RU2742080C1 - Transformer - Google Patents

Abstract

FIELD: electrical equipment.

SUBSTANCE: invention relates to electrical engineering, in particular to high-frequency transformers of low power (up to 1 kW). Substance of invention consists in fact that transformer comprises magnetic conductor, consisting of two parts, ends of which are located opposite to each other with formation of at least two gaps, on each of said two parts of magnetic conductor there is at least two windings, wherein opposed to each other ends of magnetic conductor parts are concaved to form recesses having tops and bases, wherein the size of the gap between the tops of the recesses located opposite to each other of the ends of the two parts of the magnetic conductor is at least twice as large as the gap between the bases of the corresponding recesses of the ends of the two parts of the magnetic conductor.

EFFECT: technical result is improvement of weight and dimensions and increased capacity of transformer.

12 cl, 4 dwg, 1 tbl

Description

Region techniques

This technical solution relates to electrical engineering, in particular, to low-power high-frequency transformers (up to 1 kW) and can be used in radio electronics and conversion technology.

Level techniques

Currently known transformers of various designs, the main elements of the transformer are the magnetic circuit, windings. Transformers are divided, in particular, according to the type of magnetic circuit into armored, toroidal, rod.

Armored transformers have a branched magnetic circuit. The windings are located on the middle bar. Such transformers are of simple and inexpensive construction. Their disadvantages are relatively high sensitivity to interference, large leakage flux and poor cooling of the windings. These disadvantages are especially manifested when placing a transformer up to 1 kW on a printed circuit board due to restrictions on weight and dimensions and the permissible maximum temperature.

Toroidal core transformers are the most difficult to manufacture, which also limits their possible field of application. Their main advantages are their very low sensitivity to external magnetic fields and a small value of the leakage flux.

In transformers with core magnetic circuits, in comparison with armored transformers, better cooling of the windings is provided, since the windings are located on different rods.

In addition, rod transformers are less sensitive to external magnetic fields, due to the fact that the EMF interference induced in both coils is opposite in sign and is partially or completely eliminated. The disadvantages of existing rod-type transformers are high weight and size indicators, as in armored transformers.

The objective of this technical solution is to create a rod-type transformer with improved weight and dimensions and increased power in comparison with similar armored-type transformers.

Disclosure

The object of the present technical solution is a transformer including a magnetic circuit, consisting of two parts, the ends of which are located opposite each other with the formation of at least two gaps, on each of the mentioned two parts of the magnetic circuit there are at least two windings made directly on the magnetic circuit, and connected with the terminals of the transformer, the ends of the magnetic circuit parts located opposite each other are made concave, with the formation of depressions having tops and bases, and the size of the gap between the tops of the recesses located opposite each other of the ends of the two parts of the magnetic circuit is at least twice the size of the gap between the bases corresponding indentations of the ends of the two parts of the magnetic circuit.

An embodiment is possible in which the shape of the recess in the longitudinal section of the concave end of the magnetic circuit is essentially one of the following: trapezoid, semicircle, semi-oval, triangle,

An embodiment is possible in which a dielectric is placed in the gaps between the parts of the magnetic circuit.

An embodiment is possible in which the parts of the magnetic circuit have a U- or C-shape.

An embodiment is possible in which the cross-section of the parts of the magnetic circuit has a square or rectangular or circular shape.

An embodiment is possible in which parts of the magnetic circuit are made of soft magnetic material.

An embodiment is possible in which parts of the magnetic circuit are made of a hard magnetic material.

An embodiment is possible in which at least one of the parts of the magnetic circuit is made composite and contains at least two elements with the formation of a gap between the elements, and the gap between the elements has a rectangular cross-sectional shape.

An embodiment is possible in which a dielectric is placed in the gaps between the elements of at least one of the parts of the magnetic circuit.

An embodiment is possible in which parts of the magnetic circuit are tightened with a dielectric belt along the perimeter of the transformer.

An embodiment is possible in which the transformer leads are made with the possibility of mounting on a printed circuit board.

An embodiment is possible in which the transformer comprises a contact pad associated with the terminals of the transformer and configured to be mounted on a printed circuit board.

The technical result is the creation of a rod-type transformer with improved weight and dimensions and increased power in comparison with similar armored-type transformers.

Additional and / or alternative characteristics, aspects and advantages of embodiments of the present technical solution will become apparent from the following description, the accompanying drawings and the accompanying claims.

Brief description drawings

FIG. 1 schematically shows a non-limiting embodiment of the inventive transformer.

FIG. 2 schematically shows the gap between the flat ends of parts of the magnetic circuit according to the prior art

FIG. 3 schematically shows the gap between the concave ends of the parts of the magnetic circuit according to the claimed technical solution.

