Difference between revisions of "EMI suppression cores"

Revision as of 16:13, 24 March 2013

Snap-on ferrite cores

Toroidal ferrite core

EMI suppression cores or ferrite cores are an efficient way to reduce high frequency interference from wiring. Running cables through a ferrite beads is a recommended solution attempt if signal reliability problems are encountered.

Selection

For motor control applications it is recommended to get low to medium frequency ferrite cores 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 (might make things worse)

• Core material designed for high frequency bands (above 300 MHz)
• Inductor cores
• Iron powder cores
• Most ferrite & iron powder cores look same. If unsure about material properties, its most safe to purchase new low to medium frequency cores.

As example, take a look at Laird broadband and low frequency cores.

Where to find suitable cores

Ferrite cores are available from most electronic part distributors such as:

• Digikey
• Mouser
• Farnell

Some popular ferrite core brands:

• Laird-Signal Integrity Products
• Fair-Rite

Usage

Application

Turning cable 2-3 times through core or using multiple in series increases filtering performance.

Application tips:

• Make 2-3 turns of cable through one core to maximize it's effectiveness
• Place core close to interference source, not in the middle of the cable

With servo drives

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

• Motor output cable (all motor wires through core but not earth conductor)
• High voltage power supply cable (+ and - leads through core)
• USB adapter
• CMD & control I/O cables
• Encoder/feedback device cable

Note: don't run multiple different type of signals through single core. I.e. don't combine power supply and motor leads in one core.

See also

• Wikipedia:Ferrite bead