EP0230185B1 - Method of producing magnetic cores for stabilization ballast in an assembly of lamps of varying discharge - Google Patents

Abstract

For an assembly of differing discharge-lamps, for each lamp of the assembly, an ideal air-gap value is determined for the stabilising choke for this lamp, and on the basis of the ideal air-gap values thus determined, there are chosen a minimum air-gap at least approximately suitable for one or more lamps (A, B, C, D, G) of the assembly, a maximum air-gap at least approximately suitable for one or more other lamps (I) of the assembly, and at least one intermediate air-gap at least approximately suitable for one or more of the remaining lamps (E, F, H) of the assembly, so as to at least approximately cover the differing air-gap requirements. An assembly of stabilising chokes is produced comprising a first choke produced by means of first magnetic- circuit elements each forming the chosen minimum air-gap, a second choke produced by means of second magnetic-circuit elements each forming the chosen maximum air-gap and one or more intermediate chokes produced by means of the first and second magnetic-circuit elements to form the chosen intermediate air-gap(s) by combining the minimum and maximum air-gaps.

Description

The present invention relates to magnetic circuits for producing chokes for stabilizing the operation of discharge lamps.

The calculations show that the inductance of a choke strongly depends on the width of the air gap. Indeed, the simplest of the formulas giving the value L of the inductance is of the form L = N² / R, in which N is the number of turns and R the sum of the reluctances along the path of the flux. The reluctance, or magnetic resistance, is in the form l / ps in which l represents the length of the circuit element (iron or air) in the direction of the flux lines, s the section of the circuit and p magnetic permeability. In inductors such as those used to stabilize the operation of discharge lamps, we see that the reluctance of the magnetic circuit (path in the iron) represents only 2 to 5% of the reluctance of the air gap (path in air ). Also, the inductance of the inductors can be modified to a large extent by acting only on the value of the air gap.

For a manufacturing range covering a set of discharge lamps of various types and / or wattages, each lamp corresponds to a particular ideal inductance of the stabilizing inductor. If you want to make all the chokes in the most economical way in terms of materials, you can think of using magnetic circuits of the same dimensions and vary the air gap. Ideally, the air gap should even be continuously variable not only to obtain different predetermined inductance values, but also to compensate for the tolerances on the other parameters influencing the value of the inductance, namely in particular the number of turns, the permeability of magnetic materials and the flow passage section.

There are numerous examples in the electrotechnical art of making inductors with an adjustable air gap. Of a generally, it is expected that a part of the magnetic circuit can move relative to a part of the complementary circuit. The air gap is adjusted by continuously measuring the current passing through the winding under the effect of a constant supply voltage. When this current has reached a predetermined set value, the two parts of the magnetic circuit are immobilized relative to each other by mechanical means.

In a mass production process, a machine must be produced capable of imparting a slow movement and of small amplitude to the parts of the magnetic circuit movable with respect to each other, of continuously measuring the current passing through. winding and ensuring the locking in position of the parts of the magnetic circuit. Such a machine is necessarily complicated and expensive, especially if it requires a high production rate.

Furthermore, such a machine generally acting by pressure on the parts of the magnetic circuit, this implies that the air gap is previously filled with a deformable non-magnetic material opposing a known reaction force to the pressure action exerted by the machine. Also, if this technique of making chokes has advantages in terms of the electrotechnical qualities of the finished product, it does however involve a complex installation of the parts of the magnetic circuit and the production of a specific machine for adjusting the inductance.

Another method for varying the value of an air gap in a magnetic circuit is described in document US-A-2 790 960. According to this method, the magnetic circuit is formed by assembling first magnetic circuit elements defining an air gap minimum and second magnetic circuit elements defining a maximum air gap.

The step gap variation is achieved by modifying the relative proportions of first and second magnetic circuit elements.

Document AU-A-518 715 shows a magnetic circuit for discharge lamp stabilization inductor, formed of first and second magnetic circuit elements arranged alternately and defining two respective air gap values different from each other. The object is not to vary the overall value of the air gap, but to obtain two elbows in the characteristic curve of the choke representing the variation of the current with respect to the voltage.

The present invention aims to provide a method for making magnetic circuits having different air gaps adapted to a set of different discharge lamps, without requiring the use of complex machines or fixtures to adjust the relative position of parts of magnetic circuit .

