Patent Publication Number: US-6211766-B1

Title: High voltage transformer

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention lies in the field of chambered high-voltage transformers intended for powering high-voltage electrodes of cathode-ray tubes, such as those used in television receivers or monitors. It relates more particularly to a step-up coil of such a transformer, and the transformer equipped with this coil. 
     2. Description of the Prior Art 
     From the technological standpoint, high-voltage transformers may be divided into two major families, chambered transformers and layered transformers. The transformers of these two families comprise a ferromagnetic circuit and primary and secondary windings coiled around at least part of the magnetic circuit. The secondary windings comprise two types of windings, secondary windings which serve to produce auxiliary voltages of for example 5, 12 or 30 volts and windings serving to produce the high voltages required for the operation of the cathode-ray tube, for example the focusing voltage of the order of 7 to 10 kilovolts and the anode voltage of the order of 30 kilovolts. These latter windings are commonly referred to as tertiary windings or else step-up windings. In layered transformers, the step-up windings are mounted around part of the magnetic circuit, in concentric coaxial layers situated one above another in a radial direction with respect to the axis of the magnetic circuit. The various layers of windings are galvanically insulated from one another by layers of a flexible insulating material installed before winding the following layer. In chambered transformers, the step-up windings are galvanically insulated from one another through the fact that they are housed respectively in chambers separated by insulating partitions. These chambers are distributed along an axial line of the magnetic circuit. The transformer according to the invention lies in this latter category, that of chambered transformers. These transformers are already widely known and have been described in the prior art. 
     Chambered transformers have an advantage over layered technology in so far as the cost of construction is lower, in particular because it is possible to simultaneously coil the windings of several chambers. Moreover, the interruptions required for laying an insulant, for example of the terphane type, between layers are avoided. On the other hand, they exhibit greater so-called “ringing” stray voltages. These oscillations produce perturbations to the image on the screens of cathode-ray tubes. These perturbations of the image are unacceptable on top-range television sets, monitors or televisions with a high definition image. It has been noted that these image perturbations were nonexistent or at least much reduced with layer-technology transformers. The inventors think that this difference stems from what they refer to as inactivation of the inter-layer capacitances. The various inter-layer capacitances is energized at each of their two ends by identical voltage pulses. The alternating variation in voltage across the terminals of these capacitances is therefore zero. The inter-layer stray capacitances not excited. Moreover, these layer-technology transformers benefit from the perfect coupling between the primary winding and each layer of the step-up winding. Moreover, the insertion between the earth and the first section of the step-up coil (first layer) of a dipole consisting of a resistor in parallel with an inductor helps to expunge any residual overoscillation almost completely. The inventors think that for these reasons a voltage devoid of ringing and capable after rectification of delivering a very stable DC level when the screen scanning frequency or the luminance of the image, which determines the beam current, varies is obtained at the end of any intermediate layer chosen to deliver, for example, the focusing voltage. Tracking of focusing is then said to be good. In the chambered technology, the inter-chamber capacitances are activated on account of the fact that the instantaneous voltages present on the windings of two consecutive chambers are different. This results in the generation of stray voltages due to the chargings and dischargings of these capacitances. 
     SUMMARY OF THE INVENTION 
     According to the invention it is proposed to construct the windings of each chamber and the connections of the ends of the wires making up these windings in such a way that at least one of the inter-chamber capacitances is not activated. 
     To this end, the invention relates to a step-up coil of a transformer, the coil comprising a coil former made of an insulating material, the former comprising chambers along an axial line of the former, these chambers, delimited by radial partitions housing voltage step-up wire windings including a first winding, a last winding, and intermediate windings, each of these windings having two ends, an inner end and an outer end, each end of a winding being, with the exception of one of the ends of the first winding and of one of the ends of the last winding, connected to an end of a following or preceding winding or to an electrode of a step-up diode having two electrodes, an anode and a cathode, which coil is characterized in that it comprises at least one pair of windings consisting of two windings, a first winding of the pair and a second winding of the pair, housed in two consecutive chambers, at least two diodes, a first and a second, the inner end of the first winding of the pair being connected to an electrode of the first diode, the inner end of the second winding of the pair being connected to the electrode of the second diode, B 1  or alternatively, the outer end of the first winding of the pair being connected to an electrode of the first diode, the outer end of the second winding of the pair being connected to the electrode of the second diode B 1 . 
