HK1052795A - Split inductor with fractional turn of each winding and pcb including same - Google Patents

Description

Split inductor with less than one turn per coil and PCB including the same

Technical Field

The present invention relates generally to logic integrated circuits, and more particularly to a simple separable wire-wound inductor structure that can be advantageously used in synchronous rectifier circuits. More specifically, the present invention provides an output inductor in a power supply assembly that incorporates an output inductor coil into a printed circuit board system to reduce cost and design complexity and improve noise performance.

Background

The development of the distributed power market has led to increased research in the field of power supply components. Thus, the power density of power supply components has increased by a factor of four over the past few years. And the efficiency of the power supply assembly is remarkably increased due to the improvement of the current semiconductor device and the realization of the synchronous rectification of the power supply assembly. As logic integrated circuits move to lower operating voltages at higher operating frequencies and the overall system size continues to decrease, smaller power supply designs and more efficient power supply components are needed.

In an effort to improve efficiency and increase power density, synchronous rectification has become a necessary technique for these several types of applications. Synchronous rectification has gained popularity over the last decade as low voltage semiconductor devices have developed into a promising technology. However, power supply electronics design engineers are still challenged to design power supply components with high power density, high efficiency, low output voltage, and high output current.

Power supply components that can perform synchronous rectification typically include a single wound output inductor that is connected to the output load of the synchronous rectifier circuit. It has become the most common approach generally used because of its simplicity and reduced component count. The power module structure known as "quarter block" can be used where board space is limited. There is a quarter block power module of the size: 2.28 inches long, 1.45 inches wide, and 0.5 inches high.

A quarter pack, like other similar power packs, typically has an input plug and an output plug at opposite ends of the pack. Mainly due to packaging and circuit design constraints, output inductors are required to be connected at opposite ends of the input and output terminals of the inductor. With this configuration, the coil configuration is increased by one-half turn, which in turn affects the resulting magnetic flux profile in the inductor core. In particular, less than one turn of inductance generated by the output inductor terminals increases with current, and thus the inductor is prone to saturation.

Summary of The Invention

The present invention achieves the technical advantage that the separable inductor as an output inductor can be favorably applied to a synchronous rectifier circuit. The present invention comprises a novel split inductor design that incorporates a quarter power module incorporating an inductor coil and magnetic element into a calibration platform. The optimal circuit design and packaging structure can be realized under the condition of not influencing the design of the output inductor.

According to one embodiment of the present disclosure, a separable inductor includes an inductor core configured to extend first, second, and third legs from a base member. The first and second struts are predisposed to be spaced apart on the surface of the base member to form a first recessed region. The second leg, in turn, forms a second recessed area with the third leg, the second recessed area being separated from the first recessed area by the second leg. The inductor further includes an inductor winding disposed about the inductor core to form substantially equal magnetic flux through the first, second and third legs when current flows through the inductor winding.

In one embodiment of the invention, the separable inductor is incorporated into a Printed Circuit Board (PCB) system comprising a plurality of PCB layers. Each PCB layer includes an electrically conductive core sub-layer pre-disposed between two sub-layers of base material, each of which makes a predetermined circuit path. The PCB system also comprises a plurality of insulating layers which are arranged among the PCB layers in advance, and a first opening, a second opening and a third opening which penetrate through the PCB layers. According to the invention, the opening is intended to receive an inductor core. The corresponding leg of the inductor core can be inserted into a corresponding opening in the PCB system.

In still another embodiment, in a synchronous rectifier circuit employing the present invention, the separable inductor constitutes an output inductor at the secondary side of the synchronous rectifier circuit.

One technical advantage of the present invention is that the inductor structure of the present invention is easily adopted in power supply component systems, such as quarter-block power supply components.

Yet another technical advantage of the present invention is that the novel inductor structure may be used to filter common mode noise and reduce the output noise of the filter circuit.

Another technical advantage of the present invention is that the separable inductor structures of the present invention may be employed in other power supply circuit topologies, such as full bridge circuits and push-pull circuits.

Brief Description of Drawings

The above features and advantages of the present invention may be more clearly understood by referring to the following description of the drawings.

Fig. 1 illustrates a prior art single inductor structure in a synchronous rectifier circuit.

FIGS. 2A-C illustrate a load C with_oThe output inductor of (1).

Fig. 3 shows a separable inductor of the present invention.

Fig. 4A is a top view of an inductor of the present invention having a different number of turns of wire.

Fig. 4B illustrates the magnetic characteristics of the inductor of the present invention with different numbers of turns of wire.

