Circuit arrangement for operation of at least one LED with glow prevention

Abstract

The invention relates to a circuit arrangement for operating a load, comprising a first clocked converter operating as a power factor correction circuit and a second clocked converter for converting the intermediate circuit voltage into a suitable operating current for the load. The circuit arrangement is either permanently connected to the AC voltage network or the AC voltage network is not completely switched off when the circuit arrangement is switched off. The circuit arrangement now has measures for reducing glow currents in that each possible current path between the input and the output of the circuit arrangement is either provided with an isolator switch or an isolated part of the circuit arrangement is utilised in order to avoid these glow currents. A Y capacitor is also connected to the isolated part of the circuit arrangement, so that the Y capacitor avoids the glow currents via a capacitance of the LED module by diverting these glow currents to the protective earth (PE).

Description

[0001] CIRCUIT ARRANGEMENT FOR OPERATING AT LEAST ONE LED WITH

[0002] GLIMM PREVENTION

[0003] DESCRIPTION

[0004] Technical field

[0005] The present invention relates to a circuit arrangement for operating light-emitting diodes with the ability to avoid glowing effects.

[0006] A light-emitting diode (LED) or LED module can be voltage-driven or current-driven. However, for operation, it is necessary to limit the current to an ideal value for the LED. Otherwise, the LED could flicker or, especially when operated with a voltage supply, fail due to the associated thermal stress as the power consumption increases. Electronic ballasts (ECGs) have proven effective for setting the appropriate operating parameters, particularly for current limiting. Electronic ballasts for LEDs are also known as LED drivers. LED drivers primarily contain circuit arrangements such as the one described below.

[0007] Due to their highly nonlinear characteristic curve, LEDs exhibit extremely high impedance at low power levels. Nevertheless, under certain conditions, a comparatively small forward current can occur, which, according to the flat section of their nonlinear characteristic curve, remains just below their rated voltage even up to relatively high forward voltages. This forward current then produces light, which, although very dim due to the forward current, is still clearly visible compared to absolute darkness. Thus, even minute currents supplied by a power supply unit intended for LEDs, which is normally switched off, can cause the connected LEDs to glow faintly or dimly.In particular, capacitive displacement currents, caused by the mains rectifier at the input of an LED driver and reaching the LEDs via parasitic capacitances, cause them to glow as long as at least one phase of an AC mains supply remains connected to the input of the LED driver via parasitic capacitances. These currents are often referred to as glow currents.

[0008] background

[0009] For luminaires and all other electrical equipment, EN 61140 defines three protection classes, describing whether and how a protective earth (PE) conductor must be connected. Luminaires of protection class II (SK II luminaires) have reinforced or double insulation between the mains circuit and the output voltage or the metal housing (VDE 0100 Part 410, 412.1). They normally do not have a connection to a protective earth conductor. If cables with a protective earth conductor are used, it must not be connected to the housing. In contrast, for luminaires of protection class I, the protective earth conductor must be connected to the metal housing. The protective earth conductor is also usually connected to the LED driver via a Y-capacitor to improve electromagnetic compatibility (EMC).

[0010] Safety extra-low voltage (SELV) refers to an electrical voltage that, due to its low level and its isolation from higher-voltage circuits, e.g., by means of safety isolating transformers, offers special protection against electric shock (EN 61558; IEC 61558 Safety of transformers). If the nominal voltage is less than 25 V AC or 60 V DC, a protective conductor for protection against direct contact is not required when operating a device with safety extra-low voltage. Electronic devices must comply with limits for the emission of interference signals and meet minimum requirements for susceptibility to interference. A Y-capacitor is typically used for radio interference suppression of electronic ballasts operating with safety extra-low voltage. This is a suppression capacitor, or...

[0011] Safety capacitor that enables a reduction in electromagnetic interference.

[0012] For lighting offices or shops, large-area lighting arrangements with many individual LEDs are required, which, due to their number and resulting electrical power consumption, must also be well cooled. Therefore, the LED modules are often built on so-called metal-core circuit boards, where only a relatively thin layer provides insulation between the LED connections and between the LEDs themselves and the metal core. The metal core is often—again for cooling purposes—directly connected to the luminaire or even directly to the building and is thus usually at the potential of a protective earth. The construction described above therefore unintentionally includes very high parasitic capacitances between each of the LED connections and this protective earth, to which the housing and the radio interference filter of an LED driver may also be connected.Such potential connections complete radio interference suppression, as they can be useful, for example, for shielding against non-conducted radio interference. This is because lighting installations originally designed for fluorescent lamps often need to be modernized. In these cases, the mechanical and safety features often remain unchanged.

[0013] This can even extend to the fundamental design of LED drivers intended to replace conventional fluorescent or "ballast" drivers. Such traditional drivers often lack galvanic isolation between the lamp output and the AC mains input. This design typically improves the efficiency of an LED driver. However, the output of the driver must be a DC voltage with a significantly lower ripple than that of an AC voltage supplied to fluorescent lamps to ensure uniform illumination. This is because, unlike the often very slow-responding conventional lamps, which can even filter out an unsmoothed 100Hz mains hum (such as incandescent lamps), LEDs are light sources that respond very quickly to current.This makes any ripple in the output voltage of an LED driver visible through the connected LEDs. This can also affect any capacitive coupling of the LEDs to the mains input, which then causes these LEDs to glow even though the LED driver is actually switched off. The unwanted glow is caused by a very small glow current flowing in the LEDs, or by a glow current in the form of a capacitive displacement current flowing to ground via the LEDs and their capacitive coupling.

[0014] Two different methods of switching off the LED driver should be mentioned here, which are collectively referred to as "standby mode" in the following: Firstly, switching off one of the two power conductors, where the remaining conductor is the phase of the AC mains supply. Secondly, switching off the LED driver via a communication interface such as a DALI, Zigbee, Matter, or other bus. In this case, the LED driver is permanently connected to the AC mains supply and is not truly "switched off" in the literal sense, as its internal logic continues to operate. Therefore, this is often referred to as a "standby mode," since while the converters and the power output to the connected load are switched off, the driver itself is not. With both of these methods, a glow current can still flow through the LEDs, even though the LED driver is technically switched off or in standby mode.This glowing current is very small, but can still be clearly visible in complete darkness. Therefore, measures have been taken in such LED drivers to suppress the glowing current or to keep it as small as possible.

[0015] These glowing currents are primarily caused by the mains rectifier, which generates a modulation voltage spike equal to the mains peak voltage every time the AC mains voltage switches. In a 230V AC mains supply, this modulation voltage spike is approximately 325V. These voltage spikes can reach the output through current paths opened by parasitic capacitances within the circuit, causing LEDs connected there to glow.

[0016] One method for combating the unwanted glow of supposedly switched-off LEDs takes place on the LED module itself. German patent application DE10 2016 119 448 A1 proposes connecting a capacitor in parallel to each LED, or at least to each series circuit of two LEDs. The capacitor's capacitance should be significantly larger than the parasitic capacitance between each LED terminal and the circuit board substrate. Alternatively, high-value resistors can be connected in parallel, which more reliably suppress glowing but introduce additional losses, thus reducing the LED module's efficiency. Furthermore, the already critical cooling of the LEDs is further burdened by the heat generated by the resistors.

[0017] In contrast, DE 10 2015 106268 A1 proposes extending a clocked output switching stage by adding a diode between it and the intermediate circuit capacitor supplying it. This additional diode is polarized such that it allows current to flow from the intermediate circuit capacitor into the output switching stage, but prevents current from flowing back from the positive terminal of the LED driver output to the intermediate circuit capacitor. This capacitor also connects the negative terminal of the entire LED driver to this additional diode with a low impedance, which is why it is assumed that this single additional diode is sufficient to prevent glowing.

[0018] In DE 10 2022 200 431 A1, whose circuit diagram is shown in Fig. 1 as prior art, it is proposed to connect two diodes in the output current path, one at the positive output terminal (DAGI) and the other at the negative output terminal (DAGZ), to form an additional barrier against glow currents. Additionally, a MOSFET (MAG) is connected in the LED current path, which is also switched off when the LED driver is switched off, to form a further barrier against glow currents. Thus, in this solution, the circuit arrangement contained in the driver has three additional components, which incur costs and also power losses during operation. In particular, the two diodes DAGI and DAGZ, each with the forward voltage through which the load current flows, generate considerable losses. These diodes are solely intended for glow suppression and have no other circuit function.They are therefore components solely for preventing glowing and have no other function.

[0019] Task

[0020] The object of the invention is to provide an LED driver with simplified glow suppression that is cheaper to manufacture and generates less power loss. This is because glow suppression stages in prior art LED drivers comprise several power switching stages connected in series. Since these are solely glow suppression stages with no other function, material costs, radio interference, size, price, and losses increase disproportionately.

