JPH03163803A - Low loss mn-zn system ferrite - Google Patents

Abstract

PURPOSE:To restrain loss even in the case of application to a power supply transformer for high frequency switching of 100kHz or higher, by adding a specified component to a specified fundamental component and compounding them. CONSTITUTION:Fundamental component is Fe2O3 of 52-54mol%, MnO of 33-37mol%, and ZnO of 8-13mol%. The following are added to and compounded with the fundamental component; SiO2 of 0.008-0.30wt.%, CaO of 0.02-0.15wt.%, niobium oxide of 0.01-0.08wt.%, and tungsten oxide and/or molybdenum oxide of 0.02-0.20wt%. The operating temperature of a transformer for a switching power supply is usually 60-70 deg.C, and therefore it is desirable that the iron loss is low in said temperature range and has negative temperature dependency up to the temperature range of 80-120 deg.C where the operating temperature exceeds the room temperature. From this viewpoint, the compound ratio of Fe2O3, MnO and ZnO is desirable to be in the above range. Hence the loss is reduced in the case of application to a transformer for a high frequency power supply whose switching frequency is higher than or equal to 100kHz.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a low-loss Mn-Zn ferrite suitable for use in transformers for switching power supplies and the like.

? Conventional technology) Conventionally, transformers for switching power supplies were often used at a switching frequency of about 100 kHz, but recently, in order to improve the performance and downsize of power supplies, the frequency has increased and the core Further reduction of iron loss is desired.

From this point of view, attempts have been made to add various trace amounts of Mn--Zn fluorite used as such transformer materials in order to improve electromagnetic properties. For example, in Japanese Patent Application Laid-open No. 101458/1983, CaO and SiO
A composite addition of niobium oxide and niobium oxide is proposed in Japanese Unexamined Patent Publication No. 58-15037.

(Problems to be Solved by the Invention) However, when CaO or SiO2 is added, crystal grains may become abnormally elongated, causing deterioration of magnetic properties.

In other words, many vacancies remain in the abnormally elongated crystal grains, which causes a decrease in magnetic permeability, iron loss, etc.

This invention advantageously solves the above problems, and has 10
Even when used as a lance for high-frequency switching power supplies of 0 kHz or higher, the loss can be suppressed by -F to achieve higher performance and smaller size.
- The purpose is to propose Zn-based ferrite.

(Means for Solving the Problems) That is, the present invention provides: Pez[:+: 52-54 mol%, MnO:
33 to 37 mol% and ZnO: 8 to 13 mol% as basic components, and Si (h: 0.008 to 0.030 wt%, CaO
: 0.02 to 0.15 wt%, Niobium oxide: 0.01 to 0.08 wt%, Tungsten oxide and/or molybdenum oxide: 0.02 to 0.2
This is a low loss Mn-Zn based ferrite made by adding and blending 0wt%.

(Function) First, in this invention, the reason why the blending ratio of the basic components is limited to the above range will be explained.

Fe203: 52-54 mol%, MnO: 33
~37 mol%, ZnO: 8 ~ 13 mol% The operating temperature of a switching power supply transformer is usually 60 ~
70 DEG C. Therefore, it is desirable that the iron loss is low in this temperature range, and that the iron loss has a negative temperature dependence from room temperature to a temperature range of about 80 DEG to 120 DEG C., which exceeds the operating temperature.

From this point of view, Fe20,... As a result of examining the blending ratios of MnO and ZnO, the above range was obtained.

In addition, Fe203 raw materials include p e2 0 3 to 6 <, FeO, Fe304, and even Fe203 due to combustion.
Compounds that can be converted into 203, such as iron hydroxide,
Iron oxalate, etc. can be used. Also, MnO
As a raw material, not only MnO but also MnOz, Mns
Compounds that can be converted to MnO by calcination or oxidation, such as manganese carbonate, manganese oxalate, etc., can be used. Furthermore, as a ZnO raw material, Zn
Only O? However, compounds that can be converted into ZnO by calcination, such as zinc carbonate, zinc oxalate, etc., can be used.

