While I was at Agilent in Spokane, one of the engineers or technicians claimed
that he had changed the RF characteristics of a 6-hole ferrite bead (wound with
2 1/2 turns) used on a power supply trace to a noisy assembly. The normal
current was about 1 amp, but he accidently shorted the power supply voltage
after the inductor. This caused a current spike as the power supply filter
capacitor discharged (and then the supply current limited at about 10 amps).
After this, there was a problem with RF leakage from the assembly. Replacing the
inductor fixed the problem. Apparently the effect was repeatable.
I didn't observe this personally, so I can't guarantee it.
Don Borowski
Schweitzer Engineering Labs
Sorry that I wasn't clear; I typically try to keep my questions general so
not to get too detailed about the specific application. And thanks to Bob,
Chris and Mike who have responded ... putting it into Chris's words ... I
was just trying to find out if ferrites had ratings to prevent them from
"j
ust plain blowing the ferrite to smithereens". Also, I was looking for a
shortcut if someone else had faced this question rather than reading
through all of the vendor web sites.
I understand and have used ferrites quite often for typical EMI
suppression; the ferrites typically being rated for the application
currents, voltages, etc. In this case, the program is trying to protect a
power supply input from the DO-160 waveform 5B pin injected lightning pulse
of 300 volts open circuit & 300A short circuit. If the Gas Discharge Tube
is located past (closer to the supply which was done for packaging
limitations) than the "T" EMI filter, a question was raised as to whether
the ferrite properties would be altered by the lightning pulse. Most of
the standard literature on the use of ferrites does not address these types
of transients.
Susan Beard
"Robert Wilson" <robert_wil...@tirsys.com>@majordomo.ieee.org on 06/04/2002
02:16:48 PM
Please respond to "Robert Wilson" <robert_wil...@tirsys.com>
Sent by: owner-emc-p...@majordomo.ieee.org
To: <shbe...@rockwellcollins.com>, <emc-p...@ieee.org>
cc:
Subject: RE: ferrite transient voltage/current response
Your question is not all that clear. It appears to imply that transients
have an affect on the ferrite beads, but it is the other way around
(maybe that is what you meant). But in general, small ferrite beads have
little effect, except at very high frequencies (hundreds of MHz), unless
they are no longer "beads" (i.e. they are very large).
Have a look at the various magnetics vendors data sheets and app notes.
Magnetics Inc: www.mag-inc.com
Fair-Rite Inc: www.fair-rite.com (whoever came up with THAT name should
be shot!
Steward Inc: www.steward.com
Ferroxcube: www.ferroxcube.com
Epcos (was Siemens): www.epcos.com
Bob Wilson
TIR Systems Ltd.
Vancouver.
-----Original Message-----
From: shbe...@rockwellcollins.com [mailto:shbe...@rockwellcollins.com]
Sent: June 4, 2002 8:57 AM
To: emc-p...@ieee.org
Subject: ferrite transient voltage/current response
Could someone point me to some good App Note information on the response
of
and affect on ferrite beads to transient voltage & current waveforms?
The
waveforms are based on the indirect lightning pulses specified in
Section
22 of DO-160.
Thanks in advance,
Susan Beard
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