WO1996000972A1 - Printed coil transformer - Google Patents

Abstract

A flat transformer in which the central leg (33) of an EE-shaped core or EI-shaped core is provided at the center of the spiral of a laminated coil body which is formed by stacking spiral coils with an insulating resin to magnetically couple the spiral coils to each other. The cross-sectional area of the side legs (34) of the core is nearly equal to that of the connecting part (35) of the core, and the cross-sectional area (Ae) of the central leg (33) is nearly the double of that of the side leg (34). The cross-sectional area (Ae) and the volume (Ve) of the core meets the following inequalities: 1.4 « Ve?1/3/Ae1/2¿ « 1.7. The interval (w) between the central leg (33) and side legs (34) and the height of the central leg (33) meet the following inequalities: 0.5 « h/w « 2.

Description

 Specification

Print coil type transformer

Technical field

 The present invention relates to a coil structure suitable for use in a transformer coil used in an electronic device or a power supply device, and more particularly to a device having good magnetic coupling, low loss, and good high-frequency characteristics when used as a transformer.

Background art

 Transformers are magnetic components used in electronic equipment and power supply devices. They provide insulation between the primary side and the secondary side, and the voltage on the secondary side is determined by the primary side voltage and the turns ratio. Having. Wire-wound transformers in which a conductor is wound around a bobbin are widely used as transformers for switching power supplies. In particular, the dimensions of the core, which is a magnetic core, are standardized by standards such as JIS and IEC.

 By the way, as a transformer that does not use a bobbin, for example, a printed coil type transformer in which windings are arranged on a single multilayer printed circuit board, which is disclosed in Japanese Patent Application Laid-Open No. 63-173,083, is known. ing. According to such a configuration, since the windings are arranged very close to each other, the loss through the leakage inductance is reduced. However, the present inventor has made further detailed investigations and found that the contribution of losses other than leakage inductance is large, so that a further reduction in loss is required.

 Published Japanese Patent Application No. 1-5033264 discloses that a printed coil type transformer minimizes the parasitic current of the primary circuit and the secondary circuit caused by the switching current to reduce the loss. I have. However, the present inventor has further studied in detail that it has been found that the reduction in loss is insufficient only by considering the stacking order of the multilayer printed circuit board. .

 An object of the present invention is to solve such a problem, and an object of the present invention is to provide a small-sized printed coil type transformer having a rectangular shape in which transformer loss is minimized. Disclosure of the invention

In order to achieve the above object, the present invention provides a coil laminated body 40 in which a plurality of concentric spiral coils are laminated in the thickness direction by using an insulating resin. Place 3 and 3 to set the magnetic coupling between the coils. A cross-sectional area of the core, wherein the cross-sectional area of the core is approximately equal to that of the leg core 34 and the connecting core 35. Approximately double and satisfy the following equation in relation to the volume

1.4≤V e ^1/3 / A e ^1/2 ≤l. 7

 The following equation must be satisfied between the distance w between the middle foot and the leg core and the height h of the middle foot:

 0.5 ≤h / ≤ 2

It is characterized by.

 According to the configuration of the present invention, since the cross-sectional area of the core is made uniform along the magnetic path and the magnetic flux density is kept almost constant, the loss does not locally increase. Although the coil section is surrounded by the window formed by the core's midfoot and the leg core, the coil resistance can be minimized by optimizing the shape of the coil, and the transformer can be reduced in size. Contributes to

BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a perspective view showing a configuration of an assembled state showing one embodiment of the present invention, and is partially cut away.

 FIG. 2 is a cross-sectional view of the coil laminate 40.

 FIG. 3 is a diagram illustrating the details of the shape of the core 30.

 FIG. 4 is a conceptual diagram illustrating the relationship between the transformer loss P L oss and the cross section A e.

 FIG. 5 is a configuration perspective view showing a second embodiment of the present invention.

 FIG. 6 is a configuration diagram illustrating the shape of the UU-shaped core.

 FIG. 7 is a reference in comparison between the embodiment of FIG. 8 and the embodiment of FIG. 9, and is a configuration diagram when the dimension ratio (h Zw) of the core window is 1.

 FIG. 8 is a configuration perspective view showing a third embodiment of the present invention.

 FIG. 9 is a configuration perspective view showing a fourth embodiment of the present invention.

 FIG. 10 is a configuration perspective view showing a fifth embodiment of the present invention.

 FIG. 11 is a diagram illustrating the shape of the EE-shaped core.