SiOz: 0.008~0.030wt%SiO■
coexists with CaO to increase the specific resistance of grain boundaries and effectively contribute to reducing eddy current loss, but when the content is 0.008w
If the amount is less than t%, the effect of addition is poor; on the other hand, 0.03
If it exceeds 0 wL%, abnormal grain length tends to occur during firing and the properties become unstable, so it was limited to a range of 0.008 to 0.03 kt%.

CaO: 0.02 to 0.15 wt% CaO is a useful component that increases grain boundary resistance and refines grains, resulting in low core loss. However, if the content is less than 0.02 wt%, grain boundary Poor resistance improvement effect, on the other hand, 0.15wt
If it exceeds 0.02 to 0.0%, abnormal grain length tends to occur when sintering at high temperature to increase density.
It was supposed to be added in a range of 15 wt%.

Niobium oxide: 0.01-0.08wt% niobium oxide (
Although it is not clear why the core loss5 characteristics are improved mainly by the addition of Nb205), SiO2, C
The high-resistance phase at the grain boundaries is altered by combined addition with aO,
This is thought to be because it not only increases resistivity but also works to alleviate the negative magnetic effects caused by the presence of foreign phases at grain boundaries. However, if the content is less than 0.01 wt%, the effect of its addition is poor; 08w
If the content exceeds t%, abnormal grain length tends to occur during sintering, so 0. It was supposed to be added in a range of 0.08 wt%.

Tungsten oxide and/or molybdenum oxide: 0.02
~0. 20wt% tungsten oxide (mainly Q.) and/or molybdenum oxide (mainly M003), Si02, CaO and Nb2
By adding it in combination with 05 or the like, the corrosion loss can be further improved. The reason for this is not clear, but it is thought to be due to the same effect as that of niobium oxide mentioned above. Each of these elements may be added alone or both may be added at the same time.
Addition effects of less than 0.2w t% are poor, while 0.2w
If added in large amounts exceeding t%, the magnetic properties will deteriorate, so these components should be added in amounts of 0.02 to 0.20 whether used alone or in combination.
It was supposed to be added in a range of wt%.

(Example) Fe20: 52.7 mol%, MnO: 34
．． 5 mol% and ZnO: After mixing the raw materials with a basic composition consisting of 12.8 mol%,
It was calcined at 0°C for 3 hours. SiO was added to this calcined powder in the proportions shown in Table 1. , Cab, NbzOsWO. and Mo03 were added and blended, and simultaneously ground and mixed using a wet ball mill. Next, PVA was added as a binder to the crushed rice powder, and after granulating it, it was shaped into a ring shape with an outer diameter of 36 mm, an inner diameter of 24 mm, and a height of 12 mm, and then heated at 1320 ° C for 3 hours in an atmosphere with a controlled oxygen concentration. The fire was carried out.

Frequency of the thus obtained sintered core: 100kHz
Table 1 also shows the results of measuring the iron loss value at maximum magnetic flux density: 0.2T and temperature: 80°C using an AC Bl {loop tracer.

Table 1 As is clear from Table 1, according to the present invention, sioZI CaO+ NbzOs and Question 3 and/or
Or, when Mo03 is added in combination, an excellent low core loss value is obtained.

On the other hand, those outside the appropriate range of this invention (comparative example)
In either case, the effect of improving iron loss is small, and in extreme cases, iron loss characteristics are significantly deteriorated due to abnormal grain length.

(Effect of the invention) Thus, according to this invention, the switching frequency is 10
Even when used as a transformer for a high frequency power supply of 0 kHz or more, it is possible to obtain an Mn-Zn based soft ferrite with extremely low loss.

9

Claims (1)

[Claims] 1. Fe_2O_3: 52-54 mol%, MnO: 3
The basic components are 3 to 37 mol% and ZnO: 8 to 13 mol%, and these basic components include SiO_2: 0.008 to 0.030 wt%, CaO:
Low loss Mn-Zn made by adding and blending 0.02 to 0.15 wt%, niobium oxide: 0.01 to 0.08 wt%, and tungsten oxide and/or molybdenum oxide: 0.02 to 0.20 wt%. type ferrite.