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 Posted: Jul 21, 2009 - 12:10 PM |
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Joined: May 26, 2004
Posts: 1370
Location: Thessaloniki, Hellas
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Hi there,
I have made some research for a pcb coil design. Before designing the pcb I took some measurements for the coil. Using a 0.25mm wire I made a winding with these results:
148mm x 100mm / 42 turns
12.8Ohm / 770uH
Now I need to design a pcb coil with the same characteristics. Using the same distances/turns (2 or 4 layers pcb) could I have the same results (~770uH)? If yes, how much must be the track's thickness in order to take the same resistance (~12.8Ohm) with the 0.25mm wire?
Thank you. |
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Michael.
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Posted: Jul 21, 2009 - 12:35 PM |
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Joined: Feb 12, 2005
Posts: 16271
Location: Wormshill, England
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You will have massive proximity effects and use quite a lot of PCB real estate.
If you really want to keep similar dimensions then you will be using say 12 turns per layer. You can calculate the total length of PCB trace. The track width will depend on the copper thickness, so you are stuck with relatively wide tracks.
If your principal consideration is a coil with stable inductance, then using regular enamelled wire would be simpler.
If you really want an aerial, then you could consider larger dimensions, ferrite cores ...
David. |
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Posted: Jul 21, 2009 - 12:50 PM |
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Joined: May 26, 2004
Posts: 1370
Location: Thessaloniki, Hellas
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David,
Quote:
If you really want an aerial, then you could consider larger dimensions, ferrite cores ...
What do you mean??? |
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Michael.
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Posted: Jul 21, 2009 - 02:46 PM |
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Joined: Feb 12, 2005
Posts: 16271
Location: Wormshill, England
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I assume you are either making a radio receiver or security tag identification.
David. |
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Posted: Jul 21, 2009 - 03:06 PM |
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Joined: Jan 31, 2008
Posts: 675
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Posted: Jul 21, 2009 - 03:08 PM |
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Joined: Jan 26, 2006
Posts: 146
Location: Stockport, UK
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Posted: Jul 21, 2009 - 06:40 PM |
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Joined: Nov 03, 2006
Posts: 1120
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| I doubt it is for SMPS, 12.8ohms resistance is pretty large, and would impose a hard limit on output current (around 350mA for a 5V output...). 770uH is also pretty massive, probably for use in a tuned crossover network or something... More common for SMPS is around 10 Ohms/mH, with inductance in the 100-200uH range. This makes for example a 100uH coil with a DCR of about 1 Ohm. |
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Posted: Jul 21, 2009 - 08:36 PM |
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Joined: Jan 31, 2008
Posts: 675
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Ah, I skipped the resistance..
That is a very atypical app for a PCB coil. |
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Posted: Jul 21, 2009 - 08:57 PM |
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Joined: Nov 22, 2002
Posts: 12036
Location: Tangent, OR, USA
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Lets see -- 0.25mm is about .010". That is about 30 gauge wire. Unless this wire has thick plastic insulation, will will NOT be able to get PCB traces as close to each other as the windings are. That probably means more turns.
It is also not clear what your "resistance" value is. Is that DC resistance or is it reactance at some frequency? 30 gauge wire has about 330 ohms per km of wire. If that is DC resistance, it means about 38 meters of wire. There is about 0.5m per turn and 42 turns makes 21 m. Its not waaaay off, but it is not that close.
Better help can be offered if some more details are provided.
Jim |
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Jim Wagner
Oregon Research Electronics, Consulting Div.
Tangent, OR, USA
"The only thing standing between us and victory is defeat" P.G.Wodhouse in Wooster & Jeeves series
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Posted: Jul 21, 2009 - 10:41 PM |
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Joined: May 26, 2004
Posts: 1370
Location: Thessaloniki, Hellas
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Guys,
There is no core. It is only a pcb antenna used for an RFID application at 125KHz.
The resistance ~12.8Ohms is the dc resistance of the cable.
The cable does not have plastic insulation, it's just a copper like those used for motor windings.
To tell you the truth I didn't measure the thickness, but it looks like 0.25mm, but I have to find the way to measure it. But I don't have a thickness meter. |
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Michael.
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Posted: Jul 21, 2009 - 11:32 PM |
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Joined: Oct 02, 2007
Posts: 439
Location: Norway
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