模块电源将电源上的元器件进行模块化封装，采用高密度的电路和结构设计，形成体积更小、功率密度更高的电源产品，并可根据具体需要便捷地搭建电源系统，具有设计周期短、可靠性高、应用灵活等优势。在使用模块电源的时候，应该如何提高模块电源的稳定性和可靠性呢？

　　Modular power supplies package the components on the power supply in a modular manner, using high-density circuit and structural design to form a smaller size and higher power density power supply product. They can easily build a power supply system according to specific needs, with advantages such as short design cycle, high reliability, and flexible application. When using a module power supply, how should we improve the stability and reliability of the module power supply?

　　在模块电源的实际应用中，外接输入、输出电容的选取往往会从几个方面入手：

　　In the practical application of modular power supplies, the selection of external input and output capacitors often starts from several aspects:

　　1.电容额定耐压值。

　　Rated withstand voltage value of capacitor.

　　2.电容的容值。

　　Capacitance value of capacitance.

　　3.电容的使用寿命。

　　Service life of capacitor.

　　下面重点介绍1~2点是如何去选取输入、输出电容的。

　　The following focuses on how to select input and output capacitors at points 1 to 2.

　　一、从电容的额定耐压值去选取

　　Select from the rated withstand voltage value of the capacitor

　　1、在DC-DC电源应用中，外接输入电容的耐压值我们一般会选用1.3-1.4倍耐压。

　　In DC-DC power supply applications, the withstand voltage value of the external input capacitor is generally 1.3-1.4 times the withstand voltage.

　　例如：输入电压为48V那我们选用的滤波电容耐压值就为63V。原因是DC-DC的电源启动电流大，容易导致二次冲击电压过高，从而损坏器件。

　　For example, if the input voltage is 48V, the filter capacitor withstand voltage value we choose is 63V. The reason is that the starting current of the DC-DC power supply is high, which can easily lead to excessive secondary impulse voltage, thereby damaging the device.

　　2、AC-DC整流滤波电容耐压值选取：在AC-DC整流滤波电路中，根据公式

　　Selection of withstand voltage value of AC-DC rectifier filter capacitor: In the AC-DC rectifier filter circuit, according to the formula

　　例如：在输入90-265Vac的整流电路中，通过公式计算可以得出整流后的电压范围在127-375Vdc。根据经验我们一般会选取耐压值在1.1-1.3倍理论计算电压值的电容，考虑成本因素有些设计者也会考虑1.0倍理论计算电压值的电容。

　　For example, in a rectifier circuit with an input of 90-265Vac, the voltage range after rectification can be calculated through the formula to be 127-375Vdc. Based on experience, we generally choose a capacitance with a withstand voltage between 1.1 and 1.3 times the theoretical calculated voltage. Considering cost factors, some designers also consider a capacitance that is 1.0 times the theoretical calculated voltage.

　　二、从输入电容的容值选取

　　Select from the capacitance value of the input capacitor

　　在许多文献中，对于滤波电容 C的选取，多使用经验公式

　　In many literature, empirical formulas are often used for the selection of filter capacitor C

　　图1 输入、输出等效电路

　　从理论上讲，增大电路中的滤波电容 C容量的确可以使输出电压的波形变得更为平滑、起伏更小，但在电路接通瞬间，电路中所产生的冲击电流因素却不能被忽略；在一些滤波电路的维修中对滤波电容的替换也存在冲击电流的问题，在不更换其他元件的前提下，单纯提高滤波电容的容量会使整个电路的实际使用寿命大大缩短，甚至烧毁整个电路。况且，单纯地提高滤波电容的容量对改善输出电压的作用也是有限的。做一个简单实验外接不同输入电容的大小启动时的电流曲线，如下图所示为输入外接电容大小与启动电流的关系曲线。

　　Theoretically, increasing the filter capacitor C capacity in a circuit can indeed make the waveform of the output voltage smoother and less fluctuating, but the impact current factor generated in the circuit cannot be ignored at the moment the circuit is turned on; In the maintenance of some filter circuits, there is also a problem of impulse current when replacing the filter capacitor. Without replacing other components, simply increasing the capacity of the filter capacitor can greatly shorten the actual service life of the entire circuit, or even burn the entire circuit. Moreover, simply increasing the capacity of the filter capacitor has a limited effect on improving the output voltage. Perform a simple experiment to determine the current curve at startup with different input capacitance sizes. As shown in the figure below, the relationship curve between the input external capacitance size and the startup current is shown.

