Isolated electronic circuits

Abstract

A circuit includes a first printed circuit board (60) carrying a first group of components and a second printed circuit board (62) carrying a second group of components, wherein a gap (64) is provided between the first and second printed circuit boards. A transformer (66) has a primary side connected to the first group of components and a secondary side connected to the second group of components. One of the transformer windings and its connection to the corresponding group of components includes triple-insulated wire. The gap requirement is met by providing separate printed circuit boards with a gap between them, and the creepage problem is solved or overcome by using triple-insulated wire. Therefore, high-frequency and high-voltage operation on the first printed circuit board is possible.

Description

Technical Field

[0001] The present invention relates to an electronic circuit, for example, having isolation between a high-voltage section on the input side of a circuit and a low-voltage section on the output side of a circuit. Background Technology

[0002] An example of an electronic circuit with high-voltage and low-voltage sections is an isolated switch-mode power supply (SMPS). The high-voltage section is powered by mains electricity and includes high-frequency switching components, while the low-voltage section, at the power supply's output, supplies power to a load. The load could be, for example, a lighting fixture supplied with a (relatively) low DC voltage. The output voltage or current is regulated by the switch-mode power supply.

[0003] The isolation between the high-voltage and low-voltage sections occurs across the isolation transformer.

[0004] Electrical safety considerations necessitate safety distance requirements for both the dangerous high voltage at the input side of the switch-mode power supply and the safe low voltage at the output side, as well as creepage distances.

[0005] Creepage distance is the shortest path measured along the insulating surface between two conductive parts. Proper and sufficient creepage distance prevents tracking, the process of creating a partially degraded conductive path on the surface of insulating material due to discharge on (or near) the insulating surface. The extent of tracking depends on three main factors: the voltage difference between the two conductive parts, the properties of the materials (especially the relative tracking index), and the degree of pollution in the environment. Tracking can damage insulating materials due to atmospheric humidity, pollution, corrosive chemicals, or the altitude at which equipment operates.

[0006] The gap distance is the shortest distance between two conductive parts measured through air. A sufficient gap distance prevents dielectric breakdown between the electrodes caused by air ionization. Dielectric breakdown is also affected by the voltage difference between the two conductive parts, relative humidity, temperature, and the degree of pollution in the environment.

[0007] For example, these problems typically require a switch-mode power supply to allow an 8mm creepage distance between the primary and secondary circuits.

[0008] Isolation between dangerous high voltage and safe low voltage is typically achieved by providing a physical layout that ensures adequate clearance and creepage distance, and by using solid insulation, typically in the form of insulating tape, between the primary and secondary windings in an isolation transformer.

[0009] Figure 1A known layout of an isolation transformer is shown. It includes a bobbin 10 surrounding a transformer core 12. A primary winding 14 and a secondary winding 16 are wound on the bobbin. Several insulating layers 18 are disposed between the windings. However, to ensure creepage distance requirements are met, spacers 20 are also required such that the distance between the primary and secondary windings along the surface of the insulating layers 18 meets the required minimum creepage distance. The primary winding 14 leads to a first pair of contact pins 22 for connecting the transformer to a PCB area 26 (only one is visible since one is behind the other), and the secondary winding leads to a second pair of pins 24 for connecting the transformer to a PCB area 28 (only one is visible since one is behind the other).

[0010] PCB regions 26 and 28 can be part of the same PCB, optionally with a slot between them, or they can be part of different PCBs.

[0011] The electrical, thermal, and mechanical safety requirements for isolation transformers used in LED drivers are specified, for example, by IEC 61347-1 in conjunction with IEC 61347-2-13. IEC 61347-2-13 specifies that isolation transformers used in LED drivers should comply with the relevant parts of IEC 61558. IEC 61558-1 specifically specifies insulation distances, clearance distances, and minimum creepage distances up to and including 30 kHz.

[0012] Figure 2 The required clearance for double insulation with two different assumed pollution levels (referred to as pollution level 2 and pollution level 3) according to IEC 61558-1 and as a function of the operating voltage is shown. The two plotted lines diverge only below 100V. For pollution level 1, there is no minimum clearance.