Fig. 5A is a top view of an inductor of the present invention having the same number of winding turns.

Fig. 5B illustrates the magnetic characteristics of the inductor of the present invention having the same number of turns of wire.

Fig. 6 is a simplified schematic diagram of the voltage inputs and outputs of the printed circuit board.

Fig. 7 is a simple block diagram of a printed circuit board with synchronous rectification.

Fig. 8A illustrates the layering of a printed circuit board into which the inductor of the present invention is incorporated.

Fig. 8B is a top view of the printed circuit board.

Fig. 9 is a circuit schematic of the inductor of the present invention applied to a synchronous rectifier circuit.

Fig. 10A and 10B illustrate the noise difference of the prior art circuit and the circuit of the present invention.

Corresponding numerals and symbols in the various drawings indicate corresponding parts throughout the different views unless otherwise specified.

Brief description of the preferred embodiments

The present invention is described below. First a prior art half bridge DC-DC converter circuit is discussed, then several preferred embodiments of the invention are described and the advantages thereof are discussed.

FIG. 1 illustrates a single inductor L in a synchronous rectifier circuit 10 in a half-bridge DC-DC converter_oThe use of (1). The synchronous rectifier circuit 10 includes a primary transformer T1, T1 having primary and secondary windings, 11 and 12 in sequence. The synchronous rectifier circuit 10 also includes an external drive powerLine 18, which functions to drive synchronous rectifiers Q1 and Q2.

In detail, the first and second synchronous rectifiers Q1 and Q2 are physically coupled with the primary transformer T1 and the external driving circuit 18. The timing signals for the switching synchronous rectifiers Q1 and Q2 come from the external drive circuit 18. The timing information is then transferred from the primary side of the rectifier circuit 10 to the secondary side 16 through the primary transformer T1.

Using a single output inductor L in a conventional manner_oSee fig. 1. According to the prior art, preference is given to using a single output inductor L_oBecause the apparatus is simple and the number of components can be reduced. However, in some applications, the output inductor L_oIs divided into two identical coils connected across the output capacitor to enhance common mode noise rejection. Obviously, the two-coil structure increases the cost and complexity of the structure. Another approach is to wind two coils on the same inductor core, but this configuration adds complexity to the manufacturing process. What is needed is an inductor structure that enhances its state noise rejection without increasing the complexity of the manufacturing process. The present invention provides such an output inductor structure that can be used in a power module system for a synchronous rectifier, as shown in fig. 1.

Fig. 2A-C illustrate equivalent structures of the synchronous rectifier circuit output inductor. Fig. 2A shows the structure of the conventional single inductor discussed above. Single inductor L_oIs divided into two identical coils L1 and L2, see FIG. 2B, and an output capacitor C_oAre connected in series. However, this structure does not provide the required filtering of noise in the circuit. To enhance common mode noise rejection, the two identical coils L1 and L2 shown in fig. 2B may be reconfigured to place coils L1 and L2 across the output capacitor as shown in fig. 2C.

The present invention is a separable inductor structure with two coils connected at each end of an output capacitor. However, the present invention has the added advantage of reducing the cost and complexity of the manufacturing process as compared to the prior art split inductor structure shown in fig. 2A and 2B. For a better understanding of the invention, reference may be made to FIG. 3. Fig. 3 shows inductor core 20 with first, second, and third legs 22, 24, and 26 in that order, all of the three legs extending from base member 28. The first leg 22 and the second leg 24 are predisposed, spaced apart, elongated, and generally perpendicular to the first surface 30 of the base member 28 to define a first recessed area 32. Similarly, second leg 24 and third leg 26 are also predisposed, spaced apart, elongated, and generally perpendicular to second surface 33 of base member 28 to define a second recessed area 34. The second recessed area 34 is separated from the first recessed area by the second leg 24.

Figure 4A is a top view of a three leg inductive core 20 suitable for use in the inductor structure 50 of the present invention. As shown in fig. 4, inductor winding 36 may be wound around inductor core 20 to form signal-generating paths in recessed areas 32 and 34. The coil 36 may be made of any electrically conductive material, such as copper. The coil 36 is wound through the first, second and third legs 22, 24, 26 in sequence for a full turn, and then an additional insufficient turn 38 is wound between the second and third legs 24, 26. The first notch area 32 has one signal path through it and the second notch area 34 has two signal paths through it due to the insufficient one turn 38. The effective inductance produced by the insufficient one turn 38 will vary with current and will tend to make the output inductor L easier_oSaturation, which is undesirable.