[0021] Description of the invention

[0022] The problem is solved according to the invention by a circuit arrangement for operating a load, wherein the circuit arrangement has a first and a second input terminal for inputting an input voltage. These input terminals serve to connect the circuit arrangement to an external voltage source that provides the necessary electrical energy for operating the load. The load is, for example, an LED module, but can also be any other electrical load that requires either a defined input voltage or a defined input current to operate. The circuit arrangement further comprises an input stage for inputting the input voltage and for outputting a DC link voltage at a first and second output of the input stage.The input stage serves to convert the input voltage, which can be, for example, an AC or DC voltage, into a DC link voltage suitable for further operation of the circuit. The input stage can, for example, include a rectifier to convert an AC voltage to a DC voltage. It can also include a switched-mode converter or a switched-mode converter operating as a power factor corrector to stabilize the DC link voltage and improve the power factor of the circuit. The advantage of such an input stage is that the input voltage present at the input terminals can be converted into a defined voltage range.

[0023] The circuit arrangement further includes a switched-mode converter operating as a buck converter with a series connection of a first and a second converter switch, which forms a half-bridge, a converter inductor, a converter capacitor and a trapezoidal capacitor for converting the DC link voltage into a suitable operating current for the load.

[0024] It is important to understand that the half-bridge configuration formed by the first and second converter switches can be implemented in two variants:

[0025] • Top-mounted converter switch: In this configuration, the first converter switch is a high-side switch, meaning it is referenced to the positive potential of the DC link voltage. The second converter switch is a transistor or diode acting as a freewheeling diode and is referenced to the negative potential of the DC link voltage (circuit ground).

[0026] Bottom converter switch: In this configuration, the first

[0027] The converter switch is implemented as a low-side switch, meaning it is referenced to the negative potential of the DC link voltage (circuit ground). The second converter switch in this case is a transistor or diode that acts as a freewheeling diode and is referenced to the positive potential of the DC link voltage.

[0028] Regardless of the chosen configuration, the converter operates as a buck converter to reduce the voltage and increase the current. The series connection of the first and second converter switches, forming a half-bridge, enables efficient voltage and current conversion. The converter inductor serves to store energy and smooth the current. The converter capacitor smooths the voltage. The trapezoidal capacitor shapes the current, improves the electromagnetic compatibility (EMC) of the circuit, and establishes zero-voltage switching (ZVS) conditions within the converter.

[0029] It should be noted that the term "converter switch" in this context can encompass both a transistor, such as a MOSFET, and a diode. In the case of a transistor, it is actively driven to control the current flow. In the case of a diode, the current flow is passively controlled by the polarity of the applied voltage. The converter diode can be either a natural diode or a MOSFET that is driven synchronously and thus behaves like a diode.

[0030] The circuit arrangement also includes an output with a first and a second output terminal for connecting the load. These output terminals serve to connect the circuit arrangement to the load, which could be, for example, an LED module.

[0031] A glow suppressor transistor is included in the operating current path for the load of the second switched-mode converter. This transistor prevents unwanted glow currents from passing through the load when the circuit is in its idle state. The glow suppressor acts as a switch, closed during operation to allow the operating current to flow to the load, and open during idle to block glow currents. Its placement within the circuit divides it into an input section and an output section that can be switched off. This arrangement allows the output to be completely disconnected from the input during idle to suppress glow currents.

[0032] The first and second converter switches are additional

[0033] Glow suppression elements are provided that interrupt the current paths between the circuit section located at the first and a second input terminal and the switchable circuit section located at the output. These additional switches help to further reduce glow currents and increase the efficiency of the glow suppression.

[0034] A Y-capacitor is connected between the switchable circuit section and a ground connection of the mains AC voltage. The Y-capacitor serves to dissipate high-frequency interference, which can also manifest as glow currents, and to improve the electromagnetic compatibility of the circuit arrangement without compromising safety.

[0035] The converter capacitor is entirely integrated into the switchable circuit section and is connected between an output terminal of the converter inductor and an output terminal of the glow suppression transistor. This arrangement of the converter capacitor helps to reduce glow currents, as the capacitor is disconnected from the input in quiescent mode.

[0036] At least part of the trapezoidal capacitor is connected between the center point of the half-bridge and the switchable circuit section. This arrangement of the trapezoidal capacitor also helps to reduce glow currents and improve electromagnetic compatibility. In the circuit's quiescent state, the first and second output terminals are isolated from the first and second input terminals by the glow-prevention elements. This ensures that, in quiescent state, there is no current path from the input terminals to the output terminals, thus effectively suppressing glow currents.

[0037] The combination of these features creates a circuit design that enables efficient and reliable glow suppression without compromising the circuit's performance or safety. The strategic placement of the glow suppression elements, the coupling of the Y-capacitor, and the arrangement of relevant components in the switchable circuit section all contribute to minimizing glow currents and ensuring safe and efficient operation of the circuit. The advantage of this circuit design is that the glow current is significantly reduced compared to previous state-of-the-art solutions without substantially impacting efficiency.

[0038] Another embodiment is a circuit arrangement for operating a load, comprising a first and a second input terminal for inputting an input voltage, an input stage for inputting the input voltage and for outputting it at a first and second output of the input stage, a switched-mode converter operating as a buck converter with a series connection of a first and a second converter switch forming a half-bridge, a converter inductor, a converter capacitor, and a trapezoidal capacitor for converting the DC link voltage into a suitable operating current for the load, and an output with a first and a second output terminal for connecting the load, wherein a glow suppression transistor is provided in the current path of the operating current for the load of the second switched-mode converter, and the glow suppression transistor is arranged within the circuit such thatthat it divides the circuit arrangement into a circuit part located at the input and a switchable circuit part located at the output, that the first and second converter switches are provided as further glow-prevention elements that interrupt the current paths between the circuit part located at the first and a second input terminal and the switchable circuit part located at the output, that a Y-capacitor is provided between the switchable circuit part and an earth terminal of the AC mains voltage, that the converter capacitor is provided entirely in the switchable circuit part between an output-side terminal of the converter inductor and an output-side terminal of the glow-prevention transistor, that at least part of the trapezoidal capacitor is provided between the center of the half-bridge and the switchable circuit part,wherein the first and second output terminals are separated from the first and second input terminals in the rest mode of the circuit arrangement by the glow-prevention elements.

[0039] The circuit arrangement is thus divided into two sections: a non-switched section connected to the AC input and a switched section connected to the output. All current paths that could lead to an unwanted glow current are equipped with glow-prevention elements that are switched off when the converter is off. The glow-prevention elements act like a switch that interrupts the corresponding current path. They can be transistors, diodes, or any other elements capable of interrupting a current path or circuit.

[0040] In the following, "can be switched off" means that all relevant current paths that could conduct the modulations or voltage spikes generated by the rectifier to one of the outputs are switched off, i.e., disconnected, by corresponding glow-prevention elements, such as transistors acting as switches, in their quiescent state. These current paths are thus interrupted by the glow-prevention elements, so that no relevant currents can flow to the output of the circuit arrangement in quiescent state that could cause LEDs connected to the output to glow. Since the glow-prevention elements are usually switches, these switches are consequently off in quiescent state; if transistors act as switches, these transistors are consequently off in quiescent state. The second clocked converter is preferably a buck converter with a synchronously switched half-bridge.Of course, the second clocked converter can also be a classic buck converter with a converter diode instead of the second transistor of the half-bridge.

[0041] In principle, depending on the application, a converter topology other than a buck converter may be possible and advantageous. Other topologies to consider include boost converters, SEPIC converters, and Cuk converters, to name a few. Of course, other converter topologies besides buck converters may also be suitable.

[0042] In the following, a glow suppression transistor is defined as a transistor or switch connected in the current path between the input and output of the circuit arrangement to prevent glow currents. This glow suppression transistor is permanently switched on (constantly conducting) when the circuit arrangement is powered on (i.e., when the first and second clocked converters are running) and permanently switched off (i.e., when the circuit arrangement is powered off). The glow suppression transistor may also have other functions, such as a dimming function via pulse-width modulation of the transistor. The converter switch of the second clocked converter also serves to prevent glow currents in its idle mode, but is clocked and not permanently switched on when the converter is running.

[0043] The intermediate circuit voltage, as defined below, is the voltage that the first converter outputs and inputs into the second converter. It is also often referred to as the bus voltage.

[0044] Glow suppression elements are typically active components such as diodes and transistors, connected in the current path of a circuit between the input and output to reduce or ideally eliminate parasitic currents from the input to the output of the circuit caused by parasitic capacitances. Glow suppression transistors are therefore glow suppression elements. These parasitic currents are also referred to as glow currents. Glow currents are thus all currents present at the output of the circuit despite the circuit being switched off or in standby mode, and which flow through the load connected to the output, such as LEDs. Glow currents therefore occur in the circuit in its idle state.

[0045] For the sake of clarity, all operating states in which no power is delivered to load 5, and the first and second converters are therefore switched off, are referred to as idle mode. A circuit configuration in idle mode is thus a circuit configuration in standby mode, but also a circuit configuration switched off via an external switch, regardless of which input terminal the phase of the power supply is connected to.