FIG. 12 is a configuration perspective view showing a sixth embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

 Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a configuration of an assembled state showing one embodiment of the present invention, in which a part of a coil laminate is cut away. In the figure, a coil laminated body 40 is formed by integrating a conventional bobbin and a conductive wire, and a specific detailed structure thereof is disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 6-3103545 proposed by the present applicant. Is disclosed. In the center of the coil laminate 40, a through hole 41 is formed, and the upper core 31 and the lower hole are formed.

3 A metatarsal is inserted. The terminal 42 is embedded in the other two sides of the coil laminate 40 that are orthogonal to the sides on which the leg cores 34 of the upper core 31 and the lower core 32 are mounted. FIG. 2 is a cross-sectional view of the coil laminated body 40, and shows a cross section taken along line 2-2 in FIG. Here, the secondary coil 45 has two layers in the middle, and the upper and lower layers are sandwiched between the primary coils 44. An internal connection terminal 4 3 a that connects the primary coil 44 in each of the upper and lower layers near the core hole 41, and an internal connection terminal that connects all the primary coil 44 and the secondary coil 45 4 3b is provided. Also, terminals 42 are provided on both sides of the coil laminate 40, one of which is the primary coil 44 of the upper and lower layers—the secondary terminal 42a, and the other is the secondary terminal 42a. Secondary terminal connecting layer secondary coil 4 5

4 2 b. The number of turns of the coil is 3 turns for each layer of the primary coil 44 and 2 turns for each layer of the secondary coil 45. Since each layer of the coil is filled with insulating resin, the separation distance required for obtaining various safety standards is as thin as 0.6 mm, which enables further downsizing of the transformer.

 FIG. 3 is a view for explaining the details of the shape of the core 30. (A) is a front view of an assembled state of the upper end 31 and the lower end 32, (B) is a plan view of the core, (C) () Is a perspective view illustrating the cross-sectional area of the core. The diameter of the metatarsal core 33 is denoted by D, and the diameter D is equal to the width C of the leg end 34 (D = C). The length of the connecting core 35 is A, the distance between the inner side surfaces of the leg cores 34 is E, and the thickness of the leg cores 34 is b. The distance between the inner side surface of the leg core 34 and the opposing peripheral surface of the middle leg 33 is w. Therefore, the following relationship holds.

A = E + 2 b = (D + 2 w) -f 2 b (1) In addition, the height of the communication section core 3 5 in the state where the upper section 31 and the lower section 32 are assembled. The distance between the opposing inner surfaces of the contact section 35 is h. The thickness of the contact section 35 is t, but the following relationship holds.

 H = h + 2 t ('2) Then, the cross-sectional area Ae35 of the connection part 3 5, the cross-sectional area Ae34 of the leg core 34 and the cross-sectional area A e33 of the Core 3 5—Leg end 34 → Middle leg End 3 Set to a value almost equal to the cross-sectional area per magnetic flux line passing through 3, and locally increase magnetic flux density to increase loss Is prevented. Here, the cross-sectional area Ae33 is twice as large as the cross-sectional areas Ae35 and Ae34 of the other cores since two magnetic flux lines pass through the middle cross-section. Defining the cross-sectional area of the foot core 33 as Ae33, it is as follows.

 A e ^ 2 Ae35 (= C-t)

 ^ 2 Ae34 (= Cb)

 = Ae33 (= 7r · DV4) (3) where the thicknesses t and b satisfy the following relationship.

 t = b = 7i · / S (4) In addition, assuming the sum of the volume Ve35 of the connection end 35, the volume Ve34 of the leg end 34, and the volume Ve33 of the metatarsal core 33 in the magnetic flux direction. Since the core estimation V e is expressed, the following equation holds.

 V e = 2 Ve35-f 2 Ve34 + Ve33

 = 2 CA t + 2 C b h + 7 rhhD 4

 = A e (A + 2 h)

 = A e (2 w + D + 2 b + 2 h)

 = A e {2 (h + w) + (l + 7r / 4) D} (5) Here, the ratio of the core volume V e to the core cross section A e is reduced to a dimensionless Expressed by coefficient k.

k = V e ^W2 / K e ^1/2

= (ττ _/ 4)-' ^{/ 6} {2 (h + w) ZD ÷ (l + / 4)} ^{> / 3} (6) . Here, the iron loss refers to the power consumed by the magnetic core due to the time-varying magnetizing force, and the hysteresis loss and the eddy current loss is there. Iron loss PFe is expressed by the following equation.

