GB2277204A - Invertor and reactor arrangements - Google Patents

Description

1 - 2277204 INVERTOR USING A REACTOR FABRICATED ON A METALLIC PRINTED

CIRCUIT BOARD

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an invertor unit and the design of a reactor used as a filter in the invertor.

Description of the Background Art

Fig. 7 is a block diagram and its connection diagram of a conventional invertor unit.

In the Figure are seen an alternating current input power source 50 that is connected via an invertor unit 51 to a motor 52. In the invertor unit 51 are diodes 14-19 for converting an alternating current into a direct current, a smoothing condenser 53, switching elements 2-7 for PWMmodulating the direct current, and feedback diodes 8-13 connected in reverse parallel to switching elements 2 through 7 for directing current. In the circuit arrangement are potentials VUNI VvN and VwN of output wires U, V and W which are measured against a potential -stable point N.

Fig. 8 is a diagram showing the resultant voltage wave forms when the switching elements 2 through 7 of the conventional invertor unit illustrated in Fig. 7 are operated and correspond to the potentials VuNj, VVN and VwN of Fig. 7. Further, Numeral 54 is a neutral point potential :. 2 - of outputs U, V and W, and is expressed by VC = (VUN + % + VwN) / 3.

This arrangement is the source of noise. For example, generally the voltage change dV/dt is a noise generating source, and the voltage change among the outputs U, V and W can become the cause for a normal mode noise. Also, the voltage change at a neutral point of outputs U, V and W against the potential-stable point of ground E or the direct current voltage bus bars P, N, etc., can become the cause for a common mode noise. Accordingly, it is desirable to provide a filter that is effective mainly against the common mode noise problem.

Fig. 9 is a cross sectional view of a main circuit section of conventional invertor unit. In this drawing, a main circuit substrate 1 is operative to support main circuit elements, such as the switching elements 2 through 7 and the feedback diodes 8 through 13. A cooling fin 46 is effective to transmit the heat generated by the main circuit elements 2 through 13 to a location for removal by radiation, convection and the like. An insulation layer 59 is provided as an electrical insulation between the main circuit elements 2 through 13 and the cooling fin 46.

Finally, the invertor unit has a box body 49, and the cooling fin 46 is fixed to this box body 49, but the cooling fin 46 and the box body 49 are connected electrically with each other.

Fig. 10 is an equivalent common mode noise in the main invertor unit shown floating capacitance insulating layer 59 circuit substrate 1 floating capacitance output wiring with in Fig. 55 having that is circuit diagram showing the circuit of the conventional 7. In Figure 10, a first a value Ci is formed by the disposed between the main and the cooling fin 46. A second 56 having a value Cc is formed by the respect to the ground E. A third floating capacitance 57 having a value Cm is formed between the winding wire of motor 52 and the frame (the frame being connected to ground E). Finally, an in-phase current 58 exists having a value i. expressed by io = C.dVMt.

The potential stable point N and the neutral point P1 of the AC input wiring has an identical potential against the carrier frequency of PWN. A voltage 54 having a value Vc is applied between the potential stable point N and the neutral point P3 of output wires U, V and W. Moreover, the point P3 is connected to ground E through the floating capacity Cc 56 and the floating capacity Cm 57.

The insulating layer 59 needs to provide adequate electrical insulation in Fig. 9, but it also must permit efficient heat transmission from the main circuit elements 2 through 13 to the cooling fin 46 efficiently. Typically, the layer has a thin wall and a large area. Therefore, the ": 4 - 10- value Ci of the floating capacity-55 that is formed between them is quite large. Because the neutral point P2 of main circuit elements 2 through 13 has an identical potential to that of neutral point P3 of output wires U, V and W, the floating capacity 55 with a value Ci is disposed across Vc as seen in the equivalent circuit diagram shown in Fig. 10.

In addition, because the box body 49 is directly subjected to the change in potential of main circuit elements 2 through 13 via the floating capacitance 55 with value Ci, there exists the a danger of an electric shock if a person touches the box body 49. For this reason, the box body 49 is connected to ground E for the sake of safety, as seen in the equivalent circuit of Fig. 10.

Because the in-phase voltage Vc 54 is applied to the floating capacities Ci 55, Cc 56 and Cm 57 as shown in Fig. 10, the in-phase current io 58, which is expressed by i = C.dWdt, flows through the power source wire. This current results in the common mode noise but also may have the undesired effect of being an input to an in-phase current (zero-phase current) sensor, namely a leak breaker, which may get activated although no ground fault is caused.