[0046] In a particularly preferred embodiment, the first and second converter switches and the glow suppression transistor are configured to open current paths between the input and output terminals. It has been found that using these switches and transistors as glow suppression elements has a particularly positive effect on reducing glow currents. The glow suppression transistor is especially preferably placed between the second output terminal and the second rectifier output, hereinafter also referred to as circuit ground. It has been found that this connection has a particularly positive effect on reducing glow currents.From a circuit topology perspective, this location of the connection is also considered particularly advantageous for avoiding glow currents, since many current paths that result in glow currents can be connected to the disconnected part of the circuit by this measure and thus no longer represent sources of significant glow currents.

[0047] This embodiment emphasizes the functionality of the converter switches and the glow suppression transistor as active glow suppression elements. By designing these components to actively interrupt current paths between the input and output terminals in quiescent mode, particularly effective glow suppression is achieved.

[0048] The advantage of this design lies in the fact that the components already required for the converter's function are also used for glow suppression. This leads to a reduction in the number of components and thus to a more cost-effective and efficient circuit arrangement. Furthermore, the active opening of the current paths achieves higher glow suppression performance than passive solutions, such as those based on diodes.

[0049] It is important to note that this wording does not preclude the presence of additional glow-prevention elements in the circuit arrangement. However, it emphasizes that the switches mentioned actively contribute to interrupting current paths and thus play a crucial role in glow prevention.

[0050] According to a preferred embodiment of the circuit arrangement, the trapezoidal capacitor is divided into two partial capacitances. The first partial capacitance is connected from the midpoint of a half-bridge, consisting of the first and a second converter switch, to the output-side terminal of the glow suppression transistor, and the second partial capacitance is connected from the midpoint of the half-bridge to the input-side terminal of the glow suppression transistor. This measure represents an advantageous compromise between low glow currents and good electromagnetic compatibility of the circuit arrangement.

[0051] This embodiment involves dividing the trapezoidal capacitor into two separate partial capacitances connected at different points in the circuit arrangement. The trapezoidal capacitor serves to smooth the switching edges of the current and thus improve the electromagnetic compatibility (EMC) of the circuit arrangement.

[0052] By dividing the trapezoidal capacitor into two partial capacitances, the effect of the capacitor is optimized, with the first partial capacitance (C_TR1) serving to dissipate high-frequency disturbances from the center of the half-bridge to the output of the circuit arrangement, while the second partial capacitance (C_TR2) serving to dissipate disturbances from the center of the half-bridge to the circuit ground.

[0053] The preferred configuration of the trapezoidal capacitor offers the advantage of reducing both glow currents and electromagnetic interference. Coupling the first partial capacitance to the output terminal of the glow suppression transistor ensures that high-frequency interference cannot enter the exposed circuit section. Coupling the second partial capacitance to the input terminal of the glow suppression transistor helps to shunt interference away from the input stage.

[0054] The first partial capacitance has a capacitance value of 0.0 ...

[0055] This embodiment concerns the specific value ranges for the two partial capacitances of the trapezoidal capacitor. The choice of capacitance values ​​influences both the EMC characteristics and the glow current suppression of the circuit arrangement.

[0056] Specifying a range from 0 pF to a maximum value means that the respective partial capacitance can also be completely omitted. This can be advantageous in certain applications where either the EMC requirements or the glow current requirements are less stringent.

[0057] The preferred ranges of 33 pF to 560 pF for the first partial capacitance and 33 pF to 330 pF for the second partial capacitance represent an optimal compromise between EMC performance and glow current suppression. Within these ranges, the capacitance values ​​can be selected according to the specific requirements of the application. According to a preferred embodiment of the circuit arrangement, the first converter switch is either a high-side converter switch or a low-side converter switch.

[0058] This embodiment relates to the flexibility in choosing the topology of the buck converter. It recognizes that the first converter switch, which together with the second converter switch forms the half-bridge, can be implemented as either a high-side switch or a low-side switch.

[0059] • High-side converter switch: In this configuration, the first converter switch is referenced to the positive potential of the intermediate circuit voltage.

[0060] • Low-side converter switch: In this configuration, the first converter switch is referenced to the negative potential of the intermediate circuit voltage (circuit ground).

[0061] The advantage of this design lies in the adaptability of the circuit arrangement to different requirements and boundary conditions. The choice between a high-side and a low-side converter switch can depend on various factors, such as the desired power output, the input voltage, component costs, and EMC requirements.

[0062] The wording "either...or" clarifies that these are two mutually exclusive alternative embodiments. The choice of the specific embodiment affects the control of the glow suppression transistor and the placement of other components in the circuit arrangement.

[0063] This embodiment is particularly advantageous because it gives the developer the freedom to choose the topology best suited to his specific application.

[0064] According to a preferred embodiment of the circuit arrangement, the first converter switch is located on the high side of the half-bridge and conducts during a magnetization phase of the converter inductance, while the second converter switch is located on the low side of the half-bridge and conducts during a demagnetization phase of the converter inductance and is implemented either as an actively controlled semiconductor switch or as a diode. The glow suppression transistor is connected in the current path of the operating current for the load between the second output terminal and the second output of the input stage, and the Y-capacitor is connected between the second output terminal and the ground terminal of the AC mains voltage.

[0065] In this embodiment, the term "high-side" refers to the connection to the positive potential of the DC link voltage, while the term "low-side" refers to the connection to the negative potential of the DC link voltage (circuit ground).

[0066] This embodiment describes a specific topological arrangement of the switching elements and the Y-capacitor in the circuit arrangement. It defines that the first converter switch functions as a high-side switch, while the second converter switch functions as a low-side switch.

[0067] Precisely defining the switching phases during which each switch conducts is crucial, as it determines the buck converter's behavior and the energy transfer to the load. The first converter switch conducts during the magnetization phase of the converter inductance, storing energy in the inductor. The second converter switch conducts during the demagnetization phase, releasing the stored energy to the load.

[0068] The placement of the glow suppression transistor in the current path between the second output terminal and the second output of the input stage effectively interrupts the glow current path in the circuit's quiescent state. The Y-capacitor, connected between the second output terminal and the mains AC ground, helps to dissipate high-frequency interference and improve the electromagnetic compatibility (EMC) of the circuit. This embodiment describes a classic buck converter.

[0069] The advantage of this design lies in the precise definition of the topological arrangement and the switching phases, which enables optimized glow prevention and efficient energy transfer to the load.

[0070] According to another preferred embodiment of the circuit arrangement, the first converter switch is located on the low side of the half-bridge and conducts during a magnetization phase of the converter inductance, while the second converter switch is located on the high side of the half-bridge and conducts during the demagnetization phase of the converter inductance and is implemented either as an actively controlled semiconductor switch or as a diode. The glow suppressor transistor is connected in the current path of the operating current for the load between the first output of the input stage and the first output terminal, and the Y-capacitor is connected between the first output terminal and the ground terminal of the AC mains voltage.

[0071] This embodiment describes an alternative topological arrangement of the switching elements and the Y-capacitor in the circuit arrangement, which differs from the arrangement described previously. It defines that the first converter switch functions as a low-side switch, while the second converter switch functions as a high-side switch.

[0072] In this embodiment, the term "high-side" refers to the connection to the positive potential of the DC link voltage, while the term "low-side" refers to the connection to the negative potential of the DC link voltage (circuit ground).

[0073] Here too, the precise definition of the switching phases in which the respective switches conduct is important, as it determines the behavior of the buck converter and the energy transfer to the load. The first converter switch conducts during the magnetization phase of the converter inductance, thus storing energy in the inductor. The second converter switch conducts during the demagnetization phase, thus releasing the stored energy to the load.

[0074] The placement of the glow suppression transistor in the current path between the first output of the input stage and the first output terminal effectively interrupts the glow current path when the circuit is idle. The Y-capacitor, connected between the first output terminal and the ground terminal of the AC mains voltage, helps to dissipate high-frequency interference and improve the electromagnetic compatibility (EMC) of the circuit.

[0075] This embodiment describes an inverse buck converter and is therefore complementary to the embodiment described above.

[0076] The advantage of this design lies in the alternative topological arrangement, which can be more advantageous in certain applications. By choosing the appropriate topology, the circuit layout can be optimally adapted to the specific requirements.

[0077] According to a preferred embodiment of the circuit arrangement, the glow suppressor transistor is either a MOSFET, a bipolar transistor, a Darlington transistor, or an IGBT. In the case of a bipolar transistor or a Darlington transistor, a diode is connected in parallel with it.

[0078] This embodiment relates to the selection of the appropriate switching element for the glow-prevention transistor, whereby various transistor types can be considered.

[0079] • MOS-FET: The MOS-FET can be advantageous due to its drive characteristics.

[0080] Bipolar transistors or Darlington transistors: These transistors can be more cost-effective in certain applications. When using a bipolar transistor or a Darlington transistor, a diode is connected in parallel. This diode protects the transistor from overvoltages.

[0081] • IGBT: The IGBT can be advantageous at higher voltages and currents.

[0082] The advantage of this design lies in the flexibility it offers the developer in selecting the appropriate switching element. The choice of the specific component depends on the application's requirements, such as switching speed, voltage withstand capability, current carrying capacity, and cost.

