> It's generally two inductors wound on a single core for common-mode
> choking.
> The result is that total common-mode inductance is 2*L while
> differential-mode inductance cancels and equals zero.
Total common mode inductance is 1 times L, not two times L. This is because
the windings are parallel with near infinite mutual coupling. It is exactly
like a bifilar filament choke.
The 2200pF caps are
> differential-mode shunts to ground. Some of these modules can be
> purchased
> with complex combinations of both common-mode and differential-mode
> inductance and capacitance sections. I use them for almost all
> home-brewed
> projects that require an AC supply.
It's far more effective to use two isolated inductors, provided the current
drawn by the supply does not saturate the inductors.
The main reason for bifilar or dual parallel windings is current from the
supply does not bias the core. The problem is, it has almost no differential
mode impedance.
It's a far more effective filter, if the cores are isolated, because it will
remove common just as well and have much more differential rejection on
mains lines.
I think a computer about two miles from me set the all time record for
distance. That computer was driving the Telco lines via the modem and power
lines in differential, so the Telco and power acted like a big open wire
line. It went for miles along the road with very little attenuation.
I gave them a surge suppressor / protector with terminals for Telco and
outlets. The Telco and safety ground were already bypassed together with gas
protection tubes and small bypass caps. I added .01uF UL/CSA/VDE approved
line caps from the neutral and hot to safety at the outlet feedpoint. I
added isolated chokes for each wire, none bifilar, with a string of low-Q
beads. Cleaned it up so much the computer could not be heard right in the
same room.
I did the same with a Direct TV recorder next door. It drove the mains in
differential mode with significant energy.
73 Tom
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
|