電子設備需求的不斷增加，其主要的電子元器件需求量也在增加，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高密度組裝成為電子設備的首選。在電解電容選型的過程中，需要注意哪些重要的參數(shù)和指標呢？
With the increasing demand for electronic equipment, the demand for its main electronic components is also increasing. Electrolytic capacitors with small size and large capacity, ripple current resistance, high frequency and low impedance, high temperature and long life and more suitable for high density assembly have become the first choice of electronic equipment. In the process of electrolytic capacitor selection, what important parameters and indicators should be paid attention to?
1.電容量與體積
Capacitance and volume
由于電解電容器多數(shù)采用卷繞結構，很容易擴大體積，因此單位體積電容量非常大，比其它電容大幾倍到幾十倍。但是大電容量的獲取是以體積的擴大為代價的，現(xiàn)代開關電源要求越來越高的效率，越來越小的體積，因此，有必要尋求新的解決辦法，來獲得大電容量、小體積的電容器。
Because most electrolytic capacitors adopt winding structure, it is easy to expand the volume, so the electric capacity per unit volume is very large, which is several to dozens times larger than other capacitors. However, the acquisition of large capacitance is at the cost of volume expansion. Modern switching power supply requires higher efficiency and smaller volume. Therefore, it is necessary to seek new solutions to obtain large capacity and small volume capacitors.
2.承受溫度與壽命
Temperature and life
電解電容器的壽命與電容器長期工作的環(huán)境溫度有直接關系，溫度越高，電容器的壽命越短。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。一般情況而言，電解電容器工作在環(huán)境溫度為80℃時，一般能達到10000h壽命的要求。
The life of electrolytic capacitor is directly related to the long-term working environment temperature of the capacitor. The higher the temperature is, the shorter the life of the capacitor is. At present, there are many kinds of electrolytic capacitors with high working environment temperature. When the ambient temperature is 90 ℃, the ratio of AC current through electrolytic capacitor to rated pulse current is 0.5, the service life is still 10000h. However, if the temperature rises to 95 ℃, the electrolytic capacitor will be damaged. Generally speaking, when the working temperature of electrolytic capacitor is 80 ℃, the life of electrolytic capacitor can reach 10000 H.
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的比值有關。一般說來，這個比值越大，電解電容器的壽命越短，當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。
On the other hand, the life of electrolytic capacitor is also related to the ratio of AC current to rated pulse current. Generally speaking, the higher the ratio, the shorter the life of electrolytic capacitor. When the current flowing through the electrolytic capacitor is 3.8 times of the rated current, the electrolytic capacitor is generally damaged.
3.頻率特性與阻抗
Frequency characteristics and impedance
對于中小輸出功率開關電源的工作頻率除少數(shù)因價格限制而仍采用20~40kHz外，大多數(shù)均在50kHz以上；DC/DC電源模塊大多在300kHz以上；大功率開關電源的開關頻率受主開關的開關速度限制而一般在20~40kHz。
For small and medium-sized output power switching power supply, the operating frequency is more than 50 kHz except for a few which are still 20 ~ 40 kHz due to price restriction; most DC / DC power supply modules are above 300 kHz; the switching frequency of high-power switching power supply is generally 20 ~ 40 kHz, which is limited by the switching speed of the main switch.
在開關穩(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數(shù)十千赫，甚至數(shù)十兆赫，它的要求和低頻應用時不同，電容量并不是主要指標，衡量它好壞的則是它的阻抗頻率特性。
The electrolytic capacitor used as output filter in switching power supply, because most of the switching power supply work in the state of square wave or rectangular wave, which contains rich high-order harmonic voltage and current, the frequency of sawtooth wave voltage on the switching power supply is as high as tens of kilohertz, even tens of megahertz. Its requirements are different from those in low-frequency application. Capacitance is not the main index to measure its quality Is its impedance frequency characteristic.
由于制造工藝的原因，電容量越大，寄生電感也越大，諧振頻率也越低，電容器呈感性的頻率也越低。這就要求它在開關穩(wěn)壓電源的工作頻段內(nèi)要有低的等效阻抗，同時，對于電源內(nèi)部，由于半導體器件開始工作所產(chǎn)生高達數(shù)百千赫的尖峰噪聲，亦能有良好的濾波作用，一般低頻用普通電解電容器在10kHz左右，其阻抗便開始呈現(xiàn)感性，無法滿足開關電源使用要求。
Due to the manufacturing process, the larger the capacitance, the larger the parasitic inductance, the lower the resonance frequency and the lower the inductive frequency of the capacitor. This requires that it has a low equivalent impedance in the working frequency band of the switching power supply. At the same time, it can also have a good filtering effect for the peak noise of hundreds of kilohertz generated by the semiconductor devices in the power supply. Generally, the impedance of the common electrolytic capacitor for low-frequency use at about 10kHz begins to appear perceptual, which can not meet the requirements of switching power supply.
開關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, the switching power supply improves the high frequency of the working frequency, especially in the small high output switching power supply, the input filter capacitor requires high ripple and low output impedance. In order to make the output filter capacitor low impedance at high frequency, the equivalent series resistance must be reduced.
4.紋波電流耐受度
Ripple current tolerance
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，進而縮短使用壽命。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 affecting the performance of electrolytic capacitors. The main effect of ripple current on aluminum electrolytic capacitor is to generate power consumption on ESR, which makes aluminum electrolytic capacitor heat up, thus shortening its service life. The loss on ESR caused by ripple current is directly 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撲結構。一般而言，反激式變換器產(chǎn)生的開關變換電流相對最大。
To reduce ripple current, aluminum electrolytic capacitors with larger capacity can be used. After all, the ripple current that large capacity aluminum electrolytic capacitors can bear is larger than that of small capacity aluminum electrolytic capacitors; multiple small capacity aluminum electrolytic capacitors can also be connected in parallel, and low ripple current circuit topology can be selected. Generally speaking, the switching current generated by flyback converter is relatively maximum.
隨著技術日新月異的發(fā)展變化中，電解電容的發(fā)展更加趨于小型化，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。
With the rapid development of technology, the development of electrolytic capacitor tends to be miniaturization, with better frequency characteristics, lower ESR, lower impedance, lower ESL, higher withstand voltage performance and lead-free, which is also the development direction of electrolytic capacitor in the future.