     In the commonest embodiment, the coil comprises at least two pairs of windings, a first and a second, made up as indicated above, the four windings constituting the two pairs being housed in consecutive chambers, the two pairs together making up an elementary cell, the inner end of the first winding of the first pair being connected to an electrode of the first diode, the inner end of the second winding of the first pair being connected to the electrode of like nature of the second diode, and the outer end of the first winding of the second pair being connected to the other electrode of the first diode, the outer end of the second winding of the second pair being connected to the other electrode of the second diode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood by reading the description of an exemplary embodiment and of variants which will be given hereinbelow in conjunction with the appended drawings in which: 
     FIG. 1 represents layers of a layered voltage raiser as well as the inter-layer capacitors. 
     FIG. 2 diagrammatically represents an example of windings of consecutive chambers as well as a diode separating two consecutive step-up windings such as constructed according to the prior art. 
     FIG. 3 diagrammatically represents, according to the invention, an elementary cell comprising the windings of four consecutive chambers as well as the connections of these windings to diodes separating the windings. 
     FIG. 4 diagrammatically represents, according to a variant embodiment of the invention, an elementary cell comprising the windings of four consecutive chambers as well as the connections of these windings to diodes separating the windings. 
     FIG. 5 is a perspective view of a coil constructed according to the invention. 
     FIG. 6 diagrammatically represents the electrical links of the coil represented in FIG.  5 . 
     FIG. 7 represents a transformer equipped with a step-up coil comprising windings constructed according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 2 are intended to elucidate the technical problem solved by the inventors. FIG. 1 represents layers  1 ,  2 ,  3  of a layered voltage raiser. Each layer is made up of a winding having a first and a second end,  4 ,  5  for layer  1 ;  6 ,  7  for layer  2 ; and  8 ,  9  for layer  3 . The inter-layer capacitances between the layers  1  and  2 ,  2  and  3  are made up physically by the opposing wire surfaces of each of the layers. Such capacitances are said to be physically distributed. In FIG. 1, they are located, for the convenience of the drawing, at the ends of each winding. To portray these capacitances, they have been represented, for example for the capacitance distributed between layers  1  and  2 , by capacitors  10 ,  11 , located between the first ends  4 ,  6  and the second ends  5 ,  7  of the layers  1  and  2  respectively. A capacitor  12  and a capacitor  13  represented connected in the same manner represents the inter-layer capacitance between the layers  2  and  3 . Each first end is coupled to the second end of the following layer by a diode. Thus, the first end  4  of the winding  1  making up the first layer is connected to an anode  15  of a diode  14  whose cathode  16  is connected to the second end  7  of the winding  2  making up the second layer. The voltage pulses  17 ,  19 ,  21  present at the first ends  4 ,  6 ,  8  respectively, and the voltage pulses  18 ,  20 ,  22  present at the second ends  5 ,  7 ,  9  respectively, have been represented in FIG.  1 . According to the inventors, the inter-layer capacitances are not activated because the voltage signals present at the first,  4 ,  6 ,  8  and second  5 ,  7 ,  9  ends respectively are of similar shape, like amplitude and like sign. Therefore there are no chargings and dischargings of these capacitances introducing poorly controlled voltages. 
