通常，電解電容器的等效電路可以認(rèn)為是理想電容器與寄生電感、等效串聯(lián)電阻的串聯(lián)，如圖1所示。
韓國三瑩電解電容器是開關(guān)電源中一次和二次回路濾波電路中最重要的器件之一。
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.
圖1 電解電容器的等效電路
Figure 1 Equivalent circuit of electrolytic capacitor
眾所周知，開關(guān)電源是當(dāng)今信息家電設(shè)備的主要電源，為電子設(shè)備小型輕便化作出不可磨滅的貢獻(xiàn)。開關(guān)電源不斷的小型化、輕量化和高效率，在電子設(shè)備中使用量越來越大，普及率越來越高。相應(yīng)的就要求電解電容器小型大容量化，耐紋波電流，高頻低阻抗化，高溫度長壽命化和更適應(yīng)高密度組裝。
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.電容量與體積
Capacitance and volume
在開關(guān)電源的原邊一旦采用有源濾波器電路，則鋁電解電容器的使用環(huán)境變得比以前更為嚴(yán)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:
?。?）高頻脈沖電流主要是20 kHz~100kHz的脈動電流，而且大幅度增加；
High frequency pulse current is mainly 20 kHz~100kHz pulse current, and it increases greatly;
?。?）變換器的主開關(guān)管發(fā)熱，導(dǎo)致鋁電解電容器的周圍溫度升高；
The main switch tube of the converter heats up, causing the ambient temperature of the aluminum electrolytic capacitor to rise;
?。?）變換器多采用升壓電路，因此要求耐高壓的鋁電解電容器。
Most of the converters use boost circuits, so high voltage resistant aluminum electrolytic capacitors are required.
三瑩電解電容器體積小、耐高壓，并且允許流過大量高頻脈沖電流。另外，這種電解電容器，在高溫環(huán)境下工作，工作壽命還須比較長。
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.承受溫度與壽命
Bearing temperature and service life
電解電容器的壽命與電容器長期工作的環(huán)境溫度有直接關(guān)系，溫度越高，電容器的壽命越短。普通的電解電容器在環(huán)境溫度為90℃時已經(jīng)損壞。但是現(xiàn)在有很多種類的電解電容器的工作環(huán)境溫度已經(jīng)很高在環(huán)境溫度為90℃，通過電解電容器的交流電流和額定脈沖電流的比為0.5時，壽命仍然為10000h，但是如果溫度上升到95℃時，電解電容器即已經(jīng)損壞。
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，在選擇電容器的時候，應(yīng)該根據(jù)具體的環(huán)境溫度和其它的參數(shù)指標(biāo)來選定，如果忽略了環(huán)境溫度對電容器壽命的影響，那么電源工作的可靠性、穩(wěn)定性將大大降低，甚至損壞設(shè)備和儀器。就一般情況而言，電解電容器工作在環(huán)境溫度為80℃時，一般能達(dá)到10000h壽命的要求。
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，電解電容器的壽命還與電容器長時間工作的交流電流與額定脈沖電流（一般是指在85℃的環(huán)境溫度下測試值，但是有一些耐高溫的電解電容器是在125℃時測試的數(shù)據(jù)）的比值有關(guān)。一般說來，這個比值越大，電解電容器的壽命越短，當(dāng)流過電解電容器的電流為額定電流的3.8倍時，電解電容器一般都已經(jīng)損壞。所以，電解電容器有它的安全工作區(qū)，對于一般應(yīng)用，當(dāng)交流電流與額定脈沖電流的比值在3.0倍以下時，對于壽命的要求已經(jīng)滿足。環(huán)境溫度和紋波電流對電解電容器的影響如圖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.
圖2 某鋁電解電容器的壽命與溫度、紋波電流的關(guān)系
Fig. 2 The relationship between the life of an aluminum electrolytic capacitor and temperature, ripple current
3.頻率特性與阻抗
Frequency characteristics and impedance
在開關(guān)電源輸出端用的濾波電容，與工頻電路中選用的濾波電容并不一樣，在工頻電路中用作濾波的普通電解電容器，其上的脈動電壓頻率僅有100Hz，充放電時間是毫秒數(shù)量級，為獲得較小的脈動系數(shù)，需要的電容量高達(dá)數(shù)十萬微法，因而一般低頻用普通鋁電解電容器制造目標(biāo)是以提高電容量為主，電容器的電容量、損耗角正切值以及漏電流是鑒別其優(yōu)劣的主要參數(shù)。
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.
在開關(guān)穩(wěn)壓電源中作為輸出濾波用的電解電容器，由于大多數(shù)的開關(guān)電源工作在方波或矩形波的狀態(tài)，含有及其豐富的高次諧波電壓與電流，其上鋸齒波電壓的頻率高達(dá)數(shù)十千赫，甚至數(shù)十兆赫，它的要求和低頻應(yīng)用時不同，電容量并不是主要指標(biāo)，衡量它好壞的則是它的阻抗頻率特性，如圖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.
圖3 47μF/350V鋁電解電容器的阻抗頻率特性
Figure 3 47 μ Impedance Frequency Characteristics of F/350V Aluminum Electrolytic Capacitors
由圖可知，隨著頻率的升高，容抗下降、感抗上升，容抗等于感抗并相互抵消時的頻率為鋁電解電容器的諧振頻率，這時的阻抗最低，僅剩下ESR。如果ESR為零，則這時的阻抗也為零；頻率繼續(xù)上升，感抗開始大于容抗，當(dāng)感抗接近于ESR時，阻抗頻率特性開始上升，呈感性，從這個頻率開始以上的頻率下電容器時間上就是一個電感。
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.
