JP3372049B2 - Switching power supply - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a switching power supply using a switching circuit such as a switching regulator or a DC / DC converter.

[0002]

2. Description of the Related Art In recent years, switching power supplies have been widely used as stabilizing power supplies for electronic equipment. A switching power supply generally converts an input DC voltage to a high frequency by a switching circuit, then extracts it through a transformer, further rectifies and smoothes it, and transfers it to a load. Generated switching regulator, DC / DC for boosting or stepping down DC voltage
It has been put to practical use as a converter and the like.

The voltage waveform and the current waveform from the switching element in such a switching power supply are as shown in FIG. 5, and the portion where the voltage and the current overlap when the switching element is turned off and when it is turned on (in the shaded portion in the figure). (Shown) occurs. In this way, the so-called switching loss occurs due to the overlapping of the voltage and the current.

By the way, recently, with the increasing demand for smaller and lighter power sources, the switching frequency tends to be higher. As described above, as the switching frequency becomes higher, the above-mentioned switching loss increases, which is a problem. Therefore, in order to reduce switching loss, a saturable inductor is inserted as a resonator between the secondary winding of the transformer and a rectifying / smoothing element such as a rectifying diode. That is, the saturable inductor inserted in the rectifying / smoothing circuit delays the rise of the current and suppresses the overlap between the voltage and the current to prevent the loss from occurring. As the core material of the saturable inductor, a Fe-Ni-based crystalline alloy, such as Senda-delta or Co-based amorphous alloy, which is excellent in direct current square magnetization characteristics, is used.

[0005]

As described above, the switching loss itself is reduced by inserting the saturable inductor in the switching power supply circuit. However, since the core material of the conventional saturable inductor has a large loss in the high frequency range, the loss due to the saturable inductor itself is dramatically increased when the switching frequency is increased to a high frequency such as 500 kHz or more. Is occurring. As described above, when the loss due to the saturable inductor itself increases, even if the switching loss itself is reduced, it does not lead to a reduction in the loss when considering the switching power supply circuit as a whole, and conversely leads to an increase in the loss.

Therefore, it is strongly demanded to improve the power supply efficiency of the entire switching power supply circuit by suppressing the high frequency loss due to the saturable inductor itself while securing the effect of reducing the switching loss. ing.

The present invention has been made to address such a problem, and suppresses both switching loss and high frequency loss due to the saturable inductor itself when high frequency switching such as 500 kHz or higher is performed. It is an object of the present invention to provide a switching power supply with a large improvement in power supply efficiency.

[0008]

A first switching power supply according to the present invention is a switching circuit having a switching element connected to an input circuit, a transformer having a primary winding connected to this switching circuit, and this transformer. A rectifying / smoothing element connected to the secondary winding of the rectifying / smoothing element, rectifying / smoothing the output from the secondary winding and supplying the rectifying / smoothing element to the load, and a position in series with the switching element in the switching circuit. The saturable inductor is inserted, and as the saturable inductor, a Co having a thickness of 15 μm or less is used.
It has a magnetic core consisting of a base amorphous alloy ribbon or a soft magnetic alloy ribbon with Fe-based ultrafine crystal grains, and a squareness ratio of 1 MHz is 76 % in the range of DC squareness ratio of 5 % to 52 %. ~ 9
By using the saturable inductor in the range of 0 %, the temperature rise of the saturable inductor during operation of the switching power supply is set to 45 ° C. or less. A second switching power supply according to the present invention is connected to a switching circuit having a switching element connected to an input circuit, a transformer having a primary winding connected to the switching circuit, and a secondary winding of the transformer. A rectifying / smoothing circuit having a rectifying / smoothing element and rectifying / smoothing the output from the secondary winding to supply to a load, and is inserted at a position between the transformer and the rectifying / smoothing element in the rectifying / smoothing circuit. And a saturable inductor, wherein the saturable inductor has a magnetic core comprising a Co-based amorphous alloy ribbon having a plate thickness of 15 μm or less or a soft magnetic alloy ribbon having ultrafine crystal grains based on Fe, And DC squareness ratio is 5 % to 52 %
In this range, by using a saturable inductor having a squareness ratio of 1 MHz in the range of 76 % to 90 %, the temperature rise of the saturable inductor during the operation of the switching power supply is 45 ° C. or less.

