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'[EE]: Coil Imprinted on PCB'
2000\11\30@021623 by Werner Soekoe

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Hi

I'm designing an application that requires a few small coils with low values
1uH to 150uH. I've seen a few designs where the coil is part of the layout
on the PCB, and was wondering if anyone has any formulas for these coils. Or
is it a try your luck and see what value pops out thing?

Thanks!

Friendly Regards,
Werner Soekoe
spam_OUTWernerSTakeThisOuTspamfsl.gov.za

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2000\11\30@022059 by Sean H. Breheny

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Hi Werner,

Sorry, I don't have formulas, but I doubt that you will get anywhere near
150uH with a coil printed on a PCB. Those are usually in the nH range, as
far as I know. 150uH is not really a "low value", that is around the
inductance of small DC motors (which have a fair number of turns wound on a
metal core).

Sean

At 09:06 AM 11/30/00 +0200, you wrote:
{Quote hidden}

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2000\11\30@032504 by Werner Soekoe

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I made a slight mistake. The values are not in uH, but supposed to be nH.
Therefore, the values reange from 1nH to 150nH. Sorry!


> Hi
>
> I'm designing an application that requires a few small coils with low
values
> 1uH to 150uH. I've seen a few designs where the coil is part of the layout
> on the PCB, and was wondering if anyone has any formulas for these coils.
Or
{Quote hidden}

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2000\11\30@054532 by Mark Hull

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Hi Werner

What frequency are you working at?
Most PCB coil calculations work in impedance terms as in ohms / mm when at RF frequencies.
You then just have to zigzag the track to fit into the space you're using.

Below RF you have to use conventional components.

Cheers
Mark
-------------------------------------------------------------------
Mark Hull
Engineering/Technical
EMS (Africa) (Pty) Ltd
PO Box 1026, Melville, 2109, South Africa
Ph +27 11 482 4470 Fax +27 11 726 2552

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2000\11\30@060837 by Werner Soekoe

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Mark,

You have totally confused me now. I don't have the feintest idea what the
ohms/mm is all about. But lets put it this way. I will be using the
oscillator circuits in transmitters and receivers. The one will transmit at
+- 100MHz (FM Band) and the other at approxiamately 280 MHz.

What can you tell me about this?

Thanx
Werner
.....WernerSKILLspamspam.....fsl.gov.za


{Original Message removed}

2000\11\30@092542 by Gordon Varney (personal)

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Werner,
   What you are referring to is called microstriping. The formulas that
apply are very intense. There are a few programs that you can down load
free, that will help. I don't have them handy, if I find one I will forward
the info to you. Remember that even the type of fiberglass used in the
circuit board will effect your calculations. The location of other
components around the coil will also have an effect. I assume that you meant
nH for the coils, you will not have any problems implementing the inductors
with the aid of a good program and a little knowledge of microstriping.
Good luck.

Gordon Varney

> Hi
>
> I'm designing an application that requires a few small coils with low
values
> 1uH to 150uH. I've seen a few designs where the coil is part of the layout
> on the PCB, and was wondering if anyone has any formulas for these coils.
Or
{Quote hidden}

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2000\11\30@092737 by Mark Hull

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Hi Werner

It's not easy to make a 'wound' inductor flat on a PCB.
Making use of the fact that all conductors have inductance, based on their
length and cross section, you lay out a PCB with a track length based on the
inductance you need.
Rule of thumb ids 1nH / mm, so a track 100mm long has an inductance of
100nH.
The track can be zigzagged to fit it into the required space, but according
to your earlier post, you need to fit 150mm of track onto your board for
150uH.

Does this help?

Mark
-------------------------------------------------------------------
Mark Hull
Engineering/Technical
EMS (Africa) (Pty) Ltd
PO Box 1026, Melville, 2109, South Africa
Ph +27 11 482 4470 Fax +27 11 726 2552

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2000\11\30@093607 by Spehro Pefhany

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At 04:22 PM 11/30/00 +0200, Mark Hull wrote:
>Hi Werner
>
>It's not easy to make a 'wound' inductor flat on a PCB.
>Making use of the fact that all conductors have inductance, based on their
>length and cross section, you lay out a PCB with a track length based on the
>inductance you need.
>Rule of thumb ids 1nH / mm, so a track 100mm long has an inductance of
>100nH.
>The track can be zigzagged to fit it into the required space, but according
>to your earlier post, you need to fit 150mm of track onto your board for
>150uH.

Shouldn't this be 150 metres ?

Best regards,

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2000\11\30@102816 by David VanHorn

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At 01:07 PM 11/30/00 +0200, you wrote:
>Mark,
>
>You have totally confused me now. I don't have the feintest idea what the
>ohms/mm is all about. But lets put it this way. I will be using the
>oscillator circuits in transmitters and receivers. The one will transmit at
>+- 100MHz (FM Band) and the other at approxiamately 280 MHz.
>
>What can you tell me about this?


