Generally, the equivalent circuit of electrolytic capacitor can be considered as the series connection of ideal capacitor, parasitic inductance and equivalent series resistance, as shown in Figure 1. Korean Sanying electrolytic capacitor is one of the most important devices in the primary and secondary circuit filter circuit of switching power supply.

　　图1 电解电容器的等效电路

　　Figure 1 Equivalent circuit of electrolytic capacitor

　　众所周知，开关电源是当今信息家电设备的主要电源，为电子设备小型轻便化作出不可磨灭的贡献。开关电源不断的小型化、轻量化和高效率，在电子设备中使用量越来越大，普及率越来越高。相应的就要求电解电容器小型大容量化，耐纹波电流，高频低阻抗化，高温度长寿命化和更适应高密度组装。

　　As we all know, switching power supply is the main power supply of information appliances today, making an indelible contribution to the miniaturization and portability of electronic equipment. With the continuous miniaturization, lightweight and high efficiency of switching power supply, it is used more and more in electronic equipment, and its popularity is higher and higher. Correspondingly, electrolytic capacitors are required to be small, large capacity, ripple current resistant, high-frequency and low impedance, high temperature and long life, and more suitable for high-density assembly.

　　1.电容量与体积

　　Capacitance and volume

　　在开关电源的原边一旦采用有源滤波器电路，则铝电解电容器的使用环境变得比以前更为严酷：

　　Once the active filter circuit is used on the primary side of the switching power supply, the use environment of aluminum electrolytic capacitors becomes more severe than before:

　　（1）高频脉冲电流主要是20 kHz~100kHz的脉动电流，而且大幅度增加；

　　High frequency pulse current is mainly 20 kHz~100kHz pulse current, and it increases greatly;

　　（2）变换器的主开关管发热，导致铝电解电容器的周围温度升高；

　　The main switch tube of the converter heats up, causing the ambient temperature of the aluminum electrolytic capacitor to rise;

　　（3）变换器多采用升压电路，因此要求耐高压的铝电解电容器。

　　Most of the converters use boost circuits, so high voltage resistant aluminum electrolytic capacitors are required.

　　三莹电解电容器体积小、耐高压，并且允许流过大量高频脉冲电流。另外，这种电解电容器，在高温环境下工作，工作寿命还须比较长。

　　Sanying electrolytic capacitor is small in size, high voltage resistant, and allows a large amount of high-frequency pulse current to flow. In addition, the working life of the electrolytic capacitor must be relatively long when it works under high temperature.

　　2.承受温度与寿命

　　Bearing temperature and service life

　　电解电容器的寿命与电容器长期工作的环境温度有直接关系，温度越高，电容器的寿命越短。普通的电解电容器在环境温度为90℃时已经损坏。但是现在有很多种类的电解电容器的工作环境温度已经很高在环境温度为90℃，通过电解电容器的交流电流和额定脉冲电流的比为0.5时，寿命仍然为10000h，但是如果温度上升到95℃时，电解电容器即已经损坏。

　　The life of the electrolytic capacitor is directly related to the ambient temperature of the capacitor for long-term operation. The higher the temperature is, the shorter the life of the capacitor is. Ordinary electrolytic capacitors have been damaged when the ambient temperature is 90 ℃. However, there are many kinds of electrolytic capacitors with very high operating environment temperature. When the ambient temperature is 90 ℃ and the ratio of the AC current passing through the electrolytic capacitor to the rated pulse current is 0.5, the service life is still 10,000h. However, if the temperature rises to 95 ℃, the electrolytic capacitor is damaged.

　　因此，在选择电容器的时候，应该根据具体的环境温度和其它的参数指标来选定，如果忽略了环境温度对电容器寿命的影响，那么电源工作的可靠性、稳定性将大大降低，甚至损坏设备和仪器。就一般情况而言，电解电容器工作在环境温度为80℃时，一般能达到10000h寿命的要求。

　　Therefore, capacitors should be selected according to specific ambient temperature and other parameters. If the influence of ambient temperature on capacitor life is ignored, the reliability and stability of power supply will be greatly reduced, and even equipment and instruments will be damaged. Generally speaking, when the ambient temperature is 80 ℃, the electrolytic capacitor can reach the requirement of 10000h life.

