An electrical circuit having increased creepage distance, including galvanic isolation between the high-voltage (HV) circuit portion and the low-voltage (LV) circuit portion.

Abstract

In the present disclosure, there is provided an electrical circuit having galvanic isolation between a high voltage (HV) circuit portion and a low voltage (LV) circuit portion, the electrical circuit comprising: a substrate providing the HV circuit portion and the LV circuit portion; an electrical component for providing the galvanic isolation, the electrical component being provided on the substrate such that a creepage distance is provided on the substrate between a first primary terminal and a first secondary terminal, the electrical component having a primary side connected to the HV circuit portion at the first primary terminal and a secondary side connected to the LV circuit portion at the first secondary terminal; and a conductive trace provided on the substrate and connected at a first end to a low frequency (LF) voltage node in the HV circuit portion, the frequency of a potential at the LF voltage node being lower than a frequency of a potential at the first primary terminal, the conductive trace being provided between the first primary terminal and the first secondary terminal, thereby increasing the creepage distance between the first primary terminal and the first secondary terminal.

Description

[[TECHNICAL FIELD]]

[0001] The present disclosure relates to an electric circuit that provides galvanic isolation, and more specifically, to a concept for increasing the creepage distance between the primary side and the secondary side of an electrical component that bridges the galvanic isolation in an electric circuit. [[BACKGROUND ART]]

[0002] Galvanic isolation is a known principle that electrically insulates two electrical components of an electric circuit from each other to prevent current from flowing between the two components. That is, there is no conductive portion connecting the two electrical components.

[0003] It is still possible to exchange power or any information between the electrical components by using an electrical component that bridges the galvanic isolation. These electrical components may be, for example, transformers, optocouplers or capacitors.

[0004] Galvanic isolation is used, for example, for safety purposes. Such isolation ensures that since there is no conductive portion connecting the two circuits, the high voltage present in a first circuit portion cannot migrate to the low voltage present in an insulated second circuit portion. Therefore, galvanic isolation can be used for safety, for example, to prevent unexpected current from passing through the human body to reach ground.

[0005] Galvanic isolation may be used when two or more electric circuit portions need to communicate, but their grounds may be at different potentials. It is an effective way of breaking ground loops by preventing undesirable current from flowing between two units sharing a ground conductor.

[0006] Therefore, galvanic insulation, i.e., safety insulation, can separate potentially unsafe high-voltage portions of a circuit from safe low-voltage portions of an electrical circuit. Depending on the specific conditions, the requirements of (i) clearance, (ii) creepage distance, and (iii) distance through insulation apply. All of these are expressed as (i) geometric distance through air, (ii) geometric distance along a surface, and (iii) geometric distance through a solid.

[0007] The above requirements can also be met by components that bridge galvanic isolation, such as transformers, optocouplers, and X and Y capacitors. That is, these components can be installed in both the high-voltage and low-voltage parts of a circuit. In these components, the high-voltage and low-voltage parts of the circuit are coupled to each other by a magnetic field in the case of a transformer, by light in the case of an optocoupler, and by an electric field in the case of X and Y capacitors. Transformers provide power transmission, optocouplers provide information transmission, and X and Y capacitors provide transmission of very high-frequency currents, which are used to reduce electromagnetic interference (EMI). [Overview of the initiative] [Problems that the invention aims to solve]

[0008] One of the disadvantages of the above is that the above distances must be met to ensure the safe and normal operation of the electrical circuit, which comes at the expense of design flexibility. [Means for solving the problem]

[0009] One aspect of the disclosure is to provide an electrical circuit having improved creepage distance. Another aspect of the disclosure is to provide a light-emitting diode (LED) based lighting device and a method for providing an electrical circuit according to the disclosure.

[0010] In a first aspect of this disclosure, an electrical circuit having galvanic isolation between a high-voltage (HV) circuit portion and a low-voltage (LV) circuit portion, - A substrate that supplies the HV circuit portion and the LV circuit portion, - An electrical component for supplying the galvanic insulation, provided on the substrate such that a creepage distance is provided on the substrate between a first primary terminal and a first secondary terminal, and having a primary side connected to the HV circuit portion at the first primary terminal and a secondary side connected to the LV circuit portion at the first secondary terminal, - An electrical circuit is provided, comprising a conductive trace provided on the substrate and connected at a first end to a low-frequency (LF) voltage node in the HV circuit portion, wherein the frequency of the potential at the LF voltage node is lower than the frequency of the potential at the first primary terminal, and the conductive trace is provided between the first primary terminal and the first secondary terminal, thereby increasing the creepage distance between the first primary terminal and the first secondary terminal.