FIG. 4 shows the dependence of the gap value on the equivalent gap value for the investigated transformers.

Description

FIG. 1 schematically shows a transformer 100 including a two-piece magnetic circuit 102 and 104, respectively. The ends of the portions 102 and 104 of the magnetic circuit are opposite each other with the formation of at least two gaps 1061 and 1062, respectively. As shown in FIG. 1 the end 1021 of one part 102 of the magnetic circuit is opposite the end 1041 of the other part 104 of the magnetic circuit, and, accordingly, the end 1022 of one part 102 of the magnetic circuit is opposite the end 1042 of the other part 104 of the magnetic circuit.

In a non-limiting illustrative example, the portions 102 and 104 of the magnetic circuit are U-shaped (FIG. 1). In alternative embodiments, the implementation of parts of the magnetic circuit C-shaped (not shown) is possible.

The section of the portions of the magnetic circuit 102 and 104 can be square or rectangular or circular.

The parts of the magnetic circuit 102 and 104 can be made of both magnetically soft and magnetically hard material, for example, ferrite.

Each of the two parts 102 and 104 of the magnetic circuit has at least two windings 108 and 110, respectively, made directly on the magnetic circuit. That is, the magnetic circuit is a frameless core for two windings 108 and two windings 110. As will be understood by a person skilled in the art, the number of windings 108 and 110 on each of the portions 102 and 104 of the magnetic circuit, as well as the number of turns, length of a winding turn, wire diameter, material and other possible parameters of the windings 108 and 110 are not specifically limited, and can be selected based on the desired purpose, as well as the required characteristics of the transformer. In addition, the windings 108 and 110 may each other at least in one of the parameters coincide and / or differ in at least one of the parameters.

For example, as shown in FIG. 1, each of the parts 102 and 104 of the magnetic circuit can have a U-shape with sides f and g, where f> g, while the windings 108 and 110 are respectively made on the long sides f of the parts 102 and 104 of the magnetic circuit, and the gaps 1061 and 1062 are located between short sides g of parts 102 and 104 of the magnetic circuit.

Windings 108 and 110 are coupled to respective terminals 1081 and 1101 of transformer 100.

Opposite ends 1021 and 1041, as well as 1022 and 1042 of parts 102 and 104 of the magnetic circuit are made concave, with the formation of depressions having tops 112 and bases 114. Moreover, the value n of the gap between the tops 112 of the depressions is at least twice the value m the gap between the bases 114 of the respective recesses of the ends 1021 and 1041, as well as the ends 1022 and 1042 of the two parts 102 and 104 of the magnetic circuit. As shown in FIG. 1 n ≥ 2m.

Thus, as shown in FIG. 1, the gaps 1061 and 1062 may be substantially oval in cross-section.

An embodiment is possible, in which the shape of the depression in the longitudinal section of the concave end of the magnetic circuit is essentially one of the following: trapezoid, semicircle, semi-oval, triangle.

An embodiment is possible in which a dielectric (not shown) is placed in the gaps between the parts of the magnetic circuit.

An embodiment is possible in which at least one of the parts of the magnetic circuit is made composite and contains at least two elements with the formation of a gap between the elements, and the gap between the elements has a rectangular cross-sectional shape.

For example, one or both parts of the magnetic circuit can be made of several elements, between which there are gaps. So, for example, a part of a U-shaped magnetic circuit can be made in an automated way by gluing three elements (sides), with the formation, respectively, of two gaps between these three elements. In this case, the gaps are summed up, and due to their small size (for example, 0.2 mm), there are practically no losses.

An embodiment is possible in which a dielectric is placed in the gaps between the elements of at least one of the parts of the magnetic circuit.

An embodiment is possible in which parts of the magnetic circuit are tightened with a dielectric belt along the perimeter of the transformer.

An embodiment is possible in which the transformer leads are made with the possibility of mounting on a printed circuit board.

An embodiment is possible in which the transformer comprises a contact pad associated with the terminals of the transformer and configured to be mounted on a printed circuit board.

Next, referring to FIG. 2 and 3, we give a theoretical justification and explanation of the implementation of the grooves on the opposite ends of the parts of the magnetic circuit

FIG. 2 schematically shows the ends 2021 and 2041 of two portions 202 and 204 of the prior art magnetic circuit. The surfaces of the ends represent substantially a plane with a constant clearance between ends 2021 and 2041 equal to δ ₁ . The section of parts 202 and 204 of the magnetic circuit is a rectangle with sides a and b and a sectional area S ₁ = a * b . For clarity, the diagram shows the X, Y, Z axes.

