SMD electrolytic capacitors 220UF63V12.5X13.5 / chip aluminum electrolytic capacitors

Electrolytic capacitors are widely used in various fields of power electronics, it is mainly used for smoothing, filtering stored energy or rectified AC voltage, and also for non-precision timing delays and so on. When switching power supply MTBF expected, the model results show that the main factors affecting the electrolytic capacitor switching power supply life, so understanding the factors affecting capacitor life is very important. Electrolytic capacitor life depends on its internal temperature. Thus, the electrolytic capacitor design and application conditions will affect the life of electrolytic capacitors. From a design perspective, the electrolytic capacitor design methods, materials, processing technology determines the capacitor life and stability. The application concerned, the use of voltage, ripple current, switching frequency, install the form, heat dissipation and so affect the life of electrolytic capacitors. 2 electrolytic capacitor abnormal number of factors can cause failure of the electrolytic capacitor failure, such as low temperature, capacitance temperature (soldering temperature, ambient temperature, AC ripple), high voltage, instantaneous voltage, VHF or reverse bias pressure; wherein the temperature is the biggest factor working life of electrolytic capacitors (Lop) affected. Capacitance is determined by the conductivity of the electrolyte ionization capacity and viscosity. When the temperature decreases, the viscosity of the electrolyte increases, thereby reducing the ion mobility and conductivity. When the electrolyte is frozen, the ion mobility is very low that very high resistance. On the contrary, excessive heat will accelerate the evaporation of electrolyte, while reducing the amount of electrolyte to a certain limit, the capacitor life will cease. In the alpine region (generally -25 ℃ or less) work, we need to be heated to ensure normal operating temperature of the electrolytic capacitor. Such as outdoor UPS, in northeast China are equipped with a heating plate. Capacitor easily breakdown overvoltage condition, but the practical application of surge voltage and high voltage transients often occur. In particular grid vast, complex all over the country, therefore, the AC grid is very complex, often occur outside the normal voltage of 30%, especially single-phase input, phase deviation will increase the normal range of AC input. After testing, the commonly used 2000 hours import ordinary electrolytic capacitor 450V / 470uF 105 ℃, and at the rated voltage of 1.34 times the voltage of the capacitor will appear after two hours to take gas leakage, red open top. According to statistics and analysis, close communication with the grid PFC output switching power supply electrolytic capacitor failures, mainly due to high-voltage power grid surge and damage. Electrolytic capacitor voltage selection for secondary general derating, down 80% rated the use of more reasonable. 3 life influencing factors in addition to non-normal failure, electrolytic capacitor life and the relationship between temperature exponentially. The use of non-solid electrolyte, the electrolytic capacitor life also depends on the rate of evaporation of the electrolyte, lower electrical performance resulting. These parameters include the capacitor capacitance, leakage current and the equivalent series resistance (ESR). Reference RIFA company expects life formula: PLOSS = (IRMS) & sup2; x ESR (1) Th = Ta + PLOSS x Rth (2) Lop = A x 2 Hours (3) B = reference temperature (typically 85 ℃ ) A = capacitor life reference temperature (depending on the diameter varies capacitor) C = cause capacitor life halving the required degree temperature rise from the above formula, we can clearly see the impact of several life electrolytic capacitors direct factors: the ripple current (IRMS) and equivalent series resistance (ESR), ambient temperature (Ta), transfer from the hot to the overall ambient thermal resistance (Rth). The highest point capacitive internal temperature, called the hot spot temperature (Th). Hot spot temperature is the main factor affecting the service life of the capacitor. The following factors and determine the practical application of the hot temperature outside temperature (ambient temperature Ta), transfer from the hot to the overall ambient thermal resistance (Rth) and the energy loss caused by the alternating current (PLOSS). Internal capacitor temperature rise and energy loss into a linear relationship. Results will cause charging and discharging the capacitor when current flowing through the resistor energy loss, voltage changes when passing through the dielectric can also cause loss of energy, coupled with the energy loss caused by leakage current, all of these losses are due to the internal temperature of the capacitor increased. 3.1 Design considerations factor in non-solid electrolyte capacitors, the dielectric anodic aluminum oxide layer. Electrolyte aluminum foil as an electrical contact with the cathode and anode aluminum oxide layer. Paper absorb the electrolyte interfacial layer becomes the cathode and the anode aluminum foil between the spacer layer, aluminum foil capacitor connected to the terminal via the electrode connection of tablets. ? By reducing the ESR value can be reduced by the internal temperature inside the capacitor ripple current. This can be achieved by using measures connection of a plurality of electrode sheets, laser welding electrodes. ESR values ??and ripple current determines the capacitor temperature rise. One of the major steps to promote the capacitor can have the satisfaction of ESR value is: usually connected external electrodes and a core package with one or more metal electrode connection of sheet, reducing the impedance of the core package and pins. The more the electrode connection of the die on the package, the lower the ESR value of the capacitor. By means of laser welding