Electronic converter, and corresponding method for designing a magnetic component

Abstract

A converter includes first and second input terminals and first and second output terminals. The converter also includes an output capacitor coupled between the first output terminal and the second output terminal, and a magnetic component having two input terminals and three output terminals. A first output terminal of the magnetic component is coupled through a first electronic switch to the second output terminal of the converter, a second output terminal of the magnetic component is coupled to the first output terminal of the converter, and a third output terminal of the magnetic component is coupled through a second electronic switch to the second output terminal of the electronic converter. In addition, the converter includes a switching stage configured to transfer current pulses from the first input terminal and the second input terminal of the converter to the two input terminals of the magnetic component.

Claims

1. An electronic converter comprising: first and second input terminals configured to receive a first supply signal; first and second output terminals configured to supply a second supply signal; an output capacitor coupled between the first output terminal and the second output terminal; a first electronic switch; a second electronic switch; a magnetic component having two input terminals and three output terminals, wherein: a first output terminal of the magnetic component is coupled through the first electronic switch to the second output terminal of the electronic converter, a second output terminal of the magnetic component is coupled to the first output terminal of the electronic converter, and a third output terminal of the magnetic component is coupled through the second electronic switch to the second output terminal of the electronic converter; and a switching stage configured to transfer current pulses from the first input terminal and the second input terminal of the electronic converter to the two input terminals of the magnetic component, wherein the magnetic component comprises a plurality of transformers, each transformer having a respective primary winding and a respective secondary winding, and wherein: primary windings of the plurality of transformers are coupled in series between the two input terminals of the magnetic component; secondary windings of a first and second transformers of the plurality of transformers are coupled in series between the first output terminal of the magnetic component and the second output terminal of the magnetic component; and secondary windings of third and fourth transformers of the plurality of transformers are coupled in series between the second output terminal of the magnetic component and the third output terminal of the magnetic component.

2. The electronic converter according to claim 1, wherein the first transformer and the third transformer have substantially a same first turn ratio and a same first magnetizing inductance.

3. The electronic converter according to claim 2, wherein the second transformer and the fourth transformer have substantially a same second turn ratio and a same second magnetizing inductance.

4. The electronic converter according to claim 1, wherein the primary windings of the first transformer and the third transformer are coupled directly in series.

5. The electronic converter according to claim 4, wherein the primary windings of the second transformer and the fourth transformer are coupled directly in series.

6. The electronic converter according to claim 1, wherein the magnetic component comprises a magnetic core comprising four separate zones, wherein the primary winding and the secondary winding of a respective transformer of the plurality of transformers are arranged in each zone.

7. The electronic converter according to claim 6, wherein the primary and secondary windings of the plurality of transformers comprise stacked layers of conductive material.

8. The electronic converter according to claim 1, wherein the first and second electronic switches comprise diodes.

9. The electronic converter according to claim 1, wherein the switching stage comprises at least one of a half-bridge and a full-bridge.

10. The electronic converter according to claim 1, wherein the secondary windings of the first and second transformers are directly connected in series, and the secondary windings of the third and fourth transformers are directly connected in series.

11. The electronic converter according to claim 1, wherein the magnetic component comprises a magnetic core having two E-shaped portions and a central plate disposed between the two E-shaped portions, and wherein lateral portions of each of the two E-shaped portions are separated from the central plate by respective airgaps.

12. The electronic converter according to claim 1, wherein the first and third transformers are transformers of a first type, and the second and fourth transformers are transformers of a second type different from the first type.

13. An electronic converter comprising: first and second input terminals configured to receive a first supply signal; first and second output terminals configured to supply a second supply signal; a first diode; a second diode; a magnetic component having two input terminals and three output terminals; and a switching stage configured to transfer current pulses from the first input terminal and the second input terminal to the two input terminals of the magnetic component, wherein the magnetic component comprises: a plurality of transformers, each transformer having a respective primary winding and a respective secondary winding; primary windings of the plurality of transformers coupled in series between the two input terminals of the magnetic component; secondary windings of first and second transformers of the plurality of transformers coupled in series between a first output terminal of the magnetic component and a second output terminal of the magnetic component; and secondary windings of third and fourth transformers of the plurality of transformers coupled in series between the second output terminal of the magnetic component and a third output terminal of the magnetic component.