     FIG. 2 represents the pulses present at chambers of a chambered raiser coiled in a known manner. The outer end is the end located at the termination of the winding, the wire vicinity of this end constitutes the turns which are radially furthest away from the axis of the winding coil. This expression is in contrast to inner end, that is to say the one located at the bottom of the chamber in proximity to the winding mandrel, the wire vicinity of this end makes up the turns which are radially closest to the axis of the winding coil. The winding mandrel is not represented in FIG.  2 . Only the axis AA′ of this mandrel has been represented. The figure represents two consecutive step-up winding sections, a first  23  and a second  24 . The first section  23  comprises three partial windings  25 ,  26 ,  27 . Each of these windings is housed in a chamber (not represented). The second section comprises four partial windings  28 ,  29 ,  30 ,  31 . Each of these windings is housed in a chamber (not represented). The two sections  23 ,  24  are connected by way of a diode  32 . The second section  24  is connected to a diode  33  providing the link with a following section (not represented). The outer ends  34  and  35  of the partial windings  25 ,  26  respectively are connected to the inner ends  36 ,  37  respectively of the partial windings  26 ,  27  respectively. The outer end  38  of the last partial winding of the first section  23  is connected to the anode  39  of the diode  32 , the cathode  40  of this diode is connected to the inside end  49  of the first partial winding  28  of the second section  24 . For convenience of explanation, it is assumed that each of the partial windings  25 - 31  contains the same number of turns. The signals  41 - 43  measured by the inventors at the outer end of each of the windings  25 - 27  respectively of the first cell  23  are represented in FIG. 2, alongside these windings. These signals are of substantially like shape but different amplitude. This results in potential differences at the inter-winding capacitances. The inter-winding capacitances are activated. “Ringing” stray signals result therefrom. The signals  44 ,  45  measured by the inventors at the inner end of each of the windings  28 - 29  respectively of the second cell  24  are represented in FIG. 2, alongside these windings. Likewise, the signals  46 - 47  measured by the inventors at the outer end of each of the windings  30 ,  31  respectively of the second cell  24  are represented in FIG. 2, alongside these windings. At the cell  24 , owing to the presence of the diode  32 , the signal  44  is of opposite sign to those of the signals  41 - 43 . At the point  48 , situated at the point of symmetry of the windings of the cell  24 , the alternating component of the potential is zero. The signals  46 ,  47  measured by the inventors at the outer end of each of the windings  30 ,  31  respectively are positive, of like shape but different amplitude. As in the case of the cell  23 , this results in potential differences at the inter-winding capacitances. The inter-winding capacitances are activated. Since the presence of the inter-winding capacitances results from the very existence of these windings which are necessarily close to one another for reasons of minimum bulk, it is not possible to do away with them, rather the inventors have found a means of not activating some of them. This is the means which will be explained hereinbelow in conjunction with FIG.  3 . 
     FIG. 3 represents what the inventors have referred to as an elementary cell  50  of a step-up winding. This cell  50  comprises four consecutive windings  51 - 54  distributed into two pairs  55 ,  56 . When windings are said to be consecutive, what is meant is that these windings are distributed in axially consecutive chambers. The inner end  57  of the first winding  51  of the first pair  55  is connected to the anode  58  of a first diode  59 . The inner end  61  of the second winding  52  of the first pair  55  is connected to the anode  62  of a second diode  63 . The outer end  84  of the second winding  52  of the first pair  55  is connected to the inner end  65  of the first winding  53  of the second pair  56  of the elementary cell  50 . The outer end  66  of this first winding  53  of the second pair  56  of the elementary cell  50  is connected to the cathode  60  of the first diode  59 . Lastly, the outer end  67  of the second winding  54  of the second pair  56  of the elementary cell  50  is connected to the cathode  64  of the second diode  63 . It may thus be seen that the inner end  57 ,  61  of the first and second windings  51 ,  52  of the first pair of consecutive windings  55  is connected to the anode  58 ,  62  of the diodes  59 ,  63  respectively. As a result, the signals present at these ends  57 ,  61  are of like shape, of like magnitude and of like sign. These signals are referenced  68  and  69  respectively. In this way the inter-winding capacitances C 1  between the windings  51 ,  52  making up the first pair are not activated. 