FIG. 3 schematically shows the ends 3021 and 3041 of two parts 302 and 304 of the magnetic circuit according to the claimed invention. The surfaces of the ends are essentially concave surfaces formed by depressions having peaks 312 and bases 314. Moreover, the value δ _{2 of the} gap between the tops 312 of the depressions of the ends 3021 and 3041 is at least twice the value δ _{3 of the} gap between the bases 314 of the corresponding depressions of the ends 3021 and 3041 . As shown in FIG. 3 δ ₂ ≥ 2 δ ₃ .

The section of the parts 302 and 304 of the magnetic circuit is a rectangle with sides a and b and a cross-sectional area S ₂ = a * b .

Thus, we put:

S = S ₁ = S ₂

δ = δ ₁ = δ ₂ = 2 δ ₃ , for clarity, the diagram also shows the X, Y, Z axes.

Next, referring to FIG. 2 and FIG. 3.

S <100 δ ² , where S is the cross-sectional area of the magnetic circuit, δ is the size of the gap between the ends of the parts of the magnetic circuit.

The magnetic induction (Vm) over the section is significantly reduced when approaching the surface of the magnetic circuit, due to the curvature of the magnetic lines of force at the edges in the gap. The longer the equipotential magnetic line in the gap, the lower the magnetic induction (Vm), according to formula (1)

Taking into account the boundary conditions at the separation of two media, the problem is solved to minimize the inhomogeneity of the magnetic induction in the gap. In order to significantly eliminate the inhomogeneity, it is necessary to give a special shape to the surfaces of the ends of the magnetic circuit, forming a gap. To do this, we will establish a field pattern in a gap with flat surfaces.

Consider the field component By directed from one pole (end of a part of the magnetic circuit) to the other, see Fig. 2, in the XОZ plane equidistant between the poles (ends of the parts of the magnetic circuit 2021 and 2041), this will be the observation plane. The observation point with coordinates x0, z0 is on this plane.

It is necessary to sum all the magnetic dipoles from the two surfaces of the poles, then sum up in the volume adjacent to the surfaces. As a result, we come to the calculation of the surface integral of the second kind.

Analytically it is possible to solve the integral only on the surface equidistant from the two poles (Fig. 2), in this case Bx = 0, Bz = 0.

Numerical methods can determine the vector B at any point, even outside the gap. We obtain the dependence of the magnetic field By (x0, z0).

The solution leads to the fact that at a distance of 2 * δ or more from the edge of the gap surface, the magnetic induction rapidly drops. And approximately 2 * δ or more outside the gap falls to zero at S <100 δ ² .

Now, knowing the distribution of the magnetic field with flat surfaces, we introduce a certain curvature of the surface in such a way that at all points of the surface the field is close to Bm, while, in practice, the magnetic flux will not decrease (Fig. 3). Consider again a surface equidistant from two poles (ends 3021 and 3041 of the parts of the magnetic circuit located opposite each other) XOZ.

Even in the case of the curvature of the surface symmetric about the center of the pole, Bx = 0, Bz = 0, (since they are compensated by two surfaces) By is the vector of magnetic induction (Fig. 3). Knowing the field distribution for the flat surfaces of the poles (ends 2021 and 2041 in Fig. 2), it is possible to define a certain surface, for example, in the form of a parabolic cylinder Y = f (x, z) (shown in Fig. 3) symmetric with respect to X. Considering it in the integral, we obtain a new solution.

On a line passing through the center of the pole section from the point (a / 2.0, -b / 2) -b (a / 2.0, b / 2), the value of Bm will be the same, when the poles approach, so that between the tops of 312 depressions the ends 3021 and 3041 was the distance δ ₂ = δ, and between the bases of the respective recesses 314, the ends 3021 and 3041 δ _3. Moreover, δ ₂ ≥ 2 δ ₃ As shown in FIG. 3.

от потерь при плоских полюсах.On the surface of a parabolic cylinder, the magnetic field will practically not change, although from the edge on side b it will be from Bm to Bm / 2, depending on the aspect ratio of the magnetic circuit. Thus, the loss of magnetic flux is maximum

from losses at flat poles.

According to the claimed invention, the ends 3021 and 3041 of the parts of the magnetic circuit, located opposite each other, approach each other so that the size of the gap δ ₂ between the tops 312 of the depressions is at least twice the value of δ _{3 of the} gap between the bases 314 of the corresponding depressions of the ends 3021 and 3041 ( Fig. 3). Similarly shown in FIG. 1, where the value n of the gap between the tops 112 of the recesses is at least twice the value m of the gap between the bases 114 of the respective recesses of the ends 1021 and 1041, as well as 1022 and 1042 of the two parts 102 and 104 of the magnetic circuit. ( n ≥ 2m).