14. The electronic converter of claim 13, wherein the first output terminal of the magnetic component is coupled through the first diode to the second output terminal of the electronic converter, the second output terminal of the magnetic component is coupled to the first output terminal of the electronic converter, and the third output terminal of the magnetic component is coupled through the second diode to the second output terminal of the electronic converter.

15. The electronic converter according to claim 13, wherein the first transformer and the third transformer have substantially a same first turn ratio and a same first magnetizing inductance.

16. The electronic converter according to claim 15, wherein the second transformer and the fourth transformer have substantially a same second turn ratio and a same second magnetizing inductance.

17. The electronic converter according to claim 13, wherein the primary windings of the first transformer and the third transformer are coupled directly in series.

18. The electronic converter according to claim 17, wherein the primary windings of the second transformer and the fourth transformer are coupled directly in series.

19. The electronic converter according to claim 13, wherein the magnetic component comprises a magnetic core comprising four separate zones, wherein the primary winding and the secondary winding of a respective transformer of the plurality of transformers are arranged in each zone.

20. The electronic converter according to claim 19, wherein the primary and secondary windings of the plurality of transformers comprise stacked layers of conductive material.

21. A method of making an electronic converter having first and second input terminals and first and second output terminals, the method comprising: coupling an output capacitor between the first output terminal and the second output terminal; coupling a first output terminal of a magnetic component through a first electronic switch to the second output terminal of the electronic converter; coupling a second output terminal of the magnetic component to the first output terminal of the electronic converter; coupling a third output terminal of the magnetic component through a second electronic switch to the second output terminal of the electronic converter; and transferring current pulses from the first input terminal and the second input terminal of the electronic converter to two input terminals of the magnetic component using a switching stage, wherein the magnetic component comprises a plurality of transformers, wherein each transformer has a respective primary winding and a respective secondary winding, and wherein: primary windings of the plurality of transformers are coupled in series between the two input terminals of the magnetic component, secondary windings of first and second transformers of the plurality of transformers are coupled in series between the first output terminal of the magnetic component and the second output terminal of the magnetic component, and secondary windings of third and fourth transformers of the plurality of transformers are coupled in series between the second output terminal of the magnetic component and the third output terminal of the magnetic component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present disclosure will now be described purely by way of non-limiting example with reference to the annexed drawings, wherein:

(2) FIG. 1 is a circuit diagram of converter of the prior art;

(3) FIG. 2 shows the inductive components of the converter of FIG. 1;

(4) FIG. 3 is a circuit diagram of an embodiment of a magnetic component that is able to implement the inductive components of FIG. 2 according to the invention;

(5) FIGS. 4A and 4B illustrate circuit diagrams of electronic converters that use the magnetic component of FIG. 3;

(6) FIG. 5 shows a condition of the circuit of FIG. 4A;

(7) FIG. 6 shows a different condition of the circuit of FIG. 4A;

(8) FIG. 7a is an axonometric view of a core of the magnetic component of FIG. 3;

(9) FIG. 7b is a side elevational view of the core of the magnetic component of FIG. 7a;

(10) FIG. 8a illustrates layers that implement primary windings W1 of the magnetic component;

(11) FIG. 8b illustrates layers that implement the secondary windings of the transformers Tb and Tc of the magnetic component;

(12) FIG. 8c illustrates layers that implement the secondary windings of the transformers Ta and Td of the magnetic component;

(13) FIG. 9a is a front elevational view of an embodiment of the magnetic component;

(14) FIG. 9b is a rear elevational view of the magnetic component of FIG. 9a; and

(15) FIG. 9c is a top plan view of the magnetic component of FIG. 9a.

DETAILED DESCRIPTION

(16) In the ensuing description, various specific details are illustrated aimed at providing an in-depth understanding of the embodiments. The embodiments may be provided without one or more of the specific details, or with other methods, components, materials, etc. In other cases, known structures, materials, or operations are not shown or described in detail so that various aspects of the embodiments will not be obscured.

