An isolation transformer

Abstract

The present invention provides an isolation transformer, comprising: a magnetic core, at least two groups of transformer windings, at least one shielding layer, and a shielding layer potential lead, wherein the shielding layer is located between the two groups of transformer windings, and the connection point between the shielding layer and the shielding layer potential lead is located between the two ends of the shielding layer. The present invention can not only solve the problem of large common-mode interference of the isolation transformer, reduce the electrical coupling generated by parasitic capacitance between windings, but also reduce the influence of the induced voltage at both ends of the shielding layer on other windings, eliminate the common-mode interference generated by the shielding layer itself, and meet the needs of high-speed and high-precision electrical isolation test and measurement systems.

Description

Technical Field

[0001] The present invention relates to the technical field of transformers, and in particular to an isolation transformer. Background Art

[0002] High-speed and high-precision electrical isolation test and measurement systems require not only DC low-frequency electrical isolation, but also good high-frequency electrical isolation. High-speed and high-precision electrical isolation test and measurement systems are very sensitive to common-mode interference, and often require common-mode interference to be below tens of millivolts so as not to affect high-speed precision testing. This requires the use of common-mode interference suppression measures. As we all know, adding bypass capacitors between the two isolation grounds of the isolation system will reduce common-mode interference, but the added capacitors will sacrifice high-frequency electrical isolation characteristics, which is not applicable to high-speed and high-precision electrical isolation test and measurement systems. The common-mode interference introduced by the transformer as an isolation power supply component often accounts for a large proportion, so it is particularly important to solve the common-mode interference introduced by the transformer.

[0003] There is no shielding between the windings of traditional transformers, so common-mode interference can be electrically coupled between the windings through parasitic capacitance; in the more advanced isolation transformers, a shielding layer is added between the windings, so that the common-mode interference between the windings is bypassed to the shielding layer through the parasitic capacitance, reducing the electrical coupling between the windings. However, the connection position between the shielding layer and the potential lead of the more advanced isolation transformers is at one end of the shielding layer, and the transformer is connected to the shielding potential by the lead. This connection method only considers the common-mode interference coupling between the windings, and does not consider that the winding shielding layer will also have a change in magnetic flux, thereby generating an induced voltage at both ends of the shielding layer. Due to the presence of parasitic capacitance, the induced voltage will affect other windings, generate common-mode interference, and become a new noise source. Because the previous shielding method did not recognize that the shielding layer becomes a new common-mode interference source, the common-mode interference often reaches several volts after testing, which cannot meet the needs of high-speed and high-precision electrical isolation test and measurement systems. Summary of the invention

[0004] In view of this, the main purpose of the present invention is to provide an isolation transformer, which can not only solve the problem of large common-mode interference of the isolation transformer and reduce the electrical coupling generated by parasitic capacitance between windings, but also reduce the influence of the induced voltage at both ends of the shielding layer on other windings, eliminate the common-mode interference generated by the shielding layer itself, and meet the needs of high-speed and high-precision electrical isolation test and measurement systems.

[0005] The technical solution adopted by the present invention is an isolation transformer, comprising: a magnetic core, at least two groups of transformer windings, a shielding layer between adjacent transformer windings with both ends not closed into a ring, the shielding layer being electrically connected to the shielding layer potential lead, and the connection point between the shielding layer and the shielding layer potential lead is located between the two end points of the shielding layer.

[0006] As mentioned above, there is no shielding between the windings of a traditional transformer, and common-mode interference can be electrically coupled between the windings through parasitic capacitance. By setting a shielding layer between the transformer windings, the influence of common-mode interference can be effectively reduced. However, the windings of the shielding layer itself will also have a change in magnetic flux, resulting in an induced voltage at both ends of the shielding layer, which affects other windings and generates common-mode interference. By connecting the grounding potential lead between both ends of the shielding layer, a positive voltage and a negative voltage can be generated at both ends of the shielding layer respectively. The positive voltage and the negative voltage are both less than the potential difference between both ends of the shielding layer, and they are in opposite directions and cancel each other out. Therefore, after the voltages at both ends of the shielding layer are cancelled, the influence on the windings is less than the influence of the voltages at both ends on the windings alone, thereby effectively reducing the influence of the induced voltage of the shielding layer on other windings.

[0007] For further improvement, the ratio of the length of the shielding layer from the connection point of the shielding layer and the shielding layer potential lead to one end of the shielding layer to the length of the shielding layer from the connection point to the other end of the shielding layer is less than 10 and greater than 0.1.