In order to decrease the in-phase current io 58, one approach is to reduce the C in the equation i = C.dWdt and the other approach is to decrease the voltage change factor dV/dt.

The method for decreasing the voltage change dV/dt is to be explained with respect to Fig. 11, which illustrates an in-phase filter for smoothing the change of in-phase voltage Vc 54 and its connection diagram. Numeral 60 is an in-phase reactor where three output wires are wound in the same direction around a single core. Only a non-zero component of the total of the three currents will act on the filter/reactor. Numerals 62 through 64 are condensers and are connected directly to the voltage bus bar N. Numeral 61 is a voltage clamp diode array for clamping the resonance voltage at the resonance frequency of the in-phase reactor 60 and condensers 62 through 64 to the VDC of direct voltage bus bars P and N.

Fig. 12 illustrates an equivalent circuit diagram the in-phase filter. In the figure, an in-phase reactor having a value LF and a condenser C, are connected as of 65 a filter in the equivalent circuit. Specifically, in operation, this filter acts on the in-phase voltage Vc 54 of the stage, and the io 58 is decreased by smoothing the change in potential of the in-phase voltage being imposed on the output wires, as seen across the floating capacitances Cc 56 and Cm 57.

In this case, the output in-phase filter acts on the neutral point of output wires U, V and W, and does not act on the neutral point P2 of the main circuit elements, namely on the potential of main circuit substrate 1 in Fig. 10. Accordingly, the current io 58 attributable to the floating capacitance Ci 55 will not be decreased, as shown by the equivalent circuit of Fig. 12.

Fig. 13 is a block diagram where a differential filter is used to smooth the differential voltage change of output wires U, V and W. In the figure, differential reactors 7072 and condensers 73-75 are combined to form an LC filter.

Fig. 14 shows the wiring diagram of an invertor main circuit portion equipped with an in-phase filter shown in Fig. 11. The output wires U, V and W come out of the main circuit substrate 1 into which the main circuit elements 2 though 13 are incorporated, and are connected to the invertor output through the condensers 62-64 and the voltage clamp diode 61 via the in-phase reactor 60. Moreover, both the ends of voltage clamp diode 61 are connected to the smoothing condenser 53.

Fig. 15 shows an equivalent circuit based on the wirelayout, as seen in Fig. 14. As shown in the figures, there exists a wiring inductance 76 having a value Ll in a normal mode, which increases as the wiring becomes longer in extending from the condensers 62-64, via the in-phase reactor 60 from the main circuit substrate. There also exists a wiring inductance 78 having a value L2, which increases as the wiring becomes longer from the voltage - 7 clamp diode 61 to the smoothing condenser 53.

Fig. 16b shows the effect on an in-line voltage Vuv in Fig. 16a, in the case that there exists a wiring inductance 76 having a value L1 in Fig. 15.

On the other hand, Figs. 17a and 17b show voltage wave forms across the voltage clamp diodes 61 in two different cases where there exists a wiring inductance 78 with a value L2. In a first case where the wiring in Fig. 14 is short, the value L2 of wiring inductance 76 is small and the value Lo of the in-phase reactor 60 is sufficient so the in-line voltage hardly resonates with the condensers 62-64. The result is a desired voltage that varies step wise, as seen in Fig. 17a, and effectively controls the motor. On the other hand, if the wiring is long, the value L2 of the wiring inductance 76 is high, so the voltage VO across the diodes 61 has a wave form as given in Figure 17b and the desired voltage isn't applied to the motor 52.

Furthermore, if there exists the wiring inductance 78 having a value L2, the resonance voltage exceeds the VDC as shown in Fig. 17b. As a result, the clamp-of the in-line voltage to the VDC becomes ineffective, the peak value of the in-line voltage exceeds the VDC and also exceeds the voltage threshold for breakage of the diode.

Fig. 18 shows the case of using a reactor 79 to the other section of the invertor unit. Reactor 79 is for improving the power factor, and is inserted between rectifier diodes 14- 19 and the smoothing diode 53 for smoothing the input current wave f orm of alternating current.

Fig. 19 shows the conventional in-phase reactor 60 and its assembly. In the figure, the reactor components comprise a core 42, a winding 45 that is structured of 3 phases, and a case 80 for protecting the core 42 from the winding 45. The core 42 is wrapped externally by the case 80, and its outside is wound by a winding wire 45. in completing the fabrication of an in-phase reactor 60.