[0011] The inventors had insight that the creepage distance to be taken into consideration depends not only on the voltage level but also on the potential / voltage frequency in the HV circuit portion. The higher the potential frequency of a node, the greater the creepage distance of that particular node.

[0012] Accordingly, the inventors have found that a conductive trace connected between the first primary terminal and the first secondary terminal, and more specifically connected to the low-frequency (LF) voltage node within the HV circuit portion, is introduced into the substrate.

[0013] The creepage requirements for this particular conductive trace depend on the voltage in the HV circuit portion, but also on the (expected) frequency of the potential at the LF voltage node. In this particular case, the frequency of the potential at the LF voltage node is lower than the frequency of the potential at the first primary terminal, so that the creepage requirements for the particular conductive trace are not more stringent than those for the first primary terminal.

[0014] The creepage requirements of the first primary terminal do not change with the introduction of the conductive trace. However, the actual creepage distance changes because it is no longer possible to creep directly from the first primary terminal to the first secondary terminal. The creepage distance is affected by the introduction of the conductive trace. The creep route cannot cross the conductive trace and therefore must bypass it. This increases the actual creepage distance between the first primary terminal and the first secondary terminal.

[0015] In one example, the conductive trace is connected to ground at its first end. In another example, the conductive trace may be connected to the supply voltage in the HV circuit portion.

[0016] In further examples, the electrical component is a transformer, an optocoupler, or a capacitor such as an X or Y capacitor.

[0017] In the example, the electrical component is a transformer including a primary winding having a first primary terminal and a second primary terminal, and the conductive trace is connected to the second primary terminal at the first end.

[0018] The transformer is, for example, a transformer used in a switch-mode power supply (SMPS) such as a flyback converter. The transformer provides magnetic coupling between its primary winding and its secondary winding, and therefore bridges the galvanic isolation.

[0019] The primary winding may be connected via the first primary terminal to a switch, such as a field-effect transistor (FET), more specifically, a gallium nitride (GaN) FET or a silicon carbide (SiC) FET. The switching operation of such an FET in the SMPS can give the potential at the first primary terminal a high frequency, i.e., the same frequency at which the gate of the FET is controlled. The primary winding may be connected to a supply voltage via, for example, the second primary terminal. This means that the potential at the second primary terminal does not switch in accordance with the frequency of the signal supplied to the gate of the FET. The potential at the second primary terminal is relatively static in that it is equal to the supply voltage.

[0020] This means that the creepage requirements for the second primary terminal are less stringent than those for the first primary terminal. The absolute potentials at these terminals may reach the same value, but the frequencies of the potentials at these terminals are different.

[0021] In a further example, the conductive trace is connected to the same LF voltage node at the second end.

[0022] The conductive trace may be floating in the sense that its second end is not connected to any other node in the HV circuit portion. It should also be noted that the conductive trace may be connected to the same LF voltage node at its second end. In that case, no current flows through the conductive trace.

[0023] In further examples, the electrical component is either a surface-mount device (SMD) or a through-hole mounted device.

[0024] Surface-mount technology may refer to a method in which the electrical component is directly attached to the bottom side or the top side of the substrate, e.g., a printed circuit board (PCB). In such a case, the electrical component is called a surface-mount device (SMD). Surface-mount technology may be beneficial because it enables the expansion of manufacturing automation that reduces costs and improves quality, among other things. Furthermore, said surface-mount technology may allow more components to be accommodated in a given area of the substrate.

[0025] An SMD component is usually smaller than its through-hole counterpart because it has smaller lead wires or no lead wires at all. Said SMD component may have various styles of short pins or lead wires, flat contacts, a matrix of solder balls, or terminations on the body of the component.

[0026] In a further example, the electrical component is a through-hole mounting device, the conductive trace is provided on an upper surface of the substrate, and the electrical circuit comprises: - a further conductive trace provided on a bottom surface of the substrate and connected at a first end to the LF voltage node in the HV circuit portion, the further conductive trace being provided between the first primary terminal and the first secondary terminal on the bottom side of the substrate, thereby increasing the creepage distance between the first primary terminal and the first secondary terminal.

[0027] In the case of a through-hole mounting device, the terminals may be connected to the substrate on the top side of the substrate and the bottom side of the substrate. In such a case, the required creepage distance needs to be satisfied starting from the first primary terminal connected on the top side of the substrate, but also needs to be satisfied starting from the first primary terminal connected on the bottom side of the substrate.