[0008] The reason is that when the traditional shielding potential lead is connected to any one end of the shielding layer, assuming the shielding potential is 0V, the potential at one end of the shielding layer is 0V, and the potential at the other end is V1 = ΔV1. Due to the effect of parasitic capacitance, the potential V1 at one end of the shielding layer will interfere with the windings, that is, the potential difference between both ends will interfere with other windings entirely. When the shielding potential lead is connected between both ends of the shielding layer according to the present invention, assuming the potentials at both ends of the shielding layer are V2 and V3 respectively, then V2 and V3 are in opposite directions and V3 - V2 = ΔV1. By comparison, it can be obtained that V2 < V1, V3 < V1, and V2 and V3 are in opposite directions and cancel each other out. The influence on the windings after V2 and V3 are cancelled is less than the influence of V2 and V3 on the windings alone. Therefore, the present invention effectively reduces the influence of the induced voltage of the shielding layer on other windings.

[0009] Alternatively, the ratio of the length of the shielding layer from the position where the potential in the shielding layer is the same as the shielding potential to one end of the shielding layer to the length of the shielding layer from the position to the other end of the shielding layer is less than 10 and greater than 0.1.

[0010] The reason is that the potential lead is led out from the shielding layer and connected to the external grounding terminal through the transformer outlet. Assuming the grounding terminal potential is 0V, the point at the transformer outlet mapped to the shielding layer is the same point as the shielding potential, and the potential of this point is 0V. When the mapping point is between the two ends of the shielding layer, even if, for example, the potential lead surrounds the inside of the transformer and is connected to any end of the shielding layer, due to the consistency of the direction inside the transformer, the lead part of the potential lead inside the transformer will produce a change in magnetic flux, and an induced voltage will be generated at the connection point between the potential lead and the shielding layer. However, the shielding winding part from this connection point to the point mapped to the shielding layer at the transformer outlet will also generate an induced voltage opposite to the potential lead. The two induced voltages cancel each other out. Therefore, the influence of the induced voltage of the shielding layer on other windings can still be effectively reduced.

[0011] According to a further improvement, the shielding layer wraps the transformer winding.

[0012] As described above, by wrapping the transformer winding with a shielding layer, the coupling noise generated between the primary winding and the secondary winding can be bypassed to the shielding potential through the shielding layer.

[0013] According to a further improvement, the shielding layer wraps the transformer winding lead wire.

[0014] As shown above, the voltage generated by the transformer is connected to the external load through the lead wires, and the shielding layer wraps the transformer winding lead wires to reduce the interference to the voltage derived from the lead wires.

[0015] As a further improvement, the isolation transformer has at least three groups of transformer windings, and the shielding layer between adjacent transformer windings is one layer.

[0016] From the above, in application testing, two or more secondary windings can be set adjacent to the primary winding in the transformer. This setting can obtain different voltages for use by test equipment, while also saving space and cost. Setting a shielding layer between adjacent transformer windings can effectively reduce common-mode interference between windings.

[0017] As a further improvement, the positions of the unclosed parts of the shielding layers are the same;

[0018] Alternatively, the positions of the unclosed portions of the shielding layers are uniformly distributed circumferentially;

[0019] Alternatively, the positions of the unclosed portions of the at least two shielding layers are symmetrically distributed.

[0020] From the above, since there is a gap in the shielding layer winding, when there are multiple shielding layers, in order to ensure easy installation, the gap direction can be consistent, but the electric field and magnetic field leaked by the gap will also produce electrical coupling. Therefore, in order to ensure the maximum shielding effect, the shielding layer gap direction can be installed uniformly in the circumferential direction or symmetrically at 180 degrees, so that the gaps in each shielding layer can achieve the effect of shielding each other.

[0021] The present invention can solve the problem of large common-mode interference of the transformer and eliminate the common-mode interference generated by the shielding layer itself, so that it has only a very small impact below millivolt, meeting the needs of high-speed and high-precision electrical isolation test and measurement systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of the isolation transformer of the present invention;

[0023] Figure 2 It is a schematic diagram of the position of the potential lead of the shielding layer when the windings of the present invention are arranged up and down;

[0024] Figure 3 It is a schematic diagram of the structure of two shielding layers in the isolation transformer of the present invention;

[0025] Figure 4 It is a schematic diagram of the positions of points in the shielding layer of the isolation transformer of the present invention that have the same potential as the shielding potential;

[0026] Figure 5 It is a schematic diagram of the position of the shielding layer lead wire when the winding is arranged inside and outside of the present invention;

[0027] Figure 6 This is a schematic diagram of the traditional shield lead position when the winding is arranged inside and outside. DETAILED DESCRIPTION

