Common problem
Parameter of electrolytic capacitor selection
Source：本站 | Time：2022-01-10 | Read：325
1, Capacity and volume
As most electrolytic capacitors are wound, it is easy to expand the volume, so the capacity per unit volume is very large, several times to dozens of times larger than other capacitors. However, the large capacity is obtained at the cost of volume expansion, and modern switching power supply requires higher and higher efficiency and smaller and smaller volume, so it is necessary to seek new ways to get capacitors with large capacity and small volume.
2, withstand the temperature and life
In the switching power supply planning process, it is inevitable to select the applicable capacitors. In terms of medium and large capacity products above 100μF, aluminum electrolytic capacitors are by far the most widely used because of their cheap price. However, there has been a significant change in recent years, and the avoidance of aluminum electrolytic capacitors is increasing. One reason for this change is that the life of aluminum electrolytic capacitors tends to be the weak link of the entire device. Engineers at power module manufacturers say, "For components with a limited lifespan like aluminum electrolytic capacitors, try not to use them if you can do without them." Because the electrolyte inside the aluminum electrolytic capacitor can evaporate or produce chemical changes, resulting in a reduction in electrostatic capacity or an increase in equivalent series resistance (ESR), the performance of the capacitor will definitely deteriorate over time.
The life span of electrolytic capacitors is directly related to the ambient temperature where the capacitor works for a long time, the higher the temperature, the shorter the life span of the capacitor. Ordinary electrolytic capacitors are already destroyed at an ambient temperature of 90°C. However, there are many types of electrolytic capacitors that have a high ambient temperature and the life time is still 10,000h at an ambient temperature of 90℃ and a ratio of AC current to rated pulse current of 0.5, but if the temperature rises to 95℃, the electrolytic capacitor will be destroyed. Therefore, when selecting capacitors, they should be selected according to the specific ambient temperature and other parameters. If the influence of ambient temperature on the life of capacitors is ignored, then the reliability and stability of power supply work will be greatly reduced, and even destroy the equipment and instruments. In general, electrolytic capacitors work at an ambient temperature of 80 ℃, generally can reach the requirements of 10000h life.
3, Frequency characteristics and impedance
4, the reliability of high and low
Switching power supply is a DC regulated power supply with switching control, which is widely used in various communication equipment, household appliances, computers and their terminal equipment with the characteristics of small size, light weight and high efficiency. The quality and reliability of the aluminum electrolytic capacitor, which is used for input filtering and smoothing, directly affects the reliability of the switching power supply. Once the aluminum electrolytic capacitor fails, it will lead to the problem of switching regulated power supply.
The failure modes of aluminum electrolytic capacitors for switching regulated power supply are breakdown failure, open circuit failure, liquid leakage failure and electrical parameter overrun failure. Among them, breakdown failure is divided into dielectric breakdown and thermal breakdown, for high power and high current output switching power supply electrolytic capacitors, thermal breakdown failure often accounts for a certain proportion; electric corrosion leads to aluminum lead strip fracture and capacitor core dry, so that the main failure mode of switching power supply with aluminum electrolytic capacitors open circuit failure; liquid leakage is a common failure mode of switching power supply with aluminum electrolytic capacitors, due to the application environment and The most common failure modes of aluminum electrolytic capacitors for switching power supply are capacity reduction, leakage current increase and loss angle tangent value increase.
As most electrolytic capacitors are wound, it is easy to expand the volume, so the capacity per unit volume is very large, several times to dozens of times larger than other capacitors. However, the large capacity is obtained at the cost of volume expansion, and modern switching power supply requires higher and higher efficiency and smaller and smaller volume, so it is necessary to seek new ways to get capacitors with large capacity and small volume.
2, withstand the temperature and life
In the switching power supply planning process, it is inevitable to select the applicable capacitors. In terms of medium and large capacity products above 100μF, aluminum electrolytic capacitors are by far the most widely used because of their cheap price. However, there has been a significant change in recent years, and the avoidance of aluminum electrolytic capacitors is increasing. One reason for this change is that the life of aluminum electrolytic capacitors tends to be the weak link of the entire device. Engineers at power module manufacturers say, "For components with a limited lifespan like aluminum electrolytic capacitors, try not to use them if you can do without them." Because the electrolyte inside the aluminum electrolytic capacitor can evaporate or produce chemical changes, resulting in a reduction in electrostatic capacity or an increase in equivalent series resistance (ESR), the performance of the capacitor will definitely deteriorate over time.
The life span of electrolytic capacitors is directly related to the ambient temperature where the capacitor works for a long time, the higher the temperature, the shorter the life span of the capacitor. Ordinary electrolytic capacitors are already destroyed at an ambient temperature of 90°C. However, there are many types of electrolytic capacitors that have a high ambient temperature and the life time is still 10,000h at an ambient temperature of 90℃ and a ratio of AC current to rated pulse current of 0.5, but if the temperature rises to 95℃, the electrolytic capacitor will be destroyed. Therefore, when selecting capacitors, they should be selected according to the specific ambient temperature and other parameters. If the influence of ambient temperature on the life of capacitors is ignored, then the reliability and stability of power supply work will be greatly reduced, and even destroy the equipment and instruments. In general, electrolytic capacitors work at an ambient temperature of 80 ℃, generally can reach the requirements of 10000h life.
3, Frequency characteristics and impedance
4, the reliability of high and low
Switching power supply is a DC regulated power supply with switching control, which is widely used in various communication equipment, household appliances, computers and their terminal equipment with the characteristics of small size, light weight and high efficiency. The quality and reliability of the aluminum electrolytic capacitor, which is used for input filtering and smoothing, directly affects the reliability of the switching power supply. Once the aluminum electrolytic capacitor fails, it will lead to the problem of switching regulated power supply.
The failure modes of aluminum electrolytic capacitors for switching regulated power supply are breakdown failure, open circuit failure, liquid leakage failure and electrical parameter overrun failure. Among them, breakdown failure is divided into dielectric breakdown and thermal breakdown, for high power and high current output switching power supply electrolytic capacitors, thermal breakdown failure often accounts for a certain proportion; electric corrosion leads to aluminum lead strip fracture and capacitor core dry, so that the main failure mode of switching power supply with aluminum electrolytic capacitors open circuit failure; liquid leakage is a common failure mode of switching power supply with aluminum electrolytic capacitors, due to the application environment and The most common failure modes of aluminum electrolytic capacitors for switching power supply are capacity reduction, leakage current increase and loss angle tangent value increase.