If the in-phase reactor 60 is made with a single large coil, the coil will be wound in multiple layers, and a floating capacity exists between the input and the output. Accordingly, if the power has a high frequency, the reactance value decreases and the reactor doesn't work effectively. Further, if the reactor is wound in multiple windings, the winding wire generates heat because of the resistance provided by copper. Moreover, since it works at a high frequency, resistance is provided by iron in the core, and the core temperature goes up due to the poor heat radiation because the core is wound by the winding wire. The reactance value of the core is decreased by the temperature rise of the core, which is likely to cause a magnetic saturation. As a countermeasure against it, the 10- core needs to be enlarged, which results in an increase in cost and the enlargement of unit size.

In summary, the conventional reactor that is structured as described above will have the following problems. First, if a single large coil is wound as a multiplex winding, an in-line floating capacitance will exist in the overlapped areas, causing the device not to act as a reactor when a high frequency is applied.

If the reactor is fabricated according to the conventional method, the heat tends to get accumulated in the interior, which not only results in the fall of reactance value but also tends to cause a magnetic saturation.

In addition, the conventional invertor unit has several problems if such unit was structured with the conventional reactor, as earlier described.

The reactor has a significant thickness, which prevents it from being mounted on the main circuit substrate and, for this reason, needs to be installed separately. Accordingly, the wiring from the voltage clamp diode to the smoothing condenser becomes longer. Consequently, the voltages at both the ends of voltage clamp diode go up, the in-line voltage can not be clamped to the direct current bus bar voltage, and this voltage will exceed the threshold voltage of the clamp diode and result in its failure.

For this reason, because the reactor can not be mounted directly on the surface of main circuit substrate and needs to be installed separately, a leak reactance due to a long wiring exists in the in-phase filter circuit, and the desired voltage can not be obtained because of the resulting resonance of the in-line voltage. - Unexamined Patent Publication (Kokai) No. 3-135371 and Unexamined Patent Publication (Kokai) No. 3-135373 are available to teach how to design a reactor to be more compact and thinner in size and for actually mounting it on the same substrate. However, such teachings are not sufficient to show how to make a reactor that is compact and thin in size and, moreover, which can be used with an in-line high voltage, for example in the range of 600 V, as is required for use in an invertor unit.

SUMMARY OF THE INVENTION

A reactor according to the present invention is comprised of an insulating substrate in the form of a metallic printed circuit board. In the method of making the reactor, a conductive pattern is formed on the board with a conductive film, the pattern comprising a plurality of strips that are arranged with a space provided among them on the board. An insulating layer is provided over the strips and an iron core in the shape of a ring is : 1 1 - placed over the insulation-coated strips. Wires are connected between ends of the strips so as to cross over the ring of the iron core from positions inside the ring to positions outside of the ring.

In forming the wound coil, the wires may be connected to bonding pads installed onto a land portion of the strip shape patterns.

An in-phase reactor according to the present invention may comprise a coil made of strip patterns and wires wound around a ring shaped iron core wherein the winding is for a plurality of phase portions and is conducted in the same direction for every phase so that the reactor may activate only against an in-phase voltage.

A further embodiment comprises an invertor unit having a plurality of switching elements for receiving the supply of power for a direct current power source and for converting the direct current into an alternating current, in which an in-phase filter including an in-phase reactor fabricated as described above has been installed, on the output side of said switching elements, on to the metallic substrate to load a plurality of said switching elements.

Finally, the reactor according to the present invention will lay out the ring shaped iron core in proximity to a plurality of strip shape patterns of a metallic printed circuit board having good thermal 12 - conductivity.

The present invention will result in very little in-line floating capacitance, and the reactors can operate even if the power source provides a high frequency.

Moreover, because the heat of wire is radiated from the metallic printed circuit board and the heat is not stored in its interior, there is less reduction in reactance value, thus minimizing magnetic saturation.

The present invention also involves an invertor unit consisting of a plurality of switching elements for receiving the supply of power from a direct current power source and converting the direct current into an alternating current in which an in-phase filter including the in-phase reactor described above installed on the output side of said switching elements, on to the metallic printed circuit board for loading a plurality of said switching elements. As a result, the wiring length can be shortened and the in-line voltage isn't resonated by the leak reactance, and moreover the wiring length from a clamp diode to a smoothing diode can be shortened.

BRIEF DESCRIPTION OF THE DRAWINGS

Figs. 1 (a) and 1 (b) show top and section views of a reactor in one preferred embodiment of this invention.

Fig. 2 is a view comparing the reactor in one preferred embodiment of this invention with the 1 13 - is conventional reactor.

