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AC line filter selecting proper inductor

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ku637

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Hi,

I need to design an AC line filter to clear out high frequency noises from entering into an electrical line..
The problem is choosing the right inductors

The line needs to be capable upto 15A current
So current rating should be close to that.The filter value calculated with 0.1uF which gives 160kHz cutoff is 10uH

Now most of the designs i ve seen, uses rod core choke for these type of application ..not the SMD type inductors that is being used in DC/DC output filter stage.. even if they are available with suffiicient current rating... (I think the voltage rating is not usually mentioned for inductors)

Can anyone tell me what is the exact reason.

Regards
 

I agree, that we can't expect sufficient dielectric strength from usual SMD power inductors. The other point is that 10 µH sounds somewhat small if you want relevant attenuation amounts (e.g. > 40 dB) in the conducted emission band (150k - 30 MHz).
 
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for SMD power inductor, if it can applied as filter, it can pass 120V or more voltage, normally we do not list voltage for SMD power inductor, only list Irms and Isat, e.g. for SMD power inductor, input voltage is 120V, output coltage is also 120V,inductor does not change voltage, the inductor can hand 120V.
 
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You should consider also adding a common-mode choke to the power line since noise can enter the line otherwise, even with a good normal-mode filter.
 
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    ku637

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for SMD power inductor, if it can applied as filter, it can pass 120V or more voltage, normally we do not list voltage for SMD power inductor, only list Irms and Isat, e.g. for SMD power inductor, input voltage is 120V, output coltage is also 120V,inductor does not change voltage, the inductor can hand 120V.
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Voltage across the inductor will be low in normal operation, that's right. But it should also stand the voltage transients applied in surge tests.

Common mode chokes must be in contrast rated for usual test voltages, e.g. 1500 VAC 1min.

In most cases, a common mode choke will also provide the single ended inductance by a respective design (windings separated on both halves of a toroid core). SMD common mode chokes are available, but only for the lower current range.
 
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