FBT, its bleeder resistor, and device for coupling bleeder resistor

An FBT (fly-back transformer), its bleeder resistor (installed on the top of the FBT), and a device for coupling the bleeder resistor are disclosed. The bleeder resistor 100 is accommodated within a resistor case 180, and the resistor case 180 is installed on the top of an FBT case 110. A resistor pattern 140 is printed on the substrate 130 of the bleeder resistor 100. Openings 150 are formed within the wavy portions of the resistor pattern 140, and the resistor case 180 has a plurality of isolating sheets 160 within its interior 170, so that the isolating sheets 160 can be inserted into the openings 150. When manufacturing the bleeder resistor, the glass coating, the baking, the epoxy resin dipping are eliminated, but the voltage breakdown resisting property is improved. Further, the manufacturing cost is lowered owing to the simplification of the process.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an FBT (fly-back transformer), its bleeder 
resistor (installed on the top of the FBT), and a device for coupling the 
bleeder resistor, the FBT being for generating a high voltage in cathode 
ray tube for use in television, monitor or the like. Particularly, the 
present invention relates to an FBT, its bleeder resistor, and a device 
for coupling the bleeder resistor, in which two or more openings are 
formed adjacently to a resistance pattern on a substrate, and the first 
and second openings are formed alternately and mutually facingly. Further, 
the sum total of the lengths of the first and second openings is made 
larger than the average distance between the first and second openings. 
Thus, when manufacturing the non-coated bleeder resistor, there are not 
needed the glass coating, the baking, the dipping into the epoxy resin, 
and the curing. Notwithstanding, the voltage resistant property is 
reinforced, and the manufacturing process is simplified. Thus the bleeder 
resistor can be manufactured in an easy manner with a decreased cost. 
2. Description of the Prior Art 
Generally, the conventional bleeder resistor is manufactured in the 
following manner. That is, as shown in FIG. 1, there is prepared a ceramic 
substrate 10 made of Al.sub.2 O.sub.3 having a purity of about 96%. Its 
thickness is about 0.5-1.2 mm, and its area is 400-1500 mm.sup.2. Upon the 
ceramic substrate 10, there is printed PbAg, PtAg, Ag or their combination 
paste. Then the printed substrate is baked at a temperature of about 
800.degree. C., and thus, a printed circuit board is formed, and then lead 
wires are soldered. Then RuO.sub.2 is printed thereupon, and then the 
structure is baked at a temperature of about 850.degree. C. Thus a 
resistor having a certain thickness is completed. 
Meanwhile, in this resistor, electric current can flow only if the 
electrical resistance per unit length of the resistor is smaller than the 
air contact electrical resistivity. In the case where the voltage 
breakdown resistivity of air is 0.5 KV/mm, if a voltage of 20 KV is 
supplied across a resistor 12, there has to be secured a distance of 20 
KV.div.0.5 KV/mm=40 mm. Further, if the thermal degradation and the 
environmental factors are taken into account, then the safe distance must 
be 1.8 times as large as the above distance, that is, 40 mm.times.1.8=72 
mm. Meanwhile, in the case where the resistor 12 is printed on the ceramic 
substrate 10 in a straight line, the length of the ceramic substrate has 
to be longer, with the result that the total bulk of the ceramic substrate 
becomes too large. 
Therefore, the resistor 12 on the ceramic substrate 10 has to be made 
curved, so as to reduce the bulk of the ceramic substrate 10. In this 
case, however, the potential difference over per unit length of the curved 
pattern exceeds the straight line voltage breakdown resisting distance 0.5 
KV/mm. If the environmental factors and the thermal degradation are taken 
into account, the potential difference per unit length far more exceeds 
the air voltage breakdown resisting distance, with the result that glow 
discharges may occur between the curved patterns. Therefore, 
conventionally after forming the curved resistor, the resistor patterns 
are insulated by a glass coating, and then, a sealed baking is carried 
out, thereby preventing the occurrence of the glow discharges. 
Meanwhile, although the glass coating can insulate the patterns, the 
moisture and the thermal impact during the curing of the crystalline epoxy 
resin weakens the insulation, or damage the bleeder. Therefore, a dipping 
into the epoxy resin is carried out after the glass coating. 
However, the bleeder resistor manufactured in the above method is 
accompanied by the following disadvantages. 