[0013] Operating voltage is defined as the highest (peak) voltage that the insulation under consideration can withstand when the equipment is operating at its rated voltage under normal operating conditions.

[0014] Figure 3 The creepage distance requirements for double insulation as a function of the operating voltage at an operating frequency are shown for four different material groups (and for three contamination levels 1 to 3). It demonstrates that the creepage distance depends on the degree of contamination and the material type.

[0015] Figure 4 The required insulation distance as a function of operating voltage is shown for solid material layers and thin-layer stacks. This demonstrates that layer structure affects thickness requirements.

[0016] Figures 2 to 4Various distance requirements are shown, each proportional to the operating voltage. The minimum requirement always applies to contamination level 1, where differences between material groups are negligible. Safety distances (gap distance and creepage distance) must also be observed on printed circuit boards (PCBs) with isolation transformers mounted. Therefore, the specified minimum creepage distance must be less than the length of the shortest path along the surface between the conductive portions of the two circuits to be isolated. This path can, for example, travel around the PCB slot.

[0017] IEC 61558-2-16 specifically specifies insulation distances, minimum creepage distances, and clearance distances exceeding 30 kHz and up to and including 3 MHz.

[0018] Figure 5 The minimum creepage distance is shown to vary as a function of operating voltage, but this also applies to different operating frequencies. At each operating frequency, three contamination levels 1 to 3 are shown (for the same material).

[0019] It can be seen that at typical operating frequencies of switch-mode power supplies, such as 500kHz and 700V, the creepage distance is only a few millimeters, and this can be taken into account in the design of transformers, for example... Figure 1 As shown.

[0020] However, there is a desire to use GaN power transistors in switch-mode power supplies and other circuits to form high-speed and high-power circuits. GaN power transistors are more efficient than Si power transistors and can operate at significantly higher switching frequencies. This can, for example, result in smaller, lighter, more compact, more efficient, and potentially cheaper LED drivers or other switch-mode power supplies.

[0021] Fully utilizing the advantages of GaN power transistors requires operating frequencies from several hundred kHz to several MHz and operating voltages of several hundred volts. At such high operating frequencies and voltages, the creepage distances required, for example, by IEC 61558-2-16 to achieve adequate electrical insulation for product safety are significantly higher than those specified by conventional standards that do not consider high-frequency operation. For example, Figure 5 The minimum creepage distance for 750V and 1MHz is shown to be approximately 60mm. Achieving this creepage distance within a compact transformer module is impractical and would likely require an axial length of only about 20mm.

[0022] therefore, Figure 1 The traditional isolation transformer design shown would no longer be feasible. In order to reduce their size and weight, complex mechanical structures for high-voltage transformers have been proposed to increase creepage distances, but even these are impractical and result in bulky transformers for the large creepage distances required for the high frequencies and high voltages ideally required for SMPS and isolation transformers to operate.

[0023] Therefore, a circuit design is needed that allows for isolation from high-voltage, high-frequency circuits while meeting minimum safety requirements for creepage distance and clearance distance. Summary of the Invention

[0024] This invention is defined by the claims.

[0025] According to an example of one aspect of the present invention, a circuit is provided, comprising:

[0026] The first printed circuit board that carries the first set of components;

[0027] A second printed circuit board carrying the second set of components, wherein a gap exists between the first printed circuit board and the second printed circuit board; and

[0028] A transformer having a primary winding and a secondary winding, wherein the primary winding is electrically connected to a first group of components via a first connecting device, and the secondary winding is connected to a second group of components via a second connecting device.

[0029] The primary winding and the first connecting device and / or the secondary winding and the second connecting device include insulated wires.

[0030] The gap requirement is met by providing separate printed circuit boards with spacing between them. The gap distance is not proportional to frequency in the same way as the creepage distance, so even at high frequencies, it is possible to have a compact design with sufficient space between the printed circuit boards to achieve the required gap.