　　另一方面，电解电容器的寿命还与电容器长时间工作的交流电流与额定脉冲电流（一般是指在85℃的环境温度下测试值，但是有一些耐高温的电解电容器是在125℃时测试的数据）的比值有关。一般说来，这个比值越大，电解电容器的寿命越短，当流过电解电容器的电流为额定电流的3.8倍时，电解电容器一般都已经损坏。所以，电解电容器有它的安全工作区，对于一般应用，当交流电流与额定脉冲电流的比值在3.0倍以下时，对于寿命的要求已经满足。环境温度和纹波电流对电解电容器的影响如图2所示。

　　On the other hand, the service life of electrolytic capacitors is also related to the ratio of the AC current and rated pulse current of capacitors working for a long time (generally refers to the test value at 85 ℃, but some high temperature resistant electrolytic capacitors are tested at 125 ℃). Generally speaking, the higher the ratio, the shorter the life of the electrolytic capacitor. When the current flowing through the electrolytic capacitor is 3.8 times of the rated current, the electrolytic capacitor is generally damaged. Therefore, electrolytic capacitors have their own safe working area. For general applications, when the ratio of AC current to rated pulse current is less than 3.0 times, the requirements for service life have been met. The influence of ambient temperature and ripple current on electrolytic capacitors is shown in Figure 2.

　　图2 某铝电解电容器的寿命与温度、纹波电流的关系

　　Fig. 2 The relationship between the life of an aluminum electrolytic capacitor and temperature, ripple current

　　3.频率特性与阻抗

　　Frequency characteristics and impedance

　　在开关电源输出端用的滤波电容，与工频电路中选用的滤波电容并不一样，在工频电路中用作滤波的普通电解电容器，其上的脉动电压频率仅有100Hz，充放电时间是毫秒数量级，为获得较小的脉动系数，需要的电容量高达数十万微法，因而一般低频用普通铝电解电容器制造目标是以提高电容量为主，电容器的电容量、损耗角正切值以及漏电流是鉴别其优劣的主要参数。

　　The filter capacitor used at the output end of the switching power supply is different from the filter capacitor used in the power frequency circuit. The common electrolytic capacitor used as the filter in the power frequency circuit has a pulse voltage frequency of only 100Hz, and the charge discharge time is in the order of milliseconds. In order to obtain a small pulse coefficient, the capacitance required is as high as hundreds of thousands of micro methods. Therefore, the manufacturing goal of common aluminum electrolytic capacitors for low frequency is to improve the capacitance, Capacitance, tangent value of loss angle and leakage current of capacitor are the main parameters to identify its advantages and disadvantages.

　　在开关稳压电源中作为输出滤波用的电解电容器，由于大多数的开关电源工作在方波或矩形波的状态，含有及其丰富的高次谐波电压与电流，其上锯齿波电压的频率高达数十千赫，甚至数十兆赫，它的要求和低频应用时不同，电容量并不是主要指标，衡量它好坏的则是它的阻抗频率特性，如图3所示。

　　As the electrolytic capacitor used for output filtering in switching regulated power supply, most switching power supplies work in the state of square wave or rectangular wave, and contain extremely rich high-order harmonic voltage and current. The frequency of sawtooth wave voltage on the capacitor is as high as tens of kilohertz, or even tens of megahertz. Its requirements are different from those in low-frequency applications. Capacitance is not the main indicator, but its impedance frequency characteristics are the measure of its quality, as shown in Figure 3.

　　图3 47μF/350V铝电解电容器的阻抗频率特性

　　Figure 3 47 μ Impedance Frequency Characteristics of F/350V Aluminum Electrolytic Capacitors

　　由图可知，随着频率的升高，容抗下降、感抗上升，容抗等于感抗并相互抵消时的频率为铝电解电容器的谐振频率，这时的阻抗最低，仅剩下ESR。如果ESR为零，则这时的阻抗也为零；频率继续上升，感抗开始大于容抗，当感抗接近于ESR时，阻抗频率特性开始上升，呈感性，从这个频率开始以上的频率下电容器时间上就是一个电感。

　　It can be seen from the figure that with the increase of frequency, the capacitive reactance decreases and the inductive reactance increases. When the capacitive reactance is equal to the inductive reactance and mutually cancels, the frequency is the resonant frequency of the aluminum electrolytic capacitor. At this time, the impedance is the lowest, leaving only ESR. If ESR is zero, then the impedance is zero; If the frequency continues to rise, the inductive reactance starts to be greater than the capacitive reactance. When the inductive reactance is close to the ESR, the impedance frequency characteristic starts to rise and become inductive. From this frequency, the capacitor is an inductor in time at the frequency above.

