JPH03220707A - Manufacture of switching transformer - Google Patents

Abstract

PURPOSE:To reduce a variation in a hysteresis loop and an increase in an iron loss by incorporating a transformer in an outer case, filling ore filler in the case, then pouring liquidlike insulation oil, and heating to cure the resin. CONSTITUTION:After a transformer 5 formed of a coil wound on a spool and a ferrite core is contained in a case 6, it is preheated, dried and metered ore filler 27 is filled in the case. On the other hand, debubbled and metered main agent 28 and curing agent 29 are mixed, vacuum-filled to invade into gaps of the particles of the agent 27, and then thermally cured. Thus, since a stress to the core is reduced, reverse effect of magnetostrictive ferrite core is eliminated and both the core and the coil can be buried in the insulation resin, thereby reducing temperature rise of the switching transformer.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a switching transformer that is a component of a switching regulator used as a power source for various machines and devices.

Conventional technology In recent years, small, lightweight, and highly efficient power supplies have been developed. Switching regulators, which have a characteristic of

Conventionally, the switching transformer used in this switching regulator was assembled by winding a magnet wire around a bobbin and inserting a ferrite core as a coil P, or by storing only the coil P of the transformer in a case and encasing it in an insulating resin. There was one in which the ferrite core was injected, heated and hardened, and then assembled by taking the ferrite core out of the case. The former is 24V, 12V, 5V for internal devices such as BHT computers, word processors, facsimile machines, copying machines, etc.
The latter was often used in high-voltage power supplies that supplied high DC or AC voltage to corotrons in copying machines, or in flyback transformers in television receivers. The configuration will be described below with reference to FIGS. 8 to 16.

FIGS. 11a and 11b are a front view and a side view of a conventional switching transformer. Figure 12 shows the flow 3.8. .

The ferrite core 1 is assembled by inserting the ferrite core 1 into a coil 2 wound around a bobbin 3, and is mounted on a 5-metal gold printed circuit board (not shown), and is electrically connected to the circuit on the printed circuit board through a terminal 4. Do S. The biggest problem with this switching 1-lance is the generation of heat due to iron loss and copper loss, and due to the structure, there is a lot of space between the ferrite core 1 and the coil 2 button and inside the coil 2, so heat dissipation is poor. There was a problem.

Therefore, the transformer 6 has a large shape in order to reduce the temperature rise therein. Figure 13a.

In b, the transformer 6 is housed in the case 6 and an insulating resin 7 is injected into the case 6 (vacuum injection or normal pressure injection) in order to fill the space inside the transformer and increase the thermal conductivity and at the same time increase the heat dissipation area. ), but due to the reverse effect of magnetostriction of the ferrite core 1, the hysteresis loop changes greatly, resulting in an increase in iron loss. What is the reverse effect phenomenon of magnetostriction? When a ferrite core 1 is surrounded by an insulating resin 7 with a different coefficient of linear expansion and the temperature changes, stress is applied to the ferrite core 1 due to the difference in dimensions, which affects the magnetization characteristics of the ferrite core 1. is to change. FIG. 8 and FIG. 10 are examples showing the characteristics of this state. Figure 8 compares the hysteresis loops that occur before and after insulating resin injection and curing.
becomes smaller, the area becomes larger, and iron loss increases.

Also, Figure 1o shows the temperature characteristics of iron loss. At each temperature (especially as the temperature decreases), the iron loss after injection hardening increases significantly. If the iron loss increases significantly as described above, even if the heat dissipation effect is improved by the insulating resin 7, the heat generation will become even larger and the efficiency will decrease, making it almost impossible to put it into practical use. Of course, coil 2
If it is only cast, there will be no adverse effect of magnetostriction, but the effect of reducing temperature rise cannot be expected at all.

On the other hand, FIGS. 14 and 15 show switching lances in which insulating resin is injected and hardened as a necessary condition because the coil is subjected to extremely high voltage. Figure 14 shows a flyback transformer used in color television receivers, black and white television receivers, etc. A primary coil 9 is wound around the primary bobbin 8, a secondary coil 11 is wound around the secondary bobbin 1o, and the coils are housed in a fitting case 12, and then the ferrite core 13 is inserted into the coil 9.11 to assemble. The important thing here is ferrite core 13
is outside Case 12. In this state, the insulating resin 14 is injected and hardened. In addition, the secondary coil 11 of the flyback transformer has approximately 12
~14KV, about 25-30KV for color television receiver
A high-frequency electric field of KV is generated. FIG. 15 shows a switching lance used in a high voltage power supply for a copying machine. 1
The primary coil 16 is wound around the next bobbin 16, and the secondary bobbin 1
After winding and fitting the secondary coil L/18 to the case 22, the coil 16°18 is electrically connected via the terminal 21 to the printed circuit board 20 on which the high-voltage electric component 19 is mounted. Store it in. Ferrite core 23 to coil 16,1
After inserting it into B and assembling it, insert the insulating resin 2 into the case 22.
Inject 4 and harden. Here, too, since the ferrite core 23 is exposed outside the case 22, the insulating resin 24 does not cover the ferrite core 23.

