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        The rational choice of filter capacitance in the switching power supply

        2013/12/12      view:
                Filter capacitor plays a very important role in switching power supply, how to correctly choose filter capacitance, especially the selection of the output filter capacitor is every engineering technicians are very concerned about the problem.
                50 hz frequency circuit used in ordinary electrolytic capacitor, the voltage ripple frequency is 100 hz, only charge and discharge time is ms orders of magnitude.For smaller pulsation coefficient, the electric capacity of up to hundreds of thousands of u F, therefore the goal of common low-frequency aluminum electrolytic capacitor is give priority to in order to improve the electric capacity, electric capacity, loss tangent value of capacitor and the leakage current is an important parameter to identify the advantages and disadvantages.And the output filter capacitors in the switching power supply, the sawtooth voltage frequency up to tens of kHz, or even tens of MHz, when capacitance is not its main indexes, to measure high frequency standard is the performance of aluminum electrolytic capacitor impedance - frequency characteristics, requirements within the working frequency of switch power supply should have lower equivalent impedance, for the work of semiconductor devices at the same time produce high-frequency spike has good filtering effect.
                Ordinary low frequency electrolytic capacitor at around 10 KHZ began presenting perceptual, unable to meet the requirements of the use of switching power supply.And dedicated high frequency switch power supply aluminum electrolytic capacitor has four terminals, the anode aluminum respectively at both ends of the derivation as capacitor anode, cathode aluminium plates at both ends of the extract as the cathode, respectively.Current flow from a four terminal capacitance is end, through internal capacitance, then from another is end to load;Returning from the load current is also flows from the capacitance of a negative end, again from another negative side to negative power supply.
                Because the four terminal capacitance has good frequency characteristic, to reduce the voltage ripple component and inhibit switch rush noise provides very useful tool.High-frequency aluminum electrolytic capacitor and the form of multicore, the aluminum foil is divided into short segments, with multiple leads connected in parallel to minimize the impedance component of capacitive reactance.And the adoption of low resistivity materials as leading-out terminal, increase the capacity of the capacitor under large current.