07-31-2024, 08:05 PM
Back at home for the evening, I've started modeling the circuit in KiCAD. I've attached my final schematic that I will use to order parts for testing. I mentioned it earlier on, but inductors come with a nominal self-resonant frequency (SRF, as most data sheets call it). I thought it would be appropriate to select an inductor with an SRF near to the resonant frequency I am striving for, but I was wrong. At any frequency above the SRF, and inductor will no longer behave linearly. You want to select an inductor with an SRF above your intended operating frequency. I was unable to find a 33 µH inductor with an SRF above 9.1 MHz, so I stepped it down to a 22 µH inductor. I found one with a minimum SRF of 12 MHz, which will work for my application. Thus, I need a total capacitance of 3.729 µF. I will accomplish this by using a 3.3 µF fixed capacitor and a 0.33 µF fixed capacitor in parallel, combined in parallel with a series connected 0.12 µF fixed capacitor and a 100 pF trimmer capacitor. See attached schematic for the general setup.
I will order some parts, and test this out on proto-board. Recall that I will still need to determine the appropriate separation of the two inductors in order to obtain critical coupling. And we shall see if I have refined the range enough to achieve resonance without a fuss. I should be able to adjust from 3.630099 µF to 3.75 µF, which puts the target 3.729 µF roughly in the middle of that range.
I will order some parts, and test this out on proto-board. Recall that I will still need to determine the appropriate separation of the two inductors in order to obtain critical coupling. And we shall see if I have refined the range enough to achieve resonance without a fuss. I should be able to adjust from 3.630099 µF to 3.75 µF, which puts the target 3.729 µF roughly in the middle of that range.