(17) Reference to an embodiment or one embodiment in the framework of the present description is meant to indicate that a particular configuration, structure, or characteristic described in relation to the embodiment is comprised in at least one embodiment. Hence, phrases such as in an embodiment or in one embodiment that may be present in various points of this description do not necessarily refer to one and the same embodiment. Furthermore, particular conformations, structures, or characteristics may be combined in any adequate way in one or more embodiments.

(18) The references used herein are provided only for convenience and hence do not define the sphere of protection or the scope of the embodiments.

(19) As mentioned previously, one object of the present disclosure is to provide approaches that enable a magnetic circuit to be obtained that makes it possible to implement the inductances of the current-doubler rectifier described previously.

(20) FIG. 2 shows in this context the inductances of the current-doubler rectifier described with reference to FIG. 1.

(21) In particular, also in this case, the component has two input terminals A and B that are designed to be coupled to a half-bridge or full-bridge, or in general a switching stage.

(22) The terminals R1 and R2 are coupled to the rectifier circuits of the current doubler, i.e., the switches or diodes S1 and S2, and the terminal COM are coupled to the output voltage V.sub.o, i.e., the positive terminal of the capacitor Cout, i.e., the terminal 206.

(23) Consequently, in general, the integrated magnetic component has five terminals, namely, two input terminals and three output terminals.

(24) If the magnetizing inductance of the transformer is disregarded, this component can be described as the equivalent of an ideal transformer having a turn ratio N:1, having at the primary winding a series inductance L.sub.RES that represents the leakage inductance of the transformer T, and at the secondary two inductances between the terminals R1-COM and R2-COM that have a value Lout1 and Lout2, respectively.

(25) FIG. 3 shows a possible embodiment of an electrical circuit designed to implement the ideal component described in FIG. 2.

(26) In particular, in the embodiment considered, the component comprises four transformers Ta, Tb, Tc, and Td.

(27) In the embodiment considered, the primary windings of these transformers Ta-Td are coupled in series between the terminals A and B, and the secondary windings of the transformers Ta-Td are coupled in series between the terminals R1 and R2, where the intermediate point between the secondary winding of the second transformer Tb and the secondary winding of the third transformer Tc is coupled to the terminal COM.

(28) Consequently, the transformers Ta and Tb can also be swapped around, as likewise the transformers Tc and Td. In fact, in general, it is sufficient for the primary windings of the four transformers Ta-Td to be coupled in series between the terminals A and B, for the secondary windings of the transformers Ta and Td to be coupled in series between the terminals R1 and COM, and for the secondary windings of the transformers Tc and Td to be coupled in series between the terminals R2 and COM.

(29) In one embodiment, the circuit is made up of two types of transformers electrically modelled by a turn ratio equal to N.sub.1:1 and N.sub.2:1 and by their respective magnetizing inductances L.sub.1 and L.sub.2, i.e., their equivalent output inductances. Consequently, in the embodiment considered, it is assumed that the transformers Ta-Td are designed for having an optimal efficiency, i.e., a negligible equivalent leakage inductance, which is consequently omitted in the circuit representation, for instance, lower than 100 nH.

(30) In particular, one of the transformers Ta or Tb is of the first type and the other is of the second type, and likewise one of the transformers To or Td is of the first type and the other is of the second type. For example, in the embodiment considered, the transformers Ta and Tc are of the first type (N.sub.1:1, L.sub.1) and the transformers Tb and Td are of the second type (N.sub.2:1, L.sub.2).

(31) As will be described hereinafter, from this circuit it is possible to obtain the main parameters of the ideal equivalent component of FIG. 2 by using the circuit equations. In these equations (since it is a calculation of impedances seen at the terminals of the component), since the node COM is coupled to the voltage V.sub.o, i.e., a node at extremely low impedance as represented in FIG. 1, it can also be replaced with the ground GND.sub.2.

(32) FIG. 4A shows in this context the generalized scheme of a half- bridge converter or a full-bridge converter, which substantially results from the combination of the circuit of FIG. 1 with the circuit of FIG. 3. FIG. 4B shows the circuit of FIG. 4A in which switches S1 and S2 are implemented with diodes.