     The outer end  66 ,  67  of the first and second windings  53 ,  54  of the second pair  56  of the elementary cell  50  is connected to the cathode  60 ,  64  of the diodes  59 ,  63  respectively. As a result, the signals present at these ends  66 ,  67  are of like shape, of like magnitude and of like sign. These signals are represented at  70  and  71  respectively. In this way the inter-winding capacitances C 1  between the windings  53 ,  54  making up the second pair are not activated. 
     It may be noted in FIG. 3 that the windings  51 ,  52  or  53 ,  54  of each pair have between them a distance smaller than the distance separating the two pairs  55 ,  56  from one another. This is due to the fact that the inter-winding capacitances C 1  between two windings of the same pair are inactivated. The value of these capacitances may be relatively high. On the other hand, the capacitances C 2  between the opposing faces of windings not belonging to the same pair are activated since the signals  0  and  69 , or  70  and  0  present at their ends are different. There is therefore benefit in reducing the value of these capacitances C 2 . This is the purpose of the larger distance observed between the windings of two consecutive pairs. In the preferred embodiment of the invention, which will be described hereinbelow in conjunction with FIGS. 5 and 6, the insulating partitions separating the windings of the same pair are thicker than each of the outer partitions of the pair. On the other hand, each pair is separated from the following by a separating groove. Hence, separation between the windings  52 ,  53 , which are closest together, of two pairs of a cell is catered for by the thickness of two partitions of chambers containing windings and by the axial length of the separating groove. 
     In the elementary cell just described, the inner ends of the windings  51 ,  52  are each connected to a diode anode. Likewise, the outer ends of the windings  53 ,  54  making up the second pair are each connected to a cathode. It should be noted that from the point of view of the inactivation of the inter-winding capacitances, the equivalent is achieved if the inner ends of the windings  51 ,  52  are each connected to a diode cathode, and the outer ends of the windings  53 ,  54  making up the second pair are each connected to an anode. To describe this first variant of the invention it is sufficient to repeat the description just given, while replacing “cathode  60 ,  64 ” with “anode  58 ,  62 ” respectively. The electrical diagram of this first variant is obtained from the diagram of FIG. 3 by reversing the position of the diodes as represented by a dotted line in FIG.  3 . 
     Another equivalent mode of inactivation is represented in FIG.  4 . In this mode, instead of connecting the inner ends of each one of the windings of the first pair to an anode of a diode, the outer ends are so connected. The inner end  61  of the second winding  52  of the first pair  55  is connected to the upper end  66  of the first winding  53  of the second pair  56 . The lower ends  65 ,  81  of the first and second windings of the second pair  56  are connected to the cathodes  60 ,  64  of the diodes  58 ,  63  respectively. It should be noted that the positions of the diodes may be reversed as explained above in conjunction with FIG.  3 . 
     A step-up coil constructed in accordance with the invention generally comprises several elementary cells  50 . In the embodiment represented in FIG. 3, the outer end  75  of the first winding  51  of the first pair  55  is connected to the inner end of the second winding of the second pair of a preceding cell or in the case of the first cell is coupled in a known manner to a source at reference potential. The inner end  81  of the second winding  54  of the second pair  55  is connected to the outer end of the first winding of the following cell or in the case of the last cell is coupled to the high-voltage output of the transformer either directly or by way of windings and/or diodes. 
     In the embodiment represented in FIG. 4, the inner end  57  of the first winding  51  of the first pair  55  is connected to the outer end of the second winding of the second pair of a preceding cell or in the case of the first cell is coupled in a known manner to a source at reference potential. The outer end  67  of the second winding  54  of the second pair  55  is connected to the inner end of the first winding of the following cell or in the case of the last cell is coupled to the high-voltage output of the transformer either directly or by way of windings and/or diodes. 
     Regardless of the embodiment, the inactivation of the inter-winding capacitances contributes to the decrease in the “ringing”. 