用于開關(guān)穩(wěn)壓電源輸出整流的電解電容器，要求其阻抗頻率特性在300kHz甚至500kHz時仍不呈現(xiàn)上升趨勢。電解電容器ESR較低，能有效地濾除開關(guān)穩(wěn)壓電源中的高頻紋波和尖峰電壓。而普通電解電容器在100kHz后就開始呈現(xiàn)上升趨勢，用于開關(guān)電源輸出整流濾波效果相對較差。
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電解電容器，用于開關(guān)電源輸出濾波的紋波與尖峰并不比CD03HF型4700μF，16V高頻電解電容器的低，同時普通電解電容器溫升相對較高。當(dāng)負(fù)載為突變情況時，用普通電解電容器的瞬態(tài)響應(yīng)遠(yuǎn)不如高頻電解電容器。
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.
開關(guān)電源為了高效率而提高了工作頻率的高頻化，特別是小型高輸出開關(guān)電源中輸入濾波用電容器要求高紋波性，輸出端低阻抗化。要使輸出濾波用電容器在高頻下低阻抗化，必須降低等效串聯(lián)電阻。
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.紋波電流耐受度
Ripple current withstand
影響電解電容器性能的最主要的參數(shù)之一就是紋波電流問題。紋波電流對鋁電解電容器的影響主要是在ESR上產(chǎn)生功耗使鋁電解電容器發(fā)熱，進(jìn)而縮短使用壽命。 從特性曲線中（圖2）可以看到，紋波電流在ESR上產(chǎn)生的損耗與紋波電流有效值的平方成正比，因而隨著紋波電流的增加，小時壽命曲線類似于拋物線函數(shù)曲線。
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.
降低紋波電流的方法可以采用較大容量的鋁電解電容器，畢竟大容量鋁電解電容器可承受的紋波電流比小容量的鋁電解電容器大；也可以采用多只小容量鋁電解電容器的并聯(lián)方式，還可以選用紋波電流低的電路拓?fù)浣Y(jié)構(gòu)。一般而言，反激式變換器產(chǎn)生的開關(guān)變換電流相對最大。表1是各種開關(guān)變換器電路拓?fù)涞闹绷麟娏?、整流濾波的紋波電流、開關(guān)變換電流和濾波電容上的總紋波電流。
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 各種開關(guān)變換器電路拓?fù)涞恼鳛V波的紋波電流和開關(guān)變換電流
Table 1 Ripple Current and Switching Current of Rectification and Filtering of Various Switching Converter Circuit Topologies
就平板電視來說，為了能承受大電流，就需要進(jìn)一步降低電容的ESR。其原因是，在數(shù)字設(shè)備中，隨著功能的增加，電路的電流有越來越大的趨勢。對于在液晶電視中進(jìn)行MPEG編解碼工作的圖像處理電路來說，2006年一塊芯片中電源電路的電流約為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，則在有大電流流動時，電容輸出電壓的下降量也小。伴隨著電流增大而來的降低ESR的要求，有可能成為推進(jìn)電容替換進(jìn)程的主要原因。相對于鋁電解電容將近1Ω的ESR來說，多層陶瓷電容的ESR很小，還不到10mΩ。導(dǎo)電性高分子電容的ESR通常為幾十mΩ，ESR比較小的則在10mΩ以下。鋁電解電容也在開發(fā)ESR比較小的品， 其ESR大約是一般產(chǎn)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
開關(guān)電源是一種采用開關(guān)式控制的直流穩(wěn)壓電源，它以小型、輕量和高效率的特點(diǎn)被廣泛應(yīng)用于各種通信設(shè)備、家用電器、計算機(jī)及其終端設(shè)備。作為輸入濾波和平滑作用的鋁電解電容器，它的質(zhì)量和可靠性直接影響到開關(guān)電源的可靠性。一旦鋁電解電容器失效，就會導(dǎo)致開關(guān)穩(wěn)壓電源的故障。
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.
開關(guān)穩(wěn)壓電源用鋁電解電容器的失效模式有擊穿失效、開路失效、漏液失效及電參數(shù)超差失效。其中擊穿失效又分為介質(zhì)擊穿和熱擊穿，對于大功率和大電流輸出的開關(guān)電源用電解電容器，熱擊穿失效常占一定比例；電腐蝕導(dǎo)致鋁引出條斷裂和電容器芯子干涸，使開關(guān)穩(wěn)壓電源用鋁電解電容器開路失效的主要失效模式；漏液是開關(guān)穩(wěn)壓電源用鋁電解電容器常見的失效模式，由于使用環(huán)境及工作狀態(tài)較嚴(yán)酷，常發(fā)生漏液失效；開關(guān)穩(wěn)壓電源用鋁電解電容器在使用中最常見的失效模式是電容量減少、漏電流增大及損耗角正切值增大。
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.
在電子線路中電解電容器是必不可少的，而且，隨著電子設(shè)備的小型化，越來越要求電解電容器具有更好的頻率特性、更低ESR、更低阻抗、 更低ESL，更高耐壓性能、無鉛化，這也是電解電容器今后的發(fā)展方向。在發(fā)展日新月異的信息技術(shù)領(lǐng)域，電容器將始終是關(guān)鍵元件之一，我們將不斷地順應(yīng)信息時代的需求提供高性能電容器。
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.