[0009]

[0010]

The switching power supply of the present invention may have a magnetic core made of a Co-based amorphous alloy ribbon having a plate thickness of 15 μm or less excellent in high frequency characteristics or a soft magnetic alloy ribbon having ultrafine crystal grains based on Fe. The saturation inductor is inserted at a position in series with the switching element or at a position between the secondary winding of the transformer and the rectifying / smoothing element. The Co-based amorphous alloy ribbon or the Fe-based soft magnetic alloy ribbon having ultrafine crystal grains is used, and the DC squareness ratio is 5 % to 52 %.
If a saturable inductor whose squareness ratio of 1MHz is in the range of 76 % to 90 % is used, the saturable property and high frequency characteristics are excellent.For example, even when switching at a high frequency of 500kHz or more, the current It is possible to sufficiently reduce the switching loss by delaying the rising edge of, and the high frequency loss due to the saturable inductor itself is extremely small. Specifically, the temperature rise of the saturable inductor during the operation of the switching power supply can be 45 ° C. or less. Therefore, even when switching is performed at a high frequency, improvement in power supply efficiency is achieved.

[0011]

EXAMPLES Examples of the present invention will be described below.

FIG. 1 is a circuit diagram showing the configuration of a switching power supply according to an embodiment of the present invention. In the figure, 1 is an input DC power supply, and a switching circuit 2 is connected to this input DC power supply 1. This switching circuit 2
Is a forward converter circuit composed of a transistor 3 as a switching element and a control circuit 4 for performing switching control of the transistor 3, and its output terminal is connected to a primary winding 6 of a transformer 5.

In the switching circuit 2, a saturable inductor 7 is inserted as a resonator in series with the transistor 3. This saturable inductor 7
Is a Co-based amorphous alloy ribbon with a plate thickness of 15 μm or less or
It has a magnetic core made of a soft magnetic alloy ribbon having Fe-based ultrafine crystal grains, and is a characteristic part of the present invention.

A rectifying / smoothing circuit 9 is connected to the secondary winding 8 of the transformer 5. The rectifying / smoothing circuit 9 includes rectifying diodes 10a and 10b, a choke coil 11, and
The smoothing capacitor 12 and the AC voltage sent to the rectifying and smoothing circuit 9 via the transformer 5 are:
The rectifying / smoothing circuit 9 converts the direct current into a direct current, and the direct current output is supplied to the load.

Also, a Co-based amorphous alloy ribbon or Fe
As shown in FIG. 2, a saturable inductor 7 having a magnetic core made of a soft magnetic alloy ribbon having ultrafine crystal grains based on the rectifying / smoothing circuit 8 has a rectifying / smoothing element (diodes 10a, 10b, etc.) in the above rectifying / smoothing circuit 8. ) And the secondary winding 8 of the transformer 5 are inserted, the same effect as the circuit configuration shown in FIG. 1 can be obtained. In the saturable inductor 7 in FIG. 2, the feedback control circuit is not formed. Further, the same effect can be obtained by inserting the saturable inductor 7 in the portions indicated by arrows A and B in FIGS. 1 and 2. Further, the saturable inductor 7 can be inserted at both the serial position with the transistor 3 shown in FIG. 1 and the position between the rectifying / smoothing element and the secondary winding 7 of the transformer 5 shown in FIG. The saturable inductor 7 inserted in the above-mentioned position acts as a high impedance until it saturates magnetically, so that the rising of the current can be delayed, which contributes to the reduction of switching loss.