• on détermine, pour chaque lampe de l'ensemble, une valeur d'entrefer idéale pour la self de stabilisation de cette lampe,
• à partir des valeurs idéales d'entrefer ainsi déterminées, on choisit un entrefer minimum convenant au moins de façon approchée pour une ou plusieurs lampes de l'ensemble, un entrefer maximum convenant au moins de façon approchée pour une ou plusieurs autres lampes de l'ensemble et au moins un entrefer intermédiaire convenant au moins de façon approchée pour une ou plusieurs des lampes restantes de l'ensemble, de manière à couvrir au moins approximativement les besoins en entrefers différents pour toutes les lampes de l'ensemble avec l'entrefer minimum, l'entrefer maximum et le ou les entrefers intermédiaires, l'entrefer pour chaque sous-ensemble de lampes étant choisi de façon à limiter l'erreur par rapport à la valeur idéale de chaque lampe dudit sous-ensemble à quelques pour cents, au moins un des sous-ensembles possédant plusieurs lampes, et
• on réalise un ensemble de selfs de stabilisation comprenant une première self réalisée au moyen de premiers éléments de circuit magnétique formant chacun l'entrefer minimum choisi, une deuxième self réalisée au moyen de seconds éléments de circuits magnétique formant chacun l'entrefer maximum choisi et une ou plusieurs selfs intermédiaires réalisées au moyen des premiers et seconds éléments de circuit magnétique pour former le ou les entrefers intermédiaires choisis par combinaison des entrefers minimum et maximum.

This object is achieved by a method according to which, in accordance with the invention,

• we determine, for each lamp in the set, an ideal air gap value for the stabilization choke of this lamp,
• from the ideal air gap values thus determined, a minimum air gap is chosen which is suitable, at least approximately, for one or more lamps of the set, a maximum air gap suitable at least approximately for one or more other lamps in the assembly and at least one intermediate air gap suitable at least approximately for one or more of the remaining lamps in the assembly, so as to cover at least approximately the different air gap requirements for all the lamps in the assembly with the minimum air gap, the maximum air gap and the intermediate air gap (s), the air gap for each subset of lamps being chosen so as to limit the error with respect to at the ideal value of each lamp of said subset to a few percent, at least one of the subsets having several lamps, and
• a set of stabilizing inductors is produced comprising a first inductor made by means of first magnetic circuit elements each forming the minimum chosen air gap, a second inductor made by means of second magnetic circuit elements each forming the maximum chosen air gap and a or several intermediate chokes produced by means of the first and second magnetic circuit elements to form the intermediate air gap (s) chosen by combination of the minimum and maximum air gaps.

The magnetic circuits of the different inductors are formed by two stacks of magnetic sheets located on either side of a joint plane and the sheets used for at least one of the two stacks have a partial air gap with respect to the joint plane. having one or the other of two different values forming the minimum and maximum air gaps with the partial air gap defined by the sheets of the other stack.

The two different values of partial air gap can be obtained with particular sheets, which leads, to produce one of the stacks of the different chokes, to use sheets of two different types.

As a variant, the two different partial air gap values can be obtained with the same sheets, one or the other of the two values being obtained depending on whether the magnetic sheets have one or the other on two opposite sides in look of the other stacking.

Thus, the method according to the invention makes it possible to cover at least approximately the air gap requirements for a whole set of different discharge lamps without requiring adjustments of relative positions of parts of magnetic circuits and without requiring a large assortment of magnetic sheets. of different types.

• la figure 1 est un diagrame montrant la répartition des valeurs d'entrefer idéales pour une gamme de fabrication de lampes à décharge différentes,
• les figures 2 à 4 sont des vues schématiques de circuits magnétiques avec des entrefers respectivement minimum, maximum et intermédiaire pour la réalisation de selfs de stabilisation couvrant les besoins de la gamme de lampes à décharge envisagée,
• la figure 5 est une vue en coupe suivant le plan V-V de la figure 4 montrant le circuit magnétique à entrefer intermédiaire,
• les figures 6 à 8 sont des vues schématiques de circuits magnétiques avec des entrefers respectivement minimum, maximum et intermédiaire suivant un autre mode de mise en oeuvre de l'invention, et
• la figure 9 est une vue en coupe suivant le plan IX-IX de la figure 8 montrant une variante de réalisation du circuit magnétique à entrefer intermédiaire.