(33) On the basis of the above circuit, the circuit equations may be applied to obtain the mathematical expressions that reconstruct the parameters of FIG. 2, such as L.sub.RES, N, Lout1, and Lout2.

(34) In particular, during operation of the converter and according to the switching state of the switches on the primary winding (half-bridge or full-bridge) it is possible to identify two operating areas: ZVS or magnetization of the magnetic circuit, and resonance region.

(35) ZVS and Magnetization of the Circuit

(36) As shown in FIG. 5, during this step, it is necessary to calculate the impedance at the input between the terminals A and B while the switches S1 and S2 of the current doubler are closed and hence R1 and R2 are grounded. In this case, the input impedance should be given by the resonance inductance L.sub.RES.

(37) Applying the circuit equation of the voltage mesh at input for the voltages V.sub.1, V.sub.2, V.sub.3, and V.sub.4 respectively across the secondary windings of the transformers Ta, Tb, Tc, and Td, will obtain
V.sub.IN=N.sub.1.Math.V.sub.1+N.sub.2.Math.V.sub.2+N.sub.1.Math.V.sub.3+N.sub.2.Math.V.sub.4
V.sub.2=V.sub.1
V.sub.4=V.sub.3
whence
V.sub.IN=(V.sub.1+V.sub.3).Math.(N.sub.1N.sub.2)

(38) Applying the circuit equation of the currents I.sub.CC1 and I.sub.CC2 that flow through the secondary windings of the transformers Ta/Tb and Tc/Td, respectively, will obtain
N.sub.1.Math.I.sub.IN+I.sub.CC1=I.sub.L1
N.sub.2.Math.I.sub.IN+I.sub.CC1=I.sub.L2
N.sub.1.Math.I.sub.IN+I.sub.CC2=I.sub.L1
N.sub.2.Math.I.sub.IN+I.sub.CC2=I.sub.L2

(39) From these equations it follows that I.sub.CC1=I.sub.CC2=I.sub.CC and consequently also the equalities between the voltages V.sub.1=V.sub.3 and V.sub.2=V.sub.4 apply so that no current generated in these conditions exits from the node COM towards the output. Hence, the equations become
N.sub.1.Math.I.sub.IN+I.sub.CC=I.sub.L1
N.sub.2.Math.I.sub.IN+I.sub.CC=I.sub.L2
V.sub.IN=2.Math.V.sub.1.Math.(N.sub.1N.sub.2)

(40) By solving the system of equations, will obtain

(41) $I_{\mathrm{IN}}=\frac{I_{L1}-I_{L2}}{N_1-N_2}$$V_{\mathrm{IN}}=2.Math.V_1.Math.\left(N_1-N_2\right)$$V_1=\frac{V_{\mathrm{IN}}}{2.Math.\left(N_1-N_2\right)}$

(42) Passing to the s-domain, will obtain

(43) $I_{L1}=\frac{V_1}{{\mathrm{sL}}_1}=\frac{V_{\mathrm{IN}}}{s2.Math.L_1.Math.\left(N_1-N_2\right)}$$I_{L2}=\frac{V_2}{{\mathrm{sL}}_2}=-\frac{V_1}{{\mathrm{sL}}_2}=-\frac{V_{\mathrm{IN}}}{s2.Math.L_2.Math.\left(N_1-N_2\right)}$

(44) and the input impedance can be calculated as follows:

(45) $\frac{V_{\mathrm{IN}}}{I_{\mathrm{IN}}}={\mathrm{sL}}_{\mathrm{RES}}=2.Math.s\frac{L_1.Math.L_2}{L_1+L_2}.Math.{\left(N_1-N_2\right)}^2$

(46) Hence, the equivalent inductance seen at input with the output in short-circuit is:

(47) $L_{\mathrm{RES}}=2.Math.\frac{L_1.Math.L_2}{L_1+L_2}.Math.{\left(N_1-N_2\right)}^2$

(48) Finally, the short-circuit current I.sub.CC is calculated that circulates in the secondary taking into consideration that the switches S1/S2 of the current doubler are closed and the poles R1/R2 are at ground. From the ratio between the currents in the secondary and in the primary winding, will obtain the equivalent turn ratio of the magnetic component (parameter N of FIG. 3).