The saturable inductor 7 described above has a plate thickness of 15 μm.
The magnetic core comprises a Co-based amorphous alloy ribbon of m or less or a soft magnetic alloy ribbon having Fe-based ultrafine crystal grains. Co-based amorphous alloys and soft magnetic alloy ribbons having ultrafine crystal grains based on Fe are essentially excellent in high-frequency characteristics, but if the plate thickness is too large, the material loss will be too large, especially Since it becomes a problem in the operation of 1 MHz or more, a Co-based amorphous alloy ribbon of 15 μm or less or a soft magnetic alloy ribbon having Fe-based ultrafine crystal grains is used. However, if the plate thickness is less than 2 μm,
The amount of magnetic flux becomes small, in other words, the magnetic flux density during operation becomes too large, resulting in large heat generation, which is not preferable. Therefore, the plate thickness of the soft magnetic alloy ribbon having Co-based amorphous alloy ribbon and ultrafine crystal grains based on Fe is preferably in the range of 2 μm to 15 μm, and more preferably in the range of 3 μm to 12 μm. Yes,
More preferably, it is in the range of 4 μm to 10 μm. The plate thickness in the present invention is an average plate thickness obtained from the density of the alloy, the weight of the sample, the ribbon length and the width.

As the saturable inductor 7,
The Co-based amorphous alloy ribbon or the soft magnetic alloy ribbon having ultrafine crystal grains based on Fe as described above is used, and the direct current squareness ratio of the magnetic core is in the range of 5 % to 52 %, and 1 MHz.
The squareness ratio in z is preferably in the range of 76 % to 90 %. If the squareness ratio of the direct current is less than 5 %, the saturable property cannot be seen up to the high frequency region, and it becomes difficult to suppress the rise of the current for a proper time as a resonator. On the other hand, if the squareness ratio of direct current exceeds 52 %, the loss in the high frequency range increases, resulting in a decrease in power supply efficiency . Also, similarly to the case squareness ratio of 1MHz is 76% to 90% can be heat generation during operation is small, and to suppress the rise of the appropriate amount of time equivalent current. As this, by the squareness ratio of a DC squareness ratio and 1MHz saturable inductor 7 in the above range, after to satisfy the low loss in the high frequency range, it can be obtained satisfactorily function as Rezonansa Therefore, both the switching loss and the high frequency loss due to the saturable inductor itself can be reduced.
Therefore, even when switching is performed in a high frequency range of, for example, 500 kHz or more, the power efficiency is significantly improved.

The DC squareness ratio in the present invention is Br /
Bs (Br represents the residual magnetic flux density, Bs represents the saturation magnetic flux density), and the squareness ratio of 1 MHz is Br / B ₁ (B ₁ is the magnetic flux density when the applied magnetic field is ₁ Oe, and Br is the residual magnetic flux density. Represents). The saturable inductor 7 having the above-described characteristics is, for example, represented by the general formula: (Co _1-ab Fe _a M _b ) _100-x (Si _1-c B _c ) _x (1) (where M is Is V, Cr, Mn, Ni, Cu, Nb, Mo, Ta and W
At least one element selected from a, b, c and x is 0 ≦ a ≦ 0.10, 0.005 ≦ b ≦ 0.10, 0.15 ≦ c ≦ 0.9
0, 15 ≤ x ≤ 32 (at%) are shown.) Co-based amorphous alloy ribbon whose composition is substantially represented by It can be obtained by performing an appropriate heat treatment according to the alloy composition and setting the squareness ratio within the above range. When the M element in the above formula (1) is Cr, Mn or Ni, the above squareness ratio can be achieved only by ordinary strain relief heat treatment. The heat treatment condition at this time is usually 300 ° C. or higher and crystallization temperature or lower,
It takes about 1 minute to 10 hours. Further, when the M element is other than the above element group, regardless of the presence or absence of the strain relief heat treatment,
The DC squareness ratio and the squareness ratio of 1 MHz can be controlled within the above ranges by performing heat treatment at a temperature below the Curie temperature of the alloy for about 1 minute to 10 hours while applying a magnetic field of 1 Oe or more in the width direction of the ribbon. . The atmosphere in these heat treatments is not particularly limited, and may be an inert atmosphere such as nitrogen or argon, a vacuum, a reducing atmosphere such as hydrogen, or the atmosphere.