First, the resistor 12 is printed upon the ceramic substrate 10, then a 
glass coating is carried out, then a baking is carried out, then the epoxy 
resin 15 is coated, and then its curing is carried out. Therefore, due to 
this complicated manufacturing process, the productivity is lowered, and 
the manufacturing cost rises. 
Second, the resistor 12 is printed upon the ceramic substrate 10, then a 
glass coating is carried out to insulate the resistor patterns, then a 
baking is carried out, then the epoxy resin 15 is coated, and then its 
curing is carried out. Therefore, the characteristics of the printed 
resistor 12 are degraded, and the resistance error fluctuation rate is 
increased. 
Third, due to the continued baking, the grains of the resistor are 
continuously rearranged, and therefore are easily deranged. Therefore, the 
surface of the resistor becomes rough and sharp, with the result that the 
resistance against the voltage breakdown steeply drops. 
Fourth, the resistance error become higher as described above, and 
therefore, to cater to the consumers, incomplete products are discarded. 
Ultimately, the product price has to be decided higher. 
Fifth, due to the use of glass and soft epoxy resin, the material cost is 
increased, with the ultimate result that the price is further increased. 
FIGS. 2A-2E illustrate various examples of the conventional bleeder 
resistors. The total area of the ceramic substrate 10 on which the 
resistor is printed is dipped into the molten epoxy resin to coat the 
substrate. FIG. 2A illustrates a bleeder resistor having three lead lines 
14, the lead lines being connected by soldering. Therefore, this resistor 
has the above described disadvantages. FIG. 2B illustrates a bleeder 
resistor in which the resistor patterns are formed very densely, and only 
one face of the ceramic substrate is coated. 
FIG. 2C illustrates another conventional bleeder resistor in which only a 
part of one face of the ceramic substrate is coated with silicon. FIG. 2D 
illustrates a bleeder resistor in which a focus volume substrate is formed 
integrally, the resistor 12 is coated with an epoxy resin, and an opening 
is formed at a part of the substrate. FIG. 2E illustrates an example in 
which the focus volume substrate is integrally formed (it is not a bleeder 
resistor), and the straight distance between the openings (which are for 
insulating the patterns) is smaller than the width (W) of the ceramic 
substrate. 
In the above described conventional techniques, there are the above 
described disadvantages due to the adoption of the glass coating and the 
soft epoxy coating. Besides, even if there are openings, glow discharges 
occur between the patterns all the same when the voltage rises to the 
rated level. Further, as described above, the complicated processes bring 
the lowering of the workability and the productivity. 
SUMMARY OF THE INVENTION 
The present invention is intended to overcome the above described 
disadvantages of the conventional techniques. 
Therefore it is an object of the present invention to provide an FBT and 
its bleeder resistor, in which the glass coating, the baking, the dipping 
into the epoxy resin, and its curing are all eliminated, but the voltage 
breakdown resisting property is improved, and the product can be easily 
manufactured owing to the simplification of the manufacturing process. 
It is another object of the present invention to provide a bleeder resistor 
and a coupling device for the bleeder resistor, in which openings are 
formed between wavily curved resistor patterns so as to prevent glow 
discharges at a high voltage, and the bleeder resistor is inserted into a 
casing to perfectly insulate the resistor patterns, thereby improving the 
electrical characteristics of the bleeder resistor. 
In achieving the above objects, the FBT bleeder resistor according to the 
present invention includes: a substrate, and a wavily curved resistor 
pattern formed on the substrate. The FBT bleeder resistor further 
includes: one or more pairs of openings formed in the substrate, each pair 
of the openings consisting of a first opening and a second opening; the 
first opening being open at on e edge of the substrate; the second opening 
being open at an opposite edge of the substrate; the first and second 
openings extending laterally on the substrate; and a sum total of lengths 
of the first and second openings being larger than an average width of the 
substrate between the first and second openings. 
In another aspect of the present invention, the FBT bleeder resistor 
coupling device according to the present invention includes: a bleeder 
resistor; a resistor case for receiving the bleeder resistor having 
openings alternately and mutually facingly arranged; isolating sheets 
formed within the resistor case, for being inserted into the openings of 
the bleeder resistor, and projecting above the bleeder resistor; and a lid 
for covering the top of the resistor case, after the insertion of the 
bleeder resistor into the case. 
