Line filter

A line filter arranged in such a manner that a foil conductors are used as the coil conductor and the shield plate, and a reactor is formed therein by laminating and winding the foil conductor and the shield plate with an insulating material held therebetween. A line filter arranged in such a manner that a pair of coil blocks connected to each other in parallel is provided on the iron core leg is included in the scope of the invention. Each of the coil blocks is structured in such a manner that the coil conductor and the shield plate made of the foil conductors are stacked and wound via the insulating material. A structure is included within the scope of the invention, the structure having a plurality of filter mechanisms connected to one another in series, each of the filter mechanisms being constituted by a pair of coil blocks connected to each other in parallel.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a line filter to be inserted into the 
input portion or the output portion of a power source (a single-phase 
power source). 
2. Description of the Related Art 
FIGS. 1 and 2 respectively illustrate a conventional line filter disclosed 
in, for example, "Noise Technology for Electronic Circuit", p.p 116, 
edited by Yamazaki and published by Ohm Corp. FIG. 1 illustrates an 
equivalent circuit in an electrical view point and FIG. 2 illustrates an 
example of the structure of the conventional line filter. FIG. 1 
illustrates a combination of a filter reactor 15 and a capacitor 16 for 
bypassing a noise current. FIG. 2 illustrates the reactor 15 shown in FIG. 
1 and arranged in such a manner that two coils 17 and 18 are wound around 
a core 19, the two coils 17 and 18 being wound symmetrically with respect 
to the center of the core 19. 
In the reactor 15 constituted as described above, although a signal common 
to the electric circuit does not affect the polarities of the two coils 
wound as described above, the noise of the same phase is inhibited. Noise, 
which has passed through the reactor coils 17 and 18 after inputted from 
input terminals K and L, is bypassed by the capacitor 16 so that the 
generation of the noise in the load side terminals k and l is prevented. 
In this case, the capacitor 16 is connected to the reactor 15 via lead 
wires. 
Since the conventional line filter has been constituted as described above, 
an inductance is undesirably generated due to the presence of the lead 
wires which are used to connect the capacitor. Therefore, the capacitor 
may not work as desired in a high frequency range. What is even worse, 
since the lead wire for establishing the connection of the external 
capacitor must be shortened, the connection cannot be easily completed. 
Another problem arises in that the capacitor must have excellent high 
frequency characteristics. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a line filter 
capable of overcoming the above-described problems and exhibiting an 
excellent effect of suppressing high frequency noise without a necessity 
of connecting an external capacitor. 
In order to achieve the above-described object, an aspect of the invention 
lies in a line filter comprising: an iron core; two coil conductors 
laminated and wound around the iron core, each of the two coil conductors 
being in the form of a foil conductor; and a shield plate inserted between 
the two coil conductors via an insulating material and wound around the 
iron core together with the coil conductors, the shield plate also being 
in the form of a foil conductor and grounded, wherein the coil conductors 
constitute coils and a capacitor is formed between the coil conductor and 
the shield plate. 
A line filter according to the present invention is arranged in such a 
manner that foil conductors are used as the coil conductor and the shield 
plate, and the coil of a reactor is formed therein by laminating the foil 
conductor and the shield plate alternately with an insulating material 
held therebetween and then winding them around the iron core. 
In the line filter according to the present invention, the eddy current 
loss due to the high frequency can be reduced. Furthermore, the 
electrostatic capacity obtainable between the foil conductors is utilized 
so as to make a capacitor for the line filter. That is, the capacitor is 
formed by the coil conductor and the shield plate laminated via the 
insulating material and respectively made of the foil conductors. 
A line filter, arranged in such a manner that a pair of coil blocks 
connected to each other in parallel is provided on a iron core leg, is 
included in the scope of the invention. Each of the coil blocks is 
structured in such a manner that the coil conductors and the shield plate 
respectively made of the foil conductors are laminated alternately via the 
insulating material and wound around the core leg. 
Furthermore, a structure is included within the scope of the invention, the 
structure having a plurality of filter mechanisms connected to one another 
in series, each of the filter mechanisms being constituted by a pair of 
coil blocks connected to each other in parallel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of the present invention will be described with reference to 
the drawings. 
FIG. 3 illustrates an equivalent circuit of a line filter according to an 
embodiment of the present invention. 
The line filter comprises coils 1a and 2a wound around an iron leg 5 and a 
shield plate 7 which is also wound together with the coils 1a and 2a. In a 
case where the line filter is inserted into the output portion of the 
power source, input terminals 11 and 12 are connected to the power source 
and terminals 13 and 14 are connected to the load side. In this case, the 
shield plate 7 is grounded. FIG. 4 is a plan view which illustrates a 
specific structure of the line filter. A coil block 30, which is 
manufactured by winding the stacked coils 1a and 2a shown in FIG. 3, is 
provided on one of the iron core legs 5 of the core type double leg core 
15. FIG. 5 is a cross sectional view which illustrates the coil block 30 
taken along line V--V of FIG. 4. FIG. 6 illustrates the structure of the 
coils 1a and 2a which are laminated together with the shield plate 7 and 
insulating material 20 so as to form the coil block 30. As is shown from 
the above-described drawings, the coils 1a and 2a which are laminated as 
described above and the shield plate 7 which is inserted between the two 
coils 1a and 2a are respectively made of foil conductors. The coil block 
30 is formed by winding the lamination structure shown in FIG. 6 around 
the iron core leg 5, the lamination structure being a structure 
manufactured by inserting the shield plate 7 between the coils 1a and 2a 
via an insulating material 20. The coils 1a, 2a and the shield plate 7 of 
the coil block 30 are closely wound around the iron core leg 5 so as to 
prevent the generation of a gap in the portion in which they are 
laminated. 