[0031] Using conductors for transformer windings and connections to printed circuit boards—this is done by providing sufficient length or using conductors that are considered safe and conform to regulations that allow for creepage even without meeting standard minimum creepage distances—reduces or overcomes creepage problems. This applies to triple-insulated conductors.

[0032] In particular, the use of triple-insulated wire addresses the problem of partial discharge. There are materials that are susceptible to partial discharge and materials that are not. Glass, ceramics, and mica are examples of materials that are not susceptible to partial discharge. However, testing of structures based on materials that are inherently susceptible to partial discharge has enabled such structures to be used at high frequencies and high voltages, provided their safety has been proven. Triple-insulated wire is an example of this proven safety because the materials, structure, and manufacturing processes have been tested and optimized (because it is more feasible for simple components such as conductors than for complete transformers).

[0033] In the first example, the transformer is mounted on a first printed circuit board, and the secondary winding and the second connection device include triple-insulated wires, and the second connection device extends across the gap between the first and second printed circuit boards.

[0034] In the second example, the transformer is mounted on a second printed circuit board, and the primary winding and the first connection device include triple-insulated wires, and the first connection device extends across the gap between the first and second printed circuit boards.

[0035] Therefore, the transformer can be a surface-mount component applicable to either a first or second printed circuit board. Note that, if desired, triple-insulated wire can be used for both windings and both connection devices.

[0036] Glass, ceramic, or mica gaskets can be mounted on the first and second printed circuit boards, defining the gap between the first and second printed circuit boards.

[0037] Alternatively, the first spacer can be mounted to the first printed circuit board and the intermediate support portion, and the second spacer can be mounted to the second printed circuit board and the intermediate support portion, wherein the first spacer and / or the second spacer comprises glass, ceramic or mica, and the gap between the first printed circuit board and the second printed circuit board is defined by the first spacer, the second spacer and the support portion.

[0038] One or more spacers are selected to specifically resist partial discharge. This inorganic insulating material is not damaged by corona discharge, therefore there is no creepage distance requirement between the first and second printed circuit boards, but a clearance requirement applies.

[0039] In another example according to the invention, a glass, ceramic, or mica spacer is also mounted to the first and second printed circuit boards, defining a gap between the first and second printed circuit boards, and the transformer is mounted at the spacer (e.g., mounted on the spacer). Therefore, the transformer can be separately mounted to the first and second printed circuit boards.

[0040] Alternatively, the transformer may include a spool formed by spacers, with the primary and secondary windings wound on the spool. Thus, the spacers serve to provide the required clearance but also function as part of the transformer structure.

[0041] The first group of components includes, for example, GaN or SiC or other wide-bandgap semiconductor transistors. GaN and SiC are examples of wide-bandgap semiconductor materials. These can be used as high-voltage, high-frequency transistors. For example, they can have operating voltages exceeding 400V, such as exceeding 500V, such as exceeding 700V, and operating frequencies exceeding 750kHz, such as exceeding 1MHz, such as exceeding 1.5MHz.

[0042] The second group of components includes, for example, Si transistors. They can have operating voltages below 400V.

[0043] The first and second groups of components, for example, together define the switch-mode power supply. An isolation transformer provides isolation between the input and output of the switch-mode power supply.

[0044] The present invention also provides an LED driver, comprising:

[0045] The input terminal used to receive the mains input voltage;

[0046] Switch-mode power supplies, including the circuitry defined above; and

[0047] Used to deliver a DC voltage with regulated current and / or voltage to the output of an LED arrangement.

[0048] The LED driver may also include an optical feedback system for providing optical feedback from the second set of components to the first set of components, comprising an optical emitter mounted on a second printed circuit board and an optical receiver mounted on a first printed circuit board. This is used by the LED driver to regulate the output voltage and / or current using feedback from the secondary side.

[0049] The present invention also provides a lighting circuit, comprising:

[0050] The LED driver defined above; and

[0051] The LED device is powered by an LED driver.