In still another aspect of the present invention, the FBT according to the 
present invention includes: high voltage and low voltage bobbins, with 
coils being wound thereon for generating a high voltage; an FBT case for 
accommodating the high voltage and low voltage bobbins and filled with an 
insulating resin; a bleeder resistor including a resistance pattern; a 
bleeder resistor substrate having one or more pair of adjacently disposed 
first and second openings, the first opening being open at one edge of the 
substrate, the second opening being open at the opposite edge of the 
substrate, and a sum total of lengths of the first and second openings 
being larger than an average width of the substrate between the first and 
second openings; the resistance pattern extending wavily between the first 
and second openings; a resistor case for receiving the bleeder resistor, 
and having a plurality of isolating sheets for being inserted into the 
openings of the bleeder resistor and projecting above the bleeder 
resistor; and a lid for covering the top of the resistor case, after the 
insertion of the bleeder resistor into the case.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 3 is an exploded perspective view showing the FBT, the bleeder 
resistor and the lid according to the present invention. FIG. 4 is a 
perspective view showing the bleeder resistor according to the present 
invention. 
Inside the FBT of the present invention, there are high voltage and low 
voltage bobbins with coils would thereon. An FBT case 110 accommodates the 
high voltage and low voltage bobbins, and contains an insulating resin for 
insulating the high voltage and low voltage bobbins. On the top of the FBT 
case 110, there are installed a resistor case 180. The resistor case 180 
accommodates a bleeder resistor 100 which includes a substrate 130 and a 
resistor pattern 140 formed on the substrate 130. The resistor case 180 is 
covered with a lid 210. 
As shown in FIGS. 4 and 5, the bleeder resistor 100 is formed such that a 
resistor pattern 140 is printed on the substrate 130, and that first and 
second openings 150 and 150' are formed alternately mutually facingly 
within the wavy portions of the resistor pattern 140. 
That is, one or more pairs of the first and second openings 150 and 150' 
are formed adjacently to each other on the substrate 130. The first 
opening 150 is open at one edge of the substrate 130. 
The second opening 150' is open at the opposite edge of the substrate 130, 
and the first and second openings 150 and 150' are formed laterally in the 
substrate 130. The sum total (L.sub.1 +L.sub.2) of the lengths of the 
first and second openings 150 and 150' is made larger than an average 
substrate width Ws between the first and second openings 150 and 150'. 
As shown in FIG. 3, on the top of the FBT case 110, there is installed a 
resistor case 180, and the resistor case 180 has a plurality of isolating 
sheets 160 within the interior 170 of the resistor case 180, so that the 
isolating sheets 160 can be inserted into the openings 150 and 150'. As 
shown in FIG. 6, a lid 210 is coupled to the resistor case 180, and has a 
plurality of insertion grooves 200, so that the lid can be coupled to the 
resistor case 180. The insertion grooves 200 are formed by the surrounding 
walls 190. 
The present invention constituted as above will now be described as to its 
action and effects. 
As shown in FIGS. 3 to 6, the resistor case 180 is installed on the top of 
the FBT case 110, and the bleeder resistor 100 is installed within the 
resistor case 180. On the substrate 130 of the bleeder resistor 100, there 
is printed a wavy (sweep) resistor pattern 140. Within the adjacent wavy 
portions of the resistor pattern 140, there are formed openings 150 and 
150' of a certain depth, and the openings are for insulation. 
As shown in FIG. 4, within the wavy portions of the resistor pattern 140 
which is printed on the substrate 130 of the bleeder resistor 100, there 
are formed at least one or more pairs of the first and second openings 150 
and 150'. Further, the first opening 150 is open at one edge of the 
substrate 130, and the second opening 150' is open at the opposite edge of 
the substrate 130. 
The first and second openings 150 and 150' are formed laterally in the 
substrate 130, and the sum total (L.sub.1 +L.sub.2) of the lengths of the 
first and second openings 150 and 150' is made larger than the average 
substrate width Ws between the first and second openings 150 and 150'. 
Thus through between the oppositely open first and second openings 150 and 
150', the resistor pattern 140 can be printed in a wavy (sweep) form. Thus 
sufficient insulating distances are secured, and more reinforced 
insulation is ensured owing to the openings 150 and 150'. 
FIG. 5 is a perspective view showing another embodiment of the bleeder 
resistor according to the present invention. In this case, the width of 
the substrate 130 is not constant, but the pairs of the first and second 
openings 150 and 150' are properly formed laterally in the substrate 130. 
