JPH01125809A - Magnetic core for variable inductor - Google Patents

Abstract

PURPOSE:To obtain the choke coil having excellent DC superpositional characteristics by a method wherein a small-sized magnetic core, having the magnetic characteristics different from those of the magnetic main body, is inserted into a part of a gap section. CONSTITUTION:An air gap 3 is provided in advance on the whole surface of the butt-together part of a magnetic core, and a small type magnetic core 21 having the magnetic characteristics different from those of the main body magnetic core 1 is separately inserted into said air gap part 3. Accordingly, high inductance L can be obtained in a feeble magnetic field, and on the part having an intensive superposed DC magnetic field, the choke coil having the inductance characteristics equal to the inductance provided with the ordinary air-gap for the product of a superposed DC current and the number of the coil, is constituted. As a result, excellent DC superpositional characteristics can be obtained.

Description

[Detailed Description of the Invention] [Overview of the Field] The present invention relates to a magnetic core used in a choke coil used in a switching power supply as an inductor having non-linear inductance characteristics against DC superimposed current in a secondary circuit. be.

[Contents of conventional technology and points of compromise]

Conventionally, in the case of the EE type, EI type, etc., this type of magnetic core has a step-shaped magnetic path in a part of the air gap of the middle leg joint, so that the magnetic core abutment part in the air gap is formed in a weak magnetic field. A magnetic core is used in which the effective magnetic permeability μe is increased without being saturated, and the abutting portion of the magnetic cores is saturated in a strong magnetic field, resulting in the same magnetic permeability μeg as if an air gap was inserted over the entire effective magnetic path.

However, in terms of characteristics, when the core abutting part in the air gap is saturated, a part of the middle leg flat gap part of the core body is also saturated, so the product NI of the coil turns N, which indicates the value of the DC superimposed magnetic field, and the coil current In other words, compared to an inductor whose inductance value is flat when an air gap is provided over the entire surface of the center leg of the magnetic core, the inductance value for ampere turns increases to a higher value than the NI value. There were disadvantages in that it was difficult to control the dimensions of the magnetic core abutting portions that created the step-like magnetic path by grinding, and it was difficult to handle.

[Purpose of the invention]

In order to eliminate these drawbacks, the present invention provides a gap in advance over the entire surface of the magnetic core abutting part, and separately inserts a small magnetic core with different magnetic properties from the main body magnetic core into the gap, thereby reducing the inductance L in a weak magnetic field. In places where the superimposed DC magnetic field is strong, a choke coil is constructed that has the same inductance characteristics as an inductance with a normal air gap of 1 for the product of the superimposed DC current and the number of turns of the coil. It is something to do.

[Structure of the invention]

In the magnetic core of the present invention, an air gap is provided in the center leg of the magnetic core in advance, a small magnetic core having different magnetic properties from the magnetic core of the main body is adhered to the air gap, and the abutting surfaces of the magnetic cores are polished to form the intended magnetic core. During the powder pressing of the magnetic core before final sintering, chips of materials with different characteristics are press-molded in advance with the main body magnetic core, and then sintered and integrated, and the abutting surfaces of the magnetic cores are ground to form the magnetic core of the present invention. This magnetic core for a variable inductor has a structure in which a small magnetic core having magnetic characteristics different from that of the core body is inserted into the gap and assembled into the gap.

〔Example〕 Embodiments of the present invention will be described with reference to the drawings.

Figure 5 shows the shape of a general choke coil magnetic core used in the secondary side DC smoothing circuit of a switching power supply.
When I-type magnetic cores 1 and 2 are used, a gap 3 is provided in the middle leg, and these cores constitute a choke coil by winding a coil around a coil bobbin that enters the middle leg. The characteristics of conventionally commonly used choke coils using magnetic cores of these shapes are shown in Figure 4, where the product NI of the DC current I superimposed on the choke coil and the number of turns N of the coil is
The value of inductance L for NI is approximately constant from the zero value of NI until the magnetic core is saturated.

