Hi PM,
nicely done, but how do you know the used setup (7 coils) results in the coupling factor of .07?
And i would of thought that any negative coupling factor would not be possible, at least not in the real world.
Anyway, the cop of 0.966 is very good.
Thanks Itsu
Thanks and good Questions! First, the coupling factor was determined by using just two identical air coils placed vertically on a flat surface and moved together so the windings just touch. The start of each coil winding is at the top and we'll call that the "dot". Then by using the six secondary/one primary configuration with equal centers between coils, we can tell LtSpice that the coupling factor between any two adjacent coils is a single K factor we calculate and LtSpice will generate the needed coupling matrix between any and all of the coils. To calculate the K factor, we place the coils as described above and first connect the dot of L1 to an inductance meter (IM), the finish of L1 to the dot of L2, and the finish of L2 to the IM. This results in a measurement of 612uH or Lplus. If this is confusing, picture the coils placed endtoend and we have them connected in a series inductance aid configuration. We then simply move the coils into the position as described. We then connect dot of L1 to the dot of L2 and the finish of L1 to the IM with the finish still connected also to the IM. This results in a measurement of 703uH or Lminus. With the coils again pictured endtoend we now have them connected in a buck configuration. We will now calculate the mutual coupling using M = (LplusLminus)/4 = (612e6703e6)/4 = 2.275e5 . From this we can now calculate the coupling using K = M/(L1*L2)^.5 or because L1 = L2 we can use K = M/L1 = 2.275e5/332e6 = .0685 rounding to .07 . Changing the K factors to positive does slightly change the numbers so this may all be up for interpretation. Regards, Pm