PFe = ClVeB ² f sw '(7) where CI is a constant determined by the shape and material of the coil, B is the magnetic flux density, and isw is the switching frequency. If the magnetic flux density B and the switching frequency f sw are constant, the iron loss P Fe is proportional to the core volume V e.

Copper loss refers to load loss, including I ² R loss due to eddy current and load in windings, stray loss due to leakage current, and loss caused by circulating current in parallel windings. The copper loss PCu is expressed by the following equation.

 PCu = C2N Vwh (8)

Where C2 is a constant and N is the number of turns. On the other hand, the following relationship holds between the magnetic flux density B and the number of turns N.

 B = C3 / (NAef sw) (9)

Here, C3 is a constant. By substituting equation (9) for the number of turns N in equation (8), the following equation is obtained.

 PCu = C2 (C3 / (BAef sw)} Vwh

= {C2-C3 / (B f sw)} V (Ae ² wh)

= C4 / (Ae ² wh) (10)

That is, the copper loss PCu is inversely proportional to the square of the core cross-sectional area A e.

 Figure 4 is a conceptual diagram illustrating the relationship between transformer loss P loss and core cross-sectional area A e. C Transformer loss P loss is defined by the sum of coil iron loss PFe and copper loss PCu. As expressed by Eq. (7), iron loss PFe tends to increase with increasing core cross-sectional area A e. On the other hand, the copper loss PCu tends to decrease as the core cross-sectional area A e increases. Therefore, for the transformer loss P loss that can be expressed by the sum of the two, there exists an optimal co-cutting area A e that minimizes the loss.

 Therefore, it is a problem to determine the core shape that minimizes the transformer loss P loss with reference to FIG. Now, assuming that the core shape wh related to the copper loss PCu is constant, the iron loss PFe takes the minimum value when h = w from Eq. (5). Given the core window width E, the coil passage cross-sectional width w is as follows from Eq. (1).

w = (ED) / 2 (11) When h = w is substituted into equation (10), the copper loss PCu is expressed by the following equation.

PCu = C4 / [Ae ² {(ED) / 2} ² ]

= C5 / {(ED) ² D ⁴ } (12) In order to minimize transformer loss, Equation (12) should be minimized. (12) is minimized when the following condition is satisfied.

 D = 4 (13) Next, given the core width A, the coil cross-sectional width w becomes as follows from Eqs. (1) and (4).

 w = {A- (l + ~ / 4)} / 2 (14) When h = w is substituted into equation (10), the copper loss PCu is expressed by the following equation.

PCu = C4 / [Ae ^2- {A- (l + π / 4)} V4]

= C5Z ((A— (1 + 7rZ4)} ² D ⁴ ) (15) To minimize the transformer loss, the as) equation should be minimized. The value of the expression (as) is minimized when the following condition is satisfied.

 This time, within the range of the core window width E and the core width A described above, the core shape that minimizes the transformer loss is as follows from the expressions a) and a6).

 1≤ 2 (h + w) / D≤ (l + 7Γ / 4) (17) At this time, the coefficient k is in the following range from equation (6).

 1.5≤k≤1.6 (18) FIG. 5 is a perspective view showing the configuration of the second embodiment of the present invention, wherein (A) shows a state in which a UU core is mounted on a coil laminate, and (B) shows a coil laminate. It shows a simple substance. The U-shaped connector has a connecting portion core 37 and two leg portions 36 provided at both ends thereof. The two-hole coil laminate 50 has two holes 5 la and 51 b. The detailed structure is described in, for example, Japanese Patent Application Laid-Open No. No. 9 discloses this. The terminals 52 are provided in a row on both sides of the two-hole coil laminate 50 along the direction in which the ends of the coil body 50 are mounted. A UU-shaped core or a UI-shaped core is mounted on the two-hole coil laminate 50 to form a closed magnetic circuit.

Fig. 6 is a block diagram illustrating the shape of the UU-shaped core. (B) is a plan view of the U-shaped core. For convenience of explanation, FIG. 6 uses the same reference numerals as in FIG. 3, but has values unique to FIG. The diameter of the leg core 36 is represented by D. The length of the joint 37 is A, the thickness is t, the width is C, and the distance between the inner peripheral surfaces of the legs 36 is 2 w. Therefore, the following equation holds for the core volume V e and the core cross-sectional area A e.

