Filters

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JdoubleU

Senior Member
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?
 
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.
 
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.
 
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