Further, Fe in the above formula (1) is an element capable of making the magnetostriction constant zero by balancing with Co, and its addition amount is achieved within the range of 0.01 to 0.10. The more preferable value of a is 0.02 to 0.09, and further preferably 0.03 to 0.08. The M element is an element for keeping the DC squareness ratio within the above range by heat treatment, and the thermal stability of magnetic characteristics is also improved. The effect is
If the value of b is less than 0.005, it is not remarkable, and if it exceeds 0.10, the Curie temperature becomes too low. The more preferred value of b is 0.
It is 01 to 0.09, and more preferably 0.02 to 0.08.
Si and B are effective elements for amorphization, but if the value of c is less than 0.15, it is difficult to amorphize, and if it exceeds 0.9, sufficient magnetic properties cannot be obtained.
The more preferable value of c is 0.2 to 0.8, and further preferably 0.3 to 0.7. If the total amount of these amorphizing elements is less than 15 at%, the condition for obtaining low loss becomes extremely narrow, and if it exceeds 32 at%, the Curie temperature becomes too low. More preferable value of x is 17at% to 30at%
The range is more preferably 20 at% to 28 at%.

On the other hand, the soft magnetic alloy ribbon having ultrafine crystal grains based on Fe preferably has an average crystal grain size of 50 nm or less from the viewpoint of high frequency loss. The average crystal grain size is a value obtained by the following Scherer's equation from the result of the X-ray diffraction pattern.

D = K · λ / β cos θ A preferable alloy composition of the Fe-based ultrafine grain alloy ribbon is represented by the general formula: Fe _100-efghij E _e G _f J _g Si _h B _i Z _{j ....} (2) (In the formula, E is at least one element selected from Cu and Au, and G is at least one element selected from the group consisting of 4A group elements, 5A group elements, 6A group elements, and rare earth elements. Element, J is at least one element selected from the group consisting of Mn, Al, Ga, Ge, In, Sn and platinum group elements, Z is C,
Represents at least one element selected from the group consisting of N and P, and e, f, g, h, i, and j are 0.1 ≦ e ≦
8, 0.1 ≤ f ≤ 10, 0 ≤ g ≤ 10, 12 ≤ h ≤ 25, 3 ≤ i ≤ 1
It is a number that satisfies the equations of 2, 0 ≤ j ≤ 10, and 15 ≤ h + i + j ≤ 30. However, all the numbers in the above formula indicate at%).

Here, the E element in the above formula (2) is an element effective for enhancing the corrosion resistance, preventing the coarsening of crystal grains, and improving the soft magnetic characteristics such as iron loss and magnetic permeability. Especially bcc
It is effective for the precipitation of phases at low temperatures. If this amount is too small, the above-mentioned effect cannot be obtained, and if it is too large, the magnetic characteristics are deteriorated. Therefore, the content of E is
A range of 0.1-8 atom% is suitable. The preferred range is
It is 0.1 to 5 atom%. The G element is an element that is effective in homogenizing the crystal grain size, reduces magnetostriction and magnetic anisotropy, and is effective in improving soft magnetic characteristics and magnetic characteristics with respect to temperature changes. The bcc phase can be stabilized in a wider temperature range by complex addition with Cu). If this amount is too small, the above effect cannot be obtained,
On the other hand, if the amount is too large, the material is not made amorphous in the manufacturing process and the saturation magnetic flux density is further lowered. Therefore, the content of the G element is suitably in the range of 0.1 to 10 atom%. A more preferred range is 1 to 8 atom%.

In addition to the above effects, the effect of each element in the G element is that the heat treatment conditions for obtaining optimum magnetic properties are expanded for the group 4A element, and the embrittlement resistance and cutting of the group 5A element are improved. Workability is improved, and Group 6A elements are effective in improving corrosion resistance and surface property. Among them, Ta, Nb, W
, Mo is preferable since V has a remarkable effect of improving soft magnetic properties, and V has a remarkable effect of improving surface properties together with embrittlement resistance.

The element J is an element effective for improving soft magnetic properties or corrosion resistance. However, if the amount is too large, the saturation magnetic flux density will decrease, so the content is made 10 atomic% or less. Among them, Al is an element effective for refining crystal grains, improving magnetic properties and stabilizing bcc phase, Ge for stabilizing bcc phase, and platinum group element for improving corrosion resistance.

