JPS6119086B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a low-loss transformer core in which the porosity of the sintered body is reduced to 3.5% or less. In general, as a transformer core, the molar ratio is
Mn-Zn-based ferrite whose main components are Fe ₂ O ₃ :48-56, MnO:32-40, and ZnO:8-13 is mainly used. In this case, the required characteristic of the core is the reduction of electromagnetic loss.In particular, in the transformer cores for switching power supplies, which have been growing rapidly in recent years, reduction of core loss is becoming increasingly important as the frequency increases. . Generally, transformer core loss is determined by the sum of eddy current loss, hysteresis loss, and residual loss. Among these loss terms, eddy current loss is mainly caused by additives, e.g.
Reductions are being attempted by increasing the electrical resistance by adding CaCO ₃ , V ₂ O ₅ , SiO _{2 ,} etc. In addition, the second term, hysteresis loss, is determined by the crystal grain size of the sintered body,
It is known that it changes depending on the presence or absence of different phases. Therefore, in order to reduce hysteresis loss, it is important to mainly consider the manufacturing method. Therefore, the present invention aims to reduce the core loss by reducing the hysteresis loss in Mn--Zn ferrite by considering its manufacturing method and reducing the porosity. The above Mn-Zn ferrite in the present invention is
Usually used Fe ₂ O ₃ : 48~56, MnO: 32~
40%, ZnO: 8 to 13 mol%,
For example, there is a magnetic head material that has improved workability or wear resistance by reducing the porosity of Mn--Zn ferrite and sintered bodies having such compositions. However, the relationship between porosity and loss at high frequencies has not been clarified. Furthermore, a significant difference from the transformer core of the present invention is that the second peak temperature of magnetic permeability is increased. The peak temperature of the magnetic head material is near room temperature, whereas the peak temperature of the transformer core is set near the operating temperature of the transformer (approximately 80°C). This is because the core loss generally becomes minimum near the second peak temperature of magnetic permeability. Furthermore, since it is necessary for the magnetic head material to record and reproduce signals at high frequencies, it is required to have high magnetic permeability at high frequencies. On the other hand, the transformer core of the present invention does not need to have such high magnetic permeability; for example,
It is about 1500 to 2500 at 0.1MHz. Therefore, due to the above-mentioned differences in various properties, the composition ranges of the two are naturally different. The present invention will be explained in detail below using examples. Example 1 Fe ₂ O ₃ : 53.5 mol%, MnO: 36.0 mol%,
Fe ₂ O ₃ , MnO, ZnO, and CaCO ₃ were weighed and mixed so that ZnO: 10.5 mol % and CaO 0.1 wt %. Thereafter, it was calcined at 850°C, pulverized, compression molded, and then calcined at 1300 to 1400°C. Table 1 shows the results of measuring various properties of the obtained fired body sample.

[Table] In Table 1, samples A, B, and C each have 1300,
It was fired at 1380 and 1400℃. The electrical resistance of these samples was approximately 400Ω·cm, with no significant difference. As is clear from the above examples, the transformer core of the present invention can reduce loss by reducing the porosity. Furthermore, if the porosity exceeds 3.5%, the loss of the transformer core cannot be reduced, so ideally the porosity should be 3.5% or less. Example 2 Fe ₂ O ₃ : 52.5 mol%, MnO: 37.0 mol%,
ZnO: 10.5 mol% and CaO were mixed at 0.1 wt%, calcined at 900°C, and fired at 1360°C. The characteristics of the obtained sample are compared with the characteristics of the sample in Table 1A and are shown in Table 2.

[Table] As is clear from the above examples, it can be seen that the loss of the transformer core is reduced by reducing the porosity, as in Example 1. Note that the electrical resistance of sample D was 360 Ω·cm. Example 3 Fe ₂ O ₃ : 53.5 mol%, MnO: 34.5 mol%,
ZnO: 12.0 mol % and CaO were mixed at 0.1 wt %, calcined at 950°C, and various properties of sample E were measured after firing at 1420°C. The measurement results are shown in Table 3.

[Table] As shown above, it can be seen that the loss of the transformer core is reduced by reducing the porosity as in Example 1. Example 4 For samples A and C previously obtained in Example 1, the loss value (room temperature) of the transformer core with respect to frequency was measured. The results are shown in FIG. From the figure, the intercept on the vertical axis corresponds to the hysteresis loss, but when converting that value, sample A is approximately
It can be seen that while the loss value is 570 mw/cm ³ , sample C with reduced porosity has a very small value of about 280 mw/cm ³ . Further, in FIG. 1, the magnitude of the slope of the straight line indicates the magnitude of the eddy current loss, and since the electrical resistances are almost the same, the eddy current losses of Samples A and C are the same. _CaCO3 ,
It is known that eddy current loss can be reduced by adding V ₂ O ₅ or SiO ₂ to increase electrical resistance, and in the examples CaCO ₃ was added. Apart from this effect, as can be seen from the examples, the hysteresis loss can be reduced by reducing the porosity. Furthermore, the results of measuring the temperature rise of both samples alone are shown in Figure 2. As is clear from the figure, Sample C with reduced porosity can reduce the temperature rise of the transformer core as much as possible compared to Sample A. As described in Examples 1 to 4 above, when Mn--Zn ferrite is used as a transformer core, a low-loss transformer core can be obtained by controlling the porosity of the fired body to 3.5% or less. Incidentally, at a porosity of 3.5%, the loss is at a rate of 0.89 compared to sample A whose porosity is 4%, which is a normal sample.
The claimed range has been increased to 3.5% because the range in which significant loss reduction effects are recognized is considered to be 100% or more of low sources.
The following was made.

[Brief explanation of the drawing]

FIG. 1 shows the frequency characteristics of the loss of the transformer core, and FIG. 2 shows the temperature rise value of the transformer core alone.

Claims (1)

[Claims] 1 _Fe2O3 : 48~56, MnO: 32~40, _ZnO : 8~
In the Mn-Zn ferrite core for transformers with a composition of 13 mol%, the porosity of the sintered body is
A low loss transformer core characterized by a loss of 3.5% or less.