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I want to design an higher order LC filter for filtering out a power signal. In the theoretical design, the inductors are supposed to be on separate cores. But in practice, it will be very costly and space consuming. Is it possible to wind the inductors on the same core (e.g.; a toroidal core)? If it is possible, what must be the proper dot-convention between these inductors?

schematic

simulate this circuit – Schematic created using CircuitLab

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No, this will not give you what you want because all the inductors will be coupled at nearly 98%. Any voltage across L1 will be mirrored across L2, L3 etc..

The filter topology shown is a low pass type so I'm assuming the power signal you wish to remove is higher than what you wish to pass. The higher frequency power signal will, due to the first filter capacitor being a low impedance to that frequency, appear largely across L1 and either inverted or of the same phase across L2 and L3. No matter what you do, with near 100% coupling and the capacitors being low impedance to the power signal you wish to remove, the final inductor will produce virtually the same power signal at the output as seen at the input minus a few percent due to winding losses etc..

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  • \$\begingroup\$ When you put multiple coils on the same core, you have a transformer. That's not good. In fact, to reduce inductive coupling try increasing the distance between inductors in e final design. If they're in a row, rotate every 2nd inductor by 90 degrees. \$\endgroup\$ – Alan Campbell Oct 23 '14 at 10:30

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