Since the line filter thus structured employs the foil conductors serving 
as the coils, the eddy current loss due to the high frequency factor can 
be reduced. Therefore, an efficient reactor can be realized. Furthermore, 
since there is a large coupling area in the flat portion between the coil 
conductor and the shield plate, an electrostatic capacity, that is, a 
capacitor can be formed. Therefore, the undesirable inductance, taken 
place due to the presence of the lead wire used in the case where the 
external capacitor is connected in a conventional structure, can be 
eliminated. As a result, the external capacitor can be omitted from the 
structure. Consequently, a line filter exhibiting excellent high frequency 
characteristics without a necessity of providing an external capacitor can 
be realized. 
FIG. 7 illustrates an equivalent circuit of the line filter according to a 
second embodiment of the present invention. The line filter comprises 
coils 1a, 1b, 2a, 2b wound around the iron leg 5 and the shield 7 which 
are also wound around the leg 5 together with coils. The coils 1a and 1b, 
respectively serving as first and third coil conductors, are connected to 
each other in parallel. The coils 2a and 2b, respectively serving as 
second and fourth coil conductors, are also connected to each other in 
parallel. FIG. 8 is a plan view which illustrates the specific structure 
of the second embodiment shown in FIG. 7. The first coil block 30, which 
is manufactured by winding the laminated coils 1a and 2a shown in FIG. 7, 
and a second coil block 31, which is manufactured by winding the laminated 
coils 1b and 2b, are provided on one of the iron core legs 5 of a core 
type double leg core 15. The above-described two coil blocks 30 and 31 
must have the same structure in terms of the dimension, the number of 
turns, the winding direction and other factors. Furthermore, the structure 
of the each coil blocks 30, 31 is arranged to be the same as that 
according to the first embodiment of the present invention shown in FIGS. 
5 and 6. 
In the line filter according to this embodiment, which is structured in 
such a manner that a pair of coil blocks are connected to each other in 
parallel, noise factors respectively inputted to the input terminals 11 
and 12 can be compensated each other since the two coil blocks 30 and 31 
are disposed symmetrically to each other. Therefore, the iron core 15 is 
not affected by the leakage flux. Furthermore, either of the two terminals 
11 and 12 may be used as the grounding potential line. According to this 
embodiment, the same effect obtainable according to the first embodiment 
can, of course, be obtained. 
FIG. 9 illustrates an equivalent circuit of the line filter according to a 
third embodiment of the present invention. According to this embodiment, 
two above-described line filters according to the second embodiment are 
connected in series so that a two-stage filter is constituted. That is, 
the first filter comprises coils 1a, 1b, 2a and 2b wound around the iron 
core leg 5, while the second filter comprises coils 3a, 3b, 4a and 4b 
wound around the iron core leg 6. Furthermore, the coils 1a and 1b of the 
first filter are, in series, connected to the coils 3a and 3b of the 
second filter. The coils 2a and 2b of the first filter are, in series, 
connected to the coils 4a and 4b of the second filter. FIG. 10 is a plan 
view which illustrates a specific structure of the third embodiment shown 
in FIG. 9. The coil block 30, manufactured by winding the laminated coils 
1a and 2a shown in FIG. 9, and the second coil block 31, manufactured by 
winding the laminated coils 1b and 2b, are provided on one of the iron 
core legs 5 of the core type double leg core 15. As a result, the first 
filter is constituted. A coil block 32, manufactured by winding the 
laminated coils 3a and 4a shown in FIG. 9, and a coil block 33, 
manufactured by winding the laminated coils 3b and 4b, are provided on the 
other iron core leg 6 of the core type double leg core 15. As a result, 
the second filter is constituted. The structure of each of the 
above-described coil blocks 30 to 33 is arranged to be the same as that 
according to the first embodiment of the present invention shown in FIGS. 
5 and 6. Furthermore, as described according to the second embodiment, the 
above-described coil blocks 30 and 31, as well as coil blocks 32 and 33 
must have the same structure in terms of the dimension, the number of 
turns, the winding direction and other factors respectively. Furthermore, 
the shield plates 7 which are rolled in respective coil blocks 30 to 33 
are connected to one another and then grounded. 
As described above, according to this embodiment, a two-stage filter is 
constituted in such a manner that two filter mechanisms are connected to 
each other in series, each of the two filter mechanisms being structured 
by providing a pair of coil blocks (for example, the coils blocks 30 and 
31) on the iron core leg. As a result, the filtering effect of the line 
filter can be further improved. Furthermore, the effect obtainable 
according to the first and the second embodiments can, of course, be 
obtained. 
According to the third embodiment, another structure may be employed which 
is arranged in such a manner that the iron core comprises three or more 
iron core legs each of which has the above-described filter mechanism and 
the filter mechanisms are connected to one another in series.