The invention will be better understood on reading the description given below, by way of indication but not limitation, with reference to the appended drawings in which:

• FIG. 1 is a diagram showing the distribution of the ideal air gap values for a range of manufacturing of different discharge lamps,
• FIGS. 2 to 4 are schematic views of magnetic circuits with respectively minimum, maximum and intermediate air gaps for producing stabilization inductors covering the needs of the range of discharge lamps envisaged,
• FIG. 5 is a sectional view along the plane VV of FIG. 4 showing the magnetic circuit with an intermediate gap,
• FIGS. 6 to 8 are schematic views of magnetic circuits with respectively minimum, maximum and intermediate air gaps according to another embodiment of the invention, and
• Figure 9 is a sectional view along the plane IX-IX of Figure 8 showing an alternative embodiment of the magnetic circuit with an intermediate gap.

As already indicated, for a given discharge lamp, it is possible to determine an ideal air gap of the magnetic circuit of the lamp stabilization inductor, that is to say an air gap corresponding to a maximum saving in terms of materials. used for the construction of the reactor (iron and copper). For this purpose, air gap adjustment machines or complete series of different magnetic circuits can be used. each corresponding to a particular lamp, but the resulting additional cost can largely cancel out the savings made on materials.

The invention proceeds from an observation made by the applicant. It has indeed appeared that the requirements for different air gaps for a range of manufacturing of different discharge lamps can be satisfied, at least approximately, with a minimum air gap value suitable for one or more lamps, a maximum value of air gap suitable for one or more other lamps and at least one intermediate air gap value to cover the needs of the remaining lamps. The minimum and maximum air gap values can be obtained respectively by first and second elements of magnetic circuits while the or each intermediate value is obtained by combining the minimum and maximum values, that is to say by associating first and second magnetic circuit elements.

Thus, magnetic circuits for manufacturing the stabilization inductors suitable for all the lamps considered can be produced from a reduced number of elements of different magnetic circuits and without requiring continuous adjustment of the gap width.

In order to illustrate the above, FIG. 1 shows a diagram or "air gap map" showing the different air gap values optimized for stabilization inductors intended for a set of discharge lamps corresponding to a production range. of the plaintiff. The discharge lamps and the corresponding air gaps shown in this diagram are as follows:

(1) High pressure sodium lamps (SHP)

• A - 70 W lamp for 220-240 V network (SHP 70/24): air gap equal to 0.840 mm,
• B - 100 W lamp for 220-240 V network (SHP 100/24): e = 0.855 mm,
• C - 50 W lamp for 220-240 V network (SHP 50/24): e = 0.887 mm.

(2) Fluorescent balloons (BF)

• D - 50 W lamp for 230 V network (BF 50/23): e = 0.863 mm,
• E - 80 W lamp for 230 V network (BF 80/23): e = 0.982 mm,
• F - 125 W lamp for 230 V network (BF 100/23): e = 0.957 mm.

(3) 125 W lamp for 240 V network (BF 125/24):

• G - heating of the winding of the inductor by 50 degrees centigrade above the ambient temperature: e = 0.841 mm
• H - heating of 57 degrees centigrade: e = 0.960 mm
• I - heating of 68 degrees centigrade: e = 1.065 mm.

The diagram shows that one can choose a minimum air gap 2a = 0.850 mm suitable for lamps A, B, C, D and G, a maximum air gap 2b = 1.065 mm suitable for lamp I and an intermediate air gap a + b = 0.9575 mm suitable for lamps E, F and H. As will be apparent from the description which follows, these different air gaps can be obtained with a very small assortment of different sheets, for example by means of sheets identical to the gap apart .

In this example the intermediate air gap has the average value between the minimum and maximum air gaps. However, in other cases, the intermediate air gap could take another value included in the interval between the minimum and maximum air gaps. It is also possible that circumstances impose the choice of more than one intermediate value so that the difference between each optimized air gap and the closest minimum, maximum or intermediate air gap remains less than a certain value (for example to limit the error on the real air gap compared to the value optimized to a few percent, less than 5% for information).

Returning to the envisaged example, Figures 2 to 4 illustrate an embodiment of three magnetic circuits 10, 20, 30 corresponding to the determined air gap values 2a, 2b and a + b.

