Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For transformer
Reexamination Certificate
2000-08-16
2001-10-09
Gaffin, Jeffrey (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For transformer
C361S752000, C361S753000, C361S774000, C336S090000, C336S192000
Reexamination Certificate
active
06301127
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circuit block for power supply, such as a switching power supply or AC/DC converter, which is incorporated into electronic equipment, such as TV or VTR.
2. Description of the Prior Art
There is a demand of the times that the so-called household electrical appliances, such as TV, VTR, or mini-component stereo system, have more compact size and higher performance. Therefore, it is required to increase the packaging density of components of household electrical appliances.
However, as shown in
FIG. 4
, conventionally, when configuring a circuit block for a power supply comprising a small transformer, which is used as a switching power supply or the like, the circuit block is configured in such a manner that a transformer
21
is mounted on a mounting substrate
20
for power supply via its primary-side (i.e. its input side) pin terminals
22
and secondary-side (i.e. its output side) pin terminals
23
, components, such as a control IC
24
, a FET
25
, and other appropriate electronic chip components
26
,
27
, which constitute a primary-side circuit are mounted on the mounting substrate
20
, and secondary-side components, such as a capacitor
28
, are mounted on the side of the secondary-side pin terminals
23
, the opposite side of the primary side where the primary-side components are mounted.
FIG. 5
shows an example of a feedback circuit from the secondary-side-to the primary-side. The circuit is configured in such a manner that a photocoupler
29
is mounted on the substrate
20
via its terminals, the primary-side circuit components, such as a transistor
30
, are mounted on one side of the photocoupler, and the secondary-side circuit components, such as a transistor
31
and diode
32
, are mounted on the opposite side of the photocoupler.
In such a case, a safety standard for power supply circuit, such as a switching power supply, requires that it be ensured that there is a prescribed distance between the primary-side pin terminals and the secondary-side pin terminals. The distance is prescribed for their creeping and spatial distances. The spatial distance of these distances can be reduced by interposing an insulating plate (not shown) between the primary-side and secondary-side pin terminals to the order of 0.8 mm depending on the thickness of the insulating plate.
However, with regard to the creeping distance, in the conventional circuit block for power supply shown in
FIG. 4
, the distance between the primary-side pin terminals
22
for input and the secondary-side pin terminals
23
for output is required to be 10 mm in terms of insulation, and in addition, the input-side electronic components, such as control IC
24
, are not able to be mounted within 10 mm from the output-side pin terminals
23
, so that the miniaturization and high density mounting have been constrained. The same thing can be said for the feedback circuit incorporated in the power supply circuit, shown in
FIG. 5
, and the distance between the terminals is required to be 10 mm.
In order to overcome the above-described drawback, the present applicant has already filed the Japanese Patent Application No. 11-028013 on Feb. 5, 1999.
FIG. 6
is a longitudinal section showing diagrammatically a circuit block for power supply produced based on the patent application.
FIG. 7
is an enlarged view of the portion where a terminal
120
is inserted into a terminal insertion hole (not shown) of the mounting substrate
20
.
This circuit block for power supply is configured as follows. A small transformer
300
is configured by winding a coil
80
around a coil bobbin
60
, and incorporating a core
90
into the coil bobbin
60
. Flanges
70
are provided at both ends of the coil bobbin
60
, and a primary-side pin terminals
110
and secondary-side pin terminals
120
are embedded into thick portions
100
provided at the lower portions of the flanges, respectively. Each of the pin terminals
110
,
120
is inserted into the terminal insertion hole (not shown) of the mounting substrate
20
. On the mounting substrate
20
, a control IC
40
and various electronic components
50
are mounted. An assembly configured by these elements is housed in a case
130
having an open bottom and formed from a molded insulation.
In the circuit block for power supply configured as described above, the coil
80
of the small transformer
300
consists of a primary coil and secondary coil, and it is necessary to ensure the insulation in the region of the coils, and between the primary-side pin terminals
110
and secondary-side pin terminals
120
of the small transformer
300
, etc.
For this purpose, the case
130
is filled with an insulating resin
140
, such as an epoxy resin, by a vacuum filling.
With the vacuum filling, the space between the primary-side pin terminals
110
and secondary-side pin terminals
120
is filled with the resin
140
without any bubble remaining, and the resin
140
enters into between the electronic components and between wires of the coil
80
, so that a sufficient insulating effect can be provided to insulate the components with respect to each other.
According to the Japanese Patent Application No. 11-028013, in which the case
130
is filled with the resin
140
by the vacuum filling, the insulation is enhanced so that advantages, for example, as described below are provided.
a. Since the primary coil and secondary coil can be brought close to each other, the magnetic coupling is enhanced, thereby the characteristics of the small transformer
300
can be expected to be improved.
b. As a result, the size of the portion of the coil
80
of the small transformer
300
can be reduced, so that the miniaturization becomes possible.
c. Since the distance between the primary-side pin terminals
110
and secondary-side pin terminals
120
of the small transformer
300
can be reduced, the miniaturization becomes possible, and since the electronic components can be placed at the space between the terminals, the mounting area can be reduced, so that the miniaturization also becomes possible in this respect.
d. The insulating plate conventionally used is not necessary. Therefore, miniaturization that is better than was previously possible can be attained.
However, in the circuit block for power supply configured as described above, since the volume of the resin
140
filling the case
130
is reduced when the resin is hardened, so that a residual stress is generated in the resin after the resin is hardened, and furthermore in the case where a temperature cyclic test, such as thermal shock test, is performed on the product, the residual stress and stresses due to the thermal expansion and contraction of the resin
140
is applied to the mounting substrate
20
, there is a problem of cracks that occur at the soldering parts “a” situated around the roots of the input pin terminals
110
and output pin terminals
120
projecting downwardly from the mounting substrate
20
, as shown in
FIG. 6
by “a”.
In particular, in the circuit block for power supply configured as shown in
FIG. 6
, the pin terminals
120
is press fitted into the thick portion
100
of the coil bobbin
80
. In such a case, as shown in
FIG. 7
, a cavity “b” is inevitably produced at the internal end of the press fitted pin terminals
120
. Although the length of the cavity is on the order of 0.3 mm at the minimum, the pin terminals are further press fitted into the interior by the residual stress and stresses due to the thermal expansion and contraction of the resin
140
applied to the pin terminals
120
themselves. This becomes “a” cause of the occurrence of cracks at the soldering parts a of the mounting substrate
20
.
And, an outgoing line
80
′ from the coil
80
is wrapped around the pin terminals
120
(
110
). As shown in
FIG. 7
, in order to handle the outgoing line
80
′, there is no other choice but to provide a clearance “g” between the lower surface of the thick portion
100
of the coil bobbin
60
and the upper
Dinh Tuan
Gaffin Jeffrey
LaPointe Dennis G.
Mason & Associates P.A.
Tamura Corporation
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