     A complete exemplary embodiment of a coil  100  of step-up windings will now be commented upon in conjunction with FIGS. 5 and 6. FIG. 5 represents a perspective view of a former  72  of the coil  100  and of the diodes and windings of this coil  100 . This FIG. 5 is intended to elucidate the mechanical aspects of the invention as well as the manufacturing process. FIG. 6 is intended to depict the electrical connections of the step-up coil represented in FIG.  5 . It will be seen in the course of the following description that the exemplary embodiment according to the invention comprises three elementary cells such as represented in FIG.  3 . In describing these cells, in conjunction with FIGS. 5 and 6, the same numbering will be used as in FIG.  3 . The elements having the same function as those represented in FIG. 3 will therefore have identical reference numerals accompanied by an index  1 ,  2 ,  3  . . . n, “n” representing the number of mutually similar elements, so as to distinguish them physically from one another. Likewise, the other mutually similar elements of FIG. 5 will have identical reference numerals accompanied by an index  1 ,  2 ,  3  . . . n. An unindexed reference numeral will be employed to denote an element generically. So as not to overload FIGS. 5 and 6, not all the indexed references will necessarily be shown in the figures. 
     The former  72  takes the known form of a hollow cylinder with axis AA′. In a known manner this axis is also the axis of a magnetic circuit (not represented). The outer part of the former  72  comprises  21  partitions  80   1  to  80   21  whose outer lateral surface has been indicated with a dot, so as to clarify the understanding of the drawing, since, although the drawing is on an enlarged scale, the succession of parallel lines representing the partitions and the grooves or chambers, intermediate between two partitions, is not easy to follow in FIG.  5 . In order to create a convenient lexical distinction when explaining the invention, the volume included between the outer surface of the cylinder  72  and two consecutive partitions  80  is referred to as a groove or chamber according to the distinction explained hereinbelow. As already seen earlier, some of these volumes contain wire windings and others do not contain any. The term “groove” is employed when a volume between two consecutive partitions  80  delimiting this volume does not contain wire windings. When an intermediate volume between two consecutive partitions contains wire windings, the term chamber is employed. The wire windings have been represented by a thick black line in FIG.  5 . Thus, two chambers are axially consecutive when they are not separated from one another by any chamber, whereas two axially consecutive chambers can be separated from one another by one or more grooves. The coil  100  represented thus comprises  12  partial windings grouped into three elementary cells  50   1  to  50   3  housed in  12  chambers  79   1  to  79   12 . It also comprises an additional winding  83  and an additional diode  82 . The intermediate grooves between two consecutive partitions have been marked by a small cross, again to facilitate the understanding of the figure. There are thus seven grooves  76 to  76   7  containing no windings. These  7  grooves house passages for wires. 
     The structure of the coil  100  will now be explained by describing one possible mode of manufacture. 
     The former  72  is made in a known manner by moulding. The seven diodes are firstly installed on diode supports  73 ,  74  which preferably constitute part the moulded former  72 . In FIG. 5 these supports are labelled  73   1  to  73   7  and  74   1  to  74   7 . So as not to overload the figure, only the first and last elements are actually numbered. Advantageously, the supports  73 ,  74  protrude radially from the cylindrical former  72 , at the grooves  76   1 - 76   7 , labelled in the figure with a cross. These grooves  76  do not contain windings as indicated earlier. As will be seen again later, these grooves  76  separate pairs of windings whose inter-winding capacitances C 2  (see FIG. 3) are not neutralized. Therefore, the axial length of these grooves serves a dual purpose: they contribute to decreasing the inter-winding capacitance C 2  and they house the foot of the supports  73 ,  74 . The latter must have a sufficient thickness to house hollows for receiving the connections  77 ,  78  of the diodes  59 ,  63  or  82  whilst preserving sufficient sturdiness, doing so within a minimum bulk. The fact that the diodes are mounted before carrying out the coiling is an advantageous characteristic of the process for manufacturing a coil  100  according to the invention, since this makes it possible to