(49) The short-circuit current I.sub.CC circulating in the secondary in the s-domain is

(50) $I_{\mathrm{CC}}=I_{L1}-N_1.Math.I_{\mathrm{IN}}=V_{\mathrm{IN}}.Math.\frac{\frac{L_2}{L_1+L_2}.Math.\left(N_1-N_2\right)-N_1}{s.Math.2.Math.\frac{L_1.Math.L_2}{L_1+L_2}.Math.{\left(N_1-N_2\right)}^2}=-V_{\mathrm{IN}}.Math.\frac{N_1.Math.L_1+N_2{L}_2}{s.Math.2.Math.L_1.Math.L_2.Math.{\left(N_1-N_2\right)}^2}$

(51) From this relation, and substituting the expression of L.sub.RES, will obtain

(52) $I_{\mathrm{CC}}=-\frac{V_{\mathrm{IN}}}{{\mathrm{sL}}_{\mathrm{RES}}}.Math.\frac{N_1.Math.L_1+N_2{L}_2}{L_1+L_2}$

(53) The turn ratio N of the equivalent transformer is obtained as the ratio of the current in the secondary to the current in the primary winding, as follows:

(54) $N=\frac{I_{\mathrm{CC}}}{\frac{V_{\mathrm{IN}}}{{\mathrm{sL}}_{\mathrm{RES}}}}=\frac{N_1.Math.L_1+N_2{L}_2}{L_1+L_2}$
Resonance Region

(55) As shown in FIG. 6, during this step the converter maintains the primary side shorted, appropriately driving the half-bridge or the full-bridge, and the secondary side is open, i.e., with the switches S1 and S2 of the current doubler alternatively open. To obtain the parameters Lout1 and Lout2 with reference to FIG. 3, it is sufficient to note that at the primary winding there is no voltage drop, since the primary winding is shorted, and necessarily no current I.sub.IN flows in the primary winding, and the current I.sub.OUTX that flows through the secondary side of the transformer Ta corresponds to the current I.sub.L1 supplied by the magnetizing inductance L.sub.1. Thus, obtaining
N.sub.1.Math.I.sub.IN+I.sub.OUTX=I.sub.L1
I.sub.IN=0
I.sub.OUTX=I.sub.L1

(56) Consequently the inductance L.sub.out seen at output between the terminals R1 and COM is

(57) $V_{\mathrm{SECX}}=V_{L1}+V_{L2}$$V_{L2}={\mathrm{sL}}_2.Math.I_{L1}$$V_{\mathrm{SECX}}={\mathrm{sL}}_1.Math.I_{L1}+{\mathrm{sL}}_2.Math.I_{L1}$$\frac{V_{\mathrm{SECX}}}{I_{\mathrm{OUTX}}}=s.Math.\left(L_1+L_2\right)$$L_{\mathrm{OUT}1}=L_1+L_2$

(58) where V.sub.SECX is the voltage between the terminals COM and R1 that is applied to the capacitor Cout, V.sub.L1 and V.sub.L2 are the voltages across the secondary windings of the transformers Ta and Tb, respectively, and I.sub.L1 is the current that flows through the secondary windings of the transformer Ta, which necessarily corresponds to the current I.sub.L2 that flows through the secondary windings of the transformer Tb.

(59) Similar considerations apply for calculation of the output inductance L.sub.out2 between the terminals COM and R2 on the second output branch for which the same result is obtained, by symmetry.

(60) To sum up, the magnetic circuit behaves as represented schematically in FIG. 3 and has the following concentrated parameters:

(61) $L_{\mathrm{RES}}=2.Math.\frac{L_1.Math.L_2}{L_1+L_2}.Math.{\left(N_1-N_2\right)}^2$$N=\frac{N_1.Math.L_1+N_2{L}_2}{L_1+L_2}$$L_{\mathrm{OUT}}=L_1+L_2$

(62) For instance, the inductances L.sub.1 and L.sub.2 may be between 10 and 500 nH, preferably between 20 and 200 nH. For example, assuming an inductance L.sub.1 of 45 nH and assuming an inductance L.sub.2 of 75 nH, the inductances Lout1 and Lout2 would be 120 nH.

