I am sure the surge current was well beyond 10 amps, as the filter capacitors
discharged through the bead. The 10 amps refers to the steady state short
circuit current that continued until the short circuit was opened, probably a
second later.
Visual inspection showed no damage to the ferrite.
Don
Then why would a 10 A surge change their characteristics?
Unless it cracks it?
- Robert -
-----Original Message-----
From: Robert Wilson <[email protected]>
To: Robert Macy <[email protected]>; [email protected]
<[email protected]>
List-Post: [email protected]
Date: Thursday, June 06, 2002 8:51 AM
Subject: RE: ferrite transient voltage/current response
Soft Ferrites cannot be permanently magnetized. This is precisely why
they are used as beads and cores.
Bob Wilson
TIR Systems Ltd.
Vancouver.
-----Original Message-----
From: Robert Macy [mailto:[email protected]]
Sent: June 5, 2002 11:20 PM
To: [email protected]; [email protected]
Cc: [email protected]
Subject: Re: ferrite transient voltage/current response
He may have magnetized it. Degaussing with one of those Radio Shack
thingies would probably brought it back. Can he try it again?
- Robert -
Robert A. Macy, PE [email protected]
408 286 3985 fx 408 297 9121
AJM International Electronics Consultants
619 North First St, San Jose, CA 95112
-----Original Message-----
From: [email protected] <[email protected]>
To: [email protected] <[email protected]>
Cc: [email protected] <[email protected]>
List-Post: [email protected]
Date: Wednesday, June 05, 2002 2:52 PM
Subject: RE: ferrite transient voltage/current response
>
>
>
>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" <[email protected]>@majordomo.ieee.org on
06/04/2002
>02:16:48 PM
>
>Please respond to "Robert Wilson" <[email protected]>
>
>Sent by: [email protected]
>
>
>To: <[email protected]>, <[email protected]>
>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: [email protected] [mailto:[email protected]]
>Sent: June 4, 2002 8:57 AM
>To: [email protected]
>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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