[0083] It is important to note that the optional diode is only required when using a bipolar transistor or Darlington transistor. MOSFETs and IGBTs already have an intrinsic diode, so an additional diode is not necessary.

[0084] According to a preferred embodiment of the circuit arrangement, in which the glow-prevention transistor is a bipolar transistor, a Darlington transistor, or an IGBT, the circuit arrangement includes a control circuit that drives the glow-prevention transistor, wherein a drive current of the glow-prevention transistor is set by the control circuit such that it is substantially proportional to the current through the load, wherein the drive current of the glow-prevention transistor is known to the control circuit and is taken into account when measuring the current through the load by means of a shunt.

[0085] This embodiment relates to the control of the glow-suppression transistor when it is implemented as a bipolar transistor, Darlington transistor, or IGBT. Unlike MOSFETs, these devices require a base current (in the case of bipolar transistors and Darlington transistors) or a gate current (in the case of IGBTs) to conduct. To minimize losses in the glow-suppression transistor and to ensure precise control of the load current, the control circuit adjusts the drive current of the glow-suppression transistor so that it is essentially proportional to the load current. This means that the drive current is increased when the load current is increased, and vice versa.

[0086] Since the drive current of the glow suppressor transistor contributes to the total current through the load, this current must be taken into account when measuring the load current. Therefore, the drive current of the control circuit is known and is considered when measuring the current through the load using a shunt resistor.

[0087] According to a preferred embodiment of the circuit arrangement, the control circuit controls the glow suppression transistor in such a way that it is just in saturation.

[0088] This embodiment relates to the specific way in which the control circuit drives the glow-prevention transistor. The term "saturation" refers to an operating state of the transistor in which the current through the transistor is no longer proportional to the drive voltage or drive current. In this state, the transistor is fully conducting and exhibits a minimal voltage drop.

[0089] By driving the glow suppression transistor in such a way that it is just in saturation, the control circuit ensures that the transistor conducts the load's operating current as efficiently as possible. This minimizes power dissipation in the transistor and thus contributes to the efficiency of the entire circuit arrangement.

[0090] In another embodiment, the second converter switch is a synchronously controlled MOSFET used as a synchronous rectifier. This measure has the advantage of a wider operating range that cannot be achieved with conventional diodes. In yet another embodiment, the second converter switch is a diode. In applications where the extended operating range described above is not required, this offers the advantage of a simpler and more cost-effective design.

[0091] In another preferred embodiment, the glow suppression transistor is a MOSFET or an IGBT. This has the advantage of particularly simple control of the transistor.

[0092] In another embodiment, the glow-prevention transistor is a bipolar transistor or a Darlington transistor, and a diode is connected in parallel to the bipolar transistor or Darlington transistor. Bipolar transistors are considerably less expensive than MOSFETs and are therefore preferred in certain applications.

[0093] It is advantageous if the circuit arrangement includes a control circuit that drives the glow suppressor transistor, whereby the control current of the glow suppressor transistor is set by the control circuit so that it is essentially proportional to the current through the load. This has the advantage that the control of the bipolar transistor is optimally adapted to the respective operating situation.

[0094] In another embodiment, the drive current of the glow suppressor transistor in the control circuit is known and is taken into account when measuring the current through the load using a shunt resistor. Since the drive current of the glow suppressor transistor adds to the load current, this causes a measurement error that can no longer be neglected in certain operating situations. By taking this current into account, the measurement error is compensated, and the measurement of the load current is advantageously much more accurate.

[0095] In a particularly preferred embodiment, the control circuit drives the glow-prevention transistor such that it is just in saturation. This embodiment relates to the specific way in which the control circuit drives the glow-prevention transistor. The term "saturation" refers to an operating state of the transistor in which the current through the transistor is no longer proportional to the drive voltage or drive current. In this state, the transistor is fully conducting and exhibits a minimal voltage drop. This optimizes the previously described operation of the load-proportional drive current to reduce power dissipation and increase the accuracy of load current measurement.

[0096] In a particularly preferred embodiment, the input stage includes a rectifier. This makes the circuit advantageously operable with a mains AC voltage.

[0097] In a further particularly preferred embodiment, the input stage comprises a switched-mode converter or a switched-mode converter operating as a power factor correction. This makes the circuit arrangement advantageously usable for a wide input range in DC operation, and in AC operation it meets the power factor of the input current required in many countries.

[0098] According to a preferred embodiment of the circuit arrangement, a glow suppression element is connected in each current path between the circuit part located at the input and the switchable circuit part located at the output, which contributes to a visible glow current.

[0099] This embodiment emphasizes the consistent application of the glow-prevention principle to all relevant current paths in the circuit arrangement. It states that every current path that could potentially lead to a visible glow is interrupted by a glow-prevention element.

[0100] The term "visible glow current" refers to a current large enough to cause a faint glow from the LEDs, perceptible in a dark room. The exact magnitude of this current depends on various factors, such as the sensitivity of the eye, the type of LEDs, and the ambient light. Glow suppression components can take different forms, such as transistors, diodes, capacitors, or resistors. Crucially, they must be able to interrupt or reduce the current flow when the circuit is in its resting state.

[0101] The advantage of this design lies in its particularly effective glow prevention. By consistently applying the glow prevention principle to all relevant current paths, it is ensured that no significant glow current can reach the output of the circuit arrangement.

[0102] This embodiment represents a kind of "best practice" that should be considered when developing circuit designs for glow prevention. By adhering to this principle, designers can ensure that their circuit designs meet the requirements for effective glow prevention.

[0103] According to a preferred embodiment of the circuit arrangement, a level shifter is provided for controlling the glow suppression transistor, wherein the level shifter is deactivated in the quiescent mode of the circuit arrangement, and wherein the level shifter comprises one or more glow suppression elements connected in series to reduce the glow current caused by the level shifter in quiescent mode.

[0104] This embodiment relates to the control of the glow suppression transistor, particularly in cases where the glow suppression transistor is a high-side switch. To understand the significance of this design, it is important to define the terms high-side and low-side:

[0105] • High-side: The term "high-side" refers to connecting a component (e.g., a switch) to the positive potential of a voltage source (in this case, the DC link voltage). A high-side switch is therefore a switch located between the positive voltage source and the load. • Low-side: The term "low-side" refers to connecting a component to the negative potential of a voltage source (in this case, the circuit ground). A low-side switch is therefore a switch located between the load and the circuit ground.

[0106] In the case of a high-side switch, a level shifter is required to shift the transistor's drive voltage to the correct potential.

[0107] A level shifter, also implemented as a charge pump or bootstrap circuit, generates the necessary gate-source voltage for the glow suppressor transistor to drive it. Since the glow suppressor transistor is used on the high side, the gate-source voltage must be generated relative to the positive potential of the DC link voltage.

[0108] To prevent the level shifter itself from forming a glow current path in idle mode, it includes one or more glow-prevention elements connected in series to reduce the glow current caused by the level shifter in idle mode. These glow-prevention elements can be, for example, diodes or transistors that block or reduce the current flow through the level shifter in the idle state.

[0109] The advantage of this design is that it enables efficient control of the glow-prevention transistor without affecting the glow behavior of the circuit arrangement in the idle state.

[0110] According to a preferred embodiment of the circuit arrangement, a diode is provided between the source terminal of the glow suppression transistor and a ground potential to protect the glow suppression transistor from overvoltage.

[0111] This embodiment relates to a protection mechanism for the glow suppressor transistor. In particular, when the switch is off, i.e., has a high resistance, a high voltage can be present at the switch, for example, during an overvoltage event on the supply voltage. To protect the glow suppressor transistor from such overvoltages, a diode is provided between the source terminal of the glow suppressor transistor and ground potential.

[0112] This diode is polarized so that it blocks current during normal operation. However, in the event of an overvoltage, the diode becomes conductive and diverts the excess current to ground potential, thereby limiting the voltage across the glow suppression transistor.

[0113] The advantage of this design is that it increases the reliability of the circuit by protecting the glow suppression transistor from damage caused by overvoltages. This is particularly important in applications where the circuit may be exposed to high voltage spikes or transient events.

[0114] Further preferred embodiments can be found in the dependent claims and the entire disclosure, whereby the description does not always differentiate in detail between device and use aspects; in any case, the disclosure is to be read implicitly with regard to all claim categories.

[0115] Brief description of the drawings

[0116] Further advantages, features, and details of the invention will become apparent from the following description of exemplary embodiments and from the drawings, in which identical or functionally equivalent elements are provided with identical reference numerals. These show:

[0117] Fig. 1 shows a basic circuit of a non-insulating LED driver with an LED module connected to it, with a boost converter as a power factor corrector and with a synchronously controlled buck converter as an output switching stage, as well as 3 glow suppression stages connected in series in the current path according to the prior art.

[0118] Fig. 2 shows a schematic representation of a basic circuit of a non-insulating LED driver with an LED module connected to it, with an inactive circuit section SN at the input and an active circuit section SF at the output, to which the LED module 5 is connected.