A high frequency high voltage of about 15 KVO is generated in the secondary coil 18. Figure 14 shows the flyback transformer button and the first button.
The switching transformers for the copier Yen High E power supply shown in Figure 6 both have their ferrite cores placed outside the case to prevent the insulating resin from covering the ferrite cores, but the reason for this is the above-mentioned adverse effect of the magnetostriction of the ferrite cores. This is to prevent the phenomenon, but there is one big problem here. That is, when the ferrite core comes out, a space 25 is created between the case and the ferrite core. This space 25 has a dielectric constant that is approximately 1/4 of that of the cases 12, 22 buttons, and the insulating resin 14°240, and the electric field strength is relatively large compared to those, so corona discharge (partial discharge of air) occurs. )
In order to prevent this, the dimension Ai of the space 25 must be made very large, resulting in an increase in the size of the ferrite core button and the transformer.

Note that corona discharge is a source of noise, and at the same time causes deterioration of the insulation of the case, insulating resin, bobbin, etc.

The conventional method of injecting and curing the insulating resin described above is shown in FIG. After drying and weighing the mineral filler 27, it is mixed with the base material 28 and curing agent 29, which have also been weighed, to form a compound 3o. There is also a method of mixing the curing agent 29 and then measuring and mixing the curing agent 29 again, but this method is generally more common.) On the other hand, case included 9
The transformer 26 was preheated, and the degassed compound 30 was injected into the case under vacuum and then heated and cured.

Problems to be Solved by the Invention As mentioned above, insulating resin can be expected to have an extremely large effect for the purpose of reducing temperature rise and insulating high voltage. A major problem was that the ferrite core could not be buried in the insulating resin together with the coil. The reason for this is that when the ferrite core is buried in an insulating resin and stress is applied, the reverse effect of magnetostriction causes a change in the hysteresis loop and an increase in iron loss, leading to deterioration of characteristics and a decrease in efficiency. As a result, injection hardening of the insulating resin is limited to only the coil μ, so no effect of reducing temperature rise can be expected. In order to prevent corona discharge from occurring in the space between the 1/button and the insulating resin, a large distance between the core and the outer case is required, leading to an increase in the size of the transformer.

The present invention solves the above-mentioned problems and aims to provide a method for manufacturing a switching transformer in which a ferrite core and a coil can be buried in an insulating resin while suppressing the adverse effects of magnetostriction.

Means for Solving the Problems In order to solve the above problems, a coil wound around a winding frame and a transformer formed from a ferrite core are housed in an outer case, and a mineral filler is filled in the outer case. The insulating resin is injected and heated to harden the insulating resin.

Furthermore, in order to increase the content of the filler to increase the thermal conductivity and improve the heat dissipation effect, the second mineral filler having a particle size smaller than that of the mineral filler filled in the outer case is used in the above method. The filler is pre-mixed into a liquid insulating tree: your finger.

Function The present invention uses the method described above to wrap the ferrite core in the mineral filler and insulate the insulating resin into the gaps between the individual mineral fillers, so the ferrite core is surrounded by the mineral filler with approximately the same coefficient of linear expansion. Since it is hardened, the stress it receives is small, and the change in hysteresis loop and increase in iron loss due to the reverse effect of magnetostriction are also extremely small.

EXAMPLES Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 10.

FIG. 1 is a process diagram showing a method of injecting and curing an insulating resin according to an embodiment of the present invention.

Dry, weighed mineral filler 27it preheated 1o
7<.

The cased transformer 26 is directly filled. On the other hand, main agent 2
8 and the hardening agent 29 are degassed, measured, mixed, vacuum injected into a case lance filled with a mineral filler, and then heated and hardened. Figures 2a-f illustrate this process in a transformer. Figure 2 a, b
After the transformer 5 is housed in a case 6 as shown in FIG. 2, it is preheated and a dried and weighed mineral filler 27 is filled into the case as shown in FIGS. 2c and 2d. On the other hand, the defoamed and measured base agent 28 and curing agent 29 are mixed and placed in the spaces between the individual particles of the mineral filler 27 as shown in FIG. 2e.