On the other hand, the characteristics of choke coils used in the secondary side DC smoothing circuit of switching power supplies require a high inductance value as a choke coil when the value of DC current is small in order to obtain stable control characteristics. Now, in the part of the air gap 3 of the central leg of the magnetic core shown in Fig. 3, an abutting part of a stepped magnetic path 4 is provided in a part of the middle leg, and its tip touches and butts against the facing surfaces of the E-type and 1-type cores. The magnetic core is shaped like this, and is used to construct a magnetic core for a choke coil.

The characteristics of the choke coil using the magnetic core of the shape shown in Figure 3 show the characteristic curve of Figure 6B, and in the portion where the DC superimposed current is small, the inductance value is higher than when using the magnetic core of the conventional shape. However, there was a problem in that the inductance was lower in the portion where the DC superimposition current was large compared to the DC superimposition characteristics of the conventional magnetic core with the same gap length, the characteristics shown in FIG. 6C. In the magnetic core shown in Fig. 3 (a) and (b), when the DC superimposed current 4α becomes large in the central leg A (the hatched part) following the butt part of the stepped magnetic path 4. This is considered to be because the magnetic saturation region A portion of the stepped magnetic path 4 equivalently increases the air gap length.

In order to solve the above-mentioned problems, the present invention adopts the magnetic core structure shown in FIG. 1. In FIG. This is the inserted structure.

Below is a blank Example-1 The magnetic permeability μ of the magnetic core material used for the choke coil of a switching power supply is 2500. Mn-Zn ferrite with a saturation magnetic flux density of 5000 forces (Tohoku Metal Industry Co., Ltd. 2500
B material) EI type core FEI-28 (width 28 mm, length ■
Using a coil bobbin (20 mm including the mold core and 11 mm thick), the wire was wound 100 times around a coil bobbin and inserted into the middle leg of the EI cocoa.

The main body magnetic core has the structure shown in Fig. 5(b), and the air gap length is 1.9 mm.
And so.

The DC superposition characteristics when using a magnetic core with this structure are as shown in curve 1MK in Fig. 2. On the horizontal axis NI, ■ represents the DC superimposed current value in ampere, and N represents the number of coil turns. or,
The vertical axis AL indicates the value of inductance per coil bobbin.

Example-2 Same as Example-1, the main body magnetic core material is ferrite 25
The dimensions of the EI cocoa made of 00B material and processed into the shape shown in FIG. 3(a) are the same as in Example-1, and the gap length of the middle leg is 1.
The width of the step part was 1.0 mm. The staircase part of this core is made integral with the core body, which is the same as the core structure used conventionally.

The AL value for the DC superimposition value NI is as shown in FIG. 2M.

The value of inductance increases rapidly below 5 ampere turns, but in the portion where NI is large, the value of AL decreases rapidly with respect to the value of NI.

Example-3 A Mn-Zn ferrite core with an initial permeability of 12,000 is used as the core of Example-1, and the width of the middle leg is 3 mm (the width of the middle leg is 7.5 mm), and the core thickness is the same as the E1 core. Then, a small magnetic core 21 was machined to a length that reached the core 2 and inserted into the gap 3 by adhesive bonding with resin, and the abutting surfaces of the magnetic cores were finished by grinding. The inserted magnetic core material has an initial permeability of 120.
00, the saturation magnetic flux density when the magnetizing force is 10 oersted is 3
It has 400 power. The value of inductance for DC superposition NI at this time is as shown by curve O in Figure 2.

Example-4 In the core of Example-1, a Ni-Zn ferrite core with an initial magnetic permeability of 600 was processed into a small magnetic core with the same size as in Example-3 for the width of the middle leg (the core size was It was 3 mm wide, the core thickness was the same as EI cocoa, and the length of the gap was set to reach the core.) It was glued to the gap, and the abutting part was ground. The characteristics of the magnetic core material are an initial magnetic permeability of 600. Magnetizing force 1
The magnetic flux density at zero maintenance mode is 2700 forces.

The characteristics of DC superposition NI and inductance of the core in these embodiments are as shown in FIG. 2P.