technology, connection of the electrodes can add more pieces to the core package, so the capacitor can achieve lower ESR values. This also means that the capacitor can withstand higher ripple current and has a lower internal temperature, that longer working life. It would also help to improve the ability to fight capacitance vibration, or they may cause an internal short circuit, a high drain current, capacitance loss, ESR values ??rise and open circuit. · Through the good mechanical contact between the capacitor and the bottom of the aluminum core package and through the middle of the heat sink core package can be effective internal capacitance of heat released from the bottom to the aluminum base plate coupled thereto. Internal heat transfer design is extremely important for the stability of a capacitor and working life. In Evox Rifa's design, the negative electrode foil is extended to be in direct contact with the bottom of thick aluminum capacitors. This base has become a core package of fins to allow heat hot release. Such as the selection with a bolt installation, safely installed in the end plate capacitance (typically aluminum), to obtain a more comprehensive with a lower thermal resistance (Rth.) Heat transfer solutions. * By using the whole wound electrode Bakelite marked with a special lid and double gland and aluminum tightly bite, can greatly reduce the loss of electrolyte. Electrolyte determines the long-life electrolytic capacitors working hours by evaporation gasket. When the capacitor electrolyte evaporation to a certain extent, the capacitor will eventually fail (the result will be accelerated due to internal temperature). Evox Rifa double sealing system designed to slow down the evaporation rate of the electrolyte, the capacitor has reached its maximum working life. These properties ensure that the capacitor has a long working life in the field of requirements. 3.2 Application factors affecting life according to life equation, factors that affect the life of the application can be derived as follows: ripple current (IRMS), ambient temperature (Ta), transfer from the hot to the overall ambient thermal resistance (Rth). 1) The size of the ripple current ripple current, electrolytic capacitor directly affects the temperature inside the hot spot. Discover electrolytic capacitors use manual, you can get the ripple current allowable range. If out of range, it can be used in parallel manner. 2) The ambient temperature (Ta) and thermal resistance (Rth) according to the equation hot spot temperature, ambient temperature electrolytic capacitor application is an important factor. In the application, you can consider the environmental cooling method, heat strength, and heat from the electrolytic capacitor, the electrolytic capacitor installation methods. Capacitor inside the heat conduction from the highest temperature always "hot spots" around the relatively low temperature part. There are several ways to heat transfer: One is through the aluminum foil and the electrolyte conductivity. If the capacitor is mounted on the heat sink, part of the heat will be transferred to the environment through the heat sink. Types of installation and spacing and cooling methods will affect capacitance to ambient. From the "hot spots" is transmitted to the surrounding environment Rth represented by total thermal resistance. Using clip installation, the capacitor is mounted on the thermal resistance of 2 ℃ / W heat sink, the thermal resistance of the resulting capacitor Rth = 3.6 ℃ / W; bolt installation, installed in the thermal resistance of the capacitor 2 ℃ / W heat sink, forced air cooling rate of 2m / s, the resulting capacitor thermal resistance Rth = 2.1 ℃ / W. (In PEH200OO427AM type capacitor, for example, ambient temperature around 85 ℃). In addition to prolonged direct contact with the capacitor cathode aluminum foil, it is also a good way to reduce the thermal resistance. Also note that aluminum would therefore negatively charged, can not be connected to the negative. Capacitance must be properly installed in order to reach its design service life. For example: RIFA PEH169 series and PEH200 series should be mounted vertically upwards or horizontally. While ensuring the safety valve facing up, so the heat and steam to electrolyte capacitors in case of failure, the smooth discharge from the safety valve when the adjacent capacitor arrangement is compact should remain between a capacitance of at least 5mm intervals to ensure that the right amount of air flow . When using bolt, nut torque control is very important. If you twist too loose, the capacitance between the heat sink will not be close contact; if screwed too tightly, they may cause thread damage. Also note that the capacitors should be installed upside down, or it may cause breakage of the bolt. Capacitance should be installed as far away from the heating element, or high temperature will shorten the life of the capacitor, so that the capacitor has become the shortest life expectancy throughout the circuit components. At higher ambient temperatures, try to use forced air cooling, the capacitor is mounted at the inlet. 3) If the current influence of the frequency of the fundamental frequency and multiple harmonics constituted shall be calculated for each value of the harmonics generated by the power loss, and the results obtained with respect to the total loss of value. In high frequency applications across the capacitor leads should be as short as possible to reduce the equivalent inductance. Capacitor resonant frequency (fR), due to the type of capacitor differ. For lug type and bolted between aluminum electrolytic capacitors, the resonant frequency of 1.5kHz to 150kHz. If the capacitor is used when higher than the resonant frequency, the external characteristic is inductive. 4 Conclusion In summary, in the case of non-normal failure to avoid choosing the right application conditions and environment, electrolytic capacitor life can be protected.