[0028] It should be noted that the aforementioned additional conductive traces may also be used when the electrical component is an SMD device, because there may be advantages when the SMD device is mounted near the edge of the substrate, i.e., the PCB. In that case, the creepage path may run from the top to the bottom, and therefore, in this situation, the additional conductive traces may also help increase the actual creepage path.

[0029] Furthermore, it should be noted that the conductive trace provided on the upper surface of the substrate and the further conductive trace provided on the bottom surface of the substrate may be connected to each other at at least one edge of the substrate, for example, by using PCB edge plating.

[0030] In a further example, the substrate is a printed circuit board (PCB).

[0031] In another example, the conductive trace extends between the first primary terminal and the first secondary terminal substantially perpendicular to the imaginary straight line between the first primary terminal and the first secondary terminal.

[0032] In other words, the straight line of sight between the first primary terminal and the first secondary terminal is crossed by the conductive trace, preferably substantially perpendicularly.

[0033] In further examples, the electrical circuit includes a switch-mode power supply (SMPS) using, for example, gallium nitride (GaN) or silicon carbide (SIC) technology.

[0034] One of the next steps being considered towards an energy-efficient world is the use of new materials, such as wide-bandgap semiconductors, which can enable improved power efficiency, miniaturization, weight reduction, and overall cost reduction, and sometimes all of these simultaneously.

[0035] Drivers of all kinds can benefit from small, passive components such as transformers, inductors, and capacitors. Such small passive components can be made possible by the high switching frequencies enabled by gallium nitride (GaN) technology.

[0036] The high switching frequencies enabled by GaN, for example, from several hundred kHz to several MHz, result in large minimum creepage distance requirements for safety and / or galvanic isolation. As mentioned above, the creepage distance depends not only on the voltage level but also on the frequency level. Therefore, this disclosure is particularly useful in situations where relatively high frequencies, for example in the range of 70 kHz to 20 MHz, are used in the HV circuit portion.

[0037] Further examples provide light-emitting diode (LED) based lighting devices having an electrical circuit according to any of the preceding examples.

[0038] In another embodiment, a method for supplying an electrical circuit having galvanic isolation between a high-voltage (HV) circuit portion and a low-voltage (LV) circuit portion, - A step of providing a substrate having the HV circuit portion and the LV circuit portion, - The step of assembling an electrical component for supplying the galvanic insulation onto the substrate, the electrical component having a primary side connected to the HV circuit portion at the first primary terminal and a secondary side connected to the LV circuit portion at the first secondary terminal, such that a creepage distance is provided on the substrate between the first primary terminal and the first secondary terminal. - A method is provided comprising the steps of: providing a conductive trace on the substrate at a first end, which is connected to a low-frequency (LF) voltage node in the HV circuit portion, wherein the frequency of the potential at the LF voltage node is lower than the frequency of the potential at the first primary terminal, and the conductive trace is provided between the first primary terminal and the first secondary terminal, thereby increasing the creepage distance between the first primary terminal and the first secondary terminal.

[0039] These and other aspects of the present invention will be described and clarified with reference to the embodiments described below. [Brief explanation of the drawing]

[0040] [Figure 1] An example of an electrical circuit having galvanic isolation is disclosed. [Figure 2] An example of a printed circuit board (PCB) layout having a transformer that provides galvanic isolation is disclosed. [Figure 3] Examples of actual creepage distances between high-voltage (HV) and low-voltage (LV) circuit sections are disclosed. [Modes for carrying out the invention]

[0041] Figure 1 discloses an example of an electrical circuit 1 having galvanic insulation, as indicated by the dashed line with reference numeral 2.

[0042] The electrical circuit 1 shown in Figure 1 is a so-called flyback converter. Flyback converters can be used to convert alternating current (AC) to direct current (DC), but they can also be used to convert DC to DC. The latter is shown in Figure 1.

[0043] The electrical circuit shown in Figure 1 has a high-voltage (HV) circuit section 3 and a low-voltage (LV) circuit section 4. The high-voltage circuit section 3 may be designed for relatively high voltages, such as above 48V DC or above 30Vrms AC, or above 400V DC or above 230Vrms AC, or similar. The low-voltage circuit section 4 may be designed for relatively low voltages, such as below 48V DC or below 30Vrms AC, or similar.

