[0001] The invention lies in the field of processes for winding the coils of high-voltage
transformers used in particular for the high-voltage supply to the grids of the cathode-ray
tube of monitors or televisions.
[0002] Such transformers may be divided from the manufacturing technology viewpoint into
two major families, chamber-type transformers and layered transformers. The transformers
of these two families include a ferromagnetic circuit and primary and secondary windings
coiled around a part at least of the magnetic circuit. In chamber-type transformers
the primary and secondary windings are galvanically insulated from one another on
account of the fact that they are respectively accommodated in primary and secondary
chambers separated by insulating partitions. These chambers are distributed along
an axial line of the magnetic circuit. In layered transformers the primary and secondary
windings are mounted around a part of the magneto circuit, in concentric coaxial layers.
The transformer according to the invention lies in this latter category, that of layered
transformers. These transformers are already widely known and have been described
in numerous publications. Patent No. FR 2,726,686 in the name of the applicant or
alternatively Patent Application GB 2298318-A, in the name of Murata, may be cited
by way of examples of such publications.
[0003] An exploded view of a known layered transformer is represented in Figure 1 and will
be discussed below:
[0004] The high-voltage transformer 100 represented in Figure 1 is intended for the supply
to a cathode-ray tube (not represented). It comprises, around a core made of ferromagnetic
material (not represented), a first coil former 1 carrying primary and secondary windings
globally referenced 2. A second coil former referenced 3 carries windings referred
to as tertiary 4 so as to distinguish them from the secondary windings carried by
the coil former 1. It is this second coil former which carries the high-voltage windings
for supplying the grids of the cathode-ray tube. The two coil formers 1 and 3 are
in the mounted position, concentric with one another, the primary coil former 1 being
situated inside the tertiary coil former 3. Together, the two coils as well as that
part of the core around which the coils 1 and 3 are mounted is accommodated in a casing
5 generally made of an insulating plastic material. This casing 5 includes two output
pillars for the high voltages referenced 6 and 7 respectively, a first output 6 for
the anode high voltage and a second output 7 for the focusing high voltage. The latter
can be adjusted by means of a potentiometric block 8 mounted removably on an open
face 9 of the insulating casing 5.
[0005] It will also be noted that the second coil former 3 carries diodes 10. These diodes
10 serve to unite the ends of the windings forming the tertiary as will be explained
below in conjunction with Figure 2.
[0006] This figure represents the arrangements for connecting up various windings represented
physically in Figure 1. Naturally, the diagram of Figure 2 is given merely by way
of example and there are numerous variants which are also known. The primary winding
of the transformer consists of the winding 11 connected between contacts P labelled
1 & 2. When contacts rather than reference numbers are involved, the numerals of the
label are circled in Figure 2. This primary winding 11 is coupled across a magnetic
circuit 30 represented diagrammatically in Figure 2 by two vertical lines, to several
secondary windings, secondary windings referred to as auxiliary since they produce
auxiliary voltages, and high-voltage secondary windings since they produce the high
voltage necessary for the operation of the cathode-ray tube. The auxiliary secondary
windings are referenced 12 to 15 in Figure 2. The winding 12 connected between contacts
3, 4 is intended to produce a regulated voltage of 4 volts. The windings 13, 14 and
15 are intended to produce respectively voltages of 40, 14 volts and a Heater voltage
intended for heating the cathode of the tube. The windings 11 to 15 are physically
situated around the first coil former 1. Together, they constitute the primary and
secondary windings which have been referenced 2 in Figure 1.
[0007] The high-voltage secondary windings are referenced 16 to 18. A first end 19 of the
first winding 16 is connected by way of a contact 7 of the transformer to earth. The
second end 20 of the winding 16 is connected by way of a diode 10 to a first end 21
of the second winding 17. The second end 22 of this same winding 17 is connected by
way of a second diode 10 to the third winding 18 of the tertiary 4. For the sake of
clarity the diagram of Figure 2 is limited to three windings connected together by
two intermediate diodes 10, and likewise in Figure 1 only three intermediate diodes
10 have been represented. However, it is well known to a person skilled in the art
that these windings are present in larger numbers and that the tertiary windings generally
include diodes numbering between 5 and 7. These diodes are represented for example
in the figure enclosed with the abstract of Patent GB 2298318-A already cited. The
focusing voltages have been represented as tapped off from the first end 21 of the
second tertiary winding 17. These voltages are intended after adjustment by means
of the potentiometer 8 for the supply to the grids G2 and those for focusing the tube.