[0052] These and other aspects of the invention will become apparent and will be clarified with reference to the embodiments described below. Attached Figure Description

[0053] To better understand the invention and to more clearly illustrate how to implement it, reference will now be made to the accompanying drawings by way of example only, wherein:

[0054] Figure 1 A known layout of an isolation transformer is shown;

[0055] Figure 2The gap requirements for double insulation with two different assumed pollution levels and as a function of operating voltage are shown.

[0056] Figure 3 The creepage distance requirements for double insulation are shown as a function of operating voltage for four different material groups (and three contamination levels 1 to 3).

[0057] Figure 4 The required insulation distance for solid material layers and thin-layer stacks as a function of operating voltage is shown;

[0058] Figure 5 The minimum creepage distance is shown to vary as a function of the operating voltage, but this also applies to different operating frequencies above 30 kHz;

[0059] Figure 6 A to 6D illustrate various possible implementations of the present invention in the form of schematic diagrams;

[0060] Figure 7 A plan view of the arrangement with ceramic spacers is shown;

[0061] Figure 8 This illustrates how the invention can be modified. Figure 1 Transformer;

[0062] Figure 9 This demonstrates that a ceramic frame can form the central core of a transformer;

[0063] Figure 10 It shows Figure 9 How can the transformer design achieve the arrangement of the transformer itself spanning the gap between the first and second printed circuit boards?

[0064] Figure 11 An exemplary simplified existing technology topology of a known driver is shown; and

[0065] Figure 12 The triple-insulated wire is shown. Detailed Implementation

[0066] The invention will be described with reference to the accompanying drawings.

[0067] It should be understood that while the detailed description and specific examples indicate exemplary embodiments of the apparatus, system, and method, they are for illustrative purposes only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, system, and method of the present invention will become more readily apparent from the following description, the appended claims, and the accompanying drawings. It should be understood that the drawings are merely schematic and not drawn to scale. It should also be understood that the same reference numerals are used in all the drawings to denote the same or similar parts.

[0068] This invention provides a circuit comprising a first printed circuit board carrying a first group of components and a second printed circuit board carrying a second group of components, wherein a gap exists between the first and second printed circuit boards. A transformer has a primary side connected to the first group of components and a secondary side connected to the second group of components. One of the transformer windings and its connection to the corresponding group of components includes an insulated wire. The gap requirement is met by providing separate printed circuit boards with a gap between them, and the use of insulated wires solves or overcomes the problem of creepage. Therefore, high-frequency and high-voltage operation on the first printed circuit board is possible.

[0069] This invention may include the use of insulated wire of a certain length (e.g., single or double insulated wire) to meet applicable creepage requirements, if these can be met within available space. In a preferred embodiment, the invention is based on a method in which safety insulation is designed in such a way that creepage requirements are no longer applicable, particularly in the case of designs based on the use of insulated wire that avoid the need for creepage requirements. Triple insulated wire is an example according to the invention. This avoids the need to provide large creepage distances when applying high frequencies and high voltages.

[0070] Dangerous high-voltage circuits and safe low-voltage circuits are mounted on separate first (primary) and second (secondary) printed circuit boards. Clearance requirements apply between the first and second printed circuit boards. However, in a preferred example, there are no creepage distance requirements between the first and second printed circuit boards because the physical connection between them is made using components unaffected by creepage distance requirements.

[0071] Figure 6 Various possible implementations of the invention are illustrated schematically. The invention will be described based on the use of triple-insulated wire as the transformer winding and the tail wire crossing or partially crossing the gap between the PCB.

[0072] In each case, there is a first printed circuit board 60 carrying a first set of components (not shown) and a second printed circuit board 62 carrying a second set of components (not shown), wherein there is a gap 64 between the first printed circuit board and the second printed circuit board.

[0073] The first printed circuit board 60 carries components that operate at high frequency and high voltage (relative to the second printed circuit board), and equivalently, the second printed circuit board 62 carries components that operate at low voltage (relative to the first printed circuit board).

[0074] The transformer 66 has a primary winding and a secondary winding. The primary winding is electrically connected to a first set of components via a first connecting device 67, and the secondary winding is connected to a second set of components via a second connecting device 68.