Further, the sum total (L.sub.1 +L.sub.2) of the lengths of the first and 
second openings 150 and 150' is made larger than the average substrate 
width Ws between the first and second openings 150 and 150'. 
As shown in FIG. 3, if the bleeder resistor 100 is to be conveniently 
installed on the top of the FBT case 110, the resistor case 180 having the 
isolating sheets 160 has to be installed on the top of the FBT case 110. 
The resistor case 180 not only secures the bleeder resistor 100 but also 
reinforces the insulating characteristics of the bleeder resistor 100. 
That is, a plurality of the isolating sheets 160 are formed within the 
resistor case 180, so that the isolating sheets 160 can be precisely mated 
with the openings 150 and 150'. Thus not only the bleeder resistor 100 can 
be firmly secured, but also the wavy portions of the printed resistor 
pattern 140 can be perfectly insulated from each other. Here the height of 
the isolating sheets 160 has to be larger than the thickness t of the 
substrate 130. 
Meanwhile, as shown in FIG. 6, the lid 210 is for covering the resistor 
case 180, and the lid 210 has a plurality of surrounding walls 190 to form 
a plurality of insertion grooves 200. After the bleeder resistor 100 is 
installed within the resistor case 180, the lid 210 is fitted to the 
resistor case 180, with the isolating sheets 160 being closely mated with 
the insertion grooves 200 of the lid 210. 
Therefore, if a high voltage is supplied to an input terminal of the 
resistor pattern 140 (which is printed on the ceramic substrate 130), the 
voltage drops across the resistor pattern 140. Under this condition, glow 
discharges do not occur owing to the isolating sheets 160 which come 
between the wavy portions of the resistor pattern 140. 
For example, if a voltage of 20 KV(dc) is supplied to the input terminal 
120 of the resistor pattern 140, and if the ceramic substrate 130 has a 
width of 10 mm and a length of 30 mm, then the total length of the 
resistor pattern 140 becomes 80 mm. If the air voltage breakdown resisting 
limit of 0.5 KV/mm and the environmental factors and the thermal 
degradation are taken into account, then a factor of 1.8 is needed. That 
is, 0.5 KV/mm.div.1.8 KV/mm=0.28 KV/mm has to be maintained, and 
therefore, 20 KV(dc).div.0.28 KV/mm=71.4 mm is needed. Meanwhile the 
resistor pattern 140 has a length of 80 mm, and therefore, a sufficient 
resistance is ensured. Further, the wavy portions of the resistor pattern 
140 are isolated by the isolating sheets 160, and therefore, any glow 
discharge can be prevented. 
Thus a perfect insulation is achieved, and therefore, the conventional 
glass coating becomes needless. Therefore, the bleeder resistor can be 
used under the air, and therefore, the conventional resin dipping which 
causes cracks needs not be carried out. 
In order to prevent the intrusion of moisture, a final sealing is carried 
out after installing the bleeder resistor and after fitting the lid 210 to 
the resistor case 180. The final sealing is carried out by dipping the 
completed FBT into epoxy resin, thereby perfectly insulating the FBT from 
the outside. Thus the bleeder resistor is not influenced by the 
contraction phenomenon of the conventional epoxy resin coating. Further, 
the final coating such as glass coating and epoxy resin dipping has to be 
done even on the soldered lead lines. Further, the input terminal 120 and 
the output terminal 120' of the resistor pattern 140 can be made of a 
contact spring or an insulating rubber. 
According to the present invention as described above, when manufacturing 
the bleeder resistor of the FBT, the glass coating, the baking, the soft 
epoxy resin dipping and the curing are eliminated. However, the voltage 
breakdown resisting property is improved. The simplification of the 
manufacturing process makes it possible to manufacture the bleeder 
resistor in an easy manner, and the manufacturing cost is significantly 
lowered. Further, the openings are formed within the wavy portions of the 
curved resistor pattern on the substrate, and therefore, any glow 
discharge can be prevented. The bleeder resistor with the openings formed 
is accommodated within the resistor case having isolating sheets, in such 
a manner that the isolating sheets are inserted into the openings of the 
bleeder resistor. Thus the wavy portions of the curved resistor pattern 
are perfectly insulated from each other, thereby further improving the 
electrical characteristics of the bleeder resistor.