Dealing with Noise Using Capacitors

In the article “Input Filters for Switching Power Supplies,” we explained that capacitors, inductors, ferrite beads, and resistors are used in differential mode filters for the input stage of switching power supplies. From here, we discuss measures to address noise using capacitors and inductors, explaining what might be called the fundamentals of noise countermeasures. Here we use a simple four-element model. In order to represent resonances at still higher frequencies, models based on still more elements may be used.

First, we will start with noise suppression using capacitors. The explanation is given in the following sections.

• ・Understanding the Frequency Characteristics of Capacitors, Relative to ESR and ESL
• ・Measures to Address Noise Using Capacitors
• ・Effective Use of Decoupling (Bypass) Capacitors Point 1
• ・Effective Use of Decoupling Capacitors　Point 2
• ・Effective Use of Decoupling Capacitors, Other Matters to be Noted
• ・Effective Use of Decoupling Capacitors, Summary