Re: shielded inductor -> low frequency?
- From: Joerg <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx>
- Date: Fri, 21 Sep 2007 17:15:53 -0700
LVMarc wrote:
Joerg wrote:
LVMarc wrote:ARE YO MENAING THAT WINFDINGING THE COIL ON A TORRUS, CNTAINS THE STRAY MAGNETCI FEILD FLINES? IF SO .yes THIS WOULD BE A GREAT WAY T GO AND THEY HAVE STEP UP AND DOWN TRANSFORMERS TTHAT ARE WOUND ON A CLOSED FORM, IE TORRUS.. BIT EXPENSIVE AS T IS HARDER TO WIND!
Michael wrote:
Greetings gents of the SED variety - I have a couple quick questions
for you all:
I am working on a DC/DC switcher that will use the Linear LT1930A. It
switches at 2.2MHz. I need to find a ~8-10uH inductor that can handle
about .5-1A for this. I identified the Sumida CR43 series as a good
candidate. For example, there is a 8.2uH (at 7.96MHz) CR43 series with
166.2mohms DCR speced at 0.84A. It also has a very small 4.3x4.8mm
footprint. It would be perfect, except that it isn't shielded. I would
really prefer it to be shielded. I started looking at other Sumida
inductors, and it seems that all the shielded ones are speced in the
low KHz region. Am I missing something here?
Also, what is the relationship between inductance and frequency? I
googled around about that for a bit but couldn't find anything.
Thanks,
-Michael
Electrostatic (conductive) Shielding does not effect the magnetic lines of flux you need high u material for that. and high u magnetic shielding material only works at low < 100Kc frequency.
so placing a metal can around a coil is only partially effective in reducing radiated emissions.
I believe what Michael meant is a closed versus open magnetic path. Closed path is what inductor company marketeers call "shielded". For example, a ferrite toroid would be quite good in that respect, that's what I usually use. I found that custom fab in Taiwan/China is actually less expensive than a fancy catalog inductor. Provided the quantities are at least a few thousand a month.
Well, yes, that's why those are usually outsourced. At large qties you can get that done for well under 50c for a half-incher with a few dozen turns including materials and shipping.
--
Regards, Joerg
http://www.analogconsultants.com
.
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