 V e = A e {2 (h + w) + 2 D} (19)

 A e = · DV4 (20) Therefore, the coefficient k is as follows.

k = (, T / 4) ^-1/6 {2 (h + w) / D + 2} ^1/3 (21) Therefore, the shape of the transformer that minimizes the transformer loss P loss is shown in Fig. 6. It is a problem to decide. Now, assuming that the core shape wh related to the copper loss PCu is constant, the iron loss P Fe takes the minimum value when h = w from Eq. (19). Given the core window width E, the coil cross-sectional width w is as follows from Fig. 6 (B).

 w = (ED) / 2 (22) Assuming h = w, the copper loss PCu becomes the same as the above equation (12) when substituting into equation (10), so the value that minimizes the value of equation (12) Also, in the case of the above formula (3), the transformer loss P loss is minimized.

 D = 4 w (13) Next, if the end width A is given, the coil cross-sectional width w is as follows from Fig. 6 (B).

 w = {A-2 D} / 2 (23) When h = w, the copper loss PCu is expressed by the following equation by substituting into the θ) equation.

PCu = C4 / [Ae ^2- {A-2 D} V4]

= C5 / {(A-2 D) ² D ⁴ } (24) In order to minimize the transformer loss, the equation (24) should be minimized. (24) is minimized when the following condition is satisfied.

2D = 4w (25) Now, within the limits of the window width E and the core width A described above, the core shape that minimizes the transformer loss is given by the following range from Equations 3) and (25). Become. 1≤2 (h + w) / D≤2 (26)

At this time, the coefficient k is in the following range according to the equation (6).

 1.5≤k≤1.7 (27)

 Now consider the case of h ^ w, while satisfying the condition hw = —constant. Fig. 7 is a reference for the embodiment of Fig. 8 and Fig. 9 and shows the configuration when the dimensional ratio (h / w) of the window is 1; (B) is a cross-sectional view taken along the line BB of (A), showing a state after the apparatus of FIG. 1 is substantially assembled. As described in Eq. (11), iron loss PFe takes the minimum value when h = w. O

 FIG. 8 is a configuration diagram showing a third embodiment of the present invention, in which the dimensional ratio (h / w) of the window is 1/2, and FIG. (B) is a cross-sectional view taken along line BB of (A). The coefficient k that minimizes transformer loss when hZw = l / 2 is calculated as follows in the same procedure as in the formulas αι) to α8).

 1.4≤k≤l.5 (28)

 Iron loss PFe increases by about 5% compared to when h / w = l. However, it is considered to be acceptable for practical use as a transformer.

 On the other hand, when the dimensions of the core window are flat, the cross section of the coil laminate 40 can be flattened, and the conductor can be further flattened. Therefore, the AC resistance related to copper loss can be reduced by increasing the conductor surface area due to the skin effect, and the copper loss is reduced. Therefore, the substantial increase in transformer loss is less than 5%.

 FIG. 9 is a configuration diagram showing a fourth embodiment of the present invention, in which the dimensional ratio (hw) of the end window is 2, and FIG. 9 (A) shows a state in which the EE core is mounted on the foil laminate. Plan view of the

(B) is a BB sectional view of (A). The coefficient k that minimizes the transformer loss when hZw == 2 is calculated by the same procedure as in the above equations (11) to (18).

 1.5≤k≤l.7 (29)

Iron loss PFe increases about 5% compared to when hZw == 1. However, it is considered to be acceptable for practical use as a transformer. On the other hand, when the size of the core window is vertically long, the cross section of the coil laminate 40 can be vertically long. As a result, the planar dimensions of the coil laminate 40 are reduced, and the transformer mounting area can be reduced. For example, comparing FIG. 9 and FIG. 7, when the transformer mounting area is made vertically long, it is only half that in the case of the same size. Therefore, it is suitable for applications that require a small transformer mounting area, such as fields where high-density mounting is required.

 As described in the above Examples 1 to 4, when the dimension ratio (hZw) of the window is in the range of 1/2 to 2, the transformer shape that minimizes the transformer loss is expressed by (18), (27) ), (28) and (29), the coefficient k may be in the following range.

 1. 4≤k≤1.7 (l / 2≤h / w≤2): (30)

 Next, a comparison between a conventional transformer using JIS FEER25.5 and the product of the present invention corresponding to the first embodiment will be described. Table 1 compares the characteristics of the conventional transformer and the product of the present invention (coefficient k = 1.61). The upper six items relate to the shape of the transformer and the lower two items relate to the transformer loss.

