Hello everyone,

I've been attempting to design a planar coil inductor on PCB for a while now, but I can't seem to find the resources that I need. I've found a few equations that describe single layer planar coils, but for the inductance that I need, one layer would be too large. Also, simply doubling the values of one layer to a second doesn't seem to work, as I get very difference values than what I've measured some prefabbed coils to be. I'm looking to make a coil in the 10-20uH range, with an outer diameter of about 2 inches.

So, if anyone could point me in the right direction I'd be very grateful.

Thanks!

 

You want to etch the inductor onto the PCB that will give you a 10 to 20 uH range?

It may be a odd question, but why print it on the board rather than using a through-hole or SMD inductor? If the bottom of the board (Or any other layer) was a groung plane, it may be ok, but on a single layer PCB, it would be an antenna for parasitic signals.

Here is a calculator for pcb trace inductance.
http://www.daycounter.com/Calculators/Microstrip-Inductor-Calculator.phtml

So a PCB trace .3 inch wide that was .1 inch from the ground plane, would need to be 270 inches long to achieve around 10.57255 uH.


I would use this:
http://cpc.farnell.com/1/1/5447-inductor-axial-10uh-b82144a2103k-epcos.html
or
http://parts.digikey.co.uk/1/1/6797-inductor-fixed-smd-10uh-10-elj-fa100kf.html

 

why print it on the board

I'm tinkering with some wireless power transfer. I've wound some coils myself, but I'd like to see how they compare with PCB. I've got some ferrite that I'm using to block parasitics.

Thanks for the link. Would that work for a coil, or is that just the inductance of a single microstrip line?

 

Ahh, this is what you want:
http://www.circuits.dk/calculator_planar_coil_inductor.htm

Here is a calculator that takes layout shape into consideration for the PCB layout planar air core coils:
http://www-smirc.stanford.edu/spiralCalc.html

 

Those look like they'll be quite helpful, thanks! With any luck it'll give me a line to calculating for multiple layers, though I've had trouble finding that.

 

To try to help you out, the most effecient way to do wireless power transmission, it to make 2 toriodal transformers. One that fits into the other.
The big one is the base, and the small one is on the device. You "plug" one toroid into the other. That works well.

Wireless toothbrushes have been using this type of solution for years. That way there are no contacts that may touch water causing a shock.

Both coils are encased in plastic to stay waterproof, but when the toothbrush is placed on the charger dock, the power is transfered via the magnetic field.

 

Thanks for the info, retched.

I had considered a toroidal or normal coil setup, but my design doesn't have room for that. A planar coil is the best fit. Unfortunately for the size and inductance I need, one layer is insufficient, and the mutual inductance between multiple layers means the equations for single layer planar coils aren't accurate when you simply multiply by the number of layers desired.

 

That is true. It isn't just connecting them in series. The Air-coil then becomes a coil-coil

So the flux from one coil is going to have an effect on the inductance of the other.

I would etch up a handful of 2" x 2" very thin, scissor cutable pcb with the same exact coils etched on each. Then do stack tests to see how the stacking affects things.

 

You might consider using a ferrite tuning slug or a short ferrite rod thru a hole in the board, in the center of your PCB coil - or maybe just slice a chunk off a rod and epoxy it to the board. The choice of ferrite to use will depend upon the frequency you're attempting to operate at.

Amidon stocks ferrite rod in various materials:
https://www.amidoncorp.com/categories/6

Material 77 has an initial permeability of 2000, good for 2kHz to 2MHz; in low power applications you can go up to 30MHz.

Having a ferrite at the center of your coil means you'll need far shorter traces.

 

Very good idea, sgt. I never thought of that.

 

Very good idea, sgt. I never thought of that.

That's why they pay me the big bucks around here.










Yeah, right.

 

Heres free dollars kid, good work.