[0075] The connection device can preferably be simply a pair of tail wires of the respective windings, such that the length of a single conductor defines two connection lines between the winding itself and the opposite end of the winding and the printed circuit board. The ends of these tail wires then define contact terminals for connection to the printed circuit board. The tail wires (of one or both windings) themselves extend through the gap, and in this example, these tail wires and the associated winding are formed of triple-insulated wire.

[0076] Alternatively, the transformer can be a module with a separate external wire connected to it, extending between the printed circuit board and the module. Therefore, the external wire connection that needs to cross the gap is formed as a triple-insulated wire.

[0077] In one example, the end of the tail wire is soldered to a pin. These pins are then inserted into through-holes on the PCB, and then soldered to those through-holes.

[0078] In some examples according to the invention, the primary-side winding and the first connecting device comprise triple-insulated wire, and the first connecting device passes through gap 64. In other examples according to the invention, the secondary-side winding and the second connecting device comprise triple-insulated wire, and the second connecting device passes through gap 64. Alternatively, triple-insulated wire may be used for both the winding and the connecting device.

[0079] Transformers provide electrical insulation between dangerous high-voltage circuits and safe low-voltage circuits.

[0080] Figure 6 A illustrates a first example according to the invention, wherein a transformer 66 is mounted on a first printed circuit board 60, and the secondary winding and second connection device 68 comprise triple-insulated wires. The second connection device 68 extends through a gap 64 between the first and second printed circuit boards.

[0081] The tail of the primary winding terminates, for example, at a pin connected via the first PCB 60. The tail of the secondary winding forms a second connection device 68. The ends of the tails of the secondary winding are attached to a second printed circuit board, for example, by soldering them to pads or by using connectors. These connectors may include, for example, plugs and sockets.

[0082] Figure 6 B illustrates a second example in which a transformer 66 is mounted on a second printed circuit board 62, and the primary winding and the first connection device 67 include triple-insulated wires, and the first connection device 67 extends across the gap between the first and second printed circuit boards.

[0083] The tail of the secondary winding terminates, for example, at a pin connected via a second PCB 62. The tail of the primary winding forms a first connection device 67. The ends of the tail of the primary winding are attached to the second printed circuit board, for example, by soldering them to pads or by using connectors.

[0084] Therefore, the transformer can be a surface mount component or through-hole component applicable to either the first or second printed circuit board. Note that, if desired, triple-insulated wire can be used for both windings and both connection devices.

[0085] Figure 6 Example C illustrates an example according to the invention having a glass, ceramic, or mica spacer 70 mounted to a first and a second printed circuit board, defining and providing a gap 64 between the first and second printed circuit boards to meet gap requirements. Thus, the spacer provides a mechanical connection between the printed circuit boards. The spacer 70 is selected to be particularly resistant to partial discharge. Therefore, suitable materials can avoid introducing creepage distance requirements between the first and second printed circuit boards.

[0086] Spacers can be located at different positions on the transformer (e.g.) Figure 7 (As shown). However, in Figure 6 In section C, transformer 66 is mounted on spacer 70, specifically on spacer 70. Therefore, transformer 66 can be mounted separately from the first and second printed circuit boards.

[0087] The transformer is connected via a tail wire to two printed circuit boards, or it can be wired inside the spacer 70.

[0088] Figure 6 D illustrates an example where spacer 70 forms the spool of the transformer, and the primary and secondary windings are wound on the spool. Pins can be used to terminate the tail wires of both windings.

[0089] Figure 7 An arrangement with ceramic spacers 70 separate from the transformer 66 is shown in a plan view. In this example, the transformer 66 is mounted on the first printed circuit board 60. Alternatively, the first PCB 60 can be connected to the housing via the spacers 70, and the second PCB 62 can be connected to the same housing via the spacers 70. Not all of these spacers need to be ceramic.

[0090] Two printed circuit boards, for example, together define a switch-mode power supply that forms part of an LED driver. Switch-mode power supplies are widely used in LED driver circuits.

