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Compensating Magnet for Linearity Coil Stray Field

IP.com Disclosure Number: IPCOM000110925D
Original Publication Date: 1994-Jan-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Kohlrausch, WF: AUTHOR

Abstract

The linearity coil of a video monitor provides a linearizing inductance with the characteristic L = f(i). A permanent magnet pill is commonly used to saturate a rod or bobbin ferrite to which it is glued, and which also carries a winding. Yoke deflection current flows through the winding and drives the ferrite deeper into or out of saturation, thus achieving the desired current-dependent inductance at the winding terminals.

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Compensating Magnet for Linearity Coil Stray Field

      The linearity coil of a video monitor provides a linearizing
inductance with the characteristic L = f(i).  A permanent magnet pill
is commonly used to saturate a rod or bobbin ferrite to which it is
glued, and which also carries a winding.  Yoke deflection current
flows through the winding and drives the ferrite deeper into or out
of saturation, thus achieving the desired current-dependent
inductance at the winding terminals.

      The stray field from this structure consists of an AC magnetic
field from the winding that is superpositioned over the DC field from
the permanent magnet.  Unfortunately, the DC field interacts with the
commonly used convergence correcting magnets, i.e., convergence rings
and "spoilers".

      In order to avoid such interaction, a cancelling field of equal
strength and opposite direction is created to make the net effect on
the convergence magnets as small as possible.  Best compensation is
achieved by a dummy linearity coil without winding and with the
magnet attached in reverse.  This dummy coil is positioned in close
proximity to the real one, so that their DC fields cancel totally at
the most critical point and nearly so at other points surrounding
both structures.

      Point-specific compensation can be achieved at less cost by
omitting the ferrite structure, or even by a magnet of lesser
strength (and opposite polarity) attached to the coil itself with a
non-m...