JPH08148322A - Oxide magnetic material and switching power supply employing the same - Google Patents

Abstract

PURPOSE: To obtain a magnetic material exhibiting low magnetic loss in high frequency band and a small-sized, high efficiency, low heat generation switching power supply employing it. CONSTITUTION: A perminvar type oxide magnetic material principally comprises 55mol.% or more of Fe2 O3 or 53mol.% or more of Fe2 O3 and specified quantity of CoO, as a subconstituent. It is admixed with at least CaO and SiO2 to produce an MnZn ferrite containing metal ions exhibiting magnetic anisotropy. The magnetic material thus produced is employed in the core for main transformer. Magnetic loss can be reduced in a switching power supply when it is driven with flux density of 150mT or less at a switching frequency of 500kHz to 5MHz.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide magnetic material and a switching power supply using the same. More specifically, the present invention relates to an oxide magnetic material used for an inductance component, a power supply transformer core, and the like, particularly a low-loss MnZn-based ferrite magnetic material excellent in high frequency characteristics, and a switching power supply using the same.

[0002]

2. Description of the Related Art With the recent development of electronics technology, downsizing and high density of equipment are required, and the operating frequency is increasing. For example, even in magnetic materials used for transformer magnetic cores for switching power supplies and others,
Correspondence to high frequency is required, and in order to prevent heat generation especially when miniaturized, low magnetic loss is required at high frequency.

For example, magnetic materials used as magnetic core materials are roughly classified into metallic materials and oxide ferrite materials. Metal-based materials have the advantage of high saturation magnetic flux density and high magnetic permeability, but have an electrical resistivity of 10 ^-6 to 10 ^-4.
Since it is as low as Ω · cm, there is a drawback that magnetic loss due to eddy current increases at high frequencies. This drawback is ameliorated by reducing the thickness of the magnetic material, so that a metal foil is processed into a thin foil and an insulating material is sandwiched between the metal material and the metal material. However, there is a problem that the thinning is limited to about 10 μm, and it is difficult to form a complicated shape, and the cost is high. Therefore, it could only be used commercially up to a frequency band of about 100 kHz.

On the other hand, the ferrite-based material has a saturation magnetic flux density as low as about 1/2 that of the metal-based material, but has a higher electric resistivity than the metal-based material. For example, the commonly used M
The nZn-based material has an electric resistivity of about 0.01 Ω · m, which is much higher than that of metal-based materials. In addition, CaO and Si
By using additives such as O ₂ , the electrical resistivity can be reduced to 1
It can be increased up to about 0 Ω · m, and the magnetic loss due to eddy current is relatively small up to high frequencies, and it can be used without special measures. In addition, it has advantages that it can be easily made into a complicated shape and that the cost is low. For this reason, this ferrite-based material has been widely used as a power supply transformer core material at a switching frequency of, for example, 100 kHz or more.

Generally, among magnetic characteristics of ferrite, saturation magnetic flux density, Curie temperature, minimum loss temperature, etc. depend on the main composition, while magnetic permeability, residual magnetic flux density, coercive force, magnetic loss, etc. Although affected by it, it is said to be a property dominated by the fine structure. Since the high frequency magnetic loss is mainly caused by the eddy current loss, it is considered that the loss becomes smaller as the electrical resistivity becomes higher, but the electrical resistivity of the MnZn ferrite itself is higher than that of the metal-based material as described above, Not enough. For this reason, the mainstream of the development of low magnetic loss MnZn ferrite for high frequencies is to increase the electrical resistivity by using various additives and controlling the fine structure.

Further, as characteristics other than the magnetic loss of the high-frequency low-loss material, it is necessary that the saturation magnetic flux density, the Curie temperature, and the magnetic permeability are high. These properties are basically required properties of a soft magnetic material and are considered to be important properties for reducing loss ("Powder and powder metallurgy" Vol. 34, No. 5, P191). . The saturation magnetic flux density increases as the amount of Fe ₂ O ₃ increases. However,
It is known that if the amount of Fe ₂ O ₃ is too large, the magnetic permeability and electric resistivity decrease. For the above reasons, low loss M
The amount of Fe ₂ O _{3 in} the main composition of nZn ferrite is 53-
The optimum content is about 54 mol%.
("Electronic Ceramics" Winter 1985 P
44). Most of the low-loss ferrites actually developed are within this composition range, and the reduction of loss has been centered on the investigation by the additives and the fine structure already described using the main composition in the vicinity.