The saturation phenomenon is illustrated in fig. 4B. Fig. 4B shows an inductor L with an insufficient one turn 38_oThe magnetic circuit of (2). The P1, P2, P3 are flux guides for the first, second, and third supports 22, 24, 26, respectively. Flux1, F1ux2, Flux3 represent the magnetic Flux flowing through each leg 22, 24, 26. N is a radical of^±1、1^*1 is the MMFs in each strut. As the current increases, more magnetic flux is pushed away from the third leg 26 and into the second leg 24. Basically, the load current increases and the effective inductance decreases. As too much magnetic flux is pushed into the second leg 24, eventually the inductor core 20 reaches saturation.

The present invention provides an inductor structure 50 in which inductor winding 36 is disposed around inductor core 20 to balance the magnetic flux in each leg 22, 24, 26. To make the magnetic flux in the first, second, and third legs 22, 24, 26, respectively, approximately equal, the inductor is configured to provide an equal signal path to a first notch area 32 defined by the first leg 22 and the second leg 24 and a second notch area 34 defined by the second leg 24 and the third leg 26 when current flows through the inductor 36. This structure is shown in fig. 5A, labeled 50.

Fig. 5B shows an equivalent magnetic circuit of the inductor structure of the present invention. The MMFs and flux guide in the first and third legs 24, 26 are exactly equal, and therefore the magnetic flux in the first and third legs 24, 26 is balanced. The fact that equal numbers of signal paths are generated in recessed regions 32 and 34 indicates that inductor core 20 is not saturated.

Thus, inductor structure 50 may be incorporated into a Printed Circuit Board (PCB) system and used as output inductor L in a synchronous rectifier circuit_oSuch a rectifier circuit may be used in a power regulation facility. Inductor structure 50 is exemplified by the output inductance of a power supply module of one quarter, but the present invention provides a general solution to the optimal PCB packaging and circuit design without affecting the input and/or output inductor design.

Figure 6 shows a typical mechanical diagram of a standard quarter-block power module. Packaging and circuit design constraints require that the output inductor be connected across the structure, thus creating a coil with half a turn. As shown, the input pin Vin +, Vin-and the output pin Vout +, Vout-are positioned at opposite ends of the assembly. The normal position of the components in the power block assembly 40 is shown in fig. 7. The component 40 may be divided into several units: primary switch 42, transformer 44, rectifier 46, output inductor 48, output capacitor 49. Ideally current flows from the rectifier unit 46 of the inductor into the inductor unit 48 (terminal 1 close to the rectifier unit) and out of the output capacitor 49 (terminal 2 close to the output capacitor unit).

Fig. 8A illustrates the layering of a Printed Circuit Board (PCB)51 into which the inductor structure 50 of the present invention may be incorporated. PCB51 includes a plurality of PCB layers 53. Each of the PCB layers 53 includes a conductive core sub-layer 52 that is pre-disposed between two base material sub-layers 54. The conductive core sub-layers may comprise any conductive material, such as aluminum or copper, or other similar conductors. Each of the conductive core sub-layers 52 forms a predetermined circuit path for connecting a circuit element (i.e., an inductor, a capacitor, a transformer, etc.) to the system 51.

PCB51 further includes a plurality of insulating layers 56 pre-disposed between PCB layers 53 and having three openings 58, 60, 62 (see fig. 8B) in sequence between the first, second and third openings extending through the plurality of PCB layers 53 for insertion of three-leg inductor core 20. In particular, each leg 22, 24, 26 of inductor core 20, is inserted into a corresponding opening 58, 60, 62. A portion of each conductive core sub-layer 52 further forms a separable inductive coil 36, providing an equal number of signal paths through the first and second recessed regions 32, 34.

The processes and fabrication techniques for making such inductors 36 in the core sub-layer 52 are well known in the art. The inductor 36 may be divided into two coil portions (not shown) that contain one half turn for package and circuit design optimization, but have an active coil that does not contain such a half turn or less than one turn. Thus, the PCB51 is optimally located without affecting the design and performance of the inductor.

Since the inductor 36 can be built into the PCB51 and no terminations are required, one advantage of the PCB51 is that the power components can be incorporated with the magnetic elements, making the manufacturing process more simplified.

A circuit schematic diagram illustrating the separable inductor structure 50 of the synchronous rectifier circuit is shown in fig. 9 and designated by the numeral 100. The separable inductor structure 50 not only can make the circuit layout better, but also can filter common mode noise and reduce output noise. The common mode current is shown in FIGS. 10A-B. In the conventional method, the switching of the generated common-mode current generates abnormal noise at the output (fig. 10A), which is caused by the different impedances of each current path. In the new method, the impedances in each current path are similar or matched, so that the anomaly noise will be reduced or the common-state current does not generate the anomaly noise, see fig. 10B. Furthermore, this principle can be extended to input inductors.