[0091] A controllable LED driver can be used to change the voltage and / or current supply provided to an LED load. One known application of such a controllable driver is the controllable dimming of an LED output load. In this driver, an isolation transformer 66 provides isolation between the input and output of the switch-mode power supply. Typically, control circuitry is present on the primary side of the isolation transformer to receive and switch the input power supply in response to feedback signals from the secondary side.

[0092] The first printed circuit board receives, for example, an AC input voltage, and the output from the second printed circuit board delivers a DC voltage with regulated current and / or voltage to the LED device.

[0093] For the regulation function, an optical feedback system is provided to transmit optical feedback signals from the second set of components to the first set of components. A light emitter 80 is mounted on a second printed circuit board 62, and a light receiver 82 is mounted on a first printed circuit board 60. This is used by the LED driver to regulate the output voltage and / or current using feedback from the secondary side. Therefore, the optical feedback system includes an optocoupler that bridges an isolation barrier and is separated between the primary and secondary printed circuit boards.

[0094] Figure 8 This illustrates how the invention can be modified. Figure 1 The transformer. In this example, the primary winding 14 is formed of triple-insulated wire and is therefore shown as having a larger diameter than the secondary winding 16. This avoids the need for insulation tape (or insulation wrapping at the transformer tail wire).

[0095] The transformer core 12 is shown as a split core, comprising an upper core 12a and a lower core 12b of a soft magnetic ferrite core passing through the spool 10. They may include, for example, two E-shaped core halves. A strip 18 is present between the winding and the outer winding 19, primarily for mechanically fixing the winding.

[0096] Figure 9 It is shown that it is mounted on PCB 83 Figure 8 Transformer 66. A bobbin 10, core halves 12a and 12b of the transformer, and outer winding 19 are shown. The windings are not shown because they are located beneath the outer winding 19.

[0097] Transformer 66 is shown mounted on PCB 83 with slot 84, thus creating a creepage path 86 around the slot from the primary side to the secondary side. At high voltages and frequencies, this path may still be too short to meet creepage requirements.

[0098] Figure 10 It shows Figure 9 How can transformer design be implemented? Figure 6The arrangement of D, wherein the transformer itself spans the gap 64 between the first printed circuit board 60 and the second printed circuit board 62. (As shown) Figure 8 As shown, spool 10 is attached to the PCB. Spool 10 serves as a ceramic spacer. Figure 9 The creepage path shown no longer exists. The connection between the two printed circuit boards consists of triple-insulated wires or ceramic spools 10.

[0099] For the sake of completeness, Figure 11 An exemplary simplified prior art topology of a known driver 90 is shown. A flyback converter topology is shown, known for both AC / DC and DC / DC conversions with current isolation between the input and any output. A flyback converter is a buck-boost converter with separate inductors to form an isolation transformer, thus combining the advantages of scaling the primary to the output voltage while also achieving isolation. The controllable driver 90 includes a primary converter 92, feedback control circuitry 94, and opto-isolators 80, 82.

[0100] Primary converter 92 uses power generator 93 to receive and convert input power supply Vsup (e.g., AC mains power) to generate a power signal Vload for supplying to LED load 98. Primary converter 92 and LED load 98 are electrically isolated from each other via first winding 100 and second winding 102, which are magnetically coupled together via a shared core 104. The level of the power signal (voltage Vload and / or current) can be adjusted by power generator 93 in response to adjustment signal Vad.

[0101] The power generator 93 includes, for example, an EMI filter, a fuse, a rectifier, a high-frequency switch for a switch-mode power converter, and associated switch-mode control circuitry for adjusting the output in response to feedback from the feedback control circuitry 94.

[0102] Feedback control circuit 94 receives the sensing signal Ifb or Vfb (only when...) Figure 11 (Illustrated schematically) and a reference signal generate an error signal, and a comparator circuit derives an adjustment signal Vad from this error signal. In the example shown, the dimming interface 106 receives the input voltage Vin and generates a reference voltage used by the feedback control circuit 94 to generate the error signal, which in turn generates the adjustment signal Vad. In another example, the feedback control circuit 94 and the dimming interface 106 are located on the primary side (between the optical isolators 80, 82 and the power generator 93). The separate unit then receives Ifb or Vfb and drives the optical isolators 80, 82, causing these to be transmitted.

