Inductor for high frequency applications
The invention provides an inductor assembly suitable for use in high frequency switched mode power converters, where the rate of change of voltage can exceed 10 9 Volts per second. The inductor is formed from a ribbon ( 30 ) of conductor wound around a magnetic core ( 140 ), and further includes electrostatic screens positioned between successive windings of the conductor to provide capacitive screening, substantially reducing high frequency voltage signals propagating from one end of the inductor to the other.
1. An inductor assembly suitable for use in a power conversion circuit, comprising:
a magnetic core;
a ribbon of conductor wound around the core to form a coil, wherein successive turns of the coil are insulated from each other;
a plurality of electrostatic screens, each screen positioned between different turns of the coil and electrically insulated from the coil, wherein each screen functions to reduce capacitive coupling between successive turns of the coil, and wherein the electrostatic screens are each independently connected to electrical ground; and
an external electrostatic screening surrounding the coil, the external electrostatic screening being connected to ground, wherein the external electrostatic screening includes a conductive bobbin around which the ribbon of conductor is wound, wherein the bobbin is electrically insulated from the ribbon of conductor, and wherein the bobbin is constructed not to provide a conductive path around the complete circumference of the core, and wherein the bobbin comprises a central tube formed from conductive material around which the conductive ribbon is wound, the tube being constructed not to provide a conductive path around the complete circumference of the core, and cheek plates positioned at each end of the central tube, wherein the cheek plates have at least one surface partially or fully covered in an electrically conductive material constructed not to provide a conductive path around the complete circumference of the core.
2. An inductor assembly according to claim 1 , wherein one or more of the electrostatic screens is connected to ground via a resistor.
3. An inductor assembly according to claim 1 , wherein the ribbon of conductor is wound around a ferrite core.
4. An inductor assembly according to claim 1 , wherein the cheek plates being formed from a printed circuit board (PCB) material.
5. An inductor assembly according to claim 1 , wherein a resistor is mounted on at least one cheek plate, and wherein the electrostatic screen is connected to electrical ground via the resistor.
6. An inductor assembly according to claim 1 , wherein in the external electrostatic screening includes a conductive sheet extending around an outer circumference of the coil and connected to the bobbin, but constructed so that no part of the assembly provides a conductive path around the complete circumference of the core.
7. An inductor assembly according to claim 1 , wherein the ribbon of conductor is part of a conductor assembly comprising a plurality of laminated ribbons each insulated from the other in the coil but connected in parallel externally.
8. An inductor assembly according to claim 1 , wherein the ribbon of conductor has a long axis of cross section and a short axis of cross section, wherein the ribbon is wound around an axis of winding and wherein the ribbon is wound such that its long axis of cross section is parallel to the axis of winding.
9. An inductor assembly according to claim 1 , wherein the ribbon of conductor has a long axis of cross section and a short axis of cross section, wherein the ribbon is wound around an axis of winding and wherein the ribbon is wound such that its long axis of cross section is radial to the axis of winding.
10. An inductor assembly according to claim 9 , wherein the coil has a cross-section viewed along the axis of winding of square, triangular, pentagonal, hexagonal or circular shape.
11. An inductor assembly according to claim 9 , wherein the coil is formed from a folded ribbon of conductor.
12. An inductor assembly according to claim 1 , wherein the core is formed from a magnetic material and includes an air gap or is constructed in whole or in part from a material of reduced relative permeability.
13. An inductor assembly according to claim 1 , further comprising an external casing formed from electrically conductive material, wherein the electrostatic screen is connected to ground via the external casing.