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Re: Filter Choke Design

On Thu, 7 Mar 1996 tesla-at-grendel.objinc-dot-com wrote:
> >Why is nobody using the setup often seen in filters ie. wind two
> >windings to the same core. Properly phased they will cancel each
> 	Great idea, but , the RF voltage from the TC primary will be
> out of phase and cancel. Oh! put the windings on the common-mode-choke
> out of phase from each other (switch on windings polarity) this will
> make the RF and 60/50 Hz both common mode . Cancel that, it just makes
> the core saturation problem worse.

Nope. High frequency will be transformed in the" transformer" (common
mode choke) but low frequency will be shunted through. Inductance of
say 2mH is not much of impedance at the current levels there is at
high voltage side. The few tens of mA going there should not be
anything signifficant when compared to the spikes!

Proof: (for single coil)
E dt = NA dB => dB/dT = E/NA
let voltage between the ends of the coil be low like it is for low
freq. signals. Then magnetic flux will be low too. On the other hand,
for high freq. E will be signifficant when the coil is ringing and
dB/dt will lead to change in magnetic flux.

Same idea can easily be applied to mutally coupled coils which are
actually used in commercial filters! Anyone disagree or have I perhaps
misunderstood something?
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