Re: Transformer coupling coefficients


<wendell.boucher@xxxxxxxxxxx> wrote in message
Hi Don

I just found this site so in this case am late in replying but can help
if you want me to.

I have been designing switch mode power supplies since 1980. Am
currently employed and have held top engineering positions including
Senior Staff Scientist for Emerson Electric in 1980 thru 1989. In my
earlier years, designed pulse transformers, now designing switch mode
transformers, so am very experienced in calculating leakage inductance,
ac conductor losses both skin and proximity effect and effective
capacity of stepup HV transformers.

I can send you the appropriate formulas which are quite easy to use
that will allow you to calculate leakage inductance referred to any
winding (usually the driven primary winding). The only rules for the
equations to valid for are: (1) all windings must be of the same
traverse or length-of-winding. (2) the length of the windings must be
at leat 30 times the thickness of the insulation between the windings.
These conditions are what you want anyway to reduce the leakage figure.

If you wish I can phone you to discuss how its done and send the
documentation to you. If you are in the USA I can call you for nothing
since I use Vonage as my phone service. My email is
wendell.boucher@xxxxxxxxxxx

Email me and I will call you back.

By the way the coupling coefficient for real practical switch mode
transformers is typically about 1% of the primary open circuit
inductance (OCL) or a figure of 0.99498
It has nothing to do with the OCL but is often close to the figure
above. It is in fact the square root of the value (1-LLP/LP) where LLP
is the leakage inductance referred to the primary winding.

Also a good choice for your forward converter, subject to the
specification details, would be a forward diagonal topology which
clamps the two switches to the DC line voltage and returns any stored
leakage energy to the DC source capacitor.

Best Regards

Wendell Boucher

Hi Wendell,
I think we all would be interested in your formulas, please publish to
this group.
Above you state that coupling coefficient (K) has nothing to do with OCL,
then you state: K=SQRT(1-LLP/LP). But is not OCL the same as LP? Please
explain.
Harry


.

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