Re: magnetics design -- 60mJ energy impedance matching

"Jon Kirwan" <jonk@xxxxxxxxxxxxxxxxxxx> wrote in message news:oeo9151m50cc1fq5m5ta8tuv7l05279j6u@xxxxxxxxxx

However, I've got another problem with this "reflect" concept. I've
seen it in books, obviously, and I'm aware of arguments about turns
ratios reflecting the secondary load to the primary according to
(N1/N2)^2, as you'll talk about here. And that capacitive loads
reflect back as inductive and visa versa, due to the presence of the
impedance in the denominator (memory serving.)

I have never heard that last part before. Wouldn't that mean that the
transformer has to invert the phase of either the current or the voltage but
not both? I don't see how that is possible.

Well, I've been skimming over so much material lately, I feel like
I've gone crazy. This particular piece came from a section on coupled
impedance. Zin = Zp + (wM)^2/(Zs+ZL). The second term is the coupled
impedance term. They write, "Note that since secondary impedances
appear in the denominator, they reflect into the primary with reversed
reactive parts. Thus, capacitance in the secondary circuit looks
inductive to the source and visa versa for inductance."

Since I was skimming and didn't take the "sit down" time to think
about any of this, yet, I just spouted something I'd read without any
real study on my part. My fault. The M term appears to be the
leakage inductance term. If it is tiny, that whole factor goes by-by
and so I'm just wrong. It only comes into play, as I now understand
it, in cases of LOOSELY coupled transformer action!!


The M may be mutual inductance. If w = 2*pi*f, then the second term looks like the square of the mutual inductance's reactance divided by the sum of the secondary impedance and load impedance. I think this applies where the inductances are small relative to the load. The relation looks vaguely familiar, but please don't hold my feet to the fire on this.

Do you have LTSpice? If so, I encourage you to set up a source, a 10:1 transformer (with K=1) and a secondary capacitor. Make sure that the primary inductance is high enough to make the magnetizing current insignificant (say, 1/1000 the load current). Then look at the voltage/current relationship on the primary. Compare to a secondary resistor. Let me know if the phase relationship is looks like an inductor. Also, if you look at the ratio of voltage to current on the primary, it will look as if the capacitance has been cut to 1/100 the actual value. Now you can play with the winding inductances, coefficient of coupling, leakage inductances, winding resistances, and winding stray capacitances.

(Big snip)

Happy Thursday,
John

.

Relevant Pages