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Basics of Noise Countermeasures in Switching Power Supplies
2018.08.09
Points of this article
・In order to reduce differential mode noise, the area of the loops of large-current paths is decreased, and optimal decoupling and an input filter are added.
・It is important that differential mode noise, which is a noise source, be suppressed to the extent possible; this will result in reduced common mode noise as well.
・To reduce common mode noise, wires are shortened to suppress crosstalk, and common mode paths are interrupted (filtered).
In the previous section, we explained four steps in procedures to address noise. From here on, we further elaborate on the fourth of these steps, “add filters or other components to address the noise”.
Basics of Noise Countermeasures in Switching Power Supplies
Up to this point, we have explained basic topics related to differential (normal) mode noise and common mode noise as well as crosstalk. The following diagram summarizes these types of noise and basic measures to address them.
In order to reduce differential mode noise (shown in blue), in addition to decreasing the area of the loops of large-current paths on the circuit board, optimized decoupling and an input filter are added. It is important that differential mode noise, which is a noise source, be suppressed insofar as possible, and this also results in reduction of common mode noise.
On the other hand, methods to reduce common mode noise (shown in red) include shortening wires to suppress crosstalk, and interrupting common mode paths (increasing the impedance).
Hereafter we will explain in order the addition of filters (input filters and common mode filters), and decoupling, indicated by red characters in the figure.
【Download Documents】 Switching Power Supply Basic of EMC and Noise Countermeasures
This is a handbook on the basics of EMC (electromagnetic compatibility) and noise countermeasures for switching power supplies. Based on the understanding of the basics of noise, it explains the noise countermeasures using capacitors and inductors in switching power supplies.
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Switching Noise
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Dealing with Noise Using Capacitors
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Dealing with Noise Using Inductors
- Frequency-Impedance Characteristics of Inductors and Determination of Inductor’s Resonance Frequency
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- Dealing with Noise Using Common Mode Filters
- Points to be Noted: Crosstalk and Noise from GND Lines
- Summary of Dealing with Noise Using Inductors
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- Basics of EMC – Summary
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