You can definitely get there, but there's some things to watch out for..
Coils built in this manner couple easily to external circuits, and nearby
components will affect their inductance.  A conventional inductor (toko,
from digikey) is way more predictable, if not lower cost.

You can get to larger values too, just clamp an RM-4 core around it,
through cutouts in the PCB.
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2000\11\30@122438 by Robert Rolf

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There is also the issue of patent infringement.
Radio Electronics carried a contruction article many years ago ('80s)
where the author used the PCB inductor method in the project (UHF TV
Transmitter if I recall correctly).
RE had to publish a notice some
months later warning readers that using this project was infringing
on a current patent.  With luck the 17 year limit on that
patenet has expired. The patent would also have details on computing
the inductance I would think.
R

Werner Soekoe wrote:
{Quote hidden}

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2000\11\30@153823 by M. Adam Davis

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Some info on coil on PCB:

This person uses 4 pcbs to create a 20uH coil:
hem.passagen.se/sm0vpo/info/pcb-coil.htm
(no calculations)

The Eagle web board has the following message:
www.eagleware.com/wwwboard/messages/968.html
Two recent articles I have written cover this subject. The September 1999
issue of RF Design magazine had an article entitled Designing a Low-Noise
VCO on FR4. This article used a printed inductor and techniques for
reducing effects associated with the poor dielectric of FR4. The October
1999 issue of Applied Microwave & Wireless had an article entitled High-Q
Resonators on FR4. This article explained how to obtain printed inductors
with Q higher than the inherent Q of FR4. Both articles may be downloaded
at this site at the What's New page. Also the Examples manual of Version 7
includes a spiral inductor example in =EMPOWER=,the electromagnetic
simulator.

A demo of a magnetic, inductor and choke design software (with free
schematic capture):
http://www.i-t.com/engsw/intusoft/magdesgn.htm
Looks like you can specify the inductor construction (planar), wire, core
and everything.  This may be your best bet.

This message gives a simple example:
http://fstewart.ne.mediaone.net/DaEtiCpesIdcosEtchedNews.shtml

Another message idicates the book "Introduction to Microwave Engineering"
has this info in it.

There's a whole slew of papers on inductors and various methods of
construction here:
http://nickel.arai.riec.tohoku.ac.jp/yamaguti/general/j_papers.html

There is an FM transmitter (100MHz) with three etched inductors on its PCB
here:
http://members.tripod.com/rclindia/trans.html
(PCB inductors aren't necessarily spiral or even wound about themselves,
every track features inductance)

If you have a SUN workstation and lots of money you could use SPIRAL:
solutions.sun.com/catalogs/now/Electronic_Design_Automation/Design_Analysis/34633.html
A 3D inductor design package meant to deal with PCB inductors
specifically.

You can find a few other messages (including journals) to spiral inductors
here:
http://fstewart.ne.mediaone.net/DaEtiCpesIdcosSpiral.html#Spiral

Here is a demo analog simulator that has a model for spiral inductors:
http://www.ednmag.com/reg/download/analog.asp

Someone wrote a bibliography of inductor calculations, including
references to 22 works which include impedance calculations relating to
spiral inductors specifically:
http://members.aol.com/marctt/Technical/Inductance_References.htm

Here's a short "Guesstimating inducatance of wire loops"
http://members.aol.com/marctt/CV/Abstracts/inductance.htm

And "Inducatance Calculation Techniques - Part II: Approximations and
Handbook Methods"
www.pcim.com/articles/1999/art0006/art1.html
quote "Included are inductance calculations for polygons, disk coils,
finite-length solenoids and flat planar spirals"

This company appears to distribute shareware, one program (spirlind #2259)
does the calculations for spiral inductors:
http://www.marblehead.com/business/034/
The page referring to the program is here:
http://www.marblehead.com/business/034/electron.htm

There are others, I found these by doing various searchs on google for
inductors, spiral, planar, etched, etc.  I hope this helps.

-Adam

Werner Soekoe wrote:
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2000\11\30@160910 by M. Adam Davis

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It occurs to me that tesla coils use a spiral wound primary.  You might
try going in that direction.

In fact, here is the exact equation you're looking for:
http://home.earthlink.net/~electronxlc/formulas.html#spiral

And here is a javascript calculator for it:
http://www.geocities.com/CapeCanaveral/Hangar/3108/calculat.html#Pancake

(Found searching for "tesla coil equations" on google)

-Adam

For those interested in tesla coils (perhaps brought to this message by
searching for tesla coil, there is a tesla coil designer program here:
http://www.noonco.com/tesla/
And a tesla coil cookbook here:
http://home.sprynet.com/~halldo/teslatc.htm

Werner Soekoe wrote:
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'[EE]: Coil Imprinted on PCB'
2000\12\01@024436 by Mark Hull
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Hi Spehro

Yes, it should be 150m for 150uH, I just slipped up in typing the nH :-)

Cheers
Mark
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Mark Hull
Engineering/Technical
EMS (Africa) (Pty) Ltd
PO Box 1026, Melville, 2109, South Africa
Ph +27 11 482 4470 Fax +27 11 726 2552

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