The novel method and system of the present invention provide the advantages of using standard manufacturing processes and techniques and reducing costs. Another advantage is that common mode noise is reduced due to the use of the split inductor structure 50. It is also an advantage of the present invention to prevent the inductor coil 20 from saturating.

While the invention has been described with reference to exemplary embodiments, the description is not intended to be construed in a limiting sense. Modifications of the described embodiments, as well as combinations with other embodiments, will be apparent to persons skilled in the art upon reference to the description.

Claims (23)

1. A printed circuit board system, the system comprising:

a plurality of PCB layers, wherein each layer comprises a conductive magnetic core sub-layer pre-disposed between two layers of base material, each conductive magnetic core sub-layer making a predetermined circuit path;

a plurality of insulating layers previously arranged between each layer of PCB;

a first, second and third opening through the plurality of PCB layers for inserting a three-leg inductor core;

wherein a portion of each of the conductive core sub-layers is further formed into a separable inductor winding structure for providing an equal number of signal paths to a first region and a second region, the first region being defined by the first and second openings and the second region being defined by the second and third openings.

2. The PCB system of claim 1 further comprising a self-contained top and bottom layer, said plurality of PCB layers and insulating layers being pre-positioned between said self-contained top and bottom layers.

3. The PCB system of claim 2 further including top and bottom solder resist films, the top solder resist film being on the top self-contained layer, the bottom solder resist film being on the bottom self-contained layer, and the power module circuit components being connected to said printed circuit board through the bottom self-contained layer.

4. The printed circuit board system of claim 1, wherein said PCB and insulating layer have a minimum thickness of 0.003 inches.

5. The printed circuit board system of claim 1, wherein the minimum dielectric breakdown voltage of the PCB and the insulating layer is 3000 dc.

6. The printed circuit board system of claim 1, further comprising 6 PCB layers.

7. The printed circuit board system of claim 1, further comprising dummy bars on all sides.

8. The printed circuit board system of claim 1, wherein the base material comprises a 170 degree celsius base material.

9. The printed circuit board system of claim 1 wherein the thickness of the printed circuit board above the solder resist film ranges between 0.108 inches and 0.131 inches.

10. The printed circuit board system of claim 1 wherein the maximum thickness of the printed circuit board above said solder resist film between the first and second openings and between the second and third openings is 0.121 inches.

11. The printed circuit board system of claim 1, wherein the printed circuit board system further comprises an outer edge, wherein the etching is performed on the PCB layer at a minimum of 0.400 inches from the outer edge of the printed circuit board system.

12. An inductor, the inductor comprising:

an inductor core with first, second, and third legs extending from a base, the first and second legs being predisposed and spaced apart from a surface of the base to form a first recessed area, the second and third legs being predisposed and spaced apart to form a second recessed area, the first and second recessed areas being separated by the second leg; and

an inductor winding is disposed around the inductor core to provide substantially equal magnetic flux in the first, second and third legs when current flows through the winding.

13. The inductor of claim 1 wherein said inductor winding is configured to provide an equal number of current paths through the first and second recessed areas of the inductor core.

14. The inductor of claim 1 wherein the inductor core comprises iron.

15. The inductor of claim 1 wherein the first and second recess regions are equal in length and width.

16. The inductor of claim 1 wherein the first, second and third legs are equal in length, width and height.

17. The inductor of claim 1 wherein the inductor winding comprises copper.

18. The inductor of claim 1 wherein the inductor winding includes a first terminal for receiving an input current and a second terminal for discharging the input current.

19. The inductor of claim 18 having a via wherein the second terminal is connected to an output terminal from which an input current is input to the connected circuitry.

20. The inductor coil of claim 19 wherein the via comprises copper.

21. The inductor of claim 1 further configured to filter common mode noise and reduce output noise.

22. A synchronous rectifier circuit, the circuit comprising:

a primary transformer having a primary and a secondary winding, the secondary winding having first and second terminals;

first and second synchronous rectifiers coupled to the primary transformer;

an external drive circuit with a timing circuit, the first and second synchronous rectifiers thereby obtaining a timing signal; and

a separable inductor coupled with a secondary coil of the primary transformer.

23. The synchronous rectifier circuit of claim 22 wherein the separable inductor comprises:

an inductor core; and

an inductor coil wound around the inductor core provides approximately equal magnetic flux through the inductor when current flows through the coil.