The applicant carried out practical tests of the claimed transformer design. Table 1 below shows the characteristics obtained in comparison with the known design of the armored type transformer.

In the prior art, an EF25 / 25/7 ferrite core transformer is known, widely used in, for example, LED lighting drivers. The well-known transformer EF25 / 25/7 has the following parameters: an armor-type core when joining two halves of type E 25 mm * 25 mm, height 7.2 mm, central core 7.2 * 7.2 mm, dimensions with a frame 30 * 30 * 22 mm (length, width, height).

The applicant has assembled and tested several versions of a rod-type transformer with a design according to the present invention, conventionally denoted as PL29-1, PL29-2, PL29-3 and PL29-4, with the following parameters: rod-type core when joining 29 mm * 20 mm, cross-section core 6.6mm * 6.6mm. Assembled 31 * 27 * 17 mm (length, width, height). As the specialist will understand, an example with similar weight and dimensions is deliberately taken for testing.

The occupied area, the height on the board with these transformers is the same, and the masses of the magnetic cores are the same (for EF25 / 25/7 Sо without frame 94 mm ² , with frame 62 mm ² ). The maximum number of turns is considered until the window is filled with the maximum possible gap.

The tests were carried out in flyback converters with the same duty cycle D, frequency, input voltage Uin (except for PL29-1 to compare power when the masses of copper are equal to EF25) and relative magnetic permeability μ of the material.

Table 1. Test results

The primary winding of the famous EF25 transformer is 2 * 0.28 mm, the secondary winding is 3 * 0.28 mm.

For PL29, the primary winding is 2 * 0.25 mm, the secondary one is 3 * 0.25 mm (the windings on different rods are connected in parallel).

Explanations for table 1 above:

So - window area

Sк - cross-sectional area of the magnetic circuit at the gap

W1 - number of turns of the primary winding

W2 - number of turns of the secondary winding

d - wire diameter

Lsrv - average turn length

Mm - mass of copper

Uout - rated value of the output voltage

Wmak, eq - maximum stored energy in a core with an equivalent gap

Pout, ek output power with an equivalent clearance

Wmak = Bmak ² * δ e * Sc / (2 * μ0) (CC.1)

Wmak is the maximum energy of the magnetic field in the magnetic circuit.

Bmak - maximum magnetic induction in the magnetic circuit

μ0 is the magnetic permeability of the vacuum.

Sc - cross section of the magnetic circuit

Bmak = μ0 * W1 * Imak / δ (for flyback converters)

W1 - number of turns in the primary winding

Imak - maximum current of the primary winding (for flyback converters)

δ is the geometric length of the gap.

Since the magnetic flux in the area of the air gap is not uniform, then

But nevertheless, in the central part, including (a / 2, y, b / 2), it is necessary to obtain Bmak due to the geometric clearance.

It is more convenient to use δ e - the value of the equivalent gap.

Replacing δ by δ e in all formulas, a real result is obtained.

where δ is the geometric length of the gap; p is the perimeter of the magnetic circuit section at the gap; S is the cross-section of the end of the magnetic circuit at the gap (i.e., the cross-section of the pole); 2с - winding height; a is the distance from the core to the centerline of the longitudinal section of the winding (that is, approximately the half-width of the winding).

With the same geometric clearances for the EF25 and PL29, the equivalent clearance for the PL29 is much larger, because it has two spaced gaps (geometrical gaps are added) as shown in FIG. 4

PL29-1 is a pulse transformer, in which the mass of copper is equal to the mass of copper EF25 , Pout is 60% higher, but the window is not fully occupied.

PL29-2 is a pulse transformer in which the window is fully occupied. The decrease in magnetic flux is 30%. Pout practically did not change.

Exceeding a certain value of the geometric clearance, the equivalent clearance according to formulas (2) and (3) begins to decrease as shown in FIG. 4.

When the window was completely filled, the number of turns was too large. From formulas (2) and (3) above, it can be seen that this problem can be solved by increasing the cross-section of the ends of the parts of the magnetic circuit that form the gap. The section grows quadratically with the growth of the perimeter.

PL28-3 - the cross-section of the ends has been doubled (which cannot be done with an armored one, due to the presence of a frame), which gives tangible results. At the same time, PL29-3 has 30% more copper mass than EF25.

The ends of the magnetic circuit parts are made in the form of a part of an expanding conical pyramid (on side d), in which the base is a surface that delimits the gap. The mass of the magnetic circuit and its overall dimensions have practically not changed.