From the results of Example-1 to Example-4, Fig. 3(b)
The DC superimposition characteristics of an inductor made using a core with the shape of are shown by the curve M in Figure 2. When the DC superposition NI is small, the inductance value is large, but when the DC superposition NI is 200 amperes or more, the inductance value is large. In contrast, saturation is reached at a lower value of DC superposition NI compared to the O and P characteristic curves, whereas when a small magnetic core with different core material properties is inserted in the air gap, The DC superposition NI with respect to the inductance value is higher than that of the inductance using a magnetic core of the conventional structure, and increases by about 20%. This value indicates that the cross-sectional dimension of the magnetic core can be reduced by approximately 10%, and that the core size can be reduced by using the magnetic core with the structure shown in Figure 1, and that when the dimensions are the same, it has redundancy against DC superimposed current. The present invention has a great industrial effect.

Further, in the present invention, as a method for attaching materials with different magnetic properties to be inserted into the gap, pre-processed blocks are attached by resin bonding, but it is also possible to make materials with different magnetic properties to be inserted into the gap in advance before sintering the magnetic core. Then, the desired magnetic core may be produced by integral press molding during powder press molding of the magnetic core, sintering, and processing. Also, Example-1 to Example-4
Although the above was explained using an example using an EI type magnetic core, magnetic cores of other shapes such as EE type and UU type can also be used.

It goes without saying that the effects of the present invention can also be obtained when the present invention is implemented using a UI type magnetic core.

〔Effect of the invention〕

In contrast to the air-gap molding method that has a stepped magnetic path, which was conventionally made by integrally molding the magnetic core of a choke coil used in the secondary side rectifier circuit of a switching power supply, the present invention creates an air gap in the magnetic path of the magnetic core in advance. By attaching a small magnetic core with different magnetic properties smaller than the volume of the gap to the air gap with resin or forming an integrally press-molded magnetic core, a choke coil with excellent DC superimposition characteristics can be obtained.

Furthermore, while it is difficult to process a gap with a stepped magnetic path, in the method of the present invention, the gap part is ground in advance to a predetermined gap length over the entire magnetic path of the magnetic core, and then a small magnetic core is attached. It is made by grinding the mating surfaces and is easy to process.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the structure of a magnetic core for a variable inductor according to the present invention. Figure 2 shows the characteristic curves of the inductance and DC superposition NI of a choke coil made using the magnetic core with the magnetic core shape shown in Figure 1, and the characteristic curve of the choke coil with the conventional shape shown in Figures 3(b) and 5(b). The characteristic curve of the inductance of the choke coil and the DC superposition NI when using the magnetic core of FIG. K: DC superimposed ampere turns (AT) of the magnetic core with the shape shown in Figure 5(b) and inductance per coil turn (A
FIG. M: A diagram showing the DC superimposed ampere turns of the magnetic core having the shape of FIG. 3(b) and the inductance per coil turn. ○: The magnetic core has the shape shown in Figure 1, and the magnetic permeability μ is 21 small magnetic cores.
DC superposition characteristics when using a small Mn-Zn ferrite core of m2000. P: The magnetic core has the shape shown in Figure 1, and the magnetic permeability μ is 21 small magnetic cores.
DC superposition characteristics when using a small magnetic core of 600 Ni-Zn ferrite core. FIG. 3 is a diagram showing the shape of the magnetic core used in the secondary choke coil of the switching power supply. (a) is an EE type magnetic core. (b) is an EI type magnetic core. A indicates the magnetic saturation region. FIG. 4 shows the values of DC superposition Nl and inductance when the magnetic core of FIG. 3 is used as a choke coil. Figure 5 shows the shape of the magnetic core commonly used in choke coils. (a) is an EE type magnetic core. (b) is an E1 type magnetic core. Figure 6 shows a curve B showing the DC superposition characteristics when the magnetic core in Figure 3 is used as a choke coil, and a curve B showing the characteristics of a choke coil using a conventionally commonly used magnetic core as shown in Figure 5. A diagram showing C. 1...E-type magnetic core (magnetic core body). 2... ■ type magnetic core. 3...Void. 4...Stepped magnetic path. 5... Middle leg. 21...Small magnetic core. Patent applicant Tohoku Metal Industry Co., Ltd. Figure 1 Figure 312 Figure 5 I N/

Claims (1)

[Claims] A magnetic core for a variable inductor, characterized in that a magnetic core for a variable inductor has an air gap provided in the magnetic path of the magnetic core, and has an assembled structure in which a small magnetic core with magnetic characteristics different from that of the magnetic core body is inserted into a part of the air gap. .