I'd like to ask for advice on when and where in the power supply the ferrite bead should be used. Also, I see there is a large selection of iron powder RFI filters and how do I select between ferrite and various types of iron powder beads?
Actual problem:
I lost the ferrite bead that was on the power supply wires of my SMPS for a mixer. The SMPS outputs +/-17v dc. I remember the bead was about 2cm outer diam and had 2-3 turns of wire on it. What would be the right bead to use in this application?
thanks,
Herman
Actual problem:
I lost the ferrite bead that was on the power supply wires of my SMPS for a mixer. The SMPS outputs +/-17v dc. I remember the bead was about 2cm outer diam and had 2-3 turns of wire on it. What would be the right bead to use in this application?
thanks,
Herman
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Did the bead have all three PSU wires going through it? If so it was a common-mode choke, practically any bead the same physical size is going to work.
As regards iron powder vs ferrite, iron powder can tolerate a higher maximum flux so is suited to where you need higher inductance and/or a higher current capability.
As regards iron powder vs ferrite, iron powder can tolerate a higher maximum flux so is suited to where you need higher inductance and/or a higher current capability.
It was common-mode choke -- all three PSU wires going through the bead and wrapped together making 2 or 3 turns.
Is possible to improve this or nothing else needed for on the dc outputs?
thank you again!
Is possible to improve this or nothing else needed for on the dc outputs?
thank you again!
Its possible to improve the common-mode choking effect which often improves the audio quality - a few turns through a bead only has significant effect at RF (MHz and up) whereas the switching frequency (normally tens of kHz, plus harmonics) is the primary cause of audio degradation. To suppress CM noise down to 50kHz or so a significantly higher inductance value is needed. You can achieve that with more turns on the bead or with several beads in series.
Adding extra turns will improve the lower frequency filtering, but reduce the higher frequency filtering. It is the latter which may be needed to pass EMC regulations. Better to put two filters in series, so each is good for its own frequency range.
Common-mode EMC chokes usually use ferrite, as this is usually deliberately lossy so that you make a filter and not a resonator. Iron dust is more commonly used when you want to make an inductor or an HF transformer.
Common-mode EMC chokes usually use ferrite, as this is usually deliberately lossy so that you make a filter and not a resonator. Iron dust is more commonly used when you want to make an inductor or an HF transformer.
>>Better to put two filters in series
The original design calls for 18 x 13 mm ferrite bead. What size or spec should the second bead be?
The original design calls for 18 x 13 mm ferrite bead. What size or spec should the second bead be?
You would need to reverse engineer the first one and determine what it was supposed to do. Then decide what you want the second one to do and design for that.
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