Dual-function Chokes Address Differential-, Common-mode Noise in a Single Compact Component

Circuit designers must deal with many types of noise: internal, external, RF, line frequency and more. Regardless of type or source, noise can be a limiting factor in system performance and so must be addressed and minimized. The noise-reduction challenge usually comes down to this: “at what effort and cost?”

Even the ubiquitous switched-mode power supply (SMPS) has noise issues. Due to its efficiency and small size, this architecture is widely used in applications including LED drivers and electronic ballasts. Unfortunately, SMPS units also are subject to differential mode (DM) noise and common mode (CM) noise, both of which must be suppressed for both performance and regulatory reasons.

Understand the Noise Mechanisms and Solutions

Differential mode and common mode noise have different causes and thus different solutions. Differential mode noise is noise that is conducted on the line and neutral in opposite directions (Figure 1, left). The basic DM filter uses a single-winding choke (inductor) inserted into the line path, along with a capacitor from line to neutral, thus blocking noise from propagating through the system (Figure 1).

Figure 1. Source: Triad Magnetics