But this is precisely where you can get into trouble: if you don’t check the DC resistance spec, or if you get into the habit of throwing the same ferrite bead in front of every IC, you might not notice that an unusually high-power device could draw enough current to cause a problem.

The one shown here is not the “official” IEEE symbol, but it helps us to remain cognizant of the functional similarity between beads and inductors.)Ī ferrite bead’s DC resistance-much less than an ohm for typical surface-mount parts-is rarely an issue in this age of low-power ICs. ( Note: A few different circuit symbols are used to represent ferrite beads. Unlike bypass capacitors, ferrite beads are used in series with the power line, which means that any DC current flowing through the bead will create a voltage drop proportional to the DC resistance. This is a fundamental aspect of maximizing your bead’s ability to suppress noise, but there are other specifications that you need to keep in mind-namely, DC resistance and rated current. frequency characteristics when choosing a ferrite bead: whenever possible, the targeted noise frequencies should fall within the bead’s “resistive band,” meaning the range of frequencies in which the resistive impedance dominates the reactive impedance. The previous article discussed the importance of carefully considering impedance vs.

Clean Power for Every IC, Part 3: Understanding Ferrite Beads.

Clean Power for Every IC, Part 2: Choosing and Using Your Bypass Capacitors.

Clean Power for Every IC, Part 1: Understanding Bypass Capacitors.Use ferrite beads to improve your PCB’s power quality.

Ferrite inductor calculator