　　由此曲线可以看出外接输入电容越大，启动电流就越大，伴随的对电路中冲击电流也越大。对整个电路的威胁也就越来越大。

　　From this curve, it can be seen that the larger the external input capacitance, the greater the starting current, and the accompanying impact current in the circuit. The threat to the entire circuit is also increasing.

　　上图为外接电容大小不同的启动电流波形。外接电容在一定情况下，启动电流达到最低值，对整个电路的输入，输出环境有很大的改善。当外接电容超过这个范围就会导致启动电流增大，对其他器件的威胁也就随之增大，导致出现不同程度的器件损坏。

　　The above figure shows the startup current waveform with different sizes of external capacitors. Under certain conditions, the starting current of the external capacitor reaches the minimum value, which greatly improves the input and output environment of the entire circuit. When the external capacitance exceeds this range, it will lead to an increase in the starting current, which will increase the threat to other devices, leading to varying degrees of device damage.

　　三、输出电容的选取

　　Selection of output capacitance

　　输出电容的选取，一般考虑的因素是电源的输出纹波噪声和电源的负载能力（容性负载）。在成本允许的情况下，很多人都会认为外接输出滤波电容是越大，可以减小纹波噪声干扰，对系统供电更为稳，这是一种错误的观念。

　　The factors generally considered in the selection of output capacitance are the output ripple noise of the power supply and the load capacity (capacitive load) of the power supply. When costs allow, many people will assume that the larger the external output filter capacitance, the less ripple noise interference can be caused, and the more stable the power supply to the system. This is a misconception.

　　输出滤波的电容的选取，不单单是考虑纹波噪声因数，还要考虑模块电源的启动能力和承受输入冲击电流的能力。如下图所示：是致远模块输出25w的一款产品，在输出外接大小容值不同情况下的输入电流波形和输出纹波噪声图。

　　The selection of the output filter capacitance is not only about considering the ripple noise factor, but also about the startup ability of the module power supply and the ability to withstand input impulse current. As shown in the figure below, it is a product with a Zhiyuan module output of 25w, and the input current waveform and output ripple noise map are displayed under different output external capacitance values.

　　外接输出电容4700uf测试的输入输出波形图

　　从图上数据可以看出，外接输出电容容值在一定大小的时候对纹波噪声起到减小作用，但随着外接电容的不断增大纹波噪声会处于一个平衡值。反观输入电流波形，在输出电容增大情况下启动时，输入电流维持在大电流时间会越长。假如使用的模块抗输入冲击电流小，这样就可能导致模块在一定时间下受冲击电流过大而损坏。所以外接输出电容也不是越大越好，这要根据模块的启动能力和承受电流冲击能力来选定的。

　　From the data on the figure, it can be seen that the ripple noise is reduced when the external output capacitance value is at a certain size, but the ripple noise will be at a balanced value as the external capacitance continues to increase. In contrast to the input current waveform, when starting with an increase in output capacitance, the longer the input current remains at a high current for. If the module used is low in resistance to input impulse current, it may result in damage to the module due to excessive impulse current for a certain period of time. Therefore, the external output capacitance is not as large as possible, which depends on the starting capacity and withstand current impact capacity of the module.

　　在模块电源的使用过程中合理外接输入、输出电容是对模块模块电容的一种保护，同时也大大提高了电源的使用寿命，减小了因电源输入、输出不稳定而带给整个工作系统存在的不必要隐患。

　　During the use of the module power supply, reasonably connecting the input and output capacitors is a protection for the module capacitance, and it also greatly improves the service life of the power supply, reducing unnecessary hidden dangers brought to the entire working system due to unstable power supply input and output.