[0119] Fig. 3 shows a first embodiment of a basic circuit of a non-insulating LED driver with an LED module connected to it, with a boost converter as a power factor corrector and with a synchronously controlled buck converter as an output switching stage.

[0120] Fig. 4 shows a second embodiment of a basic circuit of a non-insulating LED driver with an LED module connected to it, with a different connection of a trapezoidal capacitor and a schematically shown control of the MOSFETs.

[0121] Fig. 5 shows a third embodiment of a basic circuit of a non-insulating LED driver with an LED module connected to it, and a Darlington stage consisting of two NPN transistors instead of a MOSFET as a glow suppression transistor.

[0122] Fig. 6 shows a fourth embodiment of a basic circuit with a Y-capacitor network connected to the disconnected part of the circuit arrangement to improve the avoidance of glow currents.

[0123] Fig. 7 shows a fifth embodiment of a basic circuit with a further Y-capacitor network, which is connected to the disconnected part of the circuit arrangement to improve the avoidance of glow currents, wherein parts of the Y-capacitor network are switchable.

[0124] Fig. 8 shows a sixth embodiment of a basic circuit with a buck converter with a bottom-mounted converter transistor, a top-mounted glow suppression transistor and a charge pump for controlling this glow suppression transistor,

[0125] Fig. 9 shows a seventh embodiment of a basic circuit with a buck converter with a bottom-mounted converter transistor, a top-mounted glow suppression transistor and a cascaded bootstrap circuit for controlling this glow suppression transistor.

[0126] Preferred embodiment of the invention

[0127] Since the following explanations mainly discuss circuit details of an LED driver or LED control gear that implements a corresponding electronic circuit, the terms "circuit arrangement", "LED driver" and "LED control gear" are used synonymously.

[0128] Glow prevention concept with multi-use active components

[0129] Fig. 2 shows a schematic representation of a basic circuit of a non-insulating LED driver with an LED module connected to it, with an inactive circuit section SN at the input and an active circuit section SF at the output, to which the LED module 5 is connected. The core of the invention will be explained using this schematic representation. After years of development, it has been found that a few simple rules need to be followed for a circuit strategy against glow effects, which produce the desired effect. One rule is that each current path in the circuit arrangement between the input L, N and the output LED+, LED- must be evaluated, and if it contributes significantly to a glow current, a glow suppression element, e.g., in the form of a switch, must be connected in this current path. This glow suppression element is then switched off in its idle mode.Blocking, so that current flow through this current path is interrupted in quiescent mode. This divides the circuit arrangement into a non-enabled circuit section SN, which is connected to input L, N, and an enabled circuit section SF, which is connected to output LED+, LED-. The glow-prevention elements M2, M1, and SW_AG are located between these sections. Another rule states that each current path, or each element that opens such a current path between input L, N and output LED+, LED-, must either be connected to the circuit ground of the enabled circuit section SF, so that there is no longer a current path to the input, or another glow-prevention element, e.g., in the form of a switch or transistor, must be introduced into this current path to interrupt it in quiescent mode.If these simple rules are followed, then in standby mode there is no current path between the non-enabled circuit section SN and the enabled circuit section SF that could produce a visible glow at the LED+, LED- output of the circuit arrangement. The enabled circuit section SF is thus practically completely isolated from the L, N inputs, and no relevant glow currents can flow. They are relevant because, in practice, glow currents still flow, for example, due to parasitic or intentional capacitances between the non-enabled circuit section SN and the enabled circuit section SF. However, these are so small that no visible glow effect is present. Larger capacitances, such as...In all embodiments according to the invention, the converter capacitor C_B or the trapezoidal capacitor C_TR1 are now referenced to the circuit ground of the disconnected circuit part SF, so that in standby mode they are completely decoupled from the input L, N by means of the glow-prevention elements.

[0130] The glow suppression elements present in all embodiments are the upper converter switch M2, the lower converter switch M1, and the glow suppression switch SW_AG. The upper converter switch M2 is preferably a fast MOSFET, while the lower converter switch M1 can also be a fast MOSFET in a synchronous buck converter, or a fast diode in a conventional buck converter. The glow suppression switch SW_AG can be either a simple MOSFET or a bipolar transistor, such as a Darlington stage described below. Of course, other switches, such as an IGBT, are also conceivable and possible.

[0131] It is important that the converter switches can switch quickly, whereas the simple glow-prevention switches such as the SW_AG switch can be relatively slow.

[0132] Optionally, the measurement path transistor Q_S is connected to the measurement path depending on the presence of a measurement path referenced to the circuit ground of the non-enabled circuit section SN. If further measurement paths referenced to the non-enabled circuit section SN are required for other conceivable embodiments, additional measurement path transistors can be provided. Since these are then normally referenced to the same circuit ground, they can be easily controlled together to block in standby mode and conduct during operation. For this, only a pin of, for example, a microcontroller present in the circuit arrangement is necessary. This microcontroller is part of the control circuit CTRL shown in Fig. 2. The control circuit CTRL controls the entire circuit arrangement and thus also all switches.

[0133] Glow prevention elements M1, M2, SW_AG, Q_S etc.

[0134] Fig. 3 shows a first embodiment of a basic circuit of a non-insulating LED driver with an attached LED module, a boost converter as a power factor corrector, and a synchronously driven buck converter as the output switching stage. Synchronously driven here means that instead of a "naturally" conducting and blocking diode, a MOSFET M1 is used, which is driven in such a way that it takes over the function of a diode. This drive has the advantage that, compared to a "naturally" conducting diode, the MOSFET can be driven in such a way that certain operating states in the converter can be achieved that cannot be reached with a "naturally" conducting diode due to physical conditions, for example, the switching off of the converter MOSFETs M2 only when the inductor current through L2 is negative.Of course, instead of the synchronously controlled buck converter shown, a normal buck converter with a diode instead of the MOSFET can also be used.

[0135] Furthermore, an inverse buck converter with a "top-mounted" diode and a "bottom-mounted" transistor SW_Buck, referenced to circuit ground, can also be used. The MOSFET or diode M1 would thus be referenced to the voltage U_R, which corresponds to the DC link voltage U_ZK, and the converter MOSFET M2 would then be referenced to the circuit ground PW_GND.

[0136] It should be noted that only the power section of the basic circuit is shown here, and not the entire circuit, as the following explanations refer primarily to the power section, and other circuit components inherent in an LED driver play only a very minor role in the following considerations. It should also be noted that the LED driver is an externally controllable device with an input for a bus system, which allows the output to be switched on and off. Consequently, the LED driver is permanently connected to the mains supply. However, a DC voltage can also be applied to the input terminals L and N instead of the mains supply. This can be the case with an LED driver in emergency lighting mode or on a DC power supply.Therefore, the LED driver can be in operating mode, i.e., supplying power to the load connected to it, or it can be in standby mode, i.e., with the boost and buck converters switched off and consequently not supplying power to the load. The following explanations also apply to an LED driver connected to an external switch in such a way that one of the two mains input terminals is permanently connected to the mains supply. Both scenarios lead to the aforementioned problems: a current—albeit a very small one—can flow at the output of the LED driver. This current flows from the mains phase at the input, through parasitic capacitances, to the output of the LED driver, and through the connected LEDs back into the mains supply, even though the LED driver is switched off. This current is referred to as glow current in the following explanations.In the circuit arrangement according to the prior art shown in Fig. 1, the glow current was suppressed by essentially three additional components connected in the current path, besides the two half-bridge switches: Firstly, two diodes, each connected in the current path of the two output terminals. And secondly, a MOSFET, which is additionally connected in the current path at the negative output of the LED driver. This leads to the additional losses mentioned above. It should be noted that two of these three components are dedicated solely to suppressing the glow currents and otherwise have no function in the LED driver. Therefore, these components will henceforth be referred to as the dedicated glow suppression elements.In some embodiments, the glow-prevention transistor SW_AG was additionally used as a dimmer switch operated with pulse width modulation and is therefore not to be regarded as an exclusive glow-prevention element.

[0137] It should be noted that in Fig. 3 and the following figures, the circuit symbol for MOSFETs is shown with the diode that is intrinsic to MOSFETs. The circuit symbol for MOSFETs in this and the following figures shows a Schottky diode. This Schottky diode refers to the intrinsic diode of the MOSFETs, which is not usually a Schottky diode.

[0138] Compared to the prior art circuit arrangement shown in Fig. 1, the circuit arrangement according to the invention incorporates several different details. Each measure reduces the glow current slightly; however, all measures combined reduce this glow current so considerably that the two exclusive glow suppression elements mentioned in the prior art, i.e., the two diodes, can be omitted without increasing the glow current compared to the prior art solution. The two exclusive glow suppression elements mentioned in the prior art are the two diodes DAGI and DAG2 of Fig. 1 at the two outputs of the LED driver or the circuit arrangement. Due to their forward voltage, these diodes generate significant losses, which can amount to up to 3% of the power of the LED driver. This corresponds to approximately 15% of the power dissipation generated by the LED driver.

