Maximizing Secondary Q
I have been making a lot of calculations on the Q of the secondary coil with
consideration of self capacitance recently, and have made a few findings.
Could any of you tell me if I've reinvented the wheel here?
Based on the following equivalent to the sencondary coil, I have derived a
more complete formula for the Q of the secondary coil.
| | | |
| |----------| |------------------------| |
| self C |
The formula is
Q = (Xl/R) - ((Xl^2 + R^2)/(R*Xcs))
Xl = inductive reactance
Xcs = reactance of the coil's self capacitance
R = RF resistance of the wire
Also, based upon the previous formula, I derived a formula to find the optimum
frequency for a coil to operate at (resulting in maximum Q). I substituted the
actual electrical value and frequency variables for the reactance variables.
Instead of Xl, I used 2*pi*F*L, and so on. I took the derivative of the
formula (dQ/dF), and solved for frequency (F), where the derivative equaled
zero (Q reached its peak). I got the following formula.
F = 1,000,000/(2*pi*root(3*L*C))
F = optimum frequency in hertz
L = secondary inductance in henrys
C = self capacitance in picofarads
I was rather surprised when I found this, because it looks so similar to the
formula for resonance. Please let me know what you think of this! Let me know
if I didn't consider any other SIGNIFICANT factors. Also, would any of you
like to try this on your coil? Please post the results.
I have created a page on my web site that gives a more detailed explanation of
how I came to my findings.