従来型トランスに比較して本発明品では、 EE形コ了の高さ Hが低く、 また長 さ Aも 1 0%程度短くなつている。 そこで、 コ了体積 V eは 2 0%程度小さくな つており、 逆にコア断面積 A eは 30%程度大きくなつている。 コア体積 Veが 小さくなれば、 磁性材料の使用量が少なくてすむから、 軽量且つ安価に製造でき ることになる。 コア窓の寸法比は、 従来型トランスが と偏平である のに対して、 本発明品では hZw½l.5と縦長になっている。 そして、 トランス 損失は銅損が 4 0%小さくなり、 鉄損も 1 8%小さくなつているから、 トランス としての性能は良好になっていることが判る。

Compared to the conventional transformer, the product of the present invention has a lower height H of the EE type, and a shorter length A by about 10%. Therefore, the core volume V e has been reduced by about 20%, and conversely, the core cross-sectional area A e has been increased by about 30%. If the core volume Ve is small, the amount of the magnetic material used can be small, so that it can be manufactured lightly and inexpensively. The dimension ratio of the core window is hZw½l.5 in the product of the present invention, while that of the conventional transformer is flat. As for the transformer loss, the copper loss is reduced by 40% and the iron loss is also reduced by 18%, indicating that the performance as a transformer is improved.

 FIG. 10 is a perspective view showing the configuration of a fifth embodiment of the present invention, in which (A) shows a state in which the EE type is mounted on a coil laminate, and (B) shows a coil laminate alone. . FIGS. 11A and 11B are configuration diagrams illustrating the shape of the EE-type core. FIG. 11A is a front view of an assembled state of the EE-type core, and FIG. 11B is a plan view of the E-type core. This embodiment 5 is a modification of the embodiment of FIG. 3. In the case of the embodiment of FIG. 3, the diameter D of the middle foot 33 is equal to the width C of the connection 35, but here, D <C has been selected. With this configuration, the thickness b of the leg portion can be reduced, and the dimensions h and w of the core window can be increased, so that the area hw of the core window can be increased. As a result, there is an effect that the transformer can be further reduced in size and thickness.

FIGS. 12 and 13 are perspective views showing the configuration of the sixth embodiment of the present invention. FIG. 12 (A) shows a state in which an EI type coil is mounted on a coil laminate, FIG. 12 (B) shows a coil laminate alone, and FIG. Fig. 7 is an explanatory diagram of a state in which an EI type is assembled. This embodiment 6 is a modification of the embodiment of FIG. 3, and is different from the embodiment shown in FIG. Even in this case, the same effect as in the first embodiment can be obtained by making the core window shapes h and w substantially the same. As described above, according to the present invention, the dimensional ratio (hw) of the core window is set in the range of 0.5 to 2, and the coefficient k (= ^{Vel /} VAe ^{, / 2} ) representing the shape of the core is set to Since the selection is made in the range of 1.4 to 1.7, there is an effect that the transformer loss determined by copper loss and iron loss is minimized. Also, there is an effect that the transformer shape can be reduced in size as compared with the transformer specified in the conventional JI SFEER25.5 or the like.

In this case, there are 1-hole type 40 and 2-hole type 50 in the body, and EE type and UU type are selected for mounting, respectively. Window The dimensional ratio and coefficient k are defined by equation 30.

Claims

The scope of the claims  1. In the coil laminate (40) in which a plurality of concentric spiral coils are laminated in the thickness direction using insulating resin, the center of the spiral is the center of the EE type core or EI type core (33). ) To obtain magnetic coupling between the plurality of coils,  The cross-sectional area of the end of the leg is approximately the same at the end of the leg (34) and the end of the connecting portion (35), and the cross-sectional area (Ae) of the midfoot is approximately 2 times the cross-sectional area of the leg. In addition to satisfying the following equation in relation to the core volume (V e), 1.4≤V e ^1/3 / Ae ^1/2 ≤1.7  The following formula is satisfied between the interval (w) between the end of the metatarsal and the end of the leg, and the height (h) of the metatarsal,  0.5≤h / w≤ 2  Printed coil type transformer characterized by the following.  2. A plurality of concentric spiral coils are laminated in the thickness direction using an insulating resin, and a UU-shaped core or a UI-shaped coil is formed on a two-hole coil laminate (50) having a plurality of spiral centers. A flat transformer for arranging legs (36) to obtain magnetic coupling between the coils,  The cross-sectional area (Ae) of the leg portion is approximately equal to the cross-sectional area of the connecting portion (37), and the following expression is satisfied in relation to the volume (V e), 1.4≤V e ^{, /} VAe ^1/2 ≤l.7  The following formula must be satisfied between the interval (2w) between the inner peripheral surfaces of the legs and the height (h) of the legs.  0.5≤h / w≤ 2  Printed coil type transformer characterized by the following.