[0139] The primary glow-prevention element in the LED driver discussed here remains the MOSFET SW_AG, which is connected in the current path from the negative output to the neutral conductor or ground input of the mains supply. This is referred to below as the glow-prevention MOSFET. To optimally utilize this glow-prevention element, all circuit components—and especially the converter capacitor C_B—that exhibit parasitic or intentional capacitances, which could contribute to establishing a current path from the phase to the LED+ / LED- output, have been modified so that they are not connected to the circuit ground PW_GND, but rather to the negative output LED-, thus preventing a current path from U_IN_DC or PW_GND to the LED+ / LED- output.

[0140] It should be noted that in AC power networks, it is common practice not to always distinguish precisely between phase and neutral conductors in devices. This means that the phase conductor of the mains supply can be connected to either the L input or the N input of the circuit arrangement. Similarly, the neutral conductor of the mains supply can be connected to either the N input or the L input of the circuit arrangement. In both cases, if the phase conductor is connected to either the N input or the L input of the circuit arrangement, current paths can develop to the positive output LED+ as well as to the negative output LED-, resulting in glow currents, which are prevented by this invention.Once the mains connections are connected to the circuit arrangement, the outputs of rectifier BR1 are modulated with the mains half-wave, and current paths are formed via the aforementioned parasitic capacitances, causing the LEDs connected to the LED+ / LED- output of the circuit arrangement to glow. It should be noted that other embodiments of the circuit arrangement may exist, optimized for operation on DC networks. In these cases, the rectifier BR1 and the PFC converter, which functions as a power factor correction, are omitted in the input stage ES shown in Fig. 3. The rectifier can be completely eliminated, whereas the PFC converter, as a standard boost converter, can be retained even in DC network operation, depending on the application. Therefore, in addition to the embodiments discussed here, further embodiments are possible that do not depart from the inventive concept.Even in DC networks, current paths can form that cause LEDs connected to the LED+ / LED- output of the circuit arrangement to glow.

[0141] The invention therefore includes three essential measures to suppress the glowing currents.

[0142] The first measure involves positioning the glow suppression MOSFET SW_AG in the current path from the negative output LED- to the circuit ground PW_GND such that it is essentially located "in" the second switched-mode converter. It has been shown that glow currents are suppressed very effectively precisely when this glow suppression MOSFET is positioned between the half-bridge HB and the converter capacitor C_B. In other words, the converter capacitor C_B is no longer connected to the circuit ground PW_GND, but rather to the output terminal of the glow suppression MOSFET SW_AG. This ensures that the glow suppression MOSFET SW_AG also disconnects the converter capacitor C_B in its quiescent mode, i.e., it disconnects the converter capacitor C_B in addition to the negative output LED.If the circuit arrangement includes a trapezoidal capacitor C_TR, this capacitor, like the converter capacitor C_B, must also be at least partially coupled to the output-side connection of the glow-prevention MOSFET SW_AG, and not to the circuit ground PW_GND, as otherwise a current path from PW_GND to the positive output LED+ would be opened.

[0143] In previous circuit designs, these components were always coupled to the circuit ground PW_GND, i.e., from the mains input perspective, "before" the glow-prevention MOSFET SW_AG. This meant that, depending on the capacitor values, an alternating current could reach the LED+ output. This is prevented by the present design, as the glow-prevention MOSFET is off when switched off, and only a very small alternating current can flow through the parasitic capacitances of the glow-prevention MOSFET itself. This current is so small that any glow from LEDs connected to the output is not visible even in complete darkness.

[0144] The glow-suppression MOSFET SW_AG divides the circuit arrangement into a section SN, which is connected to the mains input (illustrated in Fig. 3 as the circuit section "to the left" of the glow-suppression MOSFET SW_AG), and an unconnected section SF, which is illustrated in Fig. 3 as being "to the right" of the glow-suppression MOSFET SW_AG, i.e., from the power flow perspective, "behind" the glow-suppression MOSFET SW_AG. Both circuit sections are represented by dashed lines. Strictly speaking, the drain of the upper converter transistor M2, the source and gate of the lower converter transistor M1, and the gate and source of the glow-suppression transistor SW_AG belong to the unconnected section SN. The source and gate of the upper converter switch M2, the drain of the lower converter switch M1 and the drain of the glow suppression transistor SW_AG as well as the half-bridge center HBM actually belong to the unlocked circuit part SF.For the sake of clarity, this is not reflected in the lines of boxes SN and SF, and is therefore mentioned. Similarly, the gate and source of the measurement path transistor Q_S belong to the inactive circuit section SN, and the drain of the measurement path transistor Q_S belongs to the active circuit section SF. The input stage ES is therefore part of the inactive circuit section SN.

[0145] Since all switches, i.e., all MOSFETs, are deactivated when the LED driver is switched off or in standby mode, this specific arrangement of the glow suppression MOSFET SW_AG creates a barrier against glow currents. This is because a deactivated MOSFET is present in all current paths between the mains input and output of the circuit arrangement—either the converter MOSFET M2 or the glow suppression MOSFET SW_AG. However, the converter MOSFET M2 does not serve solely as a glow suppression element. Its primary function is that of the second switched-mode converter HBC, and glow suppression is merely a secondary function. This design, which utilizes multiple components, saves components in the LED driver, thus reducing costs and power loss.

[0146] The second measure consists of selectively connecting the Y-capacitor C_Y, which is connected to the ground terminal PE of the mains supply L, N, to the disconnected circuit section SF. This measure diverts most of any glow currents flowing into this disconnected circuit section via remaining parasitic capacitances to the ground terminal PE. As a result, virtually no glow current reaches the positive output LED+ of the LED driver and can cause the connected LEDs to glow. In this embodiment, the residual modulation arising from high-impedance residual current paths (e.g., high-impedance resistors and diodes representing the high-impedance paths in the second converter HBC), which cannot be disconnected, is further reduced on the disconnected circuit section SF, thus also further reducing the glow effect at load 5.

[0147] The third measure now consists of establishing the rules already outlined at the beginning: In every circuit part that could form a significant (alternating) current path between mains input L, N and output LED+, LED- of the circuit arrangement, either a disconnect switch should be inserted as a glow prevention element to prevent such a current path, or the current path should be referenced to the disconnected circuit part SF.

[0148] In the present embodiment, in addition to the converter capacitor C_B and the trapezoidal capacitor C_TR already mentioned above, there is a measuring path 7 that measures the output voltage at the LED+ output. Since the control unit CTRL is located in the section SN, which is connected to the mains input, the measuring path 7 must be referenced to this potential. Therefore, the measuring path 7, which consists of a voltage divider made up of two resistors R_B1 and R_B2 connected in series, is located between the positive output LED+ and the circuit ground PW_GND. To prevent a current path to the LED+ output, a MOSFET Q_S is connected between the two resistors R_B1 and R_B2 as a glow suppressor. This MOSFET is closed (conducting) when the converter HBC is running and blocking (non-conducting) when the converter HBC is switched off.This MOSFET is also a glow suppression transistor and can be controlled with the same logic as the glow suppression MOSFET SW_AG, i.e., closed when the converter HBC is operating, and blocked when the converter HBC is switched off, i.e., in standby mode.

[0149] Of course, this basic rule can be deviated from in certain cases if necessary for other reasons. For example, the trapezoidal capacitor C_TR can be split into one capacitor connected to the circuit ground PW_GND and another connected, as mentioned, to the negative output (the disconnected part SF). In certain cases, this results in better electromagnetic compatibility and can therefore be connected without a disconnect switch, as this measure, if properly designed, does not significantly increase the glow current.

[0150] Fig. 4 shows this configuration and also schematically depicts the arrangement of the CTRL control circuit along with its AUX power supply. Since the control circuit is referenced to PW_GND, measurement path 7 cannot simply be referenced to LED-. The CTRL control circuit, in turn, must be referenced to PW_GND, as it must also operate when the converter is switched off, i.e., when the LED driver is in standby mode, in order to receive the bus commands. For clarity, the bus is not shown in this figure, but it is connected to the CTRL control circuit. The bus can be any suitable bus for controlling the LED driver. In the lighting industry, DALI, DALI+, Thread, Zigbee, Bluetooth, Bluetooth Mesh, KNX, or another well-known bus or protocol is preferred.As can be seen from the list, no strict distinction is made here between bus and protocol, since it is only about controlling the LED control gear in a suitable way and sending commands to the LED control gear.

[0151] In this second embodiment of the circuit arrangement according to the invention, the trapezoidal capacitor C_TR is divided into two partial capacitances C_TR1 and C_TR2 for EMC reasons. Both partial capacitances are coupled to the center point of the half-bridge, with the first partial capacitance C_TR1 being referenced to the disconnected circuit section LED-, and the second partial capacitance C_TR2 to the circuit ground PW_GND. This measure, together with the coupling of the Y-capacitor C_Y according to the invention, leads to improved electromagnetic compatibility, with the glow current being increased only slightly and to an acceptable degree.