[0044] Galvanic isolation is the principle of insulating the HV circuit section 3 and the LV circuit section 4 of electrical circuit 1 to prevent the flow of current between these sections. Direct conduction paths between these circuit sections are not permitted. Energy or information can still be exchanged between circuit sections 3 and 4 by other means such as capacitance, induction, or electromagnetic waves, or by optical, acoustic, or mechanical means.

[0045] Galvanic isolation is used when two or more electrical circuits must communicate, but their grounds may be at different potentials. It is an effective way to break ground loops by preventing unwanted currents from flowing between two units that share a ground conductor. Galvanic isolation is also used for safety reasons, preventing unexpected currents from reaching ground through the human body.

[0046] Galvanic insulation can be used to ensure dielectric breakdown thresholds up to a reasonably safe level as defined by recognized standards, such as IEC standards and international safety organizations.

[0047] The electrical circuit 1 has a substrate that supplies the HV circuit portion 3 and the LV circuit portion 4. The substrate, although not shown in Figure 1 itself, may consist of a carrier such as a printed circuit board (PCB) on which the electrical circuit 1 is mounted.

[0048] The electrical circuit 1 further comprises at least one electrical component 5 that provides galvanic isolation 2. Thus, the electrical component 5 bridges the galvanic isolation in such a way that it has a primary side connected to the HV circuit portion 3 at the first primary terminal 6 and a secondary side connected to the LV circuit portion 4 at the first secondary terminal 8, so that a creepage distance is provided on the substrate between the first primary terminal 6 and the first secondary terminal 8.

[0049] The creepage distance can be defined as the shortest distance between two conductive parts, measured along the surface of the substrate. In this particular case, the creepage distance can be determined between a first primary terminal 6 and a first secondary terminal 8 on the substrate.

[0050] In the electrical circuit 1 shown in Figure 1, the electrical component 5 can be connected to the HV circuit portion 3 at two terminals, namely a first primary terminal 6 and a second primary terminal 7. Due to the fact that the first primary terminal 6 is connected to the switch 10 of the flyback converter, the frequency of the potential at the first primary terminal 6 may be higher than the frequency of the potential at the second primary terminal 7. The topology of the flyback converter is considered to be known and is not disclosed in further detail herein.

[0051] Furthermore, it should be noted that the potential of the first primary terminal 6 and the potential of the second primary terminal 7 may be equal.

[0052] The inventors have noticed that the required creepage distance, as imposed by, for example, the corresponding safety standard, depends not only on the expected voltage level in the HV circuit section 3 but also on the frequency of the potential at the corresponding node in the HV circuit section 3. It is expected that the higher the potential frequency, the greater the creepage distance.

[0053] The inventors have found that by introducing a conductive trace between a first primary terminal and a first secondary terminal on a substrate, the actual creepage distance between the first primary terminal and the first secondary terminal can be affected.

[0054] The conductive trace is connected at its first end to a low-frequency (LF) voltage node within the HV circuit section. This means that the potential frequency at the LF voltage node is lower than the potential frequency at the first primary terminal. The effect is that the creepage distance required for the conductive trace on the substrate is smaller than the creepage distance required for the first primary terminal. This is due to the difference between the potential frequency at the first primary terminal and the potential frequency at the LF voltage node.

[0055] Therefore, the conductive trace is provided between the first primary terminal 6 and the first secondary terminal 8. This will be explained in more detail with reference to Figure 2.

[0056] Figure 2 discloses an example of a printed circuit board (PCB) layout having a transformer that provides galvanic isolation. More specifically, the PCB footprint 21 of the transformer is shown.

[0057] Footprint 21 again shows the HV circuit section 3 and the LV circuit section 4, as well as the galvanic isolation 2.

[0058] In this case as before, the first primary terminal is indicated by reference numeral 6. The second primary terminal is indicated by reference numeral 7. The first secondary terminal is indicated by reference numeral 8. The conductive trace is indicated by reference numeral 23.

[0059] As shown in Figure 2, a conductive trace 23 is provided between the primary and secondary sides of the transformer. This directly affects the actual creepage path between the primary and secondary sides of the transformer, as also shown in the footprint 31 in Figure 3.

[0060] In Figure 3, the introduction of the conductive trace 23 affects the actual creepage path 22 between the primary and secondary sides of the transformer, and therefore, the actual creepage distance. The creepage path is not the shortest distance between the primary and secondary pins of the transformer. As shown in Figure 3, the creepage path must bypass the conductive trace 23. The creepage path 22 partially passes through the air. This means that the creepage distance requirement no longer applies, and only less stringent clearance requirements apply at higher frequencies.