　　用于开关稳压电源输出整流的电解电容器，要求其阻抗频率特性在300kHz甚至500kHz时仍不呈现上升趋势。电解电容器ESR较低，能有效地滤除开关稳压电源中的高频纹波和尖峰电压。而普通电解电容器在100kHz后就开始呈现上升趋势，用于开关电源输出整流滤波效果相对较差。

　　Electrolytic capacitors used for output rectification of switching regulated power supply are required to have impedance frequency characteristics that do not show an upward trend at 300 kHz or even 500 kHz. Electrolytic capacitors have low ESR, which can effectively filter high-frequency ripple and peak voltage in switching power supply. However, ordinary electrolytic capacitors began to show an upward trend after 100kHz, and the filtering effect of switching power supply output rectifier is relatively poor.

　　普通CDII型中4700μF，16V电解电容器，用于开关电源输出滤波的纹波与尖峰并不比CD03HF型4700μF，16V高频电解电容器的低，同时普通电解电容器温升相对较高。当负载为突变情况时，用普通电解电容器的瞬态响应远不如高频电解电容器。

　　4700 in common CDII type μ F. 16V electrolytic capacitor, the ripple and peak used for switching power supply output filtering are no better than CD03HF 4700 μ F. The 16V high-frequency electrolytic capacitor is low, and the temperature rise of ordinary electrolytic capacitor is relatively high. When the load is sudden change, the transient response of ordinary electrolytic capacitor is far less than that of high-frequency electrolytic capacitor.

　　开关电源为了高效率而提高了工作频率的高频化，特别是小型高输出开关电源中输入滤波用电容器要求高纹波性，输出端低阻抗化。要使输出滤波用电容器在高频下低阻抗化，必须降低等效串联电阻。

　　In order to achieve high efficiency, switching power supply improves the high frequency of working frequency, especially in small high output switching power supply, the input filter capacitor requires high ripple, and the output terminal has low impedance. In order to reduce the impedance of output filter capacitor at high frequency, the equivalent series resistance must be reduced.

　　4.纹波电流耐受度

　　Ripple current withstand

　　影响电解电容器性能的最主要的参数之一就是纹波电流问题。纹波电流对铝电解电容器的影响主要是在ESR上产生功耗使铝电解电容器发热，进而缩短使用寿命。 从特性曲线中（图2）可以看到，纹波电流在ESR上产生的损耗与纹波电流有效值的平方成正比，因而随着纹波电流的增加，小时寿命曲线类似于抛物线函数曲线。

　　Ripple current is one of the most important parameters that affect the performance of electrolytic capacitors. The ripple current mainly affects the aluminum electrolytic capacitor by generating power consumption on the ESR to make the aluminum electrolytic capacitor heat up, thereby shortening its service life. From the characteristic curve (Fig. 2), it can be seen that the loss of ripple current on ESR is proportional to the square of the effective value of ripple current. Therefore, with the increase of ripple current, the hourly life curve is similar to a parabolic function curve.

　　降低纹波电流的方法可以采用较大容量的铝电解电容器，毕竟大容量铝电解电容器可承受的纹波电流比小容量的铝电解电容器大；也可以采用多只小容量铝电解电容器的并联方式，还可以选用纹波电流低的电路拓扑结构。一般而言，反激式变换器产生的开关变换电流相对最大。表1是各种开关变换器电路拓扑的直流电流、整流滤波的纹波电流、开关变换电流和滤波电容上的总纹波电流。

　　The ripple current can be reduced by using aluminum electrolytic capacitors with large capacity. After all, large capacity aluminum electrolytic capacitors can withstand more ripple current than small capacity aluminum electrolytic capacitors; The parallel connection of several small capacity aluminum electrolytic capacitors can also be used, and the circuit topology with low ripple current can also be used. In general, flyback converter generates the largest switching current. Table 1 shows the DC current, ripple current of rectifier filter, switching current and total ripple current on filter capacitor of various switching converter circuit topologies.

　　表1 各种开关变换器电路拓扑的整流滤波的纹波电流和开关变换电流

　　Table 1 Ripple Current and Switching Current of Rectification and Filtering of Various Switching Converter Circuit Topologies

　　就平板电视来说，为了能承受大电流，就需要进一步降低电容的ESR。其原因是，在数字设备中，随着功能的增加，电路的电流有越来越大的趋势。对于在液晶电视中进行MPEG编解码工作的图像处理电路来说，2006年一块芯片中电源电路的电流约为3A。

　　As for flat panel TV, in order to withstand large current, it is necessary to further reduce the ESR of capacitance. The reason is that in digital equipment, with the increase of functions, the current of the circuit has a growing trend. For the image processing circuit for MPEG encoding and decoding in LCD TV, the current of power circuit in a chip was about 3A in 2006.

