Correct selection of filter capacitors in switching power supplies
Filter capacitor in the switching power supply plays a very important role, how to correctly select the filter capacitor, especially the output filter capacitor selection is each engineering and technical personnel are very concerned about the problem.
The staff are very concerned about the problem.
The required capacitance is as high as hundreds of thousands of μF, so the goal of ordinary low-frequency aluminium electrolytic capacitors is to improve the capacitance, capacitance, loss angle tangent and leakage current of the capacitor. Capacitance, loss angle tangent value and leakage current of capacitors are the main parameters to identify their advantages and disadvantages. The output filtering electrolytic capacitors in switching power supplies have a sawtooth wave voltage frequency of up to tens of kHz or even tens of MHz. kHz, or even tens of MHz, the capacitance is not the main index, the standard of measuring the advantages and disadvantages of high-frequency aluminium electrolytic capacitors is the "impedance-frequency" characteristic, which requires that the capacitance of aluminium electrolytic capacitors should be maintained within the operating frequency of the switching power supply. Switching power supply operating frequency to have a low equivalent impedance, while the semiconductor device work for the high-frequency spike signal has a good filtering effect.
Ordinary low-frequency electrolytic capacitors begin to show inductance at about 10kHz, which cannot meet the requirements of switching power supply. Switching power supply special high-frequency aluminium electrolytic capacitors have four terminals. The high-frequency aluminium electrolytic capacitor for switching power supply has four terminals, the two ends of the positive aluminium piece are led out as the positive pole of the capacitor, and the two ends of the negative aluminium piece are also led out as the negative pole. The current flows from one positive end of the four-terminal capacitor to the other. positive terminal of the capacitor, through the capacitor, and then from the other positive terminal to the load; from the load back to the current also flows from the negative terminal of the capacitor, and then from the other negative terminal to the power supply negative terminal, and then from the other negative terminal to the power supply negative terminal. Another negative terminal flows to the negative side of the power supply.
50Hz industrial frequency circuit using ordinary electrolytic capacitors, its pulsating voltage frequency is only 100Hz, charge and discharge time is milliseconds order of magnitude. In order to obtain a smaller pulse As the four-terminal capacitor has good high-frequency characteristics, it provides an extremely favourable means of reducing the pulsating component of the voltage as well as suppressing the switching spike noise. High Frequency
Aluminium electrolytic capacitors are also available in multi-core form, whereby the aluminium foil is divided into shorter segments and connected in parallel with multiple lead-outs to reduce the impedance component in the capacitive reactance. And the use of Low resistivity materials are used as the lead terminals to improve the capacitor's ability to withstand large currents.
