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Capacitance characteristics of the switching power supply EMC design

Issuing time:2015-07-16

1: Many electronics designers know that the power supply filter capacitor in the role, but the switching power supply output filter capacitor used with the selected frequency circuit filter capacitor is not the same as used in the frequency filter circuit general electrolytic capacitor, the ripple voltage frequency on which only 100 HZ, charge and discharge time is milliseconds, in order to obtain a smaller ripple factor, demand for electric capacity of up to hundreds of thousands of microfarads, which generally use low-general aluminum electrolytic capacitor production, capacity-based policy is forward, the capacitance of the capacitor, loss tangent and leakage current is the primary parameter to identify its good and bad.

2: In the switching power supply electrolytic capacitor as the output filter used on which sawtooth voltage frequency up to tens of kilohertz, even tens of megahertz, it's not the same as pleading and low-frequency applications, the capacity is not the primary policy , measure it is good or bad is it a frequency characteristic impedance, pleading it to have low impedance at the working frequency switching power supply, together, for the internal power supply, since the semiconductor equipment preliminary work happen up to hundreds of kilohertz The spike noise, can also have an excellent filtering effect, ordinary low frequency electrolytic capacitor with the general 10KH mercy in its initial impedance will appear rational use of switching power supply can not meet the pleading.

3: a dedicated high-frequency switching power supply electrolytic capacitors, which have four-terminal tall, respectively, at both ends of the aluminum anode as a capacitor of the positive leads and negative ends of aluminum were also drawn as a negative. Power supply current from one end of the four-terminal capacitor positive inflows through the internal capacitance, and then from the other positive terminal to the load; back from the load current from a negative terminal of the capacitor flows into, and then flows to the negative terminal of the power supply from another negative terminal.

4: As the four-terminal capacitor with excellent high frequency characteristics, it serves a very favorable way to reduce the output voltage ripple component and suppress the switching noise spikes.

5: There are multi-core approach, a number of small pieces of aluminum foil dividends it shorter high frequency electrolytic capacitors, lead plates in parallel with more cohesion to reduce the resistance capacitance components together, the selection of low resistivity material and a screw As a lead-out terminal to enhance the acceptance of a large current to the capacitor.

6: laminated capacitor also called no sense of capacitors, electrolytic capacitors in general are rolled into a cylindrical core, a large equivalent series inductance; laminated capacitor structure and a book similar to the magnetic flux direction of the current flowing in the opposite occurred were offset, thereby reducing the inductance value, has more excellent high-frequency characteristics, such capacitors are generally made of square, easy fixed, can also be appropriate to reduce the size of the machine account.

In addition, there is a combination of the four-terminal and four-terminal laminate laminated high frequency electrolytic capacitor, which outlines the benefits of both, high-frequency characteristics better.

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