Si and B are elements that assist the non-crystallization of the alloy at the time of production, and can improve the crystallization temperature,
It is an effective element for heat treatment to improve magnetic properties. In particular, Si dissolves in Fe, which is the main component of fine crystal grains, and contributes to the reduction of magnetostriction and magnetic anisotropy. If the amount is less than 12 at%, the soft magnetic properties are not significantly improved, and if it exceeds 25 at%, the effect of ultra-quenching is small, and relatively coarse crystal grains of μm level are precipitated, resulting in good soft magnetic properties. I can't. Further, Si is an essential element constituting the ordered lattice, and 12 to 22 atomic% is particularly preferable for the appearance of this ordered lattice. Also
If B is less than 3 atomic%, relatively coarse crystal grains precipitate and good characteristics cannot be obtained.
It is not preferable because the B compound is likely to precipitate and the soft magnetic properties are deteriorated. Further, as another amorphizing element, Z element (C 3, N 2, P) may be contained in the range of 10 atomic% or less.

The total amount of Si and B and other amorphizing elements is preferably in the range of 15 to 30 atomic%, and Si / B ≧
1 is preferable for obtaining excellent soft magnetic properties. In particular, by setting the Si content to 13 to 21 atomic%, a magnetostriction λs of about zero can be obtained, the deterioration of the magnetic characteristics due to resin molding can be eliminated, and the desired excellent soft magnetic characteristics can be effectively exhibited. Become. Further, even if the Fe-based soft magnetic alloy contains a small amount of unavoidable impurities such as those contained in ordinary Fe-based alloys such as O 2 and S 3, the effect of the present invention is not impaired.

The Fe-based ultrafine crystal grain alloy ribbon having the composition as described above is once made into an amorphous ribbon by the liquid quenching method, and then the obtained amorphous ribbon is used as the amorphous alloy. It can be obtained by precipitating ultrafine crystal grains with a grain size of 50 nm or less by heat-treating for 30 minutes to 15 hours at an appropriate temperature higher than the crystallization temperature of, for example, a temperature in the range of 500 to 600 ° C. Further, as the heat treatment, heat treatment in a magnetic field (thin band width direction, plate thickness direction, rotating magnetic field heat treatment) may be added. The atmosphere in these heat treatments is not particularly limited, and an inert gas such as N ₂ or Ar, in vacuum, or H 2
_It may be in a reducing atmosphere such as ₂ or in the atmosphere.

The fine crystal grains having a grain size of 50 nm or less in the Fe-based ultrafine crystal grain alloy ribbon thus obtained have an area ratio of 2
It is preferably present in the range of 5% to 95%. If the area ratio of the fine crystal grains is too small, that is, if the amorphous phase is too much, the iron loss is large, the magnetic permeability is low, and the magnetostriction is large. On the contrary, if the amount is too large, the magnetic characteristics are deteriorated. The more preferable abundance ratio of the fine crystal grains in the alloy is in the range of 40% to 90% in area ratio, and in this range, soft magnetic characteristics can be obtained particularly stably.