[0152] This optimization is particularly effective for very high frequencies above 200 kHz. The value of the first partial capacitance, C_TR1, is between 0.10 F and 4.7 nF, preferably between 33 pF and 560 pF. The value of the second partial capacitance, C_TR2, is between 0.10 F and 1 nF, preferably between 33 pF and 330 pF. Thus, the capacitance C_TR2 is so small that no significant current flows through this capacitor in quiescent mode that could be perceived as a glow current. Therefore, this capacitance falls under the previously mentioned rule that it makes no significant contribution to the glow current and thus does not need to be disabled.

[0153] The following is a supplementary description of how to connect C_B and C_TR1, C_TR2.

[0154] The capacitors C_B and C_TR1, C_TR2 are connected as follows. In all embodiments, both terminals of the converter capacitor C_B are connected within the switchable circuit section SF. In all embodiments, either all or at least part of the trapezoidal capacitor C_TR is connected within the switchable circuit section SF. Both terminals of C_TR or C_TR1, respectively, are connected within the switchable circuit section SF. Only a relatively small portion of the trapezoidal capacitor C_TR, referred to here as C_TR2, is not fully connected within the switchable circuit section SF.

[0155] Fig. 5 shows another embodiment with a Darlington NPN transistor as a glow-prevention transistor SW_AG. Here, the glow-prevention transistor SW_AG is divided into a first bipolar transistor SW_AG1, a second bipolar transistor SW_AG2, and a diode D_AG. These three components together form the glow-prevention transistor SW_AG. The three components together are hereinafter also referred to as the Darlington stage, and the first bipolar transistor SW_AG1 is connected in the current path of the LED output, specifically, like the MOSFET before it, between the base of the half-bridge HB of the second converter and the converter capacitor C_B. Ultimately, the glow-prevention transistor SW_AG is thus connected between the circuit ground PW_GND and the second output terminal LED. In reality, further components such as, for example, a capacitor, can be connected between PW_GND and LED.A current-measuring shunt and small chokes to improve EMC (electromagnetic compatibility) may be inserted, but these will not be discussed in detail here. It should be noted, however, that the wording "connected between the circuit ground PW_GND and the second output terminal LED" does not necessarily imply a direct connection, but rather that components such as those mentioned above can be present in the current path without affecting the concept of the invention.

[0156] These components do not significantly impair the current flow and therefore have no relevant influence on the concept of the invention presented here. The diode D_AG is connected in parallel to the collector-emitter junction of the first bipolar transistor SW_AG1, with its cathode connected to the output LED- and its anode to the circuit ground PW_GND. The collector of the second bipolar transistor SW_AG2 is also connected to the output LED, and its emitter is connected to the base of the first bipolar transistor SW_AG1. The base of the second bipolar transistor SW_AG2 serves as the input and is connected to the input AG. The use of bipolar transistors has two advantages. First, bipolar transistors are considerably less expensive than MOSFETs, thus allowing for a more cost-effective circuit design.Secondly, due to their physical properties, bipolar transistors cause less loss at high currents, thus they are the better choice for LED drivers with high output currents, since with a MOSFET the losses increase quadratically with the output current l_LED.

[0157] For example, transistor SW_AG1 can be a 3DD4243DT NPN transistor with 30W power, and SW_AG2 a 3DD4244DM NPN transistor with 40W power.

[0158] A resistor of approximately 10 kΩ (not shown here) can be connected between the base and the emitter of the first bipolar transistor. This serves to dissipate leakage currents (e.g., from SW_AG2).

[0159] Since bipolar transistors require a certain base current to fully switch on, an estimation of this required base current is necessary. When using a MOSFET for the glow suppression transistor SW_AG, the current gain hfe is approximately 20 in the considered operating range of the MOSFET. The same current gain hfe = ~20 must therefore also be used for the two NPN transistors of the Darlington stage. The Darlington stage thus has a current gain of 20 * 20 = 400. When the Darlington circuit is saturated, the current gain hfe per transistor is approximately half as large and is therefore 10 * 10 = 100.

[0160] With an output current of 0.5A, a base current of 0.5A / 100=5mA would therefore be necessary.

[0161] A simple bipolar transistor instead of the Darlington stage is also possible and has the advantage of a low collector-emitter voltage of only 0.2V.

[0162] Otherwise, the operating principle is the same as with the Darlington transistor described above and includes the points described below: 1. The base current is adjusted to the dimming level, i.e., the output current of the LED driver.

[0163] 2. The base current is measured or is known to the microcontroller.

[0164] 3. The microcontroller calculates the base current and thus corrects its influence.

[0165] Since the base current is known due to the fixed component parameters, the measurement error can be calculated when using a microcontroller by subtracting the known base current from the measured current. It is advantageous that the temperature drift of the base current is relatively small due to the base-emitter diode.

[0166] For setting the base current, which according to point 1 above is ideally set proportionally to the output current l_LED, various designs are possible.

[0167] A very simple implementation, using a microcontroller as the CTRL control circuit, involves configuring one or more microcontroller pins as outputs and applying the microcontroller's supply voltage to the AG input of the Darlington stage via series resistors. The series resistor is adjusted so that the Darlington transistor is at least just in saturation across its entire operating range (i.e., the entire output current range) at any given output current, thus enabling a low forward voltage. If multiple microcontroller pins are used, the output current range can be divided, and the base current can be better matched to the output current. For this to work, the corresponding pin must be configured as an output during operation, depending on the current flowing, so that the base current is large enough to keep the Darlington stage in saturation.This can be implemented in the microcontroller with program-controlled switching of the pins depending on the output current l_LED. An improved embodiment of the Darlington stage control can be implemented with small auxiliary switches that apply the auxiliary voltage, generated by the auxiliary power supply AUX, via series resistors to the input AG of the Darlington stage, thereby generating the base current. This has the advantage that higher currents can also be applied to the base of the Darlington stage, as there is no current limitation as with microcontroller output pins. Compared to the first, simpler version, the same number of microcontroller pins are required, but these do not need to be capable of handling high currents.

[0168] Generally, the base current is set as proportionally as possible to the output current l_LED; the more precisely one wants to follow this current, the more pins and thus stages are required by the microcontroller.

[0169] In many cases, however, a basic current setting with two coarse steps is sufficient.

[0170] The main problem with this embodiment is the distortion of the current measurement. For illustration, the measuring shunt SHT is shown in Fig. 5. This shunt is also present in the other embodiments, but for the sake of clarity, it has not been shown in Figures 3 and 4, as well as 6 to 9. The base current enters the Darlington stage SW_AG at point AG and adds to the current through the shunt SHT. Therefore, the sum of the output current l_LED and the base current is measured in the shunt SHT. With larger base currents, e.g., when using only a single bipolar transistor instead of a Darlington stage, this distorts the measurement result to an unacceptable degree. Therefore, in such cases, a correction of the current measurement is necessary, as described in point 3 above.

[0171] There are several ways to correct the current measurement:

[0172] 1. Calibration of the output current l_LED (the base current is automatically corrected here). For simplification, the measurement can be calibrated at high and low output currents, and interpolated between these values ​​for the entire output current range. 2. The base current is known by design and is compensated accordingly in the microcontroller. This is a very simple solution that can be implemented in practice. Based on the components used and their values, the base current can be determined and taken into account in the output current measurement, since this usually takes place in the same microcontroller.

[0173] 3. The base current is measured by the microcontroller via an analog-to-digital converter. This can be done, for example, at the series resistor, which then also acts as a shunt resistor. This measured value is then taken into account when measuring the output current and is compensated for accordingly in the microcontroller. This even accounts for the small temperature drift of the base current.

[0174] In saturated operation, the Darlington stage SW_AG exhibits a voltage drop V_CE of approximately 0.7V...0.9V from collector to emitter at an output current in the range of approximately 0.5A...1A.

[0175] The following are some dimensioning examples of the embodiment according to Fig. 4.

[0176] In the initial configuration, the base current is set using two microcontroller pins, which are switched to a high level (3.3V) or a low level (0V) depending on the desired base current. The microcontroller used for this purpose has so-called high-current outputs with l_max = 8mA.

[0177] The output current l_LED is in the range of 100% (l_LED = 0.5A) to 10% (l_LED = 0.05A). The required base current for operating the Darlington stage at full saturation is 5mA to 10mA. Pin 1 of the microcontroller with series resistor 1 supplies 8mA at a high level; pin 1 is at a high level. Pin 2 of the microcontroller with series resistor 2 supplies 2mA at a high level; pin 2 is also at a high level. Therefore, the resulting base current is 10mA.

[0178] A second calculation considers an output current l_LED < 10% (l_LED < 0.05A). The necessary base current for operating the Darlington stage at full saturation is 1 mA to 2 mA. Pin 1 of the microcontroller with series resistor 1 supplies 8 mA at a high level; pin 1 is at a low level, i.e., it supplies no current. Pin 2 of the microcontroller with series resistor 2 supplies 2 mA at a high level; pin 2 is at a high level. The resulting base current is 2 mA.

[0179] The dimensioning for the series resistor 1 is to be carried out as follows:

[0180] Series resistor 1 = (3.3V - 1.2V) / 8mA = 262.50 ohms. Therefore, for example, a series resistor with 2700 ohms can be used.

