The Role of Capacitors in Power Supply
Source:
|
Author:pmo646c82
|
Published time: 2019-06-21
|
3457 Views
|
Share:
Capacitor is one of the key passive components to realize the combination of voltage and current in a wide range of power supply. Although each capacitor can store electrical energy, dielectric technology plays an important role in the selection of capacitors for specific applications.
The rated voltage and current values of semiconductor devices and their switching frequencies determine the selection of surge voltage protection capacitors. Because these capacitors bear very steep DV/DT values, thin film capacitors are the appropriate choice for such applications. Typical capacitance ratings range from 470PF to 47NF at rated voltage up to 2000VDC. For high-power semiconductor devices, such as IGBT, the capacitance can be as high as 2.2 F, and the voltage is in the range of 1200 VDC. Capacitors cannot be selected only according to capacitance/voltage values. When choosing surge voltage protection capacitor, the required DV/DT value should also be considered. The dissipation factor determines the power dissipation inside the capacitor. Therefore, a capacitor with low loss factor should be selected as a replacement. 3: EMI/RFI suppression These capacitors are connected to the input end of the power supply to mitigate electromagnetic or radio interference caused by semiconductors. These capacitors are vulnerable to destructive overvoltage and transient voltage due to their direct connection to the main input line. As a result, different safety standards have been introduced in various parts of the world, including EN132400 in Europe, UL1414 and 1283 in the United States, and CSAC 22.2NO.0, 1 and 8 in Canada. X-level and Y-level capacitors using plastic film technology (such as EPCOSB3292X/B81122) provide one of the cheapest suppression methods. The impedance of the restraining capacitor decreases with the increase of frequency, allowing high frequency current to pass through the capacitor. X capacitor provides "short circuit" for this current between lines, while Y capacitor provides "short circuit" for this current between lines and grounding equipment. According to the peak value of surge voltage, X and Y capacitors are classified in more detail. For example, the rated peak surge voltage of an X2 capacitor with capacitance value up to 1_F is 2.5KV, while that of an X1 capacitor with similar capacitance value is 4KV. The appropriate level of interference rejection capacitor should be selected according to the peak voltage during load interruption. All kinds of capacitors in control and logic circuits are used in power supply control circuits. These capacitors are universal components with low voltage and low loss unless they are in harsh environment. High temperature components are usually used for power supply in harsh environments. For industrial or professional power supply, low ESR components such as EPCOSB45294 series can be selected, which is a good choice when requiring higher overall reliability.