[0007]

However, even a ferrite-based material has a problem that magnetic loss due to eddy current increases and it cannot be used even at a frequency of 500 kHz or more.

Therefore, the inventors of the present invention have found that various main composition ratios of Mn
A ferrite in which various metal oxides were added in combination to Zn-based ferrite was actually manufactured, and the effects of the additives and the main composition were examined in detail. As a result, (1) the electrical resistivity, which has been regarded as important in the past, is at most about 1 Ω · m or more at most, and even if it is higher than that, it has almost no effect on the loss. (2) The magnetic permeability is It cannot be said that the loss is high when it is high, and even if the relative magnetic permeability is 1000 or less, both hysteresis loss and eddy current loss may be extremely low. (3) Ions having large magnetic anisotropy are solid-dissolved in ferrite, and permin bar Type (Perminvar type (snake type))
It has been found that the eddy current loss is reduced.

The present invention has been made to solve the above-mentioned problems of the prior art, and an object thereof is to provide a magnetic material having extremely low magnetic loss at high frequencies.

[0010]

In order to achieve the above object, the first oxide magnetic material of the present invention has a main component of Mn, Zn, Fe and at least C as a sub-component.
It is characterized by containing a metal ion containing aO and SiO ₂ and having magnetic anisotropy.

In the oxide magnetic material having the above structure, it is preferable that the main composition contains 55 mol% or more of Fe ₂ O ₃ . In addition, it is preferable that the oxide magnetic material having the above-mentioned structure contains Fe ₂ O ₃ in an amount of 53 mol% or more as a main composition and at least CoO in an amount of 0.005 to 0.2 wt% as an auxiliary component.

The switching power supply of the present invention is Mn, Z.
n, Fe as a main component, and at least CaO as a secondary component
An MnZn-based ferrite containing metal ions having magnetic anisotropy and containing SiO ₂ and SiO ₂ is used as a magnetic core for a main transformer, and a switching frequency is 500 kHz to 5 kHz.
It is characterized by driving at MHz and magnetic flux density of 150 mT or less.

In the switching power supply having the above-mentioned structure, Fe ₂ O ₃ is contained in an amount of 55 mo as the main composition of the main transformer core.
Oxide magnetic material containing 1% or more, or F as the main composition
It is preferable that the oxide magnetic material contains 53 mol% or more of e ₂ O ₃ and 0.005 to 0.2% by weight of CoO as a secondary component.

The role of CaO and SiO ₂ in the present invention is to precipitate in the grain boundary layer of MnZn ferrite, which originally has a low electric resistance value, to increase the electric resistivity. In addition to these, ZrO ₂ , HfO ₂ , Ta ₂ O ₅ , Al
Addition of ₂ O ₃ , Ga ₂ O ₃ , In ₂ O ₃ , GeO ₂ , Sb ₂ O _{3 and the} like is also desirable because of the same effect, but the resulting DC electric resistivity is 0.5 Ω · m. It is sufficient if the amount is at least approximately, and conversely, if the amount of addition is increased until it becomes 10 Ω · m or more, the loss value rather increases. As a desirable range of the addition amount for that, it is 0.0 for CaO.
5 wt% or more and 0.2 wt% or less, SiO ₂ is 0.005 wt% or more and 0.1 wt% or less, and other is 0.01 wt% or more and 0.2 wt% or less.

