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Several solutions to PCB circuit design

  • Author:o-leading.com
  • Source:o-leading.com
  • Release on :2017-09-29
Filtering at analog power supplies is often done using the LC circuit. But why is sometimes LC worse than RC filtering?


The comparison of the LC and RC filtering effects must consider whether the filtered frequency bands and the selection of the inductor values are appropriate. Because the inductive reactance (reactance) and the size of the inductance value and frequency of. If the noise frequency of the power supply is low and the inductance is not large enough, the filtering effect may not be as good as that of RC. However, the cost of using RC filtering is that the resistor itself will consume energy, reduce efficiency, and pay attention to the power that the selected resistor can withstand.



What is the method of choosing inductance and capacitance when filtering?
The selection of inductance depends on the reactive power of the instantaneous current, in addition to the noise frequency that is desired to be filtered. If the output of the LC will have a chance to produce an instantaneous high current, the inductance will block the speed of the current flowing through the inductor and increase the ripple noise (ripple, noise). 



The capacitance value is related to the magnitude of the standard value of the tolerable ripple noise. The smaller the ripple noise requirement, the greater the capacitor value. The capacitance of the ESR/ESL will also have an impact. In addition, if the LC is placed in the switch mode power supply (switching regulation power) of the output, but also pay attention to the LC generated by the pole zero (pole/zero) negative feedback control (negative feedback control) circuit stability.