.The magnetic circuit 10 (FIG. 2) is formed of two stacks 11, 15 located on either side of a joint plane P. The stack 11 is produced in a conventional manner by means of identical sheets 12 in the form of E Likewise, the stacking 15 is produced by means of identical sheets 16 in the form of E. The sheets 16 have lateral branches which bear at their ends on the ends of the lateral branches of the sheets 12, along the plane P The sheets 12 and 16 delimit by their central branches a gap of width 2a, this gap being formed by a partial gap e1 between the central branch of the sheets 12 and the joint plane P, and a partial gap e2 between the central branch of the plates 16 and the plane P. We then have $\text{e1 + e2 = 2a}$

.

. Avantageusement, les tôles 22 sont choisies identiques aux tôles 12 afin de limiter l'assortiment de tôles magnétiques différentes destinées à la fabrication des différentes selfs. Il en résulte e1 = e'1 et, par conséquent, $\text{e'2 = e1 + 2b - 2a}$

. A titre indicatif, pour l'exemple considéré, on pourra avoir $\text{e1 = e2 = e'1 = a = 0,425 mm}$

et $\text{e'2 = 0,640 mm}$

.Likewise, the magnetic circuit 20 (FIG. 3) is formed by two stacks 21, 25 situated on either side of a joint plane P 'and produced by means of sheets 22, 26, respectively. The sheets 22 and 26 delimit by their central branches a gap of width 2b formed by a partial gap e'1 between the central branches of the sheets 22 and the joint plane P 'and a partial gap e'2 between the central branches of the sheets 26 and the joint plane P '. We then have $\text{'1 + e'2 = 2b}$

. Advantageously, the sheets 22 are chosen identical to the sheets 12 in order to limit the assortment of different magnetic sheets intended for the manufacture of the different inductors. This results in e1 = e'1 and, therefore, $\text{e'2 = e1 + 2b - 2a}$

. As an indication, for the example considered, we could have $\text{e1 = e2 = e'1 = a = 0.425 mm}$

and $\text{e'2 = 0.640 mm}$

.

avec le plan de joint P". L'empilage 35 est réalisé au moyen d'une combinaison des tôles 16 et 26 de manière à former avec le plan de joint P" un entrefer électrotechniquement équivalent à un entrefer de largeur constante e"2 telle que $\text{e"2 + e"1 = a + b,}$

c'est-à-dire e"2 = b en prenant $\text{e1 = e2 = e"1 = a}$

, ou encore e"2 = 0,5325 mm dans l'exemple considéré.The magnetic circuit 30 (FIGS. 4 and 5) is formed, like the circuits 10 and 20, of two stacks 31, 35 situated on either side of a joint plane P ". The stack 31 is produced by means of the same sheets 32 advantageously identical to the sheets 12 and 22 and therefore forming a partial air gap $\text{e "1 = e'1 = e1}$

with the joint plane P ". The stack 35 is produced by means of a combination sheets 16 and 26 so as to form with the joint plane P "an air gap electrotechnically equivalent to an air gap of constant width e" 2 such that $\text{e "2 + e" 1 = a + b,}$

that is to say e "2 = b taking $\text{e1 = e2 = e "1 = a}$

, or even e "2 = 0.5325 mm in the example considered.

The elementary air gap e "2 is obtained by a combination of the sheets in the proportion desired to obtain the desired intermediate air gap value. If, as in the example considered, the value of the intermediate air gap is the average between the values minimum and maximum air gaps, the stack 35 is formed, for one half of sheets 16 and, for the other half, of sheets 26. In this stack, the arrangement of sheets 16 and 26 may vary without significantly modifying the electrotechnically equivalent elementary air gap The arrangement shown in FIG. 5 consists in alternating stacking of bundles of sheets 16 and bundles of sheets 26, the number of sheets being the same in the different packs.

As shown in Figures 2 to 5, the sheets 12 and 16 forming the stacks 11 and 15 have different external dimensions, as well as the sheets 22 and 26 forming the stacks 21 and 25. Advantageously, it is however possible to use sheets with the same external dimensions, which makes it possible to reduce the assortment of different sheets necessary for two by choosing identical sheets 12, 16 and 22 and sheets 22 which differ only in the partial air gap.

It will also be noted that the magnetic circuit corresponding to the intermediate air gap can be produced automatically by alternately supplying packets of sheets 16 and packets of sheets 26 to form the stack 35 (instead of feeding only packets of sheets 16 or only packets of sheets 26 for the formation of stacks 15 and 25). This remains true in the case where the intermediate air gap (s) have values other than the average between the minimum and maximum air gaps, the only difference being that the sheets 16 and 26 are in different numbers in the stack 35.