Further, it is considered that the reason why the eddy current loss is reduced by using the Permin-Bar type is that the movement of the domain wall in the ferrite is restricted in the region where the magnetic flux density is low. In this case, since the magnetic domain wall becomes hard to move, the magnetic permeability becomes low, but the anomaly factor affecting the eddy current loss becomes small and the eddy current loss becomes small. However, when the magnetic flux density increases, the domain wall begins to move, so the effect of reducing loss decreases. Further, Fe ²⁺ and Co ²⁺ are examples of ions having a large magnetic anisotropy for forming the Perminber type. Of these, for Fe ²⁺ , Fe ₂ O ₃ exceeding 50 mol% in the composition
However, when the MnZn ferrite phase is generated, it becomes almost FeO, but it is necessary that the amount of Fe ₂ O ₃ be 55 mol% or more. Co ²⁺ needs to be present by addition. However, as will be described later, even if these ions are included, the domain wall may not be pinned depending on the production conditions, and the Perminber type may not be obtained.
In this case, it can be determined by measuring the BH loop in a static magnetic field.

As another characteristic required for the low magnetic loss MnZn ferrite, the relative density of the sintered body is preferably 90% or more. If the sintered density is low, the effective area is reduced and the loss is increased. If the sintered density is low,
At the time of cooling of firing, it becomes easy to be affected by the atmosphere, especially Fe
_With a composition containing a large amount of ₂ O _{3, the} original characteristics may be difficult to obtain unless the atmosphere is precisely controlled, which causes a reduction in the yield during manufacturing. Next, the magnetic permeability is preferably within the range of 500 or more and 1200 or less. The average crystal grain size is 10 μm or less, preferably about 2 to 5 μm.

[0017]

According to the above oxide magnetic material of the present invention,
The MnZn-based ferrite contains at least a specific amount of CaO and SiO ₂ , and further contains a metal ion having magnetic anisotropy. With this structure, the role of the metal ion having magnetic anisotropy causes a Perminver type BH hysteresis loop to stabilize the magnetic domain structure and reduce the magnetic loss. As a result, a magnetic material with low high frequency magnetic loss can be obtained.

Fe as the main composition of the oxide magnetic material
According to the preferable example containing 55 mol% or more of ₂ O ₃ , a permine bar-type oxide magnetic material having low high frequency magnetic loss can be obtained.

According to a preferable example, the main composition of the oxide magnetic material contains Fe ₂ O ₃ in an amount of 53 mol% or more and at least 0.005 to 0.2% by weight of CoO is contained as a sub-component. CaO and SiO ₂ as components
And the like increase the electric resistance value of the MnZn-based ferrite and reduce the magnetic loss due to the eddy current, so that a permine bar-type oxide magnetic material with low high-frequency magnetic loss can be obtained.

The switching power supply of the present invention is Mn, Z.
n, Fe as a main component, and at least CaO as a secondary component
A low-loss MnZn-based ferrite containing metal ions having magnetic anisotropy and containing SiO ₂ and SiO ₂ is used as a magnetic core for a main transformer, and a switching frequency is 500 kHz.
Since it is configured to be driven at z-5 MHz and a magnetic flux density of 150 mT or less, it can be used with a low magnetic loss in a high frequency band.

An oxide magnetic material containing 55 mol% or more of Fe ₂ O ₃ as the main composition of the magnetic core for the main transformer, or 53 mol% or more of Fe ₂ O ₃ as the main composition and at least CoO of 0 as a sub-component. 0.005-0.3
According to the preferable example of the oxide magnetic material containing wt%, it is possible to obtain a switching power supply that can be used with low magnetic loss in a high frequency band.

The MnZn ferrite material of the present invention exhibits an ultra-low magnetic loss even when the measurement frequency is in the MHz band.
Therefore, using this material as the magnetic core for the main transformer,
A switching power supply driven at a switching frequency of 500 kHz to 5 MHz and a magnetic flux density of 150 mT or less is small and highly efficient.

[0023]

EXAMPLES Examples of the oxide magnetic material of the present invention will be described below. In the examples, some compositions and additive systems will be described as examples, but the present invention is not limited thereto, and metal ions containing at least CaO and SiO ₂ and having magnetic anisotropy. By including the above, the entire MnZn ferrite which becomes a Perminber type is included.