After being injected under vacuum so that it penetrates as shown in f, it is heated and cured.

FIG. 3 is a process diagram showing another embodiment.

The difference from the process diagram in Figure 1 is that the fine mineral filler 31, which has a smaller particle size than the mineral filler 27, is dried.

After weighing, weighed main ingredient 28. It is mixed with a hardening agent 29, and everything else is the same as the process shown in FIG. The switching transformer manufactured by this method was
Shown in Figures a and b. That is, since the individual particles of the fine mineral filler 31 having a small particle size are interposed between the individual particles of the mineral filler 27, the filler content is further increased and the heat dissipation effect is also improved.

FIG. 5 shows an embodiment in which the present invention is applied to a flyback transformer for television. The same parts as in Fig. 14, which shows the conventional example, are given the same numbers.The difference with Fig. 14 is that the insulating resin 14 is injected after the mineral filler 27 is filled into the cased transformer. The ferrite core 13 is buried in a mineral filler 27 and an insulating resin 14. This is because the periphery of the filler core 13 is surrounded by the mineral filler 27 with almost the same coefficient of linear expansion, and the insulating resin 14 with a large coefficient of linear expansion exists only in the gaps 1 between the individual particles of the mineral filler 27. This is because it acts as a connector and does not apply stress to the button and ferrite core. As a result, there is no space with a small dielectric constant between the ferrite core 27 and the 2i coil 11, and no corona discharge occurs, and the distance between them can be considered only based on the insulation performance of the mineral filler 27 and the insulating resin 14. The value can be made extremely small, and a very small flyback transformer can be realized.

FIG. 6 shows an embodiment in which the present invention is applied to a switching transformer used in a high voltage power supply for a copying machine. The same parts as in Fig. 16, which shows the conventional example, are given the same numbers and are designated as buttons and parts.
The difference from Fig. 5 is that the insulating resin 24 is injected after the mineral filler 27 is filled into the cased transformer, and the ferrite core 23 is buried in the mineral filler 27 and the insulating resin 24. be. This is because the ferrite core 23 is surrounded by a mineral filler 27 having almost the same coefficient of linear expansion.
This is because the insulating resin 24 having a large coefficient of linear expansion exists only in the spaces between the individual particles of the mineral filler 27, plays the role of a connector, and does not apply stress to the ferrite core. As a result, the coil 18 is connected to the ferrite cores 27 and 2/.
There is no space with a small dielectric constant between them, and corona discharge disappears, and the distance between them is the distance between the mineral filler 27 and the insulating resin 2.
It is only necessary to consider the insulation performance of 4, and it can be set to an extremely small value, making it possible to realize an extremely small switching transformer.

13,,-7 Figure 7 is a comparison of the hysteresis loops of the ferrite core after and before injection and hardening of the insulating resin according to the manufacturing method of the present invention, that is, the process shown in Figure 3, and Figure 8 is a comparison of the hysteresis loops of the ferrite core according to the conventional manufacturing method. In other words, this is a comparison of the hysteresis loop of the ferrite core after and before injection and hardening of the absolute R resin by the process shown in Figure 16 (the ferrite core is FEER35LZ-H49N manufactured by Fuji Electrochemical Co., Ltd., and the insulating resin is epoxy resin). , the measurement frequency is 100Kilz (sine wave).

The measurement temperature is 120C. ). In FIG. 7, there is almost no change in the hysteresis loop before and after the insulating resin is injected and hardened, whereas in FIG. 8, the slope of the hysteresis loop becomes smaller and the area becomes larger. Fig. 9 is a comparison of the iron loss temperature characteristic curves of the ferrite core after and before injection of insulating resin according to the manufacturing method of the present invention, that is, the process shown in Fig. 3, and Fig. 10 is a comparison of the iron loss temperature characteristic curves of the ferrite core according to the conventional manufacturing method. In other words, it is a comparison of the iron loss temperature characteristic curves of the ferrite core after injecting and hardening the insulating resin by the process shown in Fig. 16 and before injecting it (Ferrai 14/Tokoa is FEER35LZ-H manufactured by Fuji Denki Kagaku Co., Ltd.).
49N, insulating resin is epoxy resin, measurement frequency is 1o
c) KHz (sine wave), magnetic flux density is 1500 Gauss. ). In Fig. 9, the difference between the iron loss before injection and the iron loss after insulating resin injection is very small (especially at temperatures above 40'C, there is almost no difference), but in Fig. 10, the difference is extremely small. big.

