![Chip Ferrites Get Peak Current Armor [Würth Elektronik] — Chip Beat](/og-image.svg)
That 19-amp current spike, lasting less than a millisecond, might sound like an outlier. But for systems powering up motors or switching power supplies, it’s a regular occurrence—and a death sentence for conventional chip bead ferrites. These ubiquitous components, crucial for electromagnetic interference (EMI) filtering in countless devices, are built with a layered nickel-zinc ferrite and silver conductor structure that’s inherently fragile under such transient abuse. A single surge beyond their rated current can cause catastrophic damage or immediate failure. Until now, the datasheet’s maximum rated current was the only guide, a metric that often proved insufficient for the brutal reality of inrush current.
Würth Elektronik claims to have cracked this persistent problem with their WE-MPSB series of multilayer power suppression beads (MPSBs). They’ve developed an “optimized layer design” specifically aimed at beefing up these ferrites’ resilience against these short-term, high-current assaults. The upshot? A claimed reduction in DC resistance (RDC) by up to 75% and, crucially, enhanced impedance across the entire frequency spectrum, all while handling these punishing peaks.
The Brutal Reality of Inrush Current
This isn’t just a theoretical exercise. Figure 1 from Würth’s release depicts a textbook scenario: a multilayer ferrite at the input of a circuit, tasked with EMI filtering. The moment power hits, the low Equivalent Series Resistance (ESR) of the connected capacitors dumps an enormous, brief current pulse through the ferrite. In the example shown, a component rated for a maximum of 2.1A is instantly hit with a nearly 19A spike for a mere 0.8 milliseconds. That’s nearly nine times its rated capacity, albeit for an infinitesimally short duration. Standard ferrites would likely fry.
The datasheet value for typical SMD ferrites often conflates continuous operation current with the absolute limit for short-term loading. This is where Würth’s MPSB series aims to differentiate itself by explicitly accounting for peak current considerations, providing a far more realistic operational envelope for demanding applications.
A New Standard for Pulse Testing?
The problem is well-defined: current peaks commonly manifest during the power-up sequences of switching power supplies and electric motors. Think intermittent windshield wiper motors in cars or the ballasts for high-intensity lamps. The input capacitor in a switching regulator, in particular, is notorious for creating these high-current spikes that an upstream EMC filter must endure. Würth defines these “pulses” as short-term current events lasting less than 8 milliseconds, the time it takes for the circuit’s steady DC current to stabilize.
To quantify this pulse resilience, Würth Elektronik has looked to the established methodology for testing fuse reliability. The concept of the “melting integral,