(63) From these equations, it is also possible to appreciate an advantage of the present approach as compared to the implementations proposed in the paper by Jian Sun that are substantially based upon the use of a magnetic component with just two secondary windings. In particular, in the paper by Jian Sun, the magnetic component is designed in such a way that the inductance L.sub.RES on the primary side (that serves for the resonance at the primary side) will be implemented with the magnetic flux in the winding of the component, i.e., with the leakage inductance, which increases the losses of the component. In the approaches described herein, the magnetic component comprises four transformers substantially independent of one another, and the inductance L.sub.RES on the primary side is implemented with the magnetic flux in the core/airgap of the component, i.e., with the magnetizing inductances L.sub.1 and L.sub.2 of the transformers Ta, Td, as follows:

(64) 0$L_{\mathrm{RES}}=2.Math.\frac{L_1.Math.L_2}{L_1+L_2}.Math.{\left(N_1-N_2\right)}^2$

(65) The person skilled in the art will appreciate that the above equation applies in the case where the component comprises four transformers with the respective magnetizing inductances, i.e., L.sub.1 and L.sub.2>0. In this context, the phrase substantially independent transformers is meant to indicate a component that comprises four zones detached from one another where associated to each zone is a respective primary winding and a respective secondary winding. For example, this does not apply to the component proposed by Jian Sun, because even though the windings can be virtually divided into a number of stretches, these do not implement independent transformers.

(66) Variation of the Parameters

(67) In this section, the effect of the tolerances of the magnetizing inductances is determined purely by way of illustration (the turn ratios are considered deterministic). The inductances L.sub.1 and L.sub.2 are considered not correlated with one another.

(68) $L_{\mathrm{RES}}=2.Math.\frac{L_2^2}{{\left(L_1+L_2\right)}^2}.Math.{\left(N_1-N_2\right)}^2.Math.L_1+2.Math.\frac{L_1^2}{{\left(L_1+L_2\right)}^2}.Math.{\left(N_1-N_2\right)}^2.Math.L_2$$u^2\left(L_{\mathrm{RES}}\right)=4.Math.\frac{L_2^4}{{\left(L_1+L_2\right)}^4}.Math.{\left(N_1-N_2\right)}^4.Math.u^2\left(L_1\right)+4.Math.\frac{L_1^4}{{\left(L_1+L_2\right)}^4}.Math.{\left(N_1-N_2\right)}^4.Math.u^2\left(L_2\right)$$u\left(L_{\mathrm{RES}}\right)=L_{\mathrm{RES}};u\left(L_1\right)=L_1;u\left(L_2\right)=L_2$$u_R^2\left(L_{\mathrm{RES}}\right)=\frac{L_2^2}{{\left(L_1+L_2\right)}^2}.Math.u_R^2\left(L_1\right)+\frac{L_1^2}{{\left(L_1+L_2\right)}^2}.Math.u_R^2\left(L_2\right)$$u_R\left(L_{\mathrm{RES}}\right)=\frac{L_{\mathrm{RES}}}{L_{\mathrm{RES}}};u_R\left(L_1\right)=\frac{L_1}{L_1};u_R\left(L_2\right)=\frac{L_2}{L_2}$

(69) Assuming the same tolerances for both of the inductances we obtain

(70) $u_R\left(L_{\mathrm{RES}}\right)=\frac{\sqrt{L_1^2+L_2^2}}{\left(L_1+L_2\right)}.Math.u_R\left(L\right)$

(71) Consequently, the tolerance of the inductance L.sub.RES is lower than the variation of the output inductance and hence the procedure for manufacturing the magnetic component.