The amorphous alloy ribbon as a base of the Co-based amorphous alloy ribbon or the Fe-based ultrafine grain alloy ribbon having a plate thickness of 15 μm or less as described above is formed by a single roll method in air or under reduced pressure. It can be obtained by a single roll method under an inert gas atmosphere. The former manufacturing method, especially 10μ
It is effective for obtaining a ribbon of m to 15 μm, but when the thickness is the same, the ribbon produced by the latter method is preferable in terms of characteristics.
The latter method is to inject molten metal into a cooling roll while satisfying the following conditions under reduced pressure or in an inert gas atmosphere,
Ultra-quenching the molten metal. The above-mentioned manufacturing conditions are the nozzle shape for injecting the molten alloy, the distance between the nozzle and the cooling roll, the injection pressure, the material of the cooling roll, the peripheral speed, etc., and the preferable ranges are as follows. The nozzle shape is rectangular and the short side is 0.2 mm or less. The distance between the nozzle and the cooling roll is preferably 0.2 mm or less, and the pressure during injection is
It is preferably 0.03 kg / cm ² or less. The material of the chill roll is Cu-based alloy or Fe-based alloy, and the peripheral speed is preferably 20 m / sec or more. The atmosphere for injecting the molten alloy is preferably under a reduced pressure of 10 ^-2 Torr or less or an inert atmosphere of 60 Torr or less.
Next, a specific example of the switching power supply having the above configuration and the evaluation result thereof will be described. Example 1 First, a Co-based amorphous ribbon having a composition of (Co _0.90 Fe _0.06 Cr _0.04 ) ₇₅ (Si _0.55 B _0.45 ) ₂₅ was prepared by the method described below. That is, the shape of the nozzle at the time of injecting the molten metal was a slit shape of 6 mm × 0.12 mm, and the distance between the nozzle and the cooling roll was 0.1 mm. Further, Fe was used as the material of the cooling roll. After placing such a single roll device in the vacuum chamber and evacuating the vacuum chamber to 5 × 10 ^-5 Torr, a pressure of 0.02 kg was applied on the peripheral surface of the cooling roll controlled at a peripheral speed of 40 m / sec. The molten metal having the above composition was injected at a rate of / cm ^{2 and} was rapidly cooled to obtain a long Co-based amorphous alloy ribbon having a width of 5.5 mm. The obtained ribbon was excellent in surface property and had few pinholes.

Next, the above ribbon was formed into a magnetic core having an outer diameter of 10 mm and an inner diameter of 7 mm, and then heat-treated in a nitrogen atmosphere at 420 ° C. for 60 minutes.

The DC squareness ratio and the 1 MHz squareness ratio of the magnetic core thus obtained were measured using an automatic recording magnetic flux meter (made by Yokogawa Electric Co., Ltd.) and a magnetic characteristic measuring system (made by Iwasaki Tsushinki, SY-8617), respectively. . As a result, the DC squareness ratio is 22%, 1M
The squareness of Hz was 81%. The inductor using the above magnetic core was inserted as the saturable inductor 7 in the circuit shown in FIG. 2, and the switching power supply was operated at a switching frequency of 1 MHz. The current and voltage waveforms at that time are shown in FIG.
As is clear from FIG. 3, stable operation characteristics were obtained, the power supply efficiency was 84.4%, and the temperature rise of the magnetic core during operation was 21 ° C. Further, also when the above inductor is inserted as the saturable inductor 7 of the circuit shown in FIG. 1, similarly good results are obtained.

Further, as a comparison with the present invention, a magnetic core (Comparative Example 1) was prepared in the same manner as in Example 1 except that a Co-based amorphous alloy ribbon having the same composition as that of the above Example and a plate thickness of 20 μm was used. Was manufactured and the operating characteristics were evaluated in the same manner,
A temperature rise of 67 ° C was observed, and the power supply efficiency was 81.4%.

Further, (Co _0.95 Fe _0.05 ) ₈₀ (Si _0.5 B
_Using a Co-based amorphous alloy having a composition of _0.5 ) ₂₀ , a thin strip having a plate thickness of 6 μm was produced in the same manner as in Example 1 to obtain a magnetic core having the same shape. Magnetic field heat treatment was applied to this magnetic core at 300 ° C. for 1 hour while applying a magnetic field in the longitudinal direction of the ribbon, and then magnetic characteristics were measured in the same manner as in the example. As a result, the DC squareness ratio was 88% and the 1MHz squareness ratio was 97%. When an inductor using this magnetic core was inserted as the saturable inductor 7 of the circuit shown in FIG. 2 and operated in the same manner as the embodiment, the current and voltage waveforms were similar to those of the embodiment, but during operation. The temperature rise of the magnetic core of 62 ° C was large at 62 ° C, and the power supply efficiency was 81.8%, resulting in a decrease in efficiency.