use the connections  77 ,  78  of these diodes to fix the ends of the wires to be coiled, if necessary, for example by tight winding about these connections (wrapping), so as to make the step-up windings. Therefore it is possible to do away with the joining pins which are used in a known manner in the prior art and this contributes to the compactness of the transformer. The mode of coiling the wires making up the step-up windings will now be explained. A wire is wound on the anode connection  77   1  of the first diode  59   1  and the wire is coiled in the first chamber  79   1 . The outer end  75   1  of this first winding  51  of the first pair of the first cell  50   1  is connected in a known manner to a source of constant potential for example and, as represented in FIG. 1 or  6 , to earth by way of a resistor in parallel or in series with an inductor. Likewise, a wire is wound on the anode connection  77   2  of the second diode  63   1  and the is coiled in the second chamber  79   2 . A pair of windings  55   1 , as represented at  55  in FIG. 3, is thus obtained. The inter-winding capacitances C 1  of the chambers constituting a pair being inactivated, the windings of a pair are axially consecutive windings separated by a single partition  80   3 . The outer end  84   1  of the winding  52   1  contained in the chamber  79   2  is then introduced into a guidance and retention slot (not represented) of the partition  80   4  thereby allowing it to be introduced into the empty groove  76   2 . The wire merely passes through this groove and it is introduced into a guidance and retention slot (not represented) of the partition  80   5  thereby allowing it to be introduced into the bottom of the chamber  79   3  where it constitutes the winding  53   1 . It may be noted that in this exemplary embodiment, the outer end  84   1  of the second winding  52   1  of the first pair  55   1  is in direct continuity with the inner end  65   1  of the first winding  53   1  of the second pair  56   1 . Naturally the connection between an inner end and an outer end can also be ensured by means of a joining pin. After coiling the wire in this chamber  79   3 , the outer end  66   1  of the winding  53   1  is connected to the cathode of the diode  59   1 . A new wire is wound tightly on the anode  58   2  of the diode  59   2  and it is coiled inside the chamber  79   5  so as to constitute the winding  51   2 . This winding  51   2  is the first winding of the first pair  55   2  of the second elementary cell  50   2 . The outer end  75   2  of the winding  51   2  is guided by means of a slot (not represented) of the partition  80   8  towards the groove  76   3  which it passes through so as to meet up, via a slot (not represented) of the partition  80   7 , with the chamber  79   4  where it is coiled so as to constitute the winding  54   1 . The outer end of the winding  54   1  is connected to the cathode  64   1  of the diode  63   1 . It may be noted that in this exemplary embodiment, the outer end  75   2  of the first winding  51   2  of the first pair  55   2  of an intermediate cell such as the cell  50   2  is in direct continuity with the inner end  81   1  of the second winding  54   1  of the second pair  56   1  of the preceding cell  50   1 . This direct connection between an inner end and an outer end can also be ensured by means of a joining pin. This possibility is used at least once in a coil according to the invention in particular to obtain a connection carrying the focusing voltage. FIG. 6 represents this possibility by a dotted line. According to this embodiment represented by a dotted line, the outer end  75   2  of the first winding  51   2  of the first pair  55   2  of an intermediate cell such as the cell  50   2  is joined to a pin ( 86 ). Therefore, the inner end  81   1  of the second winding  54   1  of the second pair  56   1  of the preceding cell  50   1  is itself joined to this same pin  86  for the focus voltage output. 
     After executing the coiling operations just described, it may be observed that the four windings  51   1 ,  52   1 ,  53   1 ,  54   1  making up the first cell  50   1  are coiled. The same goes for the first pair  51   2  of the second cell. The coiling of the other windings  52   2 ,  53   2  and  54   2  of the second cell  50   2  as well as that of other intermediate coils, if the coil  100  comprises more than three elementary cells  50 , is carried out in a similar manner. The coiling of the third cell, or more generally of the last cell, if the coil  100  comprises more than three elementary cells  50 , is performed in the same manner, with the possible exception of the fourth winding  54   3  or more generally  54   n  of the last cell  50   3  or  50   n . 
