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Use of ferrite beads for PS filtering ?
Use of ferrite beads for PS filtering ?
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Old 20th January 2013, 03:15 PM   #1
gurevise is offline gurevise  United States
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Join Date: Jul 2003
Location: Dayton, OH USA
Default Use of ferrite beads for PS filtering ?

I'm working on a power supply mod for my SS SUMO power amplifier (Ulysses 2).
I'd like to add a bit of filtering to quiet down rectifier diode switching noise.
Couple changes:
1. RC (10 Ohms and 0.1uF) across each rectifier diode.
2. Add LC filer in series w each power rail. Filter could consist of series cylindrical ferrite bead and 1uF quality film or ceramic capacitor to ground. Ferrite has about 10...50 ohms impedance above 500 kHz. This should clean up high frequency noise.
This should keep power supply very low impedance below 100k and clean up switching noise at higher frequencies.

BUT, I've read somewhere that ferrite's are not recommended for audio use. I do not know why.
So, any comments or suggestions?

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Old 20th January 2013, 03:35 PM   #2
DF96 is offline DF96  England
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Join Date: May 2007
The word 'ferrite' covers a wide range of ferromagnetic materials made from metal oxides, which are appropriate for a wide range of different frequency ranges and applications. Some are high Q for making transformers; some are low Q for damping RF resonances and attenuating unwanted RF. I guess for 500kHz operation you would need a high permeability ferrite, but lossy too so it attenuates and not just detunes. The ordinary small ferrite beads used for stopping parasitics tend to work at much higher frequencies. High permeability ferrites tend to be quite non-linear, and easily saturated, so I think I would be careful about getting them too close to audio currents.

In many cases the route from rectifiers into audio circuits is not conduction but induction, so ensure circuit loops are small and well separated. Good grounding also helps.
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Old 20th January 2013, 04:21 PM   #3
gurevise is offline gurevise  United States
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Location: Dayton, OH USA
It is low frequency cylindrical EMI core optimized for 300 kHz to 30MHz range.
LFB095051-000 made by Laird.
Plan is to slip it to over the power rail bus wire. Not sure how non linear it would be. Also, not sure about saturation point.

How would you clean up diode switching noise on high current power rails?

Last edited by gurevise; 20th January 2013 at 04:43 PM. Reason: typos
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Old 20th January 2013, 04:40 PM   #4
DUG is offline DUG  Canada
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Join Date: Jan 2003
Location: mississauga ontario canada
Laird Technologies does not seem to want to provide the inductance vs current information.

I was just on their site.

I would suggest finding another manufacturer that does provide that information so that you get a part that will works in your application.
Doug We are all learning...we can all help
"You can't stop the signal, Mal. Everything goes somewhere..."
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Old 20th January 2013, 09:28 PM   #5
jcx is offline jcx  United States
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rectifier diode reverse recovery current spikes can be minimized by using better diodes, Schottky are available in pretty high range today

RC snubbers can be used with slower diodes - search the forums for snubbers - "Eva" apparently designs switching PS so is well versed in the issues of diode conduction, noise has recommendations, measurements on snubbers

low ESR, ESL electrolytics are tons better today too
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