Example 2 A Co-based amorphous alloy having a composition of (Co _0.93 Fe _0.04 Mn _0.03 ) ₇₄ (Si _0.6 B _0.4 ) ₂₆ was used to prepare samples with a width of 5 mm at various plate thicknesses. At this time, a sample having a plate thickness of 12 μm or more was prepared by a normal roll method in the atmosphere, and a sample having a plate thickness of 12 μm or less was prepared by a single roll method in a vacuum as in Example 1, and the plate thickness was a roll. It was controlled by changing the peripheral speed. Each of the obtained ribbons was wound into a magnetic core having an outer diameter of 15 mm and an inner diameter of 8 mm, and then heat-treated in vacuum at 430 ° C. for 30 minutes.

These magnetic cores were used as a saturable inductor (reference numeral 7 in FIG. 2) of a switching power supply circuit having the same specifications as in Example 1, and the temperature rise of the magnetic core during operation and the power supply efficiency were evaluated. The results are shown in FIG. As is clear from FIG. 4, in the switching power supply of the present invention,
The efficiency is high and the temperature rise of the magnetic core is kept low.

Example 3 A Co-based amorphous alloy ribbon having the composition shown in Table 1 below was prepared.
Each was manufactured under the same conditions as in Example 1, formed into the same magnetic core shape as in Example 1, and then heat-treated under the conditions shown in Table 1 to obtain an inductor magnetic core. The magnetic characteristics of each of these magnetic cores were measured in the same manner as in Example 1. In addition, an inductor using each of these magnetic cores is inserted as the saturable inductor 7 of the circuit shown in FIG. 1 or the saturable inductor 7 of the circuit shown in FIG. 2 and operated in the same manner as in Example 1. The temperature rise of the magnetic core at that time was measured. The results are also shown in Table 1.

[0037]

[Table 1] As is clear from Table 1, the DC squareness ratio of the magnetic core is 5 % to 42 %.
%, And by inserting a saturable inductor 7 using a Co-based amorphous alloy ribbon having a squareness ratio of 1% to a range of 76 % to 89 % into a switching power supply circuit as a resonator, switching loss can be reduced. ,
Since the high frequency loss due to the saturable inductor 7 itself can be suppressed, the power supply efficiency can be improved.

Example 4 First, each Fe-based amorphous alloy ribbon having the composition shown in Table 2 was prepared. The conditions for producing the ribbon are the same as in Example 2
It was fabricated in the atmosphere for 12 μm and above, and in vacuum for those below 12 μm. Each of the obtained ribbons was wound into a magnetic core having an outer diameter of 12 mm and an inner diameter of 9 mm, and then heat-treated in a nitrogen atmosphere at a temperature of 540 ° C to 580 ° C for 1 hour.

The magnetic characteristics of these magnetic cores were evaluated in the same manner as in Example 1. Further, these magnetic cores were used as a saturable inductor (reference numeral 7 in FIG. 2) of a switching power supply circuit having the same specifications as in Example 1, and the temperature rise of the magnetic core during operation was evaluated. The results are also shown in Table 2. In the switching power supply of the present invention, the efficiency is high and the temperature rise of the magnetic core is suppressed low.

[0040]

[Table 2] In each of the above embodiments, an example in which the switching power supply of the present invention is applied to the forward converter circuit type has been described, but the present invention is not limited to this, and can be applied to various switching power supply circuits. It is possible.

[0041]

As described above, according to the switching power supply of the present invention, even when switching is performed at a frequency of, for example, 500 kHz or more, the high frequency loss due to the saturable inductor itself is small and the switching loss is effective. Therefore, it is possible to significantly improve the power supply efficiency.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a switching power supply according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a switching power supply according to another embodiment of the present invention.

FIG. 3 is a diagram showing current and voltage waveforms in the switching power supply according to the embodiment of the present invention.

FIG. 4 is a diagram showing the relationship between the plate thickness of the saturable inductor inserted in the switching power supply of the embodiment of the present invention, the temperature rise of the magnetic core during power supply operation, and the power supply efficiency.

FIG. 5 is a diagram showing current and voltage waveforms in a conventional switching power supply.