[0028] like Figure 6 As shown, the connection position 303 between the shielding layer 300 and the lead 400 of the conventional isolation transformer is located at one end 301 of the shielding layer, and the shielding potential of the transformer is led out by the lead 400. The shielding layer 300 is a turn of coil in the transformer, and the change of its magnetic flux causes an induced voltage ΔV1 to be generated at both ends 301 and 302 of the shielding layer. Assuming the shielding potential is 0V, the potential at one end 301 of the shielding layer is 0V, and the potential at the other end 302 is V1=ΔV1. Due to the effect of parasitic capacitance, the potential V1 at one end 302 of the shielding layer will interfere with the windings 100 and 200. After testing, this common-mode interference can often reach several volts, which cannot meet the requirements of high-speed and high-precision electrical isolation test and measurement systems.

[0029] In view of this, the main purpose of the present invention is to provide an isolation transformer. By connecting the shielding potential lead between the two ends of the shielding layer, it can not only solve the problem of large common-mode interference of the isolation transformer and reduce the electrical coupling generated by parasitic capacitance between windings, but also make the induced voltages at both ends of the shielding layer cancel each other, reduce the influence of the induced voltage at both ends of the shielding layer on other windings, eliminate the common-mode interference generated by the shielding layer itself, and meet the needs of high-speed and high-precision electrical isolation test and measurement systems.

[0030] The present invention will be described in detail below with reference to the following examples.

[0031] Embodiment 1

[0032] like Figure 1 As shown, an optimal embodiment of the present invention provides an isolation transformer with windings arranged up and down, including: a magnetic core, a magnetic core cover plate 500, a magnetic core base 600, a primary winding 100, a secondary winding 200, a shielding layer 300, and a shielding layer potential lead 400. The secondary winding 200 is located on the magnetic core base 600, on which the shielding layer 300, the primary winding 100 and the magnetic core cover plate 500 are arranged in sequence, and the connection point 303 between the shielding layer 300 and the shielding layer potential lead 400 is located between the two ends 301 and 302 of the shielding layer;

[0033] During specific installation, the turns ratio of the primary winding 100 and the secondary winding 200 is 2:1, a shielding layer 300 is provided between the primary winding 100 and the secondary winding 200, the shielding potential is grounded, the magnetic core cover plate 500 and the magnetic core base 600 are of cylindrical design, and a clamping structure can be provided on the contact surface of the magnetic core cover plate 500 and the magnetic core base 600 to ensure that the magnetic core cover plate 500 and the magnetic core base 600 can be firmly covered, the primary winding 100, the shielding layer 300 and the secondary winding 200 are sequentially clamped in the shell composed of the magnetic core cover plate 500 and the magnetic core base 600, and the magnetic core cover plate 500 and the magnetic core base 600 have outlets at both ends. When the magnetic core cover plate 500 and the magnetic core base 600 are covered Afterwards, the input and output ends of the secondary winding 200 extend from the outlet and are connected to the transformer load. At the same time, this outlet can also allow the shielding potential lead 400 to extend and be connected to the external grounding wire. At this time, when a sinusoidal excitation signal of 1KHz and 50Vrms is applied to the primary winding 100, an induced voltage with opposite potential is generated at both ends 301 and 302 of the shielding layer. Assuming the shielding potential is 0V, and the potentials at both ends 301 and 302 of the shielding layer are V2 and V3 respectively, at this time, V2 and V3 can offset each other, so that the common mode noise of the secondary winding 200 is measured below 10mV, which meets the system requirements of a high-speed and high-precision electrical isolation test and measurement system, and has better effects than previous transformers.

[0034] like Figure 2As shown, a shielding layer 300 is provided between the primary winding 100 and the secondary winding 200, the shielding potential is grounded, the turns ratio of the primary winding 100 and the secondary winding 200 is 2:1, and the ratio of the shielding layer length from the connection point 303 of the shielding layer 300 and the shielding layer potential lead 400 to one end point 301 of the shielding layer to the shielding layer length from the connection point 303 to the other end point 302 of the shielding layer is less than 10 and greater than 0.1.

[0035] In this embodiment, since a shielding layer is added between the primary winding and the secondary winding, the distance between the primary winding and the secondary winding is increased, and the size of the coupling capacitance between the primary winding and the secondary winding is inversely proportional to the distance between the primary winding and the secondary winding. Therefore, the parasitic capacitance between the primary winding and the secondary winding is reduced, and the coupling noise generated between the primary winding and the secondary winding is bypassed to the shielding potential through the shielding layer, thereby reducing the common-mode interference of the transformer to the electronic equipment.

