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60. How to choose power supply capacitors?

In Electronic Infomation Category: 6 | on February 02,2012

Capacitors is to achieve a wide range of supply voltage and 60 datasheet and current combinations of one of the most critical passive components. While each of capacitors can store energy, but for specific applications, the capacitor dielectric technology selection plays an important role.

capacitors in the power of the most important application is the storage of energy, surge protection, EMI suppression and 60 price and control circuit and 60 suppliers and so on.

1) energy storage capacitor energy storage

charge collected by the rectifier and storage of energy through the converter leads sent to the power output. Voltage rating of 40 ~ 450 VDC, capacitance value 220 ~ 150 000) uF electrolytic capacitors between (such as EPCOS B43504 company or B43505) is more commonly used. Depending on the power requirements, the device sometimes used in series, parallel or combinations thereof in the form of the power level exceeds 10 kW of power, usually larger pot screw terminal capacitors.

to select the appropriate capacitor value required to view the rated DC Bandits, allowing the voltage ripple and proud of electrical charge cycle. However, the choice for the application of the electrolytic capacitor, it should consider the following parameters.

typical power in the capacitor ripple current for each frequency ripple on the current portfolio. Ripple current RMS (root mean square) value determines the capacitors temperature.

common error is that the various frequencies by the square of the current ripple on the value of the sum to calculate the RMS current load. In fact, must take into account with the ripple frequency increases, the capacitor F. SR decline. The correct approach is based on the frequency of ripple factor graph to estimate the frequency to 100 Hz) when the ripple current. Used to estimate the square of the current value to determine the ripple current. This is the real current load.

the ambient temperature determines the load conditions of capacitor life, therefore, well-known manufacturers who have a precise definition of the ripple current load, ambient temperature and the relationship between the probability of life. Actual operating conditions, the use of ripple current load and the ambient temperature to determine the probability of life, and will be announced as the absolute value of the probability of life.

2) surge protector

high switching frequency of modern power semiconductor devices vulnerable to potentially damaging effects of voltage spikes. Across the power semiconductor devices at both ends of the surge voltage protection capacitors (such as EPCOS B32620-J or B32651 ... 56), by absorbing the voltage pulse limits peak voltage, and thus play a protective role in semiconductor devices. Power semiconductor devices are rated for voltage and current values ??of the switching frequency is about the choice of the capacitor surge voltage protection. Because these capacitors suffer steep DV / DT value, therefore, for this application, the appropriate choice for film capacitors.

rated voltage up to 2000 V DC conditions, the typical capacitor rated at 470 pF ~ 47 nF between. For high-power semiconductor devices, such as IGBT, capacitor values ??up to 2.2 MF, the 1200 V DC voltage range, can not be based solely on the value of capacitance / voltage child to select the capacitor. Surge voltage protection capacitors in the selection, you should also consider the required du / dt values.

capacitor dissipation factor determines the internal power dissipation. Therefore, we should choose a capacitor with low loss factor.

3) EMI / RFI suppression

these capacitors are connected in the power of the input generated by the semiconductor in order to reduce electromagnetic or radio interference. As the main input line directly connected to these capacitors easily subjected to destructive over-voltage and transient voltage. Therefore, all regions of the world, launched a different security standards, including the European EN132, EN 400, the United States, UL1414 and UL1283 and Canadian CSA 022.2 No.0, 1 and 8.

using plastic film technology, x-class and Y-class capacitors (such as EPCOS B3292X/B81122) provides one of the most inexpensive method of suppression. Suppression capacitor impedance decreases as frequency increases, allowing high-frequency current through the capacitor. X capacitor between the line current to provide this "short circuit", Y capacitor in line with this current between the ground equipment to provide "short."

can withstand surge voltage according to the peak, the X and Y capacitors have a more detailed classification. For example, a capacitance value of up to 1MF X2 capacitors rated peak surge voltage 2.5 kV, and capacitance values ??similar Xl capacitors, the rated peak surge was 4 kV. Should be based on the peak load voltage during power outages to select the appropriate level of interference suppression capacitors.

4) control circuitry and logic circuitry

Shuo be applied to various types of capacitors in the power control circuit, except in harsh environmental conditions, otherwise these capacitors are low voltage and low loss of general-purpose components.

use in harsh environments of power, often use high-temperature components. Industrial or professional use power, choose low ESR components, such as EP-COS B45294 series, the higher the overall reliability, is a good choice.

order of assembly automation, dimensions of the compression assembly costs down, and the resulting increase in productivity, etc. to be used, most designers try to follow the control circuit used in SMD capacitor technology . However, the selection of hybrid technology to take advantage of some of the lead element has the advantage of much lower cost of the engineers are also many.

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