[0103] The adjustment signal Vad is provided to the primary converter 92 by the feedback control circuit 94 through opto-isolators 80 and 82. Therefore, the adjustment signal realizes current or voltage feedback control.

[0104] In this example, the sensing signal Ifb or Vfb is directly connected from the second winding 102 (i.e., from the isolated power supply signal provided to the load) to the feedback control circuit 94, specifically the comparator circuit.

[0105] Therefore, the driver delivers a controllable output power signal (voltage and / or current) to the load while ensuring isolation between the load and the primary converter. The control circuitry used to control the output power is also isolated from the primary converter.

[0106] The feedback control implemented by circuit 94 can be used to regulate the output voltage or current. Some lighting loads require current regulation, while others require voltage regulation. Therefore, both current sensing and feedback control and voltage sensing and feedback control are possible.

[0107] Figure 11 The circuit can be adapted according to the present invention by providing primary-side components on a first printed circuit board and secondary-side components on a second printed circuit board and implementing the transformer and connection as described above.

[0108] This is merely a schematic example of a switch-mode power supply architecture. Other topologies can certainly be used. Typically, there is a main inductor that controls the storage of energy from the input and the delivery of that stored energy to the load. The main power switch controls the energy supply from the input to the main inductor. The operating timing of the main power switch, particularly its duty cycle, controls the energy transfer. Common low-cost switch-mode power converters are single-stage converters, such as buck converters or buck-boost converters.

[0109] The first set of components on the first printed circuit board includes, for example, GaN or SiC transistors or transistors made of other wide-bandgap materials. These can be used as high-power, high-frequency transistors. For example, particularly for GaN transistors, they can have operating voltages exceeding 500V and operating frequencies exceeding 750kHz, such as exceeding 1MHz, or even exceeding 1.5MHz. SiC transistors, for example, operate at higher voltages but lower frequencies than GaN transistors.

[0110] The second set of components on the second printed circuit board includes, for example, Si transistors. They can have an operating voltage of less than 500V.

[0111] As an example, the synchronous rectifier can be located between the secondary winding 102 and the LED load 98, or a rectifier diode can be used to allow current to flow to the load 98 without flowing in the other direction.

[0112] The operating frequency is the same on both sides of the transformer.

[0113] Wide bandgap materials are particularly interesting on the high-voltage primary side because they can also be used on the low-voltage secondary side, where they can still save space.

[0114] The first group of components and the second group of components together define, for example, as follows: Figure 11 The switch-mode power supply is shown.

[0115] Optical isolators 80 and 82 bridge the gap between the printed circuit boards. Other components may also bridge isolation barriers. For example, glass-ceramic capacitors (e.g., as disclosed in WO2015 / 173409A1) can be used as Y capacitors for RF noise reduction and can also bridge isolation barriers. The Y capacitors are then separated between the primary and secondary printed circuit boards, connected to the first winding 100 and the second winding 102 to reduce EMI. Y capacitors are generally considered safe for low frequencies. For the aforementioned high frequencies, glass-ceramic capacitors should be used, for example.

[0116] Triple-insulated wires are formed, for example, by a three-layer extrusion coating of high-performance polymer resin or a three-layer wound insulation tape coating. Figure 12 The diagram shows a copper core 110 (which can be single-stranded or multi-stranded) and three insulating layers 112, 114, and 116. This provides excellent dielectric properties. Unlike enameled wire, three layers of insulation can be extruded onto the copper core using an automated manufacturing process to ensure perfect centering of the conductor.

[0117] The outer insulator is, for example, polyamide, and the two inner insulating layers are, for example, modified heat-resistant polyester.

[0118] Various designs of triple-insulated wire are commercially available, for example from Furukawa (trademark).