Figs. 3(a) and 3(b) provide top and section views of a reactor in one preferred embodiment of the present invention.

Figs. 4(a) and 4(b) show a plane view and an equivalent circuit of the main circuit substrate of invertor unit using the reactor of this invention.

Figs. 5(a) and 5(b) provide a comparison of floating capacities between the reactor in one preferred embodiment of this invention and the reactor of conventional art.

Fig. 6 is another embodiment of this invention where a power factor improving reactor is actually mounted on the main circuit substrate.

Fig. 7 shows a block diagram of a conventional invertor unit and its connection diagram.

Fig. 8 is an explanatory view of voltage wave forms when switching the conventional invertor unit.

Fig. 9 shows a cross sectional view of main circuit section used in the conventional invertor unit.

Fig. 10 is an equivalent circuit diagram showing a channel of common mode noise in the conventional invertor unit.

Fig. 11 shows an in-phase filter for smoothing the change in in-phase voltage and its connection diagram.

Fig. 12 is an equivalent circuit diagram showing the :: 14 - 10- channel of common mode noise in the invertor equipped with an in-phase filter.

Fig - 13 is a block diagram where a dif f erential f ilter is used.

Fig. 14 is a substance wiring diagram of invertor main circuit section equipped with a conventional in-phase filter.

Fig. 15 shows an equivalent circuit diagram of Fig. 14.

Figs. 16(a) and 16(b) show voltage wave forms of Fig.

15.

Figs. 17 (a) and 17(b) show other voltage wave forms of Fig. 15.

Fig. 18 is a circuit diagram of another section of an invertor unit which can use the invention.

Fig. 19 is a view showing the assembly of a conventional in-phase reactor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention may be explained with reference to Figs. 1 (a) and 1 (b), which provides an example of a reactor structure in accordance with a preferred embodiment of the invention. Fig l(a) is a plane view of such reactor and Fig. l(b) is a cross sectional view of reactor showing the cross section A-A of Figure l(a). In these figures, an insulating substrate 110, such as a metallic printed circuit board formed by providing an insulating film on a metallic substrate having good thermal conductivity, is used. A pattern 111 is formed with a conductive film on the insulating substrate 110, and a ring shape core coated with an insulating material 112 is placed over the pattern. Wires 113 (U-phase, V-phase and W-phase portions) are connected over the core. An insulating material 114, for example an under-resist insulating material, is inserted between the ring shape core 112 and the pattern 111.

The reactor according to this invention is comprised of an insulating substrate 110. The plurality of strip shape patterns 111 are arranged on the insulating substrate such that they have a sufficient space provided among them on the insulating substrate 110 and they cross under the ring of core 112. A wire 113 is used for connecting a first one of the strip shape patterns 111 with another of the strip shape patterns 111, which is separated from the first strip pattern by other pieces of strip patterns (here two strips for a three phase device). The core 112 is placed over the insulating substrate 110 via an insulating material 114, that separates the core from the plurality of strip shape patterns 111 on the insulating substrate 110. The end of each strip shape pattern 111 inside the ring of core 112 is connected to one end of wire 113 at every phase for a 3-phase arrangement. The length of wire 113 is laid is 16 - out so as to stride over the core 112 and the other end of the wire is connected to another of strip shape patterns 111 outside the ring of core 112. Thus, winding a coil made of the pattern 111 and the wire 113 around the ring shape core 112 is effected by repeating this connection and arrangement procedure.

Fig. 2 is a view comparing the coil according to this invention with the conventional coil. In the coil of this invention, the wire 113 may be shortened in length per piece, so it doesn't need to have a sheath, and its outside diameter may be in the order of 0. 3 mm. Moreover, the pattern 111 may be in the order of 0.5 mm because it is used for a metallic substrate. In addition, the insulation distance necessary to provide the operating voltage of 60OV, as required f or use in an invertor unit, may be sufficient if it is in the order of 1 mm between the wires 113 and a silicon gel, etc., is used to seal the area of wire 113. In fact, the insulating distance may be enough if it is in the order of 0.8 mm, where the pattern 111 is coated.

Assuming that the number of turns as "n" and the magnetic path length as 1, then the inductance L of coil can be expressed by the following equation:

L co 2 /1 From this equation, as the magnetic path length 1 is made shorter, the inductance L can be made larger. Consequently, the inductance L can be fabricated more efficiently when the winding wire is wound as many turns "n" as possible around a smaller core (a core of smaller window (sectional) area).