     In the exemplary embodiment described above, the two pairs  55 ,  56  of windings which together make up a cell are housed in chambers  79  axially separated from one another by grooves  76 , whilst the windings of a pair  55  or  56  are housed in consecutive chambers  79  having a common separating partition  80 . Likewise, the fourth winding  54  of a cell  50  is housed in a chamber  79  which is axially separated from the chamber housing the first winding  51  of the following cell  50  by at least one groove  76 . As seen earlier, the groove  76  separating two axially consecutive chambers  79  houses the feet of the diode supports  73 ,  74 . 
     The mode of manufacturing the windings which has just been described, by describing a string of operations in a necessarily linear manner, should not be understood as signifying that these winding operations are performed in succession. The advantage indicated earlier of the possible simultaneity of windings of various chambers is preserved in the embodiment of the coil  100  according to the invention. 
     It will have been noted that the exemplary embodiment just described in relation to FIGS. 5 and 6 is based on the cell model  50  described in relation to FIG.  3 . Naturally, it is equivalent from the point of view of the inactivation of inter-winding capacitances to use cells  50  according to the variants described in relation to FIGS. 3 and 4. 
     Thus a coil  100  constructed on the cell model  50  represented in FIG. 4 comprises at least two pairs of windings, a first ( 55 ) and a second ( 56 ), the four windings ( 51 - 54 ) constituting the two pairs ( 55 ,  56 ) being housed in consecutive chambers ( 79   1 ,  79   12 ), the two pairs together making up an elementary cell ( 50 ), the outer end ( 75 ) of the first winding ( 51 ) of the first pair ( 55 ) being connected to the anode ( 58 ) of the first diode ( 59 ), the outer end ( 84 ) of the second winding ( 52 ) of the first pair ( 55 ) being connected to the anode ( 62 ) of the second diode ( 63 ), and the inner end ( 65 ) of the first winding ( 53 ) of the second pair ( 56 ) being connected to the cathode ( 60 ) of the first diode ( 59 ), the inner end ( 81 ) of the second winding ( 54 ) of the second pair ( 56 ) being connected to the cathode ( 64 ) of the second diode ( 63 ). 
     The inner end ( 61 ) of the second winding of the first pair ( 55 ) is connected to the outer end ( 66 ) of the first winding ( 53 ) of the second pair ( 56 ). 
     The joining of a preceding intermediate cell to a following intermediate cell or to the last cell is effected by the fact that the outer end ( 67   1 ) of the second winding ( 54   1 ) of the second pair ( 56   1 ) of the preceding cell ( 50   1 ) is connected to the inner end ( 57   2 ) of the first winding ( 51   2 ) of the following cell ( 50   2 ). 
     In a known manner, a coil  100  in accordance with one of the variant embodiments of the invention is included in a transformer  90  known per se and represented in an exploded view in FIG.  7 . An example of such a transformer differs from a known transformer only in the fact that it includes this coil  100 . 
     The high-voltage transformer  90  represented in FIG. 7 is intended for powering a cathode-ray tube (not represented). Around a core made of ferromagnetic material (not represented), it comprises a first coil former  91  carrying primary and secondary windings referenced  92  overall, and a second coil former  72  as described above. It is this second coil former which carries the high-voltage windings for powering the grids of the cathode-ray tube. The two coil formers  91  and  72  are in the mounted position, concentric with one another, the primary coil former  91  lying inside the tertiary coil former  72 . The assembly of the two coils together with that part of the core around which the coils  91  and  72  are mounted is housed in a casing  95  made in general of an insulating plastic. This casing  95  comprises two output ducts for the high voltages referenced  96  and  97  respectively, a first output  96  for the anode high voltage and a second output  97  for the focusing high voltage. The latter is in general adjustable by means of a potentiometer block  98  mounted removably or otherwise on an open face  99  of the insulating casing  95 . 
     There are embodiments (variants) in which the focus pin  86  energizes a potentiometer block from which there protrude not one but two output ducts for the focusing voltages, a static focus and a dynamic focus, as well as, very often, a voltage G 2  for accelerating the electrons (around 1500 volts maximum).