Example 1 As starting materials, powders of α-Fe ₂ O ₃ , MnCO ₃ and ZnO having a purity of 99.5% were used.
The amount of Fe ₂ O _{3 in} these powders was as shown in Table 1, the amount of ZnO was 7 mol%, the balance was MnCO ₃ , and the total weight was 3
It was weighed to be 00 g. These powders were wet-mixed and pulverized for 10 hours (or h) in a ball mill and dried. After calcining this mixed powder in air at 900 ° C. for 2 hours, CaO was 0.1% by weight, SiO ₂ was 0.03% by weight, Sb ₂ O ₃ was 0.05% by weight, and CoO was the value shown in Table 1. Such that CaCO ₃ , SiO ₂ , Sb ₂ O ₃ and CoO
Was added, and the mixture was again wet mixed and ground for 10 hours in a ball mill and dried to obtain a calcined powder.

5% of polyvinyl alcohol was added to the calcined powder.
A 10% by weight aqueous solution was added, and the mixture was passed through a 30 mesh sieve for granulation. These granulated powders are molded under a pressure of 0.5
Uniaxial mold molding was performed at t / cm ² , and the molded body was binder-out in air at 500 ° C. for 1 hour. The firing was performed at a temperature of 1200 ° C., the temperature was raised in air, and the O ₂ atmosphere was controlled according to the equilibrium oxygen partial pressure of ferrite corresponding to the amount of Fe ₂ O ₃ when the maximum temperature was maintained and when the temperature was cooled. Temperature rising rate is 200 ℃
/ H and the cooling rate was 100 ° C./h. Also, 800 ℃
A sample having the following cooling rate of 1000 ° C./h was also prepared.

From the obtained sintered body, the outer diameter is 20 mm and the inner diameter is 1
A ring-shaped sample having a thickness of 4 mm and a thickness of 3 mm was cut out. After wrapping one layer of insulating tape around this sample, wire diameter is 0.26mm
Prepare a sample in which a φ insulated conductor is wound around the entire circumference, and use a BH loop tracer to produce a magnetic flux density of 450 m.
The BH loop up to T was measured in a static magnetic field. A part of the result is shown in FIG. Due to the shape of the BH loop, it was divided into a normal magnetic material (Samples b and c in FIG. 1) and a Perminver type (Samples d and m in FIG. 1). Next, using an AC BH curve tracer, 1MHz,
The magnetic loss at 50 mT was measured in steps of 20 ° C to 120 ° C in steps of 20 ° C. The results are shown in Table 1.

[0027]

[Table 1]

As is clear from Table 1, the Fe ₂ O ₃ content is 5
A sample containing 0.005 wt% or more and 0.2 wt% or less of CoO in an amount of 5 mol% or more, or 53 mol% or more, and the Perminver type sample had a low loss value of about 300 kW / m ³ or less. On the other hand, samples a, b, c outside this range
The loss values of the ordinary samples p and q within the range of j, o, and the range were as large as about 500 kW / m ³ or more.

Example 2 In the same manner as in Example 1, the composition ratio was 64 mol% of Fe ₂ O ₃ and 19 mol of MnO.
%, ZnO was 17 mol%, CaO was 0.1% by weight, and SiO ₂ was 0.02% by weight to prepare a sintered body (r). Similarly, the composition ratio is 54 mol% Fe ₂ O ₃ , MnO
Content is 38 mol%, ZnO is 8 mol%, CaO is 0.1 wt%, SiO ₂ is 0.02 wt%, Ta ₂ O ₅ is 0.05 wt% and CoO is 0.05 wt%. body
(s) was produced. As a comparative example, the composition ratio of Fe ₂ O ₃ is 53.5 mol%, MnO is 38 mol%, and ZnO is 8.
Sintered body containing 5 mol% of CaO, 0.1 wt% of SiO ₂ , 0.02 wt% of SiO ₂ and 0.05 wt% of Ta ₂ O _5.
(t) was similarly prepared. Magnetic flux density of these sintered bodies 45
BH loop up to 0 mT was measured in static magnetic field, and 1
The magnetic loss at MHz and 50 mT was measured by the same method as in Example 1. As a result, the sintered body (r) was of the Permine bar type, had a minimum magnetic loss at 100 ° C., and had a loss value of 180 kW / m ³ . The sintered body (s) is of the Permine bar type, and the loss is minimal at 60 ° C, and the loss value is 80.
It was kW / m ³ . The above sintered bodies (r) and (s)
Is an ultra low magnetic loss material according to the present invention. Sintered body (t)
Is a conventional material that has a minimum magnetic loss at 60 ° C. and a loss value of 440 kW / m ³ and is a conventional material.