Figures 6 to 9 illustrate three other embodiments of magnetic circuits 40, 50, 60 respectively offering a minimum air gap, a maximum air gap and an intermediate air gap.

The magnetic circuit 40 (FIG. 6) comprises two stacks 41, 45 situated on either side of a joint plane Q. The stack 41 is constituted by sheets 42 in the form of E, while the sheets 46 constituting the stack 45 have, facing the sheets 42, a straight edge 47 located in the joint plane Q. In this way, the partial air gap defined by the sheets 46 is zero, and the partial air gap e1 defined by the sheets 42 is equal to the minimum air gap 2a.

.The magnetic circuit 50 (FIG. 7) also includes two stacks 51, 55 located on either side of a joint plane Q '. The stack 51 is formed of sheets 52 identical to the sheets 42 therefore defining a patial air gap e'1 = 2a. The stack 55 is formed of sheets 56 identical to the sheets 46 but occupying with respect to the latter an inverted position so as to present their edge 58, opposite the edge 57, opposite the sheets 52. The sheets 42, 56 have a form in C so that, in the position they occupy in circuit 50, they define a non-zero partial air gap e'2. The air gaps e'1 and e'2 form the maximum air gap 2b. We have then $\text{e'2 = 2b - 2a}$

.

soit égal à l'entrefer intermédiaire (c'est-à-dire $\text{e"2 = b - a}$

dans le cas considéré). Toute valeur d'entrefer intermédiaire peut être obtenue en faisant varier entre 0 et 100 % la proportion de tôles 56 dans l'empilage 65.Finally, the magnetic circuit 60 (Figures 8, 9) comprises two stacks 61, 65 located on either side of a joint plane Q ", the stack 61 being formed of sheets 62 identical to sheets 42 and 52 defining a partial air gap e "1 = e'1, while the stack 65 is formed by a mixture of sheets 46 and 56 to define an electrotechnically equivalent partial air gap e" 2 such that $\text{e "1 + e" 2}$

be equal to the intermediate air gap (i.e. $\text{e "2 = b - a}$

in the case considered). Any intermediate air gap value can be obtained by varying the proportion of sheets 56 in the stack 65 between 0 and 100%.

The number of different types of magnetic sheets required to make the different air gaps minimum, maximum and intermediate (s) desired is therefore here also reduced to a minimum. In addition, the design of the magnetic circuits of Figures 6 to 9 is also advantageous in that it allows, as known per se, to draw the sheets 46, 56 without loss of material from the recesses 43 located between the central branch and the branches side of the sheets 42, 52, 62.

The economic advantage provided by the method according to the invention will emerge from the tables given below.

• en imposant une valeur d'entrefer unique (c'est la valeur maximale e = 1,065 mm qui doit être alors choisie),
• en choisissant pour chaque lampe une self avec entrefer optimisé,
• en choisissant pour chaque lampe une self avec une valeur d'entrefer égale à celle convenant le mieux parmi les valeurs d'entrefer minimum, maximum et intermédiaire.

Tables I, II and III give different characteristics of the stabilization reactors of several of the lamps of the range considered with reference to FIG. 1, respectively:

• by imposing a single air gap value (the maximum value e = 1.065 mm which must then be chosen),
• by choosing an inductor with optimized air gap for each lamp,
• by choosing a choke for each lamp with an air gap value equal to that which best suits the minimum, maximum and intermediate air gap values.

Tables IV and V show the prices of the materials (iron and copper) required and the resulting cost differences, respectively for the chokes with single imposed air gap and the chokes with optimized air gaps, and for the chokes with single imposed air gap and the chokes with air gaps determined in accordance with the invention. For the different lamps envisaged, Tables IV and V indicate an annual production quantity and the gain achieved compared to the solution consisting in using inductors with a single imposed air gap. It can be seen that the process according to the invention makes it possible to achieve a very substantial gain in materials (iron, copper) and that this gain is of the same order as that obtained with coils with optimized individual air gaps, but without requiring any equipment. adjustment settings that are expensive and costly to implement. Table I (Single air gap chokes required) Lamp B AT VS F E D Air gap (mm) 1.065 1.065 1.065 1.065 1.065 1.065 Magnetic circuit thickness ( cm ) 5.4 4.3 3.5 4.2 2.8 2.3 * Heat exchange surface (dm2) 3.5 3.3 3 3.1 2.7 2.8 Copper wire diameter (mm) 0.5 0.45 0.4 0.53 0.425 0.375 Number of turns 538 668 847 562 850 1125 ** Filling coefficient 0.506 0.509 0.509 0.594 0.577 0.594 Copper price (FF) 4.27 3.84 3.51 4.43 3.64 3.51 Iron price (FF) 9.20 7.32 5.96 7.15 4.77 3.88 * The heat exchange surface is the total developed surface offered by the magnetic circuit and the copper winding for heat exchanges with the outside. ** The filling coefficient designates the ratio between the total section of copper wires passing through a window of the magnetic circuit and the total section of the window.