　　如果ESR小，则在有大电流流动时，电容输出电压的下降量也小。伴随着电流增大而来的降低ESR的要求，有可能成为推进电容替换进程的主要原因。相对于铝电解电容将近1Ω的ESR来说，多层陶瓷电容的ESR很小，还不到10mΩ。导电性高分子电容的ESR通常为几十mΩ，ESR比较小的则在10mΩ以下。铝电解电容也在开发ESR比较小的品， 其ESR大约是一般产品的1/2~1/3。

　　If the ESR is small, the drop of capacitor output voltage is small when there is a large current flow. With the increase of current, the requirement of reducing ESR may become the main reason to promote the process of capacitor replacement. Compared with the ESR of aluminum electrolytic capacitor of nearly 1 Ω, the ESR of multilayer ceramic capacitor is very small, less than 10 m Ω. The ESR of conductive polymer capacitors is usually tens of m Ω, while the ESR of smaller ones is less than 10m Ω. Aluminum electrolytic capacitors are also developing products with small ESR, which is about 1/2~1/3 of that of general products.

　　5.可靠性高低

　　Reliability

　　开关电源是一种采用开关式控制的直流稳压电源，它以小型、轻量和高效率的特点被广泛应用于各种通信设备、家用电器、计算机及其终端设备。作为输入滤波和平滑作用的铝电解电容器，它的质量和可靠性直接影响到开关电源的可靠性。一旦铝电解电容器失效，就会导致开关稳压电源的故障。

　　Switching power supply is a kind of DC stabilized voltage power supply with switching control, which is widely used in various communication equipment, household appliances, computers and terminal equipment with the characteristics of small size, light weight and high efficiency. As an input filter and smoothing function, the quality and reliability of aluminum electrolytic capacitor directly affect the reliability of switching power supply. Once the aluminum electrolytic capacitor fails, it will lead to the failure of switching power supply.

　　开关稳压电源用铝电解电容器的失效模式有击穿失效、开路失效、漏液失效及电参数超差失效。其中击穿失效又分为介质击穿和热击穿，对于大功率和大电流输出的开关电源用电解电容器，热击穿失效常占一定比例；电腐蚀导致铝引出条断裂和电容器芯子干涸，使开关稳压电源用铝电解电容器开路失效的主要失效模式；漏液是开关稳压电源用铝电解电容器常见的失效模式，由于使用环境及工作状态较严酷，常发生漏液失效；开关稳压电源用铝电解电容器在使用中最常见的失效模式是电容量减少、漏电流增大及损耗角正切值增大。

　　The failure modes of aluminum electrolytic capacitors for switching power supply include breakdown failure, open circuit failure, liquid leakage failure and electrical parameter out of tolerance failure. Among them, breakdown failure is divided into dielectric breakdown and thermal breakdown. For electrolytic capacitors used in switching power supply with large power and large current output, thermal breakdown failure often accounts for a certain proportion; The main failure mode of open circuit failure of aluminum electrolytic capacitors for switching voltage stabilized power supply is that the aluminum lead strip breaks and the capacitor core dries up due to electric corrosion; Leakage is a common failure mode of aluminum electrolytic capacitors for switching power supply. Due to the harsh operating environment and working conditions, leakage failures often occur; The most common failure modes of aluminum electrolytic capacitors used in switching power supply are capacitance reduction, leakage current increase and loss tangent increase.

　　在电子线路中电解电容器是必不可少的，而且，随着电子设备的小型化，越来越要求电解电容器具有更好的频率特性、更低ESR、更低阻抗、 更低ESL，更高耐压性能、无铅化，这也是电解电容器今后的发展方向。在发展日新月异的信息技术领域，电容器将始终是关键元件之一，我们将不断地顺应信息时代的需求提供高性能电容器。

　　Electrolytic capacitors are indispensable in electronic circuits. Moreover, with the miniaturization of electronic equipment, electrolytic capacitors are increasingly required to have better frequency characteristics, lower ESR, lower impedance, lower ESL, higher voltage withstand performance and lead-free, which is also the development direction of electrolytic capacitors in the future. In the rapidly developing field of information technology, capacitors will always be one of the key components. We will continue to meet the needs of the information age to provide high-performance capacitors.