[0119] This invention can be used when GaN or SiC power transistors are required as described above, but it can also be applied to other wide bandgap (WBG) power transistors.

[0120] The examples above all illustrate transformers with a single primary winding and a single secondary winding. Transformers with two or more output windings exist. If these two or more output windings are bridged with a gap, they must all be made of triple-insulated wire. The electrical connection between these windings must be made after the gap bridging.

[0121] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0122] If the term “suitable” is used in the claims or specification, it should be noted that the term “suitable” is intended to be equivalent to the term “configured to”.

[0123] Any reference numerals in the claims should not be construed as limiting the scope.

Claims

1. A circuit comprising: First printed circuit board (60) carrying the first set of components; A second printed circuit board (62) that carries the second set of components, wherein there is a gap (64) between the first printed circuit board and the second printed circuit board. as well as A transformer (66) having a primary winding and a secondary winding, wherein the primary winding is electrically connected to the first group of components via a first connecting device, and the secondary winding is connected to the second group of components via a second connecting device. The primary winding and the first connecting device and / or the secondary winding and the second connecting device include insulated wires, wherein the wires are triple-insulated wires. The circuitry includes a glass, ceramic, or mica spacer (70) mounted to the first and second printed circuit boards, the spacer defining the gap between the first and second printed circuit boards; or A first spacer is mounted to the first printed circuit board and the intermediate support portion, and a second spacer is mounted to the second printed circuit board and the intermediate support portion, wherein the first spacer and / or the second spacer comprises glass, ceramic, or mica, and the gap between the first printed circuit board and the second printed circuit board is defined by the first spacer, the second spacer, and the support portion.

2. The circuit of claim 1, wherein the transformer (66) is mounted on the first printed circuit board (60), and the secondary winding and the second connection device comprise triple-insulated wires, and the second connection device extends across the gap between the first printed circuit board and the second printed circuit board.

3. The circuit of claim 1, wherein the transformer (66) is mounted on the second printed circuit board (62), and the primary winding and the first connection device comprise triple-insulated wires, and the first connection device extends across the gap between the first printed circuit board and the second printed circuit board.

4. The circuit of claim 1 further includes a glass, ceramic, or mica spacer (70) mounted to the first printed circuit board and the second printed circuit board, the glass, ceramic, or mica spacer (70) defining the gap between the first printed circuit board and the second printed circuit board, wherein the transformer (66) is mounted at the spacer.

5. The circuit of claim 1 further includes a glass, ceramic, or mica spacer (70) mounted to the first printed circuit board and the second printed circuit board, the glass, ceramic, or mica spacer (70) defining the gap between the first printed circuit board and the second printed circuit board, wherein the transformer (66) includes a spool (10) formed by the spacer, and the primary winding and the secondary winding are wound on the spool.

6. The circuit according to any one of claims 1 to 5, wherein the first set of components comprises SiC or GaN transistors.

7. The circuit of claim 6, wherein the SiC or GaN transistor has an operating voltage of more than 400V and an operating frequency of more than 750kHz, for example more than 1MHz, for example more than 1.5MHz.

8. The circuit according to any one of claims 1, 2, 3, 4, 5 and 7, wherein the second set of components comprises Si transistors.

9. The circuit of claim 8, wherein the Si transistor has an operating voltage of less than 400V.

10. The circuit according to any one of claims 1, 2, 3, 4, 5, 7 and 9, wherein the first group of components and the second group of components together define a switch-mode power supply.

11. An LED driver, comprising: The input terminal used to receive the mains input voltage; A switch-mode power supply, including the circuit according to claim 9; as well as Used to deliver a DC voltage with regulated current and / or voltage to the output of an LED device.

12. The LED driver of claim 11, further comprising an optical feedback system for providing optical feedback from the second set of components to the first set of components, the optical feedback system comprising an optical transmitter mounted on the second printed circuit board and an optical receiver mounted on the first printed circuit board.

13. A lighting circuit, comprising: LED driver according to claim 11 or 12; as well as The LED device is powered by the LED driver.

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