Non-saturating, flux cancelling diplex filter for power line communications

• US 6,177,849 B1
• Filed: 11/18/1998
• Issued: 01/23/2001
• Est. Priority Date: 11/18/1998
• Status: Expired due to Fees

• Current Assignee: Oneline Co.
• Original Assignee: Oneline AG
• Inventors: Barsellotti, John, McGinnis, Mike
• Primary Examiner(s): Bettendorf, Justin P.
• Application Number:
  US09/195,424
• Time in Patent Office: 797 Days
• Field of Search: 333/175, 333/177, 333/181, 333/185
• US Class Current: 333/177
• CPC Class Codes: H04B 2203/5491 using filtering and bypassing
• CPC Class Codes: H04B 2203/5495 having measurements and testing channel
• CPC Class Codes: H04B 3/56 Circuits for coupling, blocking, or by-passing of signals

Abstract

A power line communications filter has an input terminal, an output terminal, and a common terminal. A transformer has primary and secondary windings, each having one end connected to the respective input and output terminals, and another end connected to a common connection. The windings are wound on a high permeability magnetic core in such a way as to promote flux leakage and with a winding polarity such that flux cancellation occurs when current flows through the windings in series. A capacitor is connected between the common terminal and the common connection of the primary and secondary windings. The capacitor has a large impedance at low frequencies such that low frequency current flows through both the windings in series and flux cancellation occurs.

Claims

1. A power line communications filter for extracting signal frequencies of at least 1 MHz from power lines, comprising an input terminal, an output terminal, and a common terminal;

a transformer having primary and secondary windings, each having one end connected to said respective input and output terminals, and another end connected to a common connection, said windings being wound on a high permeability magnetic core having, a permeability of at least about 800 up to a frequency of about 5 MHz in such a way as to promote flux leakage and with a winding polarity such that the flux in each winding cancels out the flux in the other winding when current flows through said windings in series; and

a first capacitor between said common terminal and said common connection of said primary and secondary windings, said first capacitor having a large impedance at low frequencies such that low frequency current flows through both said windings in series and flux cancellation occurs, a second capacitor between said output terminal and said common terminal to increase attenuation at high frequencies, and a third capacitor to extract said high frequency signals at said input terminal, said third capacitor acting as a high pass filter, and said transformer forming with said first capacitor a resonant circuit at frequencies in the order of 1 to 5 KHz.

2. A filter as claimed in claim 1, wherein said second capacitor has a capacitance of at least 0.05 μ

F.

3. A filter as claimed in claim 1, wherein the core geometry is such that the primary and secondary windings are physically widely separated.

4. A filter as claimed in claim 1, wherein said primary and secondary windings are wound from a single length of wire.

5. A filter as claimed in claim 1, wherein said first capacitor has a capacitance of at least 0.02 μ

F.

6. A filter as claimed in claim 1, further comprising a conductive support providing a common RF ground plane supporting the transformer and extending parallel to the transformer core in close proximity thereto.

7. A filter as claimed in claim 6, wherein said conductive support comprises a copper clad fiberglass board.

8. A method of making a power line communications filter for extracting signal frequencies of at least 1 MHz from power lines, comprising the steps of preparing self-supporting primary and secondary windings having a common connection in a jig, and placing said self-supporting windings in opposition on a high permeability core having a permeability of at least about 800 up to a frequency of about 5 MHz in such a way as to have a high leakage for high frequency attenuation and so that when current flows through both windings in series, the flux from the windings will to cancel out to achieve substantially zero loss at low frequencies, connecting said common connection to a ground plane with a first capacitor having a value such that said transformer and said first capacitor resonate at a frequency of about 1 to 5 KHz, connecting a second capacitor between an output terminal of said secondary winding and a ground plane and connecting a third capacitor to an input of said primary winding to provide a high pass filter for extracting said high frequency signals.

9. A method as claimed in claim 8, wherein said windings consist of a single piece of wire.

10. A method of extracting signal frequencies of at least 1 MHz from power lines, comprising providing a transformer having primary and secondary windings, each having one end connected to respective input and output terminals, and another end connected to a common terminal, said windings being wound on a high permeability magnetic core having a permeability of at least about 800 up to a frequency of about 5 MHz in such a way as to promote flux leakage and with a winding polarity such that the flux in each winding cancels out the flux in the other winding when current flows through said windings in series;

providing a first capacitor between said common terminal and said common connection of said primary and secondary windings, said first capacitor having a large impedance at low frequencies such that low frequency current flows through both said windings in series and flux cancellation occurs, providing a second capacitor between said output terminal and said common terminal to increase attenuation at high frequencies, and extracting said high frequency signals at said input terminal through a third capacitor, said third capacitor acting as a high pass filter; and

said transformer forming with said first capacitor a resonant circuit at frequencies in the order of 1 to 5 KHz.