poor short life electrolytic capacitors, the conclusion.

It is often said that the main reason for the short life of the LED lamp is the short life of the power supply, and the short life of the power supply is due to the short life of the electrolytic capacitor. There is some truth to these claims. Because the market is flooded with a large number of poor electrolytic capacitor short life, and now in the fight price, so some manufacturers to use regardless of the quality of these poor short life electrolytic capacitors, the conclusion.

So what is the actual situation?

1 the life of the electrolytic capacitor depends on the ambient temperature at which it operates

How is the life of electrolytic capacitors defined?. But if the life index of an electrolytic capacitor is 1000 hours, and not to say that one thousand hours after the electrolytic capacitor is bad, not only that, the electrolytic capacitor capacity in 1000 hours after the capacity is reduced by half, was 20uF, now only 10uF.

In addition, the life of the electrolytic capacitor indicators also have a characteristic, it is necessary to explain the number of degrees of working environment in the case of life. And it is usually defined as the life at 105 C ambient temperature.

This is because we are now commonly used electrolytic capacitors are liquid electrolytic capacitors, if the electrolyte is dry, of course, there is no capacitor. The higher the temperature, the easier the evaporation of the electrolyte. Therefore, the life expectancy of the electrolytic capacitor must be marked at the ambient temperature.

Therefore, all the electrolytic capacitors are marked at 105 degrees of life. For example, the most common electrolytic capacitor, at 105 degrees of life only about 1000 hours. But if you think all electrolytic capacitors have a lifetime of only 1000 hours. That's a big mistake.

Simply put, if the ambient temperature is above 105 DEG C, then it will be less than 1000 hours of life, if the ambient temperature is below the temperature of 105 degrees, then its life expectancy of more than 1000 hours. Is there a general quantitative relationship between life and temperature?!

There is a simple and easy to calculate relationship, that is, the ambient temperature increased by 10 degrees per second, life is reduced by half; in turn, the ambient temperature is reduced by about 10 degrees, the life expectancy doubled. Of course, this is a simple estimate, but also quite accurate.

Because the LED driver for the electrolytic capacitor, are certainly placed in the interior of the LED lamps, so as long as we know the temperature inside the LED lamps can know the working life of electrolytic capacitors.

2 what is the ambient temperature in the LED luminaire

Because in many lamps LED and electrolytic capacitors are placed in the same shell, in a nutshell, the two of the ambient temperature is the same. And this ambient temperature is mainly determined by the LED and the heating and heat balance of the power supply. And each LED lamp heating and cooling of the situation is not the same, then how can we know the environmental temperature?

In fact, this problem can be calculated in turn, that is, a well designed LED lamps, which allow the internal environment temperature should be a certain. This is because the junction temperature of LED chip is LED chip attenuation (life) of the main reasons, the junction temperature of LED but also by its environmental temperature, so as to know the allowed LED junction temperature, it can calculate the internal temperature of LED lamps. But there are at least three resistance, the LED chip is the thermal resistance from junction to 9 JC shell, LED shell and thermal resistance to aluminum substrate, which in fact after soldering, copper foil, and the insulating layer to the aluminum plate, but is one of the main insulation resistance, referred to as 0 LV third is the aluminum plate the thermal resistance of theta La blister in the air.

Take the type 3014 LED, its own thermal resistance theta JC is 90 /W, because it has only 0.1W of power, so the temperature difference between inside and outside is also at the temperature of 9. The thermal resistance of aluminum substrate is 1 DEG /W, for lighting a 10W because all 10W LED are installed on the same piece of aluminum substrate, so the total temperature difference is 10 degrees, a total temperature of 19 DEG C, the theta La is difficult to estimate, because it is related to the circulation and air. In the internal air flow conditions, the temperature is only about 1 degrees Celsius, so add up to 20 DEG c,. In other words, the LED junction temperature is equal to the ambient temperature plus 20 degrees C.

So the bubble inside the ambient temperature can allow 105 degrees? Just look at the following picture will know. That is the LED chip relationship between moderate decay of American Cree company.

If the ambient temperature is 105 DEG C, then it must be at least 20 degrees centigrade, so the junction temperature is about 125 degrees centigrade. On this curve has not been found, can only be roughly estimated that its life is only 4000 hours. This is absolutely unacceptable, that is to say, the ambient temperature in the LED bubble must be substantially below 105!

We can, in turn, look at how much the ambient temperature should be based on the required LED lifetime. Assuming that the life of the LED is required to be 100000 hours, the junction temperature can only be less than 65 DEG C, so the ambient temperature must be less than 45 DEG C, that is to say, the working temperature of the electrolytic capacitor must be less than 45.

3 the actual life of electrolytic capacitors of various life at ambient temperature of 45 degrees Celsius

Now it is easy to calculate the actual life of the electrolytic capacitor in the actual working temperature of the LED lamp. The following table shows the actual life of several commonly used electrolytic capacitors.

From the table we can see that even the most ordinary life of 1000 hours in the electrolytic capacitor, when the environment temperature is 45 DEG of life can reach 64000 hours, for ordinary LED lamp nominal 50000 hours is enough.

4 method for prolonging the life of electrolytic capacitor

4,1 extends its life from design

In fact, to extend the service life of the electrolytic capacitor, the method is very simple, because it is mainly because of the demise of the evaporation of the electrolyte liquid results, if improve the sealing performance, do not let it evaporate, it also extends the life of nature. For example, Evox Rifa company designed a double sealed system can slow down the evaporation rate of electrolyte.

In addition, through the adoption of a whole phenolic plastic cover with an electrode and a pair of special sealing pads which are closely connected with the aluminum shell, the electrolyte loss can be greatly reduced.

4.2 extend its life from use

Reduce the ripple current can also extend its service life, if the ripple current is too large, can be used to reduce the two parallel capacitor

4.3 choose to extend its life

In the selection of electrolytic capacitors, in addition to the use of quality assurance to ensure the quality of the electrolytic capacitor, but also in the voltage and capacity of the remaining margin. For example, after the 220V bridge rectifier DC voltage will be as high as 300V, but in the selection of electrolytic capacitors at least choose 450V voltage electrolytic capacitor. If you need to calculate the 10uF, it is best to choose 20uF. These measures can also extend the life of electrolytic capacitors. Because the equivalent resistance capacitance and the ripple current will make the temperature higher than the ambient temperature, so the room is a must.

5 Protection electrolytic capacitor

Sometimes, even if the use of a long life electrolytic capacitors, but it will often find electrolytic capacitors broken, what is the reason?

In fact, if you think that this is the quality of the electrolytic capacitor does not pass, it can really make the electrolytic capacitor suffered unrighted wrong! In fact, this is not the electrolytic capacitor but the perpetrators, victims. But why do you say that?

Because we know that in the alternating current network electricity, often due to lightning transient voltage surge, although in the big electric network for the lightning has done a lot of lightning protection measures, but still inevitably there will be leakage of a fish escaped through the Seine to residents of the home. The US power grid should be very advanced, but in my family had one thing in a lightning, I found that my fax machine does not work, after careful examination, the original is because it was struck by lightning power completely broken, can only be scrapped.

The LED lamp if it is by the electric power supply, then the lamp power inside must be in the AC input plus anti surge measures, including fuse and overvoltage protection resistor, usually called varistor, to protect the back of the components, otherwise no long-life electrolytic capacitor will be surge voltage the breakdown.

I believe that if all LED manufacturers can use the high quality electrolytic capacitor is normal, and adopting the relevant measures, so the electrolytic capacitor suffered unrighted wrong will be clean!

Source: China Lighting Network

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