Difference between revisions of "EMI suppression cores"

Revision as of 22:40, 18 April 2012

Snap-on ferrite beads

Toroidal ferrite bead

EMI suppression cores a.k.a. ferrite beads are an efficient way to reduce high frequency interference from wiring. Adding ferrute beads to signal & power wiring is recommended if signal reliability problems are encountered.

Selection

For motor control applications it is recommended to get low to medium frequency ferrite beads for maximum efficiency.

Preferred types

• Core material designed for low to medium frequency bands (attenuation between 1-300 MHz)
• Large enough to fit cable multiple rounds through it

Avoid

• Core material designed for high frequency bands (above 300 MHz)
• Inductor cores - will just add inductance and make things worse
• Iron powder cores

Where to find suitable cores

Most ferrite & iron powder cores look same. So if unsure about material properties, its most safe bet to purchase low to medium frequency beads from distributors such as:

• Digikey
• Mouser
• Farnell

Some popular ferrite bead brands:

• Laird-Signal Integrity Products
• Fair-Rite

Usage with VSD-E/XE drives

To solve an EMI problem its good to have selection of beads that can be tried on different cables. Most typical placement for beads:

• USB adapter
• CMD cable
• Encoder cable
• Motor output cable (all motor wires through core, multiple turns)
• HV DC power supply cable (+ and - leads through core, multiple turns)

See also

• Wikipedia:Ferrite bead