Finally, an example which will not be discussed of a circuit for supplying the primary
of such transformers 100 has been represented between the contacts 1 and 2 of the
primary winding 11. Examples have also been represented of load circuits between the
contacts 3, 4 and 6, 8 of the auxiliary windings 12 and 13 respectively.
[0008] The manner in which the tertiary windings are in a known manner physically installed
on the coil former 3 is represented in Figure 3. This figure diagrammatically represents
an axial section through the coil former 3 which is intended to show the windings
carried by this former. The cross-sections of the wires wound around the former 3
are represented by black dots 23. The wires are wound in the form of adjoining turns.
This means that the pitch at which the wire advances during winding is equal to a
cross-sectional diameter of the wire, per winding loop. This pitch is obtained in
a known manner by programming the motion of a wire-guide almost parallel to the axis
of the coil. The wire-guide presents the wire substantially perpendicularly to the
axis of the coil. If a large number of loops is required then the length of the coil
former 3 must be equal to the number of loops multiplied by the diameter of the wire
used to make the winding. This leads to former lengths which are incompatible with
the jigs for inserting transformers into power supplies. In order to satisfy the constraint
of low bulk, it is known to superimpose several winding layers lying one above the
other. Each winding layer is separated from the subajacent layer by an insulating
foil 24. Each end of a winding is connected to an end of the succeeding winding by
a diode 10, so that the voltages present at the ends of each winding are added together
and that high voltages of the order of 30 kV are obtained, necessary for example for
the anode voltage of the cathode-ray tube. Only two winding layers connected together
by a diode 10 and insulated from one another by an insulating layer 24 have been represented
in Figure 3. However, it is clear as already indicated above that a transformer of
this type generally includes layers numbering between 6 and 8 and that there are therefore
between 5 and 7 diodes 10 and as many separating layers 24.
[0009] On account of their concentric layered assembly, transformers of the layer type such
as that just described exhibit good electromagnetic qualities and in particular small
leakage inductance. The excitation of the stray capacitances between layers is very
small. For these reasons, they are free of disturbing signals visible on the screen
of the cathode-ray tube. On the other hand they are relatively expensive as compared
with chamber-type transformers because of the manner in which they are coiled and
because of the number of diodes. Chamber-type transformers are cheaper because of
their ease of coiling, which can be carried out entirely automatically. Their stray
capacitance is low. On the other hand they have by construction greater magnetic leakage,
this-being manifested as a visible disturbance on the screen and known as "ringing".
[0010] In order to decrease bulkiness and reduce the number of layers it has been proposed
in Japanese Patent Application No. JP 59 041811 to undertake the winding by means
of a wire-guide whose pitch per winding loop of the wire around the coil former is
less than the diameter of the wire. Such a method of winding makes it possible as
explained in this patent application to obtain a compact winding having a lowish number
of diodes and allowing easy adjustment of the point of connection of the outputs for
the intermediate voltages such as for example the focusing voltage. However, the process
leaves a certain element to chance, even if precautions are taken as explained in
this patent application to comply with the angle and distance of the wire-guide relative
to the axis of the coil former. The precaution consisting in coating the wire with
a resin which hardens under the action of ultraviolet rays so as to avoid the slippage
of the overlaid windings does not reduce this chance effect but increases the costs,
complicates the manufacture and thickens the winding. Since the chance element remains,
there is no certainty that transformers of one production line are indeed similar
to one another and similar to the specimens which served in the assessment of production.
[0011] The object of the present invention is to make in a reproducible manner a transformer
of the layer type at a lower cost than the known layer-type transformers and which
exhibits rather good electromagnetic qualities so that the "ringing" disturbances
are not perceptible on the screen.
[0012] This object is achieved according to the invention by making the layers in a controlled
manner, so that each layer includes for one and the same diameter of wire and for
one and the same length of coil former a larger number of turns. In this way the number
of layers can be reduced and consequently the number of diodes and of intermediate
insulating layers between layers. To do this the inventors have envisaged coiling
each layer by imparting a local fore to aft followed by aft to fore oscillatory motion
to the wire-guide during winding. The various neighbouring turns overlap one another
in a manner which seems a prior disordered but which is in fact controlled and which
the Inventors have dubbed "loose lay" ["en vrac range" in French] . Owing to the overlapping
of the various neighbouring turns the number of turns per layer is larger, this having
the advantages indicated above.
