Filters

[JdoubleU]

Often I see in electronic wiring the line conductors looped through a Doughnut shaped component. I was told it was a filter. Is this true and how does it work?

 

[StephenSDH]

In Europe there are stricter standards for reducing harmonics on electronics (CE compliance). Alot of devices come with the donut which serves as a line choke. It is a line reactor that is saturated at the fundamental frequency(50-60hz), but reduces current flow at higher frequencies. It is just low pass filter.

You use a line chock on switching power supplies, which are rich in harmonics. The choke delays the current flow(with no power loss), like a shock absorber, to reduce harmonics. When the transistors in the power supply turn on there is a reduced inrush current. I understand a ballast in lighting does the same thing.

 

[augie47]

The doughnut shaped component could also be a current transformer monitoring the current. You would need to see if the power line itself forms the doughnut or just passes thru it.

 

[ron]

I always specify that outdoor circuits (power, comm, etc) go through a segment of rgs before entering the building for the same reason.

 

[catchtwentytwo]

Are they internal to the equipment or on the power cord? They may be EMI suppression filters like these: Broadband Split / Snap-on Ferrite Cores for Round Cables

 

[JdoubleU]

similar to these. How does this technology work

 

[catchtwentytwo]

similar to these. How does this technology work

Try some Google searches, a quick one found this explanation but I imagine there are better explanations out there:

http://www.olympixcorp.com/rfchoke/ferrite.htm