The window area is larger in the conventional core because a sheathed wire having a thicker diameter is used. Therefore, such core is inefficient because the winding wire must be wound in many turns on a core having a long magnetic path length. For attaining the operating voltage of 60OV at SA in the conventional coil, a core having an outside diameter of 2.2 mm is required using a heat resistant vinyl sheathed electric wire AWG 26. In addition, because the conventional coil has a difficulty in radiating the heat, its core wire becomes thicker, and since the neces sary insulation is provided by the vinyl, the wire sheath becomes thicker. Further, a thicker sheath sometimes results in a further problem because its capability to radiate heat is worsened and the core wire must further be made thicker.

while the above explanation has shown the example of an in-phase reactor to be fabricated by winding the coils of 3-phase portions, consisting of U-phase, V-phase and W-phase at every phase, clearly only a single phase portion may be considered in case of the single phase.

: 18 - The first embodiment shows the example of interposing an insulating material between the pattern 111 and the core 112, but it should be clear that the invention can also use a core coated with an insulating material.

Figs. 3(a) and 3(b) is a fabrication example of the reactor in a preferred embodiment of this invention. These figures show the fabrication of a reactor on the insulating substrate 110 in a manner similar to the previous embodiment, but also has interposed a bonding pad between the pattern 111 and the wire 113 on the insulating substrate 110 in Fig. 1.

While the preferred embodiment previously described has adopted a metallic printed circuit board wherein an insulating substrate 110 is coated with an insulating film on a metallic substrate which has good thermal conductivity, but the equivalent effect can also be obtained even by using a DBC (Direct Bonding Capper).

Fig. 4 (a) is a plane view of a main circuit printed board in another preferred embodiment of and corresponds to the circuit diagram of this invention, Fig. 14. In the figure, there are in-phase reactors 20, 21 corresponding to reactor 60 in Fig. 14, and the two pieces are connected in series for their structure. Numerals 22 through 27.identify diodes, which correspond to diode 61 in Fig. 14. Condensers 28 through 30 correspond to condensers 62 - 19 through 64 in Fig. 14. Numeral 31 identify pads for bonding a wire on the bonding pad, 32 identifies wires and 33 a pattern on the main circuit substrate 1. The winding wire of reactor according to this invention is formed by thin wires 32 and patterns 33, the number of turns can be increased even in a small core and the reactor can be formed efficiently. An equivalent circuit is seen in Fig. 4(b).

Figs. 5(a) and 5(b) are views of the reactor and the floating capacitance, wherein Fig. 5(a) shows the case of a single reactor 34 and a single floating capacitance 35 in the conventional art and Fig. 5(b) shows the case of two coils 36, 38 and the related capacitances 37, 39 according to the present invention.

Because the reactor of this invention uses small cores, this coil uses two cores in series in contrast to the case of one core in the conventional arrangement, but the in-line capacity becomes half because of their serial connection as illustrated in Fig. 5(b). Therefore, because of the serial connection, the high frequency wave characteristics can be improved in comparison with the conventional art.

Also, because the wiring for main circuit elements, reactor, etc., can be shortened, the leak reactance Ll 76, L2 78, etc., in Fig. 10 can be reduced, so a filter having better characteristics can be formed.

While a preferred embodiment using the reactor of the present invention as an in-phase reactor has been described above, a power factor improving reactor 79 of Fig. 18 can be actually mounted on the main circuit substrate as shown in Fig. 6. Even in this case, the inductance value can be enlarged and, moreover, the floating capacitance can be decreased for a better heat radiation by dividing the reactor 79 of Fig. 18 into two reactors 40 and 41.

In accordance with the present invention, because parts, such as a reactor, are laid out on the same substrate as the main circuit substrate, the reactor having a small leak reactance and small floating capacitance can be formed, and because of the better heat radiation, a filter of better characteristics can be obtained.

Furthermore, a small reactor having a small leak reactance and small floating capacitance can be formed by using the reactor according to this invention. Moreover, because the core of the reactor is bonded on an insulating substrate, such as a metallic substrate, the heat being generated by the reactor can be radiated efficiently. Thus, a compact and thin invertor unit having a filter with enhanced characteristics can be obtained.

The entire disclosure of each and every foreign patent application from which the benefit of foreign priority has : 21 been claimed in the present application is incorporated herein by reference, as if fully set forth.

Although this invention has been described in at least one preferred embodiment with a certain degree of particularity, it is to be understood that the present disclosure of the preferred embodiment has been made only by way of example and that numerous changes in the details and arrangement of components may be made without departing from the spirit and scope of the invention as hereinafter claimed.

