avoid common defects of aluminum electrolytic capacitor
What kind of?
Because of its low cost, the characteristics of aluminum electrolytic capacitor has been a power of common choice.
But, their life is limited, and vulnerable to the influence of high temperature and low temperature extreme condition.
Aluminum electrolytic capacitor in saturated electrolyte place sheet metal pieces on both sides.
Will this electrolyte evaporation during capacitor life, to change its electrical properties.
If its capacitor fails, there will be a severe reaction: formed in the condenser pressure, forcing it to release flammable, corrosive gas.
The speed of the electrolyte evaporation is closely related to the temperature of the condenser.
The drop in temperature 10 degrees Celsius, life extension capacitor.
Capacitor rated life is usually at its maximum rated temperature results are obtained.
A typical 1000 hours under the rated life expectancy of 105 degrees Celsius.
Choose the capacitor used for LED bulb isometric life application shown in figure 1 (
LED the life of 25000 hours)
, aluminum manufacturer of capacitor life becomes a problem.
If you want to up to 25000 hours of life, this kind of capacitor required working temperature less than 65 degrees Celsius.
The working temperature is particularly challenging, because in this application, the environment temperature more than 125 degrees Celsius.
There are some high rated temperature of the capacitor on the market, but in most cases, the aluminum electrolytic capacitor will become the bottleneck of the LED lamp life components.
The temperature dependent on actual life the way you reduce the capacitor voltage rating.
Your first thought might be to raise the risk of capacitor voltage rating to minimize the dielectric failure.
However, doing so will make capacitor equivalent series resistance (
Usually has a high ripple current stress due to capacitor, so the high resistance will bring additional internal power consumption, and increase the temperature of the condenser.
The failure rate increases with temperature rise.
In fact, aluminum electrolytic capacitors are usually only used about 80% of the nominal voltage.
Capacitor at low temperature, the ESR increased dramatically.
In this case, -
The aluminum manufacturers, resistance under 40 oc is orders of magnitude.
This will affect the power performance in many ways.
If the capacitor is used to switch mode power output, the output ripple voltage increase orders of magnitude.
In addition, in the ESR and output capacitance formed above zero frequency, it makes the loop gain an order of magnitude, which affect the control loop.
This produces a oscillation of unstable power supply.
In order to adapt to the strong vibration, the control loop will usually make a big compromise in terms of space, and work at higher temperatures.
In short, the choice of aluminum electrolytic capacitor is usually the lowest cost.
But, you need to determine whether its shortcomings will be harmful to the application.
You need to, through its operating temperature, considering its lifespan.
In addition, you need to properly reduce its rated voltage, so that you can achieve the lowest temperature operation, can achieve the longest service life.
Finally, you need to understand the scope of the ESR must use, so that you can properly designed a control loop, the ripple specification to meet the design requirements.
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