Design rules for inductors made from traces on PC Boards

[dk-info]

I would like to lay out inductors (VHF range) on a PCB.

Does anyone have a reference that gives practical advise on laying out inductors using traces on PCB's?

The PCB layout package I use is directly linked to the ExpressPCB fabrication house. IMHO it is a good value, $51 US for 3, 3.8" x 2.5" 2-layer PCB's.

The layout package cannot make arcs in the trace, so I am limited by rectangular "spirals" for inductor layout.



Any help would be appreciated!

David W,

Melbourne, FL

 

[ronsimpson]

I have seen several papers on this on the www. Have you searched? Look at some PCB makers help files.
I use eagle cad and have made round "turns" but square and rounded turns are simple. In eagle I can set the grid to any value. Grid=0.1 and trace width=0.09 gives 0.01 gap. If i need more turns; grid=0.08 and trace = 0.07.

I made some 30 watt transformers in the PCB using 4 layer boards.

 

[atferrari]

I have seen several papers on this on the www. Have you searched? Look at some PCB makers help files.
I use eagle cad and have made round "turns" but square and rounded turns are simple. In eagle I can set the grid to any value. Grid=0.1 and trace width=0.09 gives 0.01 gap. If i need more turns; grid=0.08 and trace = 0.07.

I made some 30 watt transformers in the PCB using 4 layer boards.

Hola Ron,

Could you give some details?

 

[RadioRon]

Here is an online calculator that is useful:
http://www.circuits.dk/calculator_planar_coil_inductor.htm

Here's some other references.

**broken link removed**
https://www.electro-tech-online.com/custompdfs/2013/01/wenhuan_thesis.pdf

A common approach for RF designers is to build up the layout in a 2 or 2.5D EM simulator and many of those simulators have models already defined for all kinds of pcb structures including spiral inductors.

 

[ronsimpson]

RadioRon, those are good links.

Attached is (a small piece of a larger PCB) a picture of a transformer in a PCB. The transformer is 1 inch by 1.5 inch. The 3 holes in the board is where the core goes through the board. This was my first try. My second transformer windings are very different.

 

[dk-info]

That layout looks great!, you have inspired me to test a couple of inductors; I just have to scale the circuit descriptions - "5 turns of 1mm wire over a 7.5mm form..." (they never list the actual inductance) into something I can put on a PCB.

I am building VHF transmitters for radio locator beacons; I would like to put the main inductor on the top layer, and the PLL feedback inductor on an adjacent trace, the bottom layer if a two layer PCB, or the next layer down if a 4-layer board.

Will I have any capacitance issues with the VHF tank circuit if I put the PLL feedback "pickup" inductor on one layer vs another?



Thanks again for the great response,

David W

 

[RadioRon]

I would avoid this topology completely. You are coupling two loads into your tank circuit, one being the load presented by the oscillator transistor and its follow-on load, the other being your feedback coil. In addition, you run some risk of the switching noise that may find its way out of the feedback input to the synthesizer getting directly into your tank circuit. Why suffer this complexity when it would be simpler to simply tap off the oscillator output with a capacitor to provide your feedback?

 

[ronsimpson]

For my transformer, layer 1&3 is primary and 2&4 is secondary. I want close coupling.
There are calculators for pF between layers .
There are calculators for uH from turns ,diameters.
I would not put shielding ( ground) under a rf coil.
You can have 1/4 the coil on each layer (4).

 

[dk-info]

Why suffer this complexity when it would be simpler to simply tap off the oscillator output with a capacitor to provide your feedback?

The short answer is I do not know any better, I am trying to borrow from circuits I find on line; about the only thing I do know at this point is:
- I need to operate in the 2m band.
- I need crystal controlled frequency synthesis to mitigate drift due to mechanical inductor
vibrations, component tolerances, thermal variations...
- I need to build/buy a receiver
- I need to build/buy a directional antenna (Yagi?)
- The only thing I know about Analog design is "ground" is a place you grow Tomatoes
- I can't even spell "RF"

So, let me stop *****'in and start solder'in - Thank you for your considered comments and direction.

David W

 

[RadioRon]

Keep a running commentary here or in another thread so that we can follow your build progress. This looks very interesting and help is always available.