(72) This provides an advantage of the magnetic circuit according to the present disclosure, whereby not only is an inductance on the primary winding obtained having the desired value independent of the leakage inductance and hence of the efficiency of the transformer, but also the precision of the value of inductance is better than the one given by the manufacturing tolerances of L1 and L2.

Example of an Embodiment

(73) FIGS. 7a and 7b show a possible example of embodiment of a magnetic component having N.sub.1=2 and N.sub.2=7.

(74) In particular, in the embodiment considered, to reduce the length of the windings and hence the power losses due to the resistance thereof, the turn ratios N.sub.1 and N.sub.2 can be halved. Consequently, in the embodiment considered, the transformers Ta and Td have a turn ratio 1:0.5 and the transformers Tb and Tc have a turn ratio 3.5:0.5.

(75) In the embodiment considered, the magnetic component that implements the transformers Ta-Td is provided via a structure with layers that are positioned around a core 80.

(76) For example, FIG. 7a is an axonometric view of a possible embodiment of the core 80. In particular, in the embodiment considered, the core 80 comprises three portions 802, 804, and 806 that can be obtained also separately and fixed together during assembly. In particular, the lateral portions 802 and 806 are shaped like an E, and the central portion 804 is a plate.

(77) FIG. 7b shows a side view of the complete core 80. In particular, the portions 802 and 806 are configured in such a way that the core 80 has spaces A1, A2 (referred to as airgaps) between the outer legs of the E-shaped portions (802 and 806) and the central plate 804, i.e., the lateral portions of the portions 802/806 are shorter than the central leg. These airgaps A1, A2 are designed so as to obtain the desired inductances L.sub.1 and L.sub.2. In particular, in the embodiment considered, the bottom airgap A2 will determine L.sub.1, whereas the top airgap A1 will determine L.sub.2. In various embodiments, the portions 802 and 806 have the same width, but can have different heights, i.e., the central legs can have different lengths in such a way that a different number of layers can be obtained for the portions 802 and 806.

(78) FIGS. 8a to 8c show possible embodiments of the layers that implement the primary windings W1 (FIG. 8a), the secondary windings of the transformers Tb and Tc designated by the reference W2 (FIG. 8b), and the secondary windings of the transformers Ta and Td designated by the reference W3 (FIG. 8c).

(79) In the embodiment considered, the layers have a width that is smaller than the width between the lateral legs of the portions 802 and 804. Furthermore, the layers have a central opening for the central leg of the portions 802 and 804.

(80) Finally, FIGS. 9a to 9c show, respectively, the view from the primary side, from the secondary side, and from above of the entire magnetic component.

(81) In particular, in the embodiment considered, set between the portion 802 and the portion 804 of the core 80 is a layered structure that implements the transformers Tb and Td, and set between the portion 804 and the portion 806 of the core 80 is a layered structure that implements the transformers Ta and Tc. For example, the respective layers can be slid over the central leg of the portions 802 and 806, and the portions 802 and 806 can then be fixed to the central plate 804. For example, the layered structure may be obtained via a stack of printed circuit boards (PCB) or a multi-layer PCB.

(82) For example, in the case of the number of turns referred to previously, the top layered structure comprises seven layers of the primary winding W1. In particular, the winding starts from an electrical contact 900, which is coupled to the terminal A and develops via appropriate electrical connections between the individual layers W1 around the top central leg horizontally for seven turns (see in particular FIG. 9a). The connection proceeds through a vertical electrical connection 902 and performs a further two turns around the bottom central leg with the layers W1 and is finally coupled, through an electrical connection 904, to the terminal B.

(83) Consequently, the above windings provide the connection in series of the primary windings shown in FIG. 7, which in the specific case correspond to the sequence Tb, Td, Tc, Ta.

(84) In particular, in the embodiment considered, the layers W1 in the bottom part are coupled together in such a way that the current flux is opposite to the current flux in the layers W1 in the top part. Consequently, as represented schematically in FIG. 9a, a current that traverses the layers W1 will generate two magnetic fluxes MFa and MFc in the bottom part, which have a direction opposite to that of the corresponding magnetic fluxes MFb and MFd generated in the top part of the core 80, and consequently there is a cancelling-out of magnetic flux, with consequent reduction of the power losses of the component.