[0013] To summarize, the invention relates to a process for making a high-voltage transformer
which includes wire windings, primary windings and windings intended for the production
of high voltages, each of these windings having two ends, a first and a second, the
windings intended for the production of high voltages being located in concentric
layers lying one above the other, each preceding layer being separated from a succeeding
layer by a layer of electrically insulating material, an end of a succeeding winding
being connected to an end of a preceding winding by way of a diode, in which process
the windings intended for the production of a high voltage are made by rotating a
coil former around an axis, the wire of the winding to be made being guided by a wire-guide
which presents the wire substantially perpendicularly to the axis of rotation of the
coil, the wire-guide being movable in a direction parallel to the axis of rotation
of the coil with an advance equal to one diameter of the wire per coiling loop, a
process characterized in that for one at least of the windings intended for the production
of high voltages the wire-guide has a motion in a direction parallel to the axis of
rotation of the coil which is locally oscillatory.
[0014] The expression locally oscillatory is understood to mean a motion according to which
the wire-guide progressing along the axis of the coil so as to go from one extremity
to the other of the coil performs this motion with periodic reversals relative to
its direction of progress from one extremity to the other of the coil.
[0015] The invention will now be described in greater detail with the aid of the appended
drawings in which Figures 1 to 3 (already described) represent respectively:
- Figure 1, an exploded perspective view of the main components of a transformer according
to the prior art.
- Figure 2, an electrical diagram showing the arrangement for connecting the various
windings of the transformer.
- Figure 3, an axial diagrammatic section through a coil former carrying windings intended
for the production of high voltages and fitted to a layered transformer according
to the prior art.
- Figure 4 represents an axial diagrammatic section through a coil former carrying windings
intended to produce high voltages and included in a transformer made according to
the invention.
[0016] It should firstly be noted that the invention relates only to the coiling of the
windings intended to produce high voltages. Consequently, although Figures 1 and 2
are representative of the prior art, they are also representative as regards the architecture
of and arrangements for connecting a transformer made according to a process complying
with the present Invention.
[0017] Figure 4 diagrammatically represents an axial section through a coil former 3 carrying
windings intended for the production of high voltages. By comparison with Figure 3
it may be seen that the novelty introduced by the invention relates to the arrangement
for coiling the winding. The fact that the neighbouring turns overlap one another
makes it possible to obtain a larger thickness of winding. The expression neighbouring
turns will now be clarified. A turn is a length of wire substantially equal to the
circumference of the coil on which the wire is wound. One turn may neighbour another
since it is very close axially to this other turn. Two turns which are neighbours
in this first sense alone may however be formed by wire windings separated from one
another by a large length of wire. In the present patent application two turns are
said to be neighbours not only when they are separated from one another by a small
axial distance but also when the distance of wire separating the ends of the two turns
is small, for example and to establish an order of magnitude, less than 20 coil circumferences.
This means that the reversing of the wire-guide will be limited for each reversal
to 20 times the diameter of the wire. Thus Figure 4 depicts 3 sub-layers of wires,
the 3 sub-layers together forming a layer, separated from the succeeding layer by
an insulating foil 24. As in the prior art one end 20 of the wire forming a winding
is connected to one end 21 of the wire forming the succeeding winding by way of a
diode 10. However, since for one and the same length of coil each winding includes
a larger number of turns, the number of layers can be reduced, bringing about a corresponding
decrease in the number of intermediate insulating foils 24 and in the number of diodes
10. A less expensive transformer 100 is thus obtained. Trials undertaken by the Applicant
have shown that the transformer thus obtained did not exhibit any "ringing" perceptible
to the eye on a screen of a cathode-ray tube and that production was homogeneous.
1. Process for making a high-voltage transformer (100) which includes wire windings,
primary windings and windings (16,17,18) intended for the production of high voltages,
each of these windings having two ends, a first and a second, the windings intended
for the production of high voltages being located in concentric layers lying one above
the other, each preceding layer being, with the exception of a last layer, separated
from a succeeding layer by a layer (24) of electrically insulating material, an end
of a succeeding winding being connected to an end of a preceding winding by way of
a diode, in which process the windings intended for the production of a high voltage
are made by rotating a coil former (3) around an axis, the wire of the winding to
be made being guided by a wire-guide which presents the wire substantially perpendicularly
to the axis of rotation of the coil, the wire-guide being movable in a direction parallel
to the axis of rotation of the coil with an advance equal to one diameter of the wire
per coiling loop, a process characterized in that for one at least of the windings
intended for the production of high voltages the wire-guide has a motion in a direction
parallel to the axis of rotation of the coil which is locally oscillatory so that
neighbouring turns overlap one another and so that the winding made includes several
layers of wires lying one above the other.
2. Television or monitor fitted with a transformer made according to the process of Claim
1.