The magnetic loss of each of these three types of samples was measured by changing the magnetic flux density at a frequency of 0.5 MHz at each minimum loss temperature. The results are shown in Table 2.
It was shown to.

[0031]

[Table 2]

As is clear from Table 2, the sintered body of the present invention
(r) and (s) are magnetic flux densities of 150 mT or less,
Although the loss was lower than that of (t), the difference disappeared at 200 mT. Next, for the same sample, the magnetic flux density B and the frequency f
The magnetic loss was measured under the condition that the product was constant at B · f = 50 (mT · MHz) (under this condition, the core size is constant in the power transformer at the same output). Table 3 shows the results.

[0033]

[Table 3]

As is clear from Table 3, these sintered bodies have a minimum loss in the vicinity of 1 to 2 MHz. (r) (s) and
Comparing (t), the sintered bodies (r) and (s) of the present invention are advantageous at 330 kHz or more and 150 mT or less, but the difference becomes remarkable at 500 kHz or more.

Next, E type cores were cut out from each of these sintered bodies, a forward type switching power supply circuit was prototyped using the cores, and the temperature rise corresponding to the magnetic loss was evaluated. Under a constant light load condition, the temperature rise of the magnetic core with respect to the frequency and the magnetic flux density of the magnetic core was measured. The results are shown in Table 4.

[0036]

[Table 4]

As is clear from Table 4, when the allowable temperature rise due to the magnetic core loss of the transformer is expected to be 35 ° C., the power source using the sintered body (t) has a large temperature rise and cannot be used at a very high frequency. I understand. On the other hand, the power supply using the ferrite material (r) or (s) of the present invention has a small temperature rise and can be sufficiently used even at high frequencies. Generally, at high frequencies, the magnetic flux density used is often lowered.
From the result, it is considered that it can be used up to about 5 MHz. However, a switching power supply of 2 MHz or more increases the loss on the circuit side, and is not practical at this time.

From the above results, the switching power supply using the developed ferrite material generates less heat, has high efficiency, and can be expected to be miniaturized. Further, if the characteristic becomes particularly remarkable at 500 kHz or more and 150 mT or less and the loss on the power supply circuit side is reduced, it can be used up to 5 MHz.

[0039]

As described above, the present invention is an unprecedented material with low magnetic loss, and a switching power supply manufactured by using this material can be small in size, low in heat generation, and high in efficiency.

[Brief description of drawings]

FIG. 1 is a diagram showing a static magnetic field hysteresis loop of perminber type and normal type ferrites of the present invention.

[Explanation of symbols]

(b), (c), (d) and (m) are the samples (b), (c), (d) and
It is a static magnetic field hysteresis loop corresponding to (m).

Claims (5)

[Claims] 1. A permine bar-type oxide magnetic material containing Mn, Zn and Fe as main components, containing at least CaO and SiO ₂ as sub-components, and containing metal ions having magnetic anisotropy. . 2. Fe ₂ O ₃ is 55 mol% as a main composition.
The oxide magnetic material according to claim 1, containing the above. 3. Fe ₂ O ₃ is 53 mol% as a main composition.
CoO is contained in an amount of 0.005 to 0.005 as an accessory component.
The oxide magnetic material according to claim 1, containing 2% by weight. 4. A low-loss MnZn-based ferrite containing Mn, Zn, and Fe as main components, containing at least CaO and SiO ₂ as auxiliary components, and containing metal ions having magnetic anisotropy, as a magnetic core for a main transformer. Used, switching frequency is 500kHz-5MHz, magnetic flux density is 15
A switching power supply which is driven at 0 mT or less. 5. A switching frequency of 500 kHz to 5
A switching power supply using the oxide magnetic material according to claim 2 or 3 as a magnetic core of a main transformer driven at MHz and a magnetic flux density of 150 mT or less.