[0181] The dimensioning for the series resistor2 is to be carried out identically:

[0182] Series resistor 2 = (3.3V - 1.2V) / 2mA = 1.05kOhm. Therefore, for example, a 1 kOhm component can be used.

[0183] If the circuit arrangement is in standby with the output current l_LED = 0% (l_LED = 0mA), then the necessary base current for operation of the Darlington stage SW_AG is 0mA.

[0184] Pin 1 with series resistor 1 supplies 8mA at a high level; Pin 1 is at a low level, meaning it supplies no current. Pin 2 with series resistor 2 supplies 2mA at a high level; Pin 2 is at a low level, meaning it also supplies no current. The resulting base current is 0mA. Therefore, the Darlington stage SW_AG is switched off and prevents a glow current at the output LED+, LED-.

[0185] The measurement error in the I_LED measurement, caused by the base current, can be calculated as follows: The output current l_LED should be 4 mA. This corresponds to the output current at a very low dimming level. The operating point of the output current l_LED is therefore less than 10%. The base current is thus 2 mA.

[0186] The unknown component of the base current is approximately 10% of the base current, since the reference voltage VCC = 3.3V, the base voltage of the Darlington stage SW_AG = 1.4V, and therefore the voltage drop across the base resistor is 3.3V - 1.4V. The unknown component of the base voltage of the Darlington stage SW_AG is referred to here as U_drift and is approximately 200mV (of 1.4V). This voltage is primarily due to the temperature drift of the base-emitter diodes of the NPN transistors in the Darlington stage.

[0187] This results in an unknown fraction of the base current (i.e., a deviation in the base current) of 200 mV / (3.3 V - 1.4 V) * 2 mA = 0.105 * 2 mA = 0.2 mA, or approximately 10% of the base current. This unknown fraction of the base current is therefore 0.2 mA. After compensation or calibration using the microcontroller, it corresponds to the remaining current error of the output current l_LED.

[0188] The error in the output current l_LED of 0.2 mA is small enough to meet the current accuracy requirements of the circuit. The microcontroller has approximate knowledge of the base current and temperature of the transistor. It can measure the temperature or calculate it using the output current l_LED and a suitable temperature model. With this, the microcontroller can calculate a significant portion of the U_drift for the base voltage of the Darlington stage using a suitable temperature model.

[0189] This method allows for even better correction of the current measurement error.

[0190] Glow prevention concept with grounding network

[0191] Fig. 6 shows an embodiment of a coupling network for the grounding connection of the mains supply. This network is intended to dissipate any remaining modulations that could lead to glow currents as effectively as possible to the (silent) ground conductor of the mains supply. This ground conductor is also commonly referred to as "PE" or "protective earth". For this to work, the protective earth must, of course, also be connected to the LED driver. This embodiment is therefore only suitable for Class 1 LED drivers according to DIN EN 61140 / VDE 0140-1, where the protective earth is connected to the device. It is known in the art that a Y-capacitor, which must meet certain safety requirements, is connected to the protective conductor and usually to the circuit ground. In other words, the Y-capacitor is connected between the protective conductor and the circuit ground.The circuit ground is typically the negative output of the mains rectifier, in this embodiment rectifier BR1. In this embodiment, it is designated PW_GND. To supplement the designs shown in Figures 3 to 5 and to further reduce the glow current, a network is proposed below to replace the individual Y-capacitor and fulfill this function.

[0192] The network consists of the following components:

[0193] - A Y-capacitor C_Y, whose first terminal is connected to protective earth / PE.

[0194] - A first capacitor C_L as a high-pass filter, which is connected between the second terminal of the Y-capacitor and the negative output terminal LED-.

[0195] - A resistor R_Y connected in parallel to the first capacitor C_L, acting as an all-pass filter.

[0196] - An optional second capacitor C_Opt as a high-pass filter, which is connected between the second output of the Y capacitor C_Y and the circuit ground PW_GND.

[0197] The function and dimensioning of these components are explained below. The Y-capacitor C_Y performs the function of capacitive coupling (with high-pass coupling) and serves to reliably isolate DC current components and limit leakage currents from the device to the protective earth (PE). The capacitor used for this purpose meets the requirements for a safety capacitor or a Y-capacitor. The disconnected circuit section SF is coupled to the stable, i.e., non-modulated, reference potential of the protective earth (PE) via the Y-capacitor C_Y, in order to significantly reduce the remaining residual modulation of the disconnected circuit section. This is achieved through the principle of a voltage divider. The Y-capacitor CY fulfills the device safety requirements and enables a safe and isolated coupling of the circuit to PE.

[0198] The preferred value for the Y-capacitor C_Y ranges from 0.5nF to 22nF. A value between 2.2nF and 10nF is particularly preferred for the Y-capacitor C_Y.

[0199] The first capacitor C_L acts as a high-pass filter between the disconnected circuit section and the protective earth (PE), but without the requirement for safety-related current limiting as is the case for the Y-capacitor. This means that the requirements for a safety capacitor or Y-capacitor do not need to be met by the first capacitor C_L. Using the first capacitor C_L, the disconnected circuit section SF is coupled to the stable, i.e., non-modulated, reference potential of the protective earth (PE) at a high frequency (in the sense of a high-pass filter) in order to reduce the remaining residual modulation of the disconnected circuit section SF. The first capacitor C_L essentially functions as a high-pass filter, which, in addition to the Y-capacitor C_Y, limits the current flow to the protective earth (PE) in such a way that a residual current device (RCD) with a tripping current of 30 mA does not trip when the LED driver or...a group of LED control gears are connected to a FL / RCD.

[0200] The dimensioning of the resulting capacitance from C_Y and C_L in series is as follows: The capacitance of the first capacitor C_L is chosen together with the Y capacitor C_Y such that the resulting capacitance of the series connection of C_Y and C_L is in the range of 0.5 nF to 15 nF, and particularly preferably in the range of 1.5 nF to 5 nF. The capacitance of the first capacitor C_L is preferably from 0.5 nF to 22 nF, and particularly preferably from 2.2 nF to 10 nF.

[0201] The resistor R_Y acts as an all-pass filter or low-frequency coupling between the disconnected circuit section SF and the protective earth (PE), but without the requirement for safety-related current limiting as with the Y-capacitor C_Y. The preferred value for the resistor R_Y ranges from 330 kΩ to 10 MΩ, and preferably from 500 kΩ to 3.3 MΩ.

[0202] The optional second capacitor C_opt is connected in series with the Y capacitor C_Y and to the non-activated circuit section SN. This optional second capacitor C_opt serves to dissipate high-frequency currents, preferably for frequencies from approximately 100 kHz to approximately 5 GHz, and particularly preferably for frequencies from approximately 0.5 MHz to approximately 2.5 GHz, from the circuit arrangement or from PW_GND to protective earth (PE) for optimizing electromagnetic compatibility (EMC). Depending on the precise design of the circuit arrangement in the LED driver, this capacitor may be omitted and is therefore, as mentioned above, optional.

[0203] If it is necessary to provide this second capacitor C_opt, it preferably has a capacitance of close to OpF to 680pF, and most preferably a capacitance of 33pF to 470pF.

[0204] Fig. 7 shows another embodiment of the coupling network in which the first capacitor C_L can also be implemented in two parts. A first part, C_L1, is connected like the first capacitor C_L described above, but a second part, C_L2, is connected in parallel and in series with an auxiliary switch Q_Y. In the LED driver's standby mode, the auxiliary switch Q_Y is conducting, and in the operating mode, it is blocking. Since the disconnected circuit section does not produce any significant leakage currents to protective earth (PE), the current path from C_Y and C_L2 can be designed with a relatively low impedance. This means that the values ​​of both capacitors in this embodiment are relatively large, preferably in the range of 1 nF to 22 nF. Particularly preferably, the capacitances are in the range of 2.2 nF to 10 nF.

[0205] Figure 8 shows a seventh embodiment of a basic circuit with a buck converter having a bottom-mounted converter transistor, a top-mounted glow suppressor transistor, and a charge pump for driving this glow suppressor transistor. The circuit arrangement is designed as a non-insulating LED driver and includes an input stage ES and a buck converter HBC.

[0206] The input stage ES receives an input voltage UN at input terminals L and N. This input voltage UN is rectified by a bridge rectifier BR and passed to a switched-mode converter PFC, which operates as a power factor correction (PFC) converter. The PFC consists of a converter inductor L_PFC, a converter diode D_PFC, a converter switch SW_PFC, an input capacitor C_PFC_ln, and an output capacitor C_PFC_Out. The PFC generates a stabilized intermediate circuit voltage U_ZK at the output of the input stage ES. An auxiliary power supply AUX provides power to the control unit CTRL. The control unit CTRL outputs the control signals PFCC, BC, SC, and CPC to control the circuit arrangement. The PFCC control signal controls the power factor correction, BC controls the buck converter, SC controls the measurement path transistor, and CPC controls the charge pump.

[0207] The buck converter HBC converts the DC link voltage U_ZK into a suitable operating current l_LED for the load 5. The buck