[0061] In this particular example, the conductive trace 23 is connected at one end to a low-frequency (LF) voltage node, which is a second primary terminal 7. However, it should be noted that preferably, the conductive trace may be connected to ground at the first end. The second end of the conductive trace may be connected to the same node, for example, to ground.

[0062] The advantages of this disclosure are described with respect to the transformer, which is an electrical component 5. However, it should be noted that the advantages of this disclosure are applicable to all kinds of electrical components that bridge galvanic isolation, such as optocouplers and capacitors.

[0063] A person skilled in the art will be able to understand and achieve, in carrying out the claimed invention, other variations of the disclosed embodiments from the drawings, specification and appended claims study. In the claims, the word “has” does not exclude other elements or steps, and singular nouns do not exclude plurals. The mere fact that certain means are listed in different dependent claims does not imply that combinations of these means cannot be used to one advantage.

[0064] No reference numeral in the claims should be construed as limiting the claims.

Claims

1. A switch-mode power supply including an electrical circuit having galvanic isolation between a high-voltage circuit portion and a low-voltage circuit portion, wherein the electrical circuit is A substrate that supplies the high-voltage circuit portion and the low-voltage circuit portion, An electrical component for supplying the galvanic insulation, provided on the substrate such that a creepage distance is provided on the substrate between a first primary terminal and a first secondary terminal, and having a primary side connected to the high-voltage circuit portion at the first primary terminal and a secondary side connected to the low-voltage circuit portion at the first secondary terminal, A switch-mode power supply having a conductive trace provided on the substrate, the first end of which is connected to a low-frequency voltage node in the high-voltage circuit portion, wherein the frequency of the potential at the low-frequency voltage node is lower than the frequency of the potential at the first primary terminal, and the conductive trace is provided between the first primary terminal and the first secondary terminal, thereby increasing the creepage distance between the first primary terminal and the first secondary terminal.

2. The switch-mode power supply according to claim 1, wherein the low-frequency voltage node is ground.

3. The aforementioned electrical component is transformer, Optocapura, A switch-mode power supply according to claim 1, which is any of the capacitors.

4. The switch-mode power supply according to claim 1, wherein the electrical component is a transformer including a primary winding having a first primary terminal and a second primary terminal, and the conductive trace is connected to the second primary terminal at the first end.

5. The switch-mode power supply according to claim 1, wherein the conductive trace is connected to the same low-frequency voltage node at the second end.

6. The switch-mode power supply according to claim 1, wherein the electrical component is either a surface-mount device or a through-hole mounting device.

7. The electrical component is a through-hole mounting device, the conductive trace is provided on the upper surface of the substrate, and the electrical circuit is A further conductive trace provided on the bottom surface of the substrate and connected at a first end to the low-frequency voltage node in the high-voltage circuit portion, the further conductive trace provided on the bottom surface side of the substrate between the first primary terminal and the first secondary terminal, thereby increasing the creepage distance between the first primary terminal and the first secondary terminal, according to claim 6.

8. The switch-mode power supply according to claim 1, wherein the substrate is a printed circuit board.

9. The switch-mode power supply according to claim 1, wherein the conductive trace extends between the first primary terminal and the first secondary terminal perpendicular to a virtual straight line between the first primary terminal and the first secondary terminal.

10. The switch-mode power supply according to claim 1, wherein the electrical circuit has a switch-mode power supply using gallium nitride or silicon carbide technology.

11. The switch-mode power supply according to claim 10, wherein the switch-mode power supply uses gallium nitride technology.

12. A light-emitting diode-based lighting device having a switch-mode power supply as described in claim 1.

13. A method for supplying a switch-mode power supply including an electrical circuit having galvanic isolation between a high-voltage circuit portion and a low-voltage circuit portion, The step of providing a substrate having the high-voltage circuit portion and the low-voltage circuit portion, The steps include assembling an electrical component for supplying the galvanic insulation onto the substrate, the electrical component having a primary side connected to the high-voltage circuit portion at the first primary terminal and a secondary side connected to the low-voltage circuit portion at the first secondary terminal, such that a creepage distance is provided on the substrate between the first primary terminal and the first secondary terminal; A method comprising the steps of providing a conductive trace on the substrate at a first end, which is connected to a low-frequency voltage node in the high-voltage circuit portion, wherein the frequency of the potential at the low-frequency voltage node is lower than the frequency of the potential at the first primary terminal, and the conductive trace is provided between the first primary terminal and the first secondary terminal, thereby increasing the creepage distance between the first primary terminal and the first secondary terminal.

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