Z 22 - 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 1

Claims (13)

CLAIMS What is claimed is:

1. A reactor of a switching unit comprising:

a metallic printed circuit board comprising an insulating film on a metallic substrate; a conductive pattern formed over said insulating film as a plurality of strips arranged with a stipulated space provided among said strips, said strips having land portions; an insulation material disposed over said conductive strips; a ring shaped iron core, said ring shaped core being disposed over said insulation material, whereby said strips cross under said ring of said iron core; a bonding pad installed conductively to said land portions of saia strips; a plurality of wires each striding over a portion of said iron core and connecting a respective one of said strips with another of said strips via said bonding pads; and thus winding a coil comprising said strips and said wires disposed in a periodic sequence around said ring shaped iron core.

2. A reactor as described in claim 1, wherein said 1 ":. 2

3 - 2 reactor comprises a differential reactor.

1 2 1 2 3 4 6 1 2 3 4 5 6 7 8 9 10 11 3. A reactor as described in claim 1, wherein said reactor comprises a zero phase reactor.

4. A reactor as described in claim 1, wherein said coil winding comprises said plurality of strips and said plurality of wires around said ring shaped iron core, said strips and wires corresponding to a plurality of phase portions in the same direction as that of every phase in order to form an in-phase reactor activating only against an in-phase voltage.

5. A reactor as described in claim 1, wherein said insulation material is operative to insulate said ring shaped iron core and said strips from each other, wherein said iron core via said insulation material is in proximity to a plurality of said strips of said metallic Printed circuit board, wherein said wire striding over said iron core provides a connection between a portion of a first strip disposed outside the ring of said iron core with a portion of a second strip disposed inside the ring of said iron core, said first and second strips being isolated by other of said plurality of said strips.

-:- 24 - 1 2 3 4 5

6 7 8 9 1011 1 2 4 5 6 7 8 9 10 11 12 13 6. An invertor having a - plurality of switching elements for receiving the supply of power from a direct current power source and converting it into an alternating current, comprising: an in-phase filter, said filter comprising a plurality of in-phase reactors installed closely proximate to the output side of said switching elements, said reactors comprising a core disposed over conductive strips with connection wires joinings said strips to form a coil; and a metallic printed circuit board loading said plurality of switching elements.

7. An invertor as set forth in claim 6 wherein at least one of said reactors comprises: a portion of said metallic printed circuit board having an insulating film on a metallic surface; a conductive pattern formed over said insulating film as a plurality of strips arranged with a stipulated space provided among said strips, said strips having land portions; an insulation material disposed over said conductive strips; a ring shaped iron core, said ring shaped core being disposed over said insulation material, whereby said strips cross under said ring of said iron core; - 24 14 is 16 17 18 19 20 21 22 1 2 3 4 6 7 8 9 11 12 13 14 15 a bonding pad installed conductively to said land portions of said strips; a plurality of wires each striding over a portion of said iron core and connecting a respective one of said strips with another of said strips via said bonding pads; and thus winding a coil comprising said strips and said wires disposed in a periodic sequence around said ring shaped iron core.

8. A method of fabricating a reactor comprising: preparing a metallic printed circuit board having an insulating film over a metallic substrate; forming a conductive pattern over said insulating film as a plurality of strips arranged with a stipulated space provided among said strips, said strips having land portions; disposing an insulation material and a ring shaped iron core over said conductive strips, whereby said strips cross under said ring of said iron core; installing a bonding pad conductively to said land portions of said strips; and striding each of a plurality of wires over a portion of said iron core and connecting a respective one of said strips with another of said strips via said bonding pads; --26 - 16 17 18 1 2 3 4 6 1 2 3 1 2 1 2 3 1 2 3 thus winding a coil comprising said strips and said wires disposed in a periodic sequence around said ring shaped iron core.

9. A method of fabricating a reactor as set forth in claim 8, wherein said winding step is conducted such that said strips and wires correspond to a plurality of phase portions in the same direction as that of every phase in order to form an in-phase reactor activating only against an in- phase voltage.

10. A method of fabricating a reactor as set forth in claim 9, wherein said insulation material is coated on said core.

11. A reactor as set forth in claim 1, wherein said insulation material is coated on said core.

12. A reactor substantially as herein described with reference to Figures 1 to 5 or Figure 6 of the accompanying drawings.

13. A method of fabricating a reactor substantially as described with reference to Figures 1 to 6 of the accompanying drawings.

1