High-Current Chip Beads Suppress EMI in High Density Power Designs

A new family of high-current ferrite beads could improve electromagnetic-interference (EMI) suppression in densely packed power supplies without reducing efficiency or consuming scarce PCB space.

Ferrite beads are widely used to filter high-frequency power-supply noise while enabling multiple power rails to share the same voltage source without compromising isolation. At lower frequencies, a ferrite bead adds almost no resistance to the power rail, and current flows through it with minimal loss. At higher frequencies, however, its impedance increases sharply. The device starts to act like a resistor of sorts, attenuating unwanted noise while leaving the low frequencies largely affected.

But as power densities increase in data centers, renewable-energy storage systems, and the like, engineers face increasingly strict limits on insertion loss while still needing effective suppression of high-frequency noise. Ferrite beads used in these increasingly crowded circuit boards must carry higher currents without thermal overstress or impedance degradation. The DC resistance (DCR) of the device can cause conduction losses to add up as current races through it, reducing the system’s efficiency.

“High-density power requires ferrite beads that can carry substantial current without compromising impedance or thermal margin,” said Edward Liu, product line manager for magnetic components at Bourns.

Beads Built to Combat Noise in High-Density Power Systems

Bourns tries to cut down on these challenges with its MH3261-T series of ferrite beads. These compact SMD devices handle high currents of up to 11 A while maintaining minimal DC resistance down to 2.5 mΩ, enabling effective EMI suppression in densely populated boards. As a result, Bourns said the passive components can reduce noise in high‑current power rails without incurring overly significant losses.

The ferrite beads feature impedances ranging from 30 to 1,000 Ω at 100 MHz, giving engineers the flexibility to filter different EMI frequencies and meet a wide range of noise-suppression requirements for power-delivery designs. For instance, power beads with lower impedance and higher currents can be used for main power rails where voltage droop must be limited. Those with higher impedance and lower current are suited for secondary supplies and local power domains feeding single ICs or small groups of loads.

The bead-shaped devices are well-positioned for tightly packed boards since they come in compact 3.2- × 1.6- × 1.1-mm packages. Ferrite beads are typically placed in series with the power-supply rail; they’re also often paired with decoupling capacitors on the load side and, if necessary, the source side. The capacitors — both connected to ground — combine with the power bead to form a simple but effective LC filter that further rejects differential‑mode noise on the power-supply line.

The series comes with a wide operating temperature range of −55 to +125°C, including the heat it generates itself, which is important when placing the beads close to hot power components such as MOSFETs, controllers, or rectifiers.

The devices are designed for EMI reduction on high-current power rails and power-distribution networks handling high currents in a severely limited space. Power beads in this class are often used to decouple high‑frequency switching noise in point-of-load (POL) converters located close to analog front ends (AFEs) or timing components, positioned directly on DC power rails feeding processors or other ICs, and placed in high‑density DC‑DC converter modules on server and telecom boards.

The MH3261T can also be used for local filtering in the power-distribution paths of industrial controllers, motor drives, and sensor interfaces. In consumer electronics, it’s suited for high-density PCB designs where switching converters compete for limited space while sharing the same power-supply rails. Its wide operating temperature range is a boon for industrial applications, which are often exposed to harsh ambient temperatures as well as heat caused by varying load conditions.

Bourns said the beads should be placed as close as practical to the switching converter or other noise source, or the input of the circuit that needs the noise suppression, while keeping the PCB traces short and wide to reduce parasitic inductance and resistance.