How to choose filter capacitors correctly?

Filter capacitors refer to energy storage devices installed at both ends of rectifier circuits to reduce AC ripple coefficient and improve efficient and smooth DC output. Due to the filtering circuit's requirement for energy storage capacitors to have a large capacitance. High frequency filtering capacitors mainly work in the rectified filters of switching power supplies, with operating frequencies ranging from several thousand Hz to tens of thousands of Hz. Ordinary low-frequency electrolytic capacitors begin to produce inductance around 10000Hz, which cannot meet the requirements of switching power supplies. Ordinary low-frequency electrolytic capacitors begin to produce inductance around 10000Hz, which cannot meet the requirements of switching power supplies.

Having a general understanding of capacitor types can help in quickly selecting capacitor types. There are many types of capacitors, which can be divided into chip capacitors and plug-in capacitors according to packaging, ceramic capacitors, tantalum capacitors, electrolytic capacitors, mica capacitors, and film capacitors according to media, and BU2092FV-E2 can be divided into fixed capacitors, semi fixed capacitors, and variable capacitors according to structural conditions. There are various types of capacitors that can easily lead to syndrome, but there is no need to worry. Ceramic capacitors, electrolytic capacitors, and tantalum capacitors are most commonly used in switching power supplies. After understanding the types of capacitors, learn about their performance parameters.

Only by understanding the important internal parameters of capacitors can we quickly and reliably select and use them. The key parameters of capacitors are the same, including capacitance value, compression resistance value, and ESR of capacitors, as well as the accuracy of capacitor values and the allowable operating temperature range of capacitors. In the design of switch mode power supplies, the most commonly used capacitors are ceramic capacitors, electrolytic capacitors, and tantalum capacitors, and different characteristics need to be known. Ceramic capacitors have small capacitance, good high-frequency characteristics, wide operating temperature range, smaller capacitance than electrolytic capacitors (ESR), smaller volume, but smaller operating temperature range. Tantalum capacitors with high ESR polarity have the smallest ESR, larger than ceramic capacitors, higher polarity, and poorer safety performance.

The usage environment of capacitors can also be divided into internal circuit environment and external circuit environment. The internal circuit environment includes frequency, voltage value, current value, and the main role of capacitors in the circuit. The type of capacitor can be determined based on the frequency of the circuit. Based on the voltage value, the withstand voltage value of the selected capacitor can be determined. The main function of a circuit can refer to the capacitors of the selected capacitors, depending on the external usage environment of the circuit, the selection of capacitors, the working environment temperature of the product, safety requirements, etc. It can be used to narrow down the selection range of capacitors. Improper selection of capacitors can cause slurry explosion and electrolyte drying in applications, ultimately leading to power outages.

Filter capacitors are used in power rectification circuits to filter alternating current. Make the output DC smoother. For precision circuits, parallel capacitor circuit combinations are commonly used to improve the performance of filtering capacitors. Low frequency filtering capacitors are mainly used for mains power filtering or transformer rectification filtering, with a consistent operating frequency of 50Hz. High frequency filtering capacitors mainly work in the rectified filters of switching power supplies, with operating frequencies ranging from kilohertz to tens of thousands of hertz.

How to choose filter capacitors correctly? Especially the output filtering capacitor is a concern for every engineer. The pulsating voltage frequency of the power frequency circuit used for 50Hz ordinary electrolytic capacitors is only 100Hz, and the charging and discharging time is in the millisecond range. To achieve a smaller pulsation coefficient, a capacity of several hundred thousand microfarads is required. Therefore, the goal of ordinary low-frequency aluminum electrolytic capacitors is to increase their capacitance, and the capacitance, tangent of loss angle, and leakage current of capacitors are the main parameters that distinguish their advantages and disadvantages. The sawtooth voltage frequency of the output filtering electrolytic capacitor in the switching power supply can reach tens of thousands of hertz or even tens of megahertz. At this point, capacitors are not the main indicator, and the standard for measuring the quality of high-frequency aluminum electrolytic capacitors is the impedance frequency characteristics. The operating frequency of switching power supplies requires low equivalent impedance and good filtering effect on high-frequency peak signals generated during the operation of semiconductor equipment.

Ordinary low-frequency electrolytic capacitors begin to produce inductance around 10000Hz, which cannot meet the requirements of switching power supplies. The high-frequency aluminum electrolytic capacitor for switching power supply has four terminals. The two ends of the positive aluminum sheet are the positive electrode of the capacitor, and the two ends of the negative aluminum sheet are the negative electrode. Current flows in from one end of the four terminal capacitor. Through the capacitor, the current flowing into the load from the other end also flows out from one end of the capacitor and into one end of the power supply from the other end.