电解电容作为开关电源的重要元件，对其性能的要求也越来越高，电解电容厂家针对电解电容器的一个较为重要的特性--高频低阻抗化进行展开阐述其对开关电源的重要性。
As an important component of switching power supply, electrolytic capacitor has higher and higher requirements for its performance. In this paper, the importance of electrolytic capacitor to switching power supply is described, which is an important characteristic of electrolytic capacitor high frequency and low impedance.
尽管开关频率有所不同，但是开关电源的输出整流滤波电容器的作用基本相同，主要是通过利用滤波电容器吸收开关频率及其高次谐波频率的电流分量而滤除其纹波电压分量。
Although the switching frequency is different, the function of the output rectifier filter capacitor of the switching power supply is basically the same. The ripple voltage component is filtered by absorbing the current component of the switching frequency and its higher harmonic frequency by using the filter capacitor.
对于中小输出功率开关电源的工作频率除少数因价格限制而仍采用20~40kHz外，大多数均在50kHz以上；DC/DC电源模块大多在300kHz以上；大功率开关电源的开关频率受主开关（一般采用IGBT）的开关速度限制而一般在20~40kHz。
For medium and small output power switching power supply, the operating frequency is more than 50 kHz except for a few which are still used 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 limited by the switching speed of main switch (generally using IGBT), but it is generally 20 ~ 40 kHz.
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 switching power supply is different from the filter capacitor used in power frequency circuit. The pulse voltage frequency of ordinary electrolytic capacitor used as filter in power frequency circuit is only 100Hz, and the charge and discharge time is in the order of millisecond. In order to obtain a small pulse coefficient, the capacitance required is as high as hundreds of thousands of Micromethods. Therefore, ordinary aluminum electrolysis is used in low frequency The main purpose of vessel manufacturing is to improve the capacitance. The capacitance, loss tangent and leakage current are the main parameters to identify the 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，如图所示。
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, as shown in the figure.
47μF/350V铝电解电容器的阻抗频率特性
Impedance frequency characteristics of 47 μ f / 350V aluminum electrolytic capacitor
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。
In this case, when the frequency of the reactance and capacitance of the electrolytic capacitor increases, the frequency of the remaining reactance is equal to that of the resonant capacitor. If the ESR is zero, then the impedance is zero; if the frequency continues to rise, the inductive reactance begins to be greater than the capacitive reactance. When the inductive reactance is close to the ESR, the impedance frequency characteristic starts to rise and is inductive. From this frequency, the capacitor is an inductance in time.
由于制造工艺的原因，电容量越大，寄生电感也越大，谐振频率也越低，电容器呈感性的频率也越低。这就要求它在开关稳压电源的工作频段内要有低的等效阻抗，同时，对于电源内部，由于半导体器件开始工作所产生高达数百千赫的尖峰噪声，亦能有良好的滤波作用，一般低频用普通电解电容器在10kHz左右，其阻抗便开始呈现感性，无法满足开关电源使用要求。
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.
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。
The output impedance of the rectifier is not required to rise even at 500KHz. The ESR of electrolytic capacitor is low, which can effectively filter out the high frequency ripple and peak voltage in the switching power supply. However, the common electrolytic capacitor begins to show an upward trend after 100kHz, so the filtering effect of the output rectifier of switching power supply is relatively poor.
通过实验可发现，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。
Through the experiment, it can be found that the ripple and peak of common cdii 4700 μ F, 16V electrolytic capacitor used in switching power supply output filtering is not lower than that of cd03hf 4700 μ F, 16V high frequency electrolytic capacitor, and the temperature rise of common electrolytic capacitor is relatively higher. When the load is sudden change, the transient response of ordinary electrolytic capacitor is much worse 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, 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.