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Parallel Yoke Winding to Reduce Capacitive Coupling

IP.com Disclosure Number: IPCOM000107873D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 6 page(s) / 303K

Publishing Venue

IBM

Related People

Beck, VD: AUTHOR

Abstract

Deflection yokes have a significant capacitance between horizontal and vertical deflection coils. The large voltage pulse which occurs during flyback on the horizontal coil can couple to the vertical coil and its associated drive circuitry, causing spurious deflections. Minimizing this coupling is accomplished through the use of a new winding. An advantage of the new winding is the ability to produce yokes with lower inductance. A complete discussion of the inductance of stator deflection yokes is included to permit the design of yokes which use the winding configuration disclosed.

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Parallel Yoke Winding to Reduce Capacitive Coupling

       Deflection yokes have a significant capacitance between
horizontal and vertical deflection coils.  The large voltage pulse
which occurs during flyback on the horizontal coil can couple to the
vertical coil and its associated drive circuitry, causing spurious
deflections.  Minimizing this coupling is accomplished through the
use of a new winding. An advantage of the new winding is the ability
to produce yokes with lower inductance.  A complete discussion of the
inductance of stator deflection yokes is included to permit the
design of yokes which use the winding configuration disclosed.

      A deflection yoke uses a magnetic field to deflect an electron
beam in a CRT.  When the field is at a maximum at the end of
a line, approximately 1 milli Joule of energy is stored in the field.
The field in the yoke must be reversed before the next horizontal
line can begin, and this reversal is done in a few microseconds.
This reversal or flyback requires about 1kVA drive to the yoke, which
results in voltages of 500V to 1000V applied to the horizontal
deflection coil.  This large voltage pulse, which is a few
microseconds wide, couples through stray capacitance to the vertical
deflection coil.  The capacitance between horizontal and vertical
deflection coils ranges between 1000 pF and 50 pF.

      Stator yokes have a significant advantage over other types of
yokes because the field generated by the yoke is not especially
sensitive to the placement of wires within the stator slots.  As a
result, stator yokes have consistent electron optical performance.
Stator yokes have another advantage over other yokes in that the
stator teeth minimize the inner bore diameter of the yoke.  The
smaller diameter reduces the volume of magnetic field and hence the
stored energy.  Unfortunately, stator yokes tend to have higher
capacitance between the vertical and horizontal coils because the
coils are constrained to all fit within the stator slots.  Clearly,
the capacitance can be reduced by physically separating the windings.

      Typically, single-ended drive is used for the horizontal coil,
which means one end of the coil will not have high voltage applied
during retrace.  If the windings are suitably configured, the layer
of wire in contact with the vertical winding could have low voltage
on it during retrace.  The low end of the horizontal coil would
essentially provide an electrostatic shield for the vertical coil.
Achieving this configuration is the object of this disclosure.

      The effect of shielding will not manifest itself in a simple
two-terminal measurement of capacitance between horizontal and
vertical coils.  The proper method of measuring the coupling is to
apply a voltage to the high end of the horizontal coil, ground the
low end, and measure the displacement current which flows to the
vertical winding. This current can be converted to a capacitance.
The m...