Table II (Optimized individual air gap chokes) Lamp B AT VS F E D Air gap (mm) 0.855 0.840 0.887 0.957 0.982 0.863 Magnetic circuit thickness ( cm ) 4.6 3.95 3.0 3.8 2.4 1.85 * Heat exchange surface (dm2) 3.3 3.1 2.9 3 2.7 2.7 Copper wire diameter (mm) 0.5 0.45 0.40 0.53 0.425 0.375 Number of turns 524 622 837 561 882 1126 ** Filling coefficient 0.493 0.473 0.503 0.592 0.598 0.595 Copper price (FF) 3.84 3.43 3.26 4.22 3.58 3.29 Iron price (FF) 7.83 6.73 5.11 6.47 4.087 3.15 * The heat exchange surface is the total developed surface offered by the magnetic circuit and the copper winding for heat exchanges with the outside. ** The filling coefficient designates the ratio between the total section of copper wires passing through a window of the magnetic circuit and the total section of the window.

La production annuelle pour chaque lampe est indiquée ici en pourcentage de la production totale.

Table III (Chokes with air gaps determined according to the invention) Lamp B AT VS F E D Air gap (mm) 0.850 0.850 0.850 0.957 0.957 0.850 Magnetic circuit thickness ( cm ) 4.7 4.0 3.2 3.8 2.45 1.9 Heat exchange surface (dm2) 3.33 3.12 2.9 3 2.7 2.7 Copper wire diameter (mm) 0.5 0.45 0.40 0.53 0.425 0.375 Number of turns 520 625 799 561 867 1109 Filling coefficient 0.489 0.476 0.480 0.592 0.589 0.586 Copper price (FF) 3.84 3.47 3.19 4.22 3.54 3.27 Iron price (FF) 7.92 6.74 5.39 6.47 4.13 3.20

The annual production for each lamp is shown here as a percentage of total production.

Claims (5)

1. Process for the manufacture of magnetic circuits for stabilising chokes for discharge lamps, characterised in that, for a group of different discharge lamps, it comprises the steps of:

   - determining, for each lamp of the group, an ideal air gap value for the stabilising choke of said lamp,

   - selecting, on the basis of the thus-determined ideal air gap values, a minimum air gap suitable at least to an approximation for one or several lamps of the group, a maximum air gap suitable at least to an approximation for one or several other lamps of the group and at least one intermediate air gap suitable at least to an approximation for one or several remaining lamp(s) of the group, so as to cover at least approximately the requirements of different air gaps for all the lamps of the group with the minimum air gap, the maximum air gap and the intermediate air gap or air gaps, the air gap for each sub group of lamps being chosen so as limit the error relative to the ideal value of each lamp of the said sub-group to a few percent, at least one of the sub-groups comprising several lamps, and

   - constructing a group of stabilising chokes comprising a first choke produced from first magnetic circuit elements each defining the chosen minimum air gap, a second choke formed from second magnetic circuit elements each defining the chosen maximum air gap and one or several intermediate choke(s) produced from the first and second magnetic circuit elements to form the chosen intermediate air gap or air gaps by a combination of minimum and maximum air gaps.
2. Process according to claim 1 for the manufacture of magnetic circuits formed by stacking magnetic plates on either side of a junction plane, characterised in that it comprises the step of forming at least one of the two stacks for the different chokes by means of magnetic plates defining, in relation to the junction plane, a partial air gap having one or the other of two different values and defining said minimum and maximum air gaps with the partial air gap value defined by the other stack.
3. Process according to claim 2, characterised in that the said magnetic plates are of two different types.
4. Process according to claim 3, characterised in that the magnetic circuits have the same external dimensions and differ from one another only by the value of the partial air gap.
5. Process according to claim 2, characterised in that said magnetic plates have the same shape and define a partial air gap having one or the other of said different values depending on whether they have one or the other of two opposite sides facing the other stack.

Images