The reason for the above difference is as follows. That is, in the process shown in FIG. 3, the cased transformer 26 is completely filled with mineral filler 27.

After that, the insulating resin (base resin 28, curing agent 29) and fine mineral filler 31 are mixed, and in order to inject the defoamed material, the insulating resin permeates into the gaps 1 between the individual particles of the mineral filler 270. The stress applied to the ferrite core 1 in this state is controlled by the mineral filler 27, but since the coefficients of linear expansion of the two are almost the same, the stress is extremely small. Note that this reason also applies to the process shown in FIG. 1.

FIG. 17 shows this state. On the other hand, in the process shown in FIG. 16, a degassed mixture of insulating resin (base resin 16 28, curing agent 29) and mineral filler 27 is injected into the cased transformer 26, but at this time the state is insulated. The mineral filler 27 is dispersed in the ferrite core 1, and the stress on the ferrite core 1 is dominated by the insulating resin having a large coefficient of linear expansion. FIG. 18 shows this state. Further, for these reasons, the amount of mineral filler 27 can be increased in the examples of the present invention, and as a result, it is possible to improve the thermal conductivity and the crack resistance. The following table shows 50W using epoxy resin.
This is a comparison of class switching transformers.

Effects of the Invention As is clear from the above embodiments, according to the present invention, after filling the outer case of a cased citrans with a mineral filler, a liquid insulating resin or a mixture of a fine mineral filler and an insulating resin is produced. Since the ferrite core is injected and hardened, the stress on the ferrite core is dominated by the mineral filler with almost the same coefficient of linear expansion, so it is extremely small and there is almost no adverse effect of the magnetostriction of the ferrite core. Since it can be buried inside the switching transformer, the temperature rise of the switching transformer can be significantly reduced, and in the case of a transformer that handles high voltages, there is no space for corona discharge to occur, making it possible to significantly downsize the transformer. At the same time, the blended amount of mineral filler is increased to improve heat conductivity and crack resistance.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing one embodiment of the manufacturing method of the present invention, and FIG. 2 is a side sectional view and a front sectional view showing the process of the same switching transformer. 3 is a process diagram showing another implementation of the manufacturing method of the present invention, FIG. 4 Δ, b is a front sectional view and side sectional view of the switching transformer, and FIG. 5 is a front sectional view of the flyback transformer. FIG. 6 is a front cross-sectional view of the switching transformer of the high-voltage power supply for the copying machine, FIG. 7 is a characteristic diagram showing an example of the hysteresis loop of the ferrite core of the switching transformer of the present invention, and FIG. 8 is a switching transformer according to the conventional manufacturing method. FIG. 9 is a characteristic diagram showing an example of the iron loss temperature characteristics of the ferrite core of the switching transformer of the present invention.
Figure 0 is a characteristic diagram showing the iron loss temperature characteristics of the ferrite core of a switching transformer manufactured by the conventional manufacturing method, and Figure 11a.
, b is a front view 1 and a side view of a conventional switching transformer, FIG. 12 is a front view 1 and a side view of a conventional flyback transformer, FIG. 12 is a front sectional view of a conventional flyback transformer used in a switching transformer, and FIG. 187.
FIG. 16 is a process diagram showing a conventional manufacturing method, FIG. 17 is a partial sectional view of an embodiment of the switching transformer of the present invention, and FIG. 18 is a partial sectional view of a conventional switching transformer. It is. 1.13.23... Ferrite core, 2,9°11.16.18... Coil, 3,8,10°15.17... Bobbin, 5. ...Transformer, 6゜12.22 ...Outer case, 7,14,
24... Insulating resin, 26... Citrans in case, 27... Mineral filler, 2B.
...Main ingredient for insulating resin, 29...Curing agent for insulating resin, 31...Fine mineral filler.

Claims (2)

[Claims] (1) A transformer consisting of a coil wound on a winding frame and a ferrite core is housed in an outer case, a mineral filler is filled in the outer case, and then liquid insulating resin is injected and heated to insulate it. A method for manufacturing a switching transformer that hardens a synthetic resin. (2) The method for manufacturing a switching transformer according to claim 1, wherein a second mineral filler having a particle size smaller than the particle size of the mineral filler filled in the outer case is mixed in advance into the liquid insulating resin. .