How to choose a power module peripheral capacitor?

　　Author ：Iflowpower – Portable Power Station Supplier

With the development of the technology era, the deeper the module power supply also has the market welcome. When using the module power supply, how to enhance the stability and reliability of the module power supply? By ways, how to analyze external input, output capacitance, to enhance the service life of the module power supply and the stability, reliability of the entire power supply system. With the development of the technology era, the deeper the module power supply also has the market welcome.

When using the module power supply, how to enhance the stability and reliability of the module power supply? By ways, how to analyze external input, output capacitance, to enhance the service life of the module power supply and the stability, reliability of the entire power supply system. In the actual use of the module power supply, the selection of external inputs and output capacitors will often start from several aspects: BULL capacitance rated resistance value. BULL capacitance.

BULL capacitor service life. The following focuses on the analysis of 1 to 2 points, how to choose the input, output capacitance. First, select 1 from the rated voltage resistance value of the capacitor, in the DC-DC power supply, the pressure resistance value of the external input capacitance will generally choose 1.

3-1.4 times withstand voltage. For example: The input voltage is 48V, and the filter capacitance of our choice is 63V.

The original is that the power start current of the DC-DC is large, and it is easy to cause the second impact voltage to be too high, thereby damaging the device. 2, AC-DC rectifier filter capacitor withstand voltage value: In the AC-DC rectifier filter circuit, according to formulas, we can calculate the size of the rectified theoretical DC voltage. For example, in the rectifier circuit of entering 90-265VAC, it can be obtained by formula to draw the voltage range after the stream in 127-375VDC.

According to related experiences, we generally select capacitors for calculating voltage values ​​at 1.1-1.3 times theory.

Some designers will also consider the capacitance of 1.0 times the theoretical calculation of voltage values. Second, from the value of the input capacitance, in many documents, the selection of filter capacitance C is used, and the relevant empirical formula is used, and the larger the filter capacitor C is, the better the filter circuit; the technician often uses the original in the maintenance of some filter circuits.

Circuit capacity is large to instead of bad capacitors. Simple rectification filter circuit shown in Figure 1. Figure 1 Input, output equivalent circuit is in theory that the filter capacitance C in the increasing circuit can indeed make the waveform of the output voltage more smooth and less undulating, but in the circuit is turned on, it is born in the circuit The impact current factor cannot be ignored; there is a problem with the filtering current in the maintenance of some filter circuits, and the capacity of the filter capacitor will make the actual use of the filter capacitance without replacing other components.

The life is shortened, even burned the entire circuit. Moreover, the capacity of the filter capacitor is simply improved is also limited to improve the use of the output voltage. Make a simple test of the current curve when the size of the different input capacitance is started, as shown in the figure below is the relationship curve of the input capacitor size and the start current.

It can be seen that the larger the external input capacitance, the greater the start current, the greater the impact current in the circuit. The threat to the entire circuit is getting bigger. The above figure shows the start current waveform of different capacitance sizes.

In the case of a certain case, the start current reaches the lowest value, and the input environment is improved on the input of the entire circuit. When the outer capacitance exceeds this range, the starting current will increase, and the threat to other devices will increase, resulting in different degrees of devices damage. Third, the selection of output capacitors is selected, and the general consideration is the output ripple noise of the power supply and the load capacity of the power supply (capacitive load).

In the case of cost permit, many people think that the external output filter capacitor is, the larger, can reduce the ripple noise interference, and more stable for the system, this is a wrong concept. Output filtering capacitors, not just considering the ripple noise factor, and consider the ability to start the power supply and the ability to withstand the input shock current. As shown in the figure below: It is a product of the farm module output 25W, and the input current waveform and output ripple noise map in different cases of the output external size can.

External Output Capacitance 470uf detected input / output waveform diagram External output capacitor 4700uf detected input / output waveform map can be seen from the data, the external output capacitance value enables the ripple noise to reduce the use of the ripple noise during a certain size, but The increasing increased ripple noise of the outer capacitance will be in a balanced value. Confused input current waveforms, when starting in the case of output capacitance, the input current is maintained at a large current time. If the module used by the module is small, it may cause the module to be too large and damaged by the impact current at one time.

Therefore, the external output capacitance is not, the better, which is selected according to the startup ability of the module and the capacity to withstand current impact. IV. Summary is reasonable and external input during the use of the module power supply, the output capacitor is a protection of the module module capacitance, and it also greatly improves the service life of the power supply, which reduces the entire input, the output is unstable.

Unnecessary hidden dangers in the working system. The advantage of ZLG Zhiyuan Power Module: In our description of our far power module, we will recommend the most suitable peripheral circuit and external capacitance to the customer, which effectively guarantees the best environment under the use occasion, at the same time It also guarantees the security and reliability of customers. Prevent loss of the module and the entire system due to the outer capacitance selection.

As shown below is the peripheral circuit recommendation diagram and an external capacitance size value of the Yuanyuan module dual output. In order to further stabilize the input power source, add a capacitor Cin in the input, if the output ripple and noise can be added, the output is added a series of equivalent impedance small capacitance COUT, but the capacitance cannot exceed the product. Maximum capacitive load, otherwise it will cause poor power module to start.

Recommend an external capacitance value, as shown in Table 1. Table 1 Recommended external capacitive values.