[Explanation of symbols]

1 ... Input DC power supply 2 ... Switching circuit 3 ... Transistor as switching element 4 ... Switching control circuit 5 ... Transformer 6 ... Primary winding 7: Saturable inductor 8 ... Secondary winding 9 ... Rectifying and smoothing circuit 10a, 10b ... Diode for rectification 11 ... Choke coil 12 ... Smoothing capacitor

Continued front page    (72) Inventor Daiki Yamada               8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa               Toshiba Corporation Yokohama Office (72) Inventor Takao Kusaka               8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa               Toshiba Corporation Yokohama Office (72) Inventor Kazumi Nakajima               8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa               Toshiba Corporation Yokohama Office

Claims (5)

(57) [Claims] 1. A switching circuit having a switching element connected to an input circuit, a transformer having a primary winding connected to the switching circuit, and a rectifying / smoothing element connected to a secondary winding of the transformer. A saturable inductor inserted in a position in series with the switching element in the switching circuit, the saturable inductor having a rectifying and smoothing circuit for rectifying and smoothing an output from the secondary winding to a load; The inductor has a magnetic core consisting of a Co-based amorphous alloy ribbon with a plate thickness of 15 μm or less or a soft magnetic alloy ribbon with ultrafine Fe-based crystal grains, and a DC squareness ratio of 5 % to 52 %. At a 1MHz squareness ratio of 76 % to 90 %
A switching power supply characterized in that the temperature rise during the operation of the switching power supply of the saturable inductor is set to 45 ° C. or less by using the saturable inductor in the range. 2. A switching circuit having a switching element connected to an input circuit, a transformer having a primary winding connected to the switching circuit, and a rectifying / smoothing element connected to a secondary winding of the transformer. A rectifying / smoothing circuit having a rectifying / smoothing output from the secondary winding and supplying the rectifying / smoothing to a load; and a saturable inductor inserted between the transformer and the rectifying / smoothing element in the rectifying / smoothing circuit. The saturable inductor has a core made of a soft magnetic alloy ribbon having a Co-based amorphous alloy ribbon having a plate thickness of 15 μm or less or ultrafine crystal grains based on Fe, and has a DC squareness ratio. Squareness ratio of 1MHz is 76 % to 90 % in the range of 5 % to 52 %
A switching power supply characterized in that the temperature rise during the operation of the switching power supply of the saturable inductor is set to 45 ° C. or less by using the saturable inductor in the range. 3. The switching power supply according to claim 1, wherein the magnetic core has a general formula: (Co _1-ab Fe _a M _b ) _100-x (Si _1-c B _c ) _x (wherein , M represents at least one element selected from V, Cr, Mn, Ni, Cu, Nb, Mo, Ta and W, and a, b, c and
x is 0 ≦ a ≦ 0.10, 0.005 ≦ b ≦ 0.10, 0.15 ≦ c ≦ 0.90, 15 ≦
A switching power supply characterized by comprising the above Co-based amorphous alloy ribbon, the composition of which is substantially represented by x ≦ 32 (at%). 4. The switching power supply according to claim 1, wherein the magnetic core has a general formula: Fe _100-efghij E _e G _f J _g Si _h B _i Z _j (wherein E is Cu and Au). G is at least one element selected from the group consisting of 4A group elements, 5A group elements, 6A group elements and rare earth elements, J
Is at least one element selected from the group consisting of Mn, Al, Ga, Ge, In, Sn and platinum group elements, and Z is C, N and P.
Represents at least one element selected from the group consisting of
e, f, g, h, i and j are 0.1 ≦ e ≦ 8, 0.1 ≦ f ≦ 10, 0 ≦ g
≤10, 12 ≤h≤25, 3≤i≤12, 0≤j≤10, 15≤h + i + j≤30
Is a number that satisfies each expression of. However, all the numbers in the above formula indicate at%) and the composition is substantially represented by the above-mentioned Fe in which the fine crystal grains having a grain size of 50 nm or less are present in an area ratio of 25% to 95%. A switching power supply comprising a soft magnetic alloy ribbon having ultrafine crystal grains as a base. 5. The switching power supply according to claim 1 or 2, wherein the operating frequency is 500 kHz or higher.