[0036] Preferably, in order to ensure the shielding effect, multiple shielding layers are provided between the primary winding 100 and the secondary winding 200, and the unclosed positions of the shielding layers are the same or evenly distributed circumferentially, such as Figure 3 As shown, when two shielding layers 300 and 310 are provided between the primary winding 100 and the secondary winding 200, the shielding layers 300 and 310 are installed in an up-and-down manner, and the gap formed by the two endpoints 301 and 302 of the shielding layer 300 is in opposite directions to the gap formed by the two endpoints 311 and 312 of the shielding layer 310. By arranging the shielding layers in this manner, the gaps in the shielding layers can achieve the effect of mutual shielding, thereby preventing the electric coupling generated by the electric field and magnetic field missed by the gaps in the shielding layers from interfering with the windings, and the parasitic capacitance generated in the shielding layers is grounded through the shielding potential leads of each shielding layer. Since the gaps in the shielding layers are symmetrical, the grounding ends are also symmetrical, thereby evenly distributing the induced voltage of the shielding layers and reducing interference with other windings.

[0037] When more than two shielding layers are provided in the transformer, the shielding layers are arranged symmetrically in the direction of the notches in the above manner, so as to achieve the effect of mutual shielding between the shielding layers.

[0038] like Figure 4As shown, the potential lead 400 is connected to any point 303 of the shielding layer 300, and the potential lead inside the transformer is connected to the external grounding terminal by winding around the transformer outlet. Assuming that the grounding terminal potential is 0V, the potential of the potential lead at the transformer outlet is also 0V. The point 304 mapped to the shielding layer here is the same point as the shielding potential, and the potential of this point is 0V. When the mapping point 304 is between the two ends 301 and 302 of the shielding layer, even if the potential lead 400 is wound around the transformer and connected to any point 303 of the shielding layer, due to the consistency of the direction inside the transformer, the lead part of the potential lead 400 inside the transformer will produce a change in magnetic flux, and an induced voltage will be generated at the connection point 303 between the potential lead and the shielding layer, but the shielding winding part from this connection point 303 to the transformer outlet mapped to the point 304 of the shielding layer will also generate an induced voltage opposite to the potential lead, and the two induced voltages cancel each other out. Therefore, the influence of the induced voltage of the shielding layer on other windings can still be effectively reduced.

[0039] Embodiment 2

[0040] like Figure 5 As shown, another embodiment of the present invention provides a lead position when the winding is arranged inside and outside, including a primary winding 100, a secondary winding 200, a shielding layer 300, and a shielding layer potential lead 400. The secondary winding 200 is located at the outermost side of the transformer, and from the outside to the inside are the shielding layer 300 and the primary winding 100. The connection point 303 between the shielding layer 300 and the shielding layer potential lead 400 is located between the two ends 301 and 302 of the shielding layer, and the other end of the shielding potential lead 400 is connected to the ground end.

[0041] Specifically, the working principle of the isolation transformer with windings arranged inside and outside involved in the second embodiment is the same as the working principle of the isolation transformer with windings arranged above and below involved in the above-mentioned first embodiment. When the connection point 303 between the shielding layer 300 and the shielding layer potential lead 400 is located between the two ends 301 and 302 of the shielding layer, the induced voltages generated at the two ends of the shielding layer are in opposite directions and can offset each other, which will not be elaborated here.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An isolation transformer, comprising: A magnetic core, at least two groups of transformer windings (100) (200), and at least two layers of shielding layers (300) whose two ends are not closed into a ring shape between adjacent transformer windings; the shielding layer (300) is electrically connected to a shielding layer potential lead (400), characterized in that: The positions of the unclosed parts of the at least two shielding layers (300) are symmetrically distributed, and the grounding ends of the at least two shielding layers (300) are symmetrical; the shielding layer potential lead (400) is led out from the shielding layer (300) and connected to an external grounding end through a transformer outlet; The shielding layer (300) wraps the transformer winding and the transformer winding lead wire; The ratio of the shielding layer length from the connection point (303) of the shielding layer (300) and the shielding layer potential lead (400) to one end point (301) of the shielding layer to the shielding layer length from the connection point (303) to the other end point (302) of the shielding layer is less than 10 and greater than 0.1; or, The ratio of the length of the shielding layer from a point in the shielding layer (300) having the same potential as the shielding potential to one end point (301) of the shielding layer to the length of the shielding layer from the point to another end point (302) of the shielding layer is less than 10 and greater than 0.1.

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