EMI Filter Choke Safe?

[Sh00pus]

So i got this schematic with a EMI/RFI Filter on the input before the rectifier. This is part of a SMPS. It's switching at 132kHz. It calls for a 6 mH at 2.2A. I found a 6.6 mH Choke at 10A but its has 3 inductors instead of 2. Is this safe to use. Also if I were to chose a better one, would it have to be higher or lower than the suggested inductance. because high current 6 mH chokes are hard to find.

[infinia]

If you are not too picky I'd collect a few old PC ATX supplies to raid parts from. Most of them have switching frequencies much lower than 130 KHz. A 300W ATX has about the same current ratings too.

BTW the picture of the part you linked to, doesn't match the data sheet. Use the data sheet for the guide.

[Sh00pus]

Originally Posted by infinia

Most of them have switching frequencies much lower than 130 KHz.

So a choke from a lower frequency SMPS will work in a higher frequency SMPS?

[infinia]

yes increased attenuation of fundamental and harmonics by 6 dB (2-1 ratio) or so, everything else being equal. Some SMPS use 2 stages of common mode filter sections, each section tops out at roughly 40 dB , due to stray parasitics and RF coupling of the choke. (rule of thumb guidelines) there is a point of diminishing returns as switching freq is pushed higher due to fixed leakage inductance and switching snubbers.

[Sh00pus]

Can I just buy a choke greater than 6 mH? or should it be less?

[infinia]

That's up to you! it works with your Y and X caps to get the amount of attenuation you need as well wire size/current and SR frequency. I think there are curves on the data sheet.
EDIT> Knowing nothing else, just buy what the original design calls for. make sure it's designed for mains power!! if that's where it's going. UL or CSA safety markings would assure confidence.

[hesener]

try calculating the "characteristic impedance" of your power supply, which you see at minimum input voltage and maximum input current. then use this and the LC lowpass filter (== the EMI filter) to achieve a butterworth characteristic. that way you can avoid the input filter ringing with the power supply. any pspice simulator or filter calculation tool should do the job.

As for the component values, power supply designers will determine the required attenuation (damping) levels for the power supply noise and design the filter components accordingly, so that they are just large enough to get enough damping and not be too expensive. You can safely go for higher values, if the values are (way) too large you may impact dynamics of whatever it is you are powering it with.

the comment from infinia is absolutely valid - only use components rated for line voltage use!! everythign else is dangerous!! (e.g. using loudspeaker crossover coils or caps for this task.... simply don't!)

just my two cents...