We are often heard that the short life of the power supply lead to the short life of LED Lamp, and the reason why the power supply is short because the electrolytic capacitor life is short. It sounds reasonable, but you could find that some manufacture in order to earning the market with cheapest price wills regardless of the quality of the poor use of these short-lived electrolytic capacitors, so the market is flooded with a large number of short-lived poor electrolytic capacitors and the above results conclusion is come truth. But what is the really truth?
1. Electrolytic Capacitor life depends on the ambient temperature when it is working
Electrolytic capacitor life is how to define it? Of course, is defined in terms of hours. But if the life of an electrolytic capacitor is 1,000 hours, not means that a thousand hours later the electrolytic capacitor is broken, but only that the capacity of electrolytic capacitors in 1000 hours after the reduced capacity by half, if it’s 20uF, and now only 10uF.
In addition, the electrolytic capacitor life index also has a characteristic, it is necessary to explain how many degrees in the working environment temperature life. And in generally, it specified to be at 105 ° C ambient temperature. Because we are now commonly used in electrolytic capacitors are liquid electrolytic capacitors, if the electrolyte is dry, there is no capacitance. The higher the temperature, the easier the electrolyte will evaporate. So the electrolytic capacitor life indicator must indicate what the life of ambient temperature is.
So all electrolytic capacitors are marked out at 105 ℃ life. For example, the most common electrolytic capacitors, 105 ℃ in the life of only 1,000 hours. But if you think that all the life of electrolytic capacitor is only 1,000 hours. That will be a big mistake! Simply, if the ambient temperature is higher than 105 ℃, then its life will be less than 1,000 hours, if the ambient temperature is below 105 ℃, then its life is higher than 1,000 hours. So the life and the temperature there is not a general quantitative relationship between it?
No! One of the most simple and easy to calculate the relationship is that each 10 degrees higher ambient temperature, life is reduced by half; in turn, the ambient temperature decreased by 10 degrees, life expectancy doubled. Of course, this is only a simple estimate, but it is quite accurate. Because for the LED drive power electrolytic capacitors, LED lamps are certainly on the inside of the shell, so we just know the internal temperature of LED lamps can know the working life of electrolytic capacitors.
2. What are the LED lamps inside ambient temperature?
Because the LED and electrolytic capacitors are placed in the same shell normally this means that the two ambient temperatures is the same. This ambient temperature is base on the LED and the heat of the power. And each LED lighting and heat dissipation of heat is not the same, then how can we know the ambient temperature?
In fact, this problem can be projected in turn. A well designed LED lighting, the internal environment temperature should be certain. Because the LED chip junction temperature is to determine the LED chip light, LED junction temperature also relate to its ambient temperature, so when we know the allowable LED junction temperature, the internal Ambient temperature of LED Lamps can be calculated.
But there are at least three thermal resistance, is the LED chip junction to the thermal resistance θjc, and the LED shell to the aluminum substrate surface thermal resistance, collectively referred to as θlv, the third is the thermal resistance of the aluminum plate to bubble shell θla.
Take the 3014 LED as example, its own thermal resistance θjc is 90 ℃ / W, because its power is only 0.1W, so the internal and external temperature difference is 9 ℃. The thermal resistance of the aluminum substrate is 1 ° C / W. For a 10W lamp Since all 10W LEDs are mounted on the same aluminum substrate, the total temperature difference is 10 ° C, a total temperature difference of 19 ° C. Θla is difficult to estimate, because it is related to the flow of air, in the case of internal air does not flow, the temperature difference is only about 1 ℃, so add up to a total of 20 ℃. In other words, LED junction temperature is equal to the ambient temperature plus 20 ℃.
Is the ambient temperature within the bulb allowed to be 105 degrees? Just look at the following picture, you will know the result. Below is the United States Cree LED chip junction temperature and the relationship between the light fades.
If the ambient temperature is 105 ℃, add at least 20 ℃ junction temperature, the junction temperature will about 125 ℃.And you could not find 125 ℃ in this curve, but we could roughly estimate the life of is only 4,000 hours. This is absolutely unacceptable! In other words, LED bulb in the ambient temperature must be much lower than 105 ℃!
We can base on the expectancy required of LED life to projections how much the ambient temperature should be. Assuming that the lifetime of the LED is 100,000 hours, the junction temperature must be less than 65 ° C, so the ambient temperature must be below 45 ° C. In other words, the working ambient temperature of the electrolytic capacitor must be below 45 ° C .
3. The actual life of the electrolytic capacitors when working at 45 ℃ ambient temperature
Now we know the working environment temperature of the electrolytic capacitors, it can easily to calculate its actual life. We have listed in the below table which is the actual life of several commonly electrolytic capacitors.
We could get the information from table, even the most common 1,000-hour life of the electrolytic capacitor, at an ambient temperature of 45 ℃, the life span can reach 64,000 hours, let along for the nominal 50,000 hours of ordinary LED lighting .
4. The method to extend the electrolytic capacitor life
4.1 from the design to extend its life
In fact, to extend the life of electrolytic capacitors, the method is very simple, because it is mainly due to the liquid electrolyte evaporation, if you improve its sealing, let it evaporate, its life is naturally extended. Like EvoxRifa, designed a two-layer seal system to slow down the electrolyte evaporation rate.
And the use of an integral baked phenolic cover with electrodes and a double, specially designed gland to closely engage the aluminum housing can also significantly reduce electrolyte losses.
4.2 Base on the using to extend its life
Reduce the ripple current can also extend its life, if the ripple current is too large, you can use two capacitors in parallel to reduce .
4.3 Use higher capacitor to extend its life
The selection of electrolytic capacitors, not only to choose the quality of the brand, but also considering the voltage and capacity. For example, 220V through the bridge rectifier DC voltage after it’s up to 300V, but in the selection of electrolytic capacitors used at least 450V electrolytic capacitor voltage. If you need the 10uF electrolytic capacitors, the best choice is 20uF. These measures can also extend the life of electrolytic capacitors. Because the equivalent resistance of the capacitor and ripple current will make its internal temperature higher than the ambient temperature, so leave room is necessary.
5. Protect the electrolytic capacitor
Sometimes even with a long life electrolytic capacitor, but still often find the electrolytic capacitor is broken, why?
Because we know that in the exchange of electricity on the electricity grid, often because of lightning and instantaneous high-voltage surge, although the large power grid for lightning has done a lot of lightning protection measures, but still inevitably slip through the net to the residents Home.
If the LED lighting is supplied by the electricity grid, it must be added to the mains input at the mains input, including the fuse, and the overvoltage protection resistor, usually called the varistor. Protection of the back of the components, or long life electrolytic capacitors will be breakdown by the surge voltage.
I believe that if all the LED manufacturers can use regular high-quality electrolytic capacitors, and the adoption of the above measures, then the electrolytic capacitor suffered innocent must be able to get clean!