Experiments in PL29-3 were carried out with a ferrite core, whose cross section in the parts where there was no winding was twice as large as in the rod.

In PL28-4 - a magnetic circuit with the same cross-section along the entire length is used, including the cross-section of the ends of the magnetic circuit parts (poles). The surface of the ends of the parts of the magnetic circuit, which forms the gap, has a certain curvature, as a result, the power increases by 22%, due to an increase in the total magnetic flux than without curvature.

As shown in table 1 above, in the proposed design there is a significant increase in power compared to the known armored transformer, the claimed design allows, if necessary, to significantly reduce the weight and dimensions to achieve the same power as in armored transformers.

The inventive design can be manufactured by standard methods and on standard equipment similar to other known transformer designs.

The execution of grooves at the ends of the parts of the magnetic circuit, located opposite each other, is possible for ends with a circular cross-section, rectangular, square and other shapes. It is possible both grinding by rotation around the center of each end (pole), and using a surface grinding machine to make the curvature of the groove in one direction. Accordingly, it is possible to obtain depressions of various shapes, for example, with obtaining depressions in the longitudinal section of the concave end of the magnetic circuit, essentially in the form of: a trapezoid, a semicircle, a semi-oval, a triangle.

The shape of the depression itself may be, in particular, a truncated cone, a cone, a cylinder, a hemisphere, a half-cylinder, an elliptical half-cylinder, a prism, a triangular prism, etc.

Grinding of a magnetic core made of ferrite can be carried out with a surface grinder, which is an integral part of production equipment and for an armored transformer. In this case, a grinding disc with a grinding surface Y = f (x, z) is used. To minimize chips at the edges, a protective coating can be applied to the surface of the magnetic circuit in one or several layers.

The declared design of the transformer has improved weight and dimensions and increased power in comparison with similar armored transformers.

Due to the implementation of windings on frameless cores (directly on the magnetic circuit), it is possible to increase the number of turns / and wire diameter, and as a consequence, increase the power of the transformer.

The cooling surface area increases, therefore, an additional reduction in the diameter of the wire in the winding and an additional reduction in weight and dimensions are possible.

Thus, it is possible to increase the length of the winding by at least 2 times in comparison with the carcass core, as a consequence of the decrease in the number of layers by 2 times, which reduces copper losses several times.

The presented illustrative embodiments, examples and description are provided for understanding only and are not limiting. The explanatory drawings are not to scale. Other possible options for implementation will be clear to the specialist from the description provided. The scope of the present invention is limited only by the attached claims.

Claims (12)

1. A transformer including a magnetic circuit, consisting of two parts, the ends of which are located opposite each other with the formation of at least two gaps, on each of the mentioned two parts of the magnetic circuit there are at least two windings made directly on the magnetic circuit, and connected to the terminals of the transformer the ends of the magnetic circuit parts located opposite each other are concave with the formation of recesses having tops and bases, and the size of the gap between the tops of the recesses located opposite each other of the ends of the two parts of the magnetic circuit is at least twice the size of the gap between the bases of the corresponding recesses of the ends of the two parts of the magnetic circuit. 2. The transformer according to claim 1, in which the shape of the depression in the longitudinal section of the concave end of the magnetic circuit is essentially one of the following: a trapezoid, a semicircle, a semi-oval, a triangle. 3. A transformer according to claim 1, in which a dielectric is placed in the gaps between the parts of the magnetic circuit. 4. A transformer according to claim 1, wherein the portions of the magnetic circuit are U- or C-shaped. 5. The transformer according to claim. 1, in which the section of the parts of the magnetic circuit has a square, or rectangular, or circular shape. 6. A transformer according to claim 1, in which the parts of the magnetic circuit are made of soft magnetic material. 7. A transformer according to claim 1, in which parts of the magnetic circuit are made of a hard magnetic material. 8. The transformer according to claim. 1, in which at least one of the parts of the magnetic circuit is made composite and contains at least two elements with the formation of a gap between the elements, while the gap between the elements has a rectangular cross-sectional shape. 9. The transformer according to claim 8, wherein a dielectric is placed in the gaps between the elements of at least one of the parts of the magnetic circuit. 10. The transformer according to claim 1, in which parts of the magnetic circuit are tightened with a dielectric belt along the perimeter of the transformer. 11. The transformer according to claim 1, wherein the transformer terminals are configured to be mounted on a printed circuit board. 12. The transformer of claim. 1, in which the transformer comprises a contact pad associated with the terminals of the transformer and configured to be mounted on a printed circuit board.

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