(85) The magnetic flux generated by the winding W1 in the top part is captured by the secondary W2, the winding of which is made up, for example, of five layers coupled in parallel, which provide together half a turn (i.e., 0.5) and are coupled via an electrical contact 906 to the central node COM (see FIG. 9b). In general, even just one layer W2 could be sufficient, but a plurality of layers coupled in parallel is advantageous to reduce the electrical resistance of the connection. For example, in the embodiment considered, the layered scheme has the structure W2, W1, W1, W2, W1, W2, W1, W1, W2, W1, W1, W2.

(86) Consequently, the top structure provides the transformers Tb and Td with the inductance L.sub.2. For this purpose, the layers W1 that provide the primary windings have shapes that envelop almost completely the central leg of the portion 802 (except for a small portion for the connections between the layers W1) in such a way as to create substantially a helix (see FIG. 9a).

(87) In the embodiment considered, the layers W2 that provide the secondary windings of the transformers Tb and Td are obtained via two strips W2a and W2b that can also be coupled together by connection to the contact 906, i.e., the terminal COM. For example, as shown in FIG. 8b, U-shaped profiles may be used for this purpose for the layers W2.

(88) Likewise, the magnetic flux generated by the winding W1 in the bottom part is captured by the secondary W3. In particular, in the embodiment considered, the layer W3 that provides the secondary windings of the transformers Ta and Tc in the bottom structure comprises two strips W3a and W3b that are independent; i.e., the layer comprises two lateral portions W3a and W3b that are not coupled together (as opposed to what occurs for the layer W2). Also in this case, a number of layers W3 may be provided, for example two layers, which are coupled in parallel and together provide half a turn, i.e., 0.5 turns.

(89) The two windings W3a and W3b of the layer W3 are coupled via respective electrical connections 908 and 910 to the terminals R1 and R2 (see FIG. 9b).

(90) Finally, two further electrical contacts 912 and 914 are provided that form the connections between the secondary windings of the transformers Ta-Td. In particular, the connection 912 connects the part W2a of the layer W2 that provides the secondary of the transformer Tb to the part W3a of the layer W3 that provides the secondary of the transformer Ta, and the connection 914 connects the part W2b of the layer W2 that provides the secondary of the transformer Td to the part W3b of the layer W3 that provides the secondary of the transformer Tc.

(91) Consequently, in the embodiment considered, the secondary windings of the transformers Ta-Td are obtained via a single respective half turn (W2a, W2b, W3a or W3b), obtained for example via a strip of a metal material. This half turn may be obtained also from a plurality of layers coupled in parallel, for example to reduce the electrical resistance. The number of turns of the primary winding W1 in the top part and in the bottom part are sized accordingly, taking into account that a single turn of the layer W1 corresponds to half a turn for the transformer Tb and half a turn for the transformer Td, and likewise half a turn for the transformer Ta and half a turn for the transformer Tc. Consequently, the number of layers W1 coupled in series will correspond to the number N.sub.2 for the top part and to the number N.sub.1 for the bottom part.

(92) Consequently, in the embodiment considered, no complex connections are required for connecting the respective portions W2a, W2b, W3a and W3b together in series (as in any case occurs for the primary winding).

(93) Thanks to the above connection in parallel, the contacts 906, 908, 910, 912 and/or 914 can also perform a function of mechanical support for the layers. For example, in one embodiment, the contacts 900, 904, 906, 908, and 910 may be fixed with respect to the core 80, for example via a base plate, for instance made of a plastic material. In this case, the contacts 908 and 910 can support the layers W3, and the contact 906 can support the layers W2. The contacts 912 and 914 can further block the layers W2 and W3.

(94) Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to what has been described and illustrated herein purely by way of example, without thereby departing from the scope of the present invention, as defined in the ensuing claims.

(95) For example, the person skilled in the art will appreciate that numerous variants are possible in the choice of N.sub.1 and N.sub.2, in the construction and alternation of the primary and secondary windings, in the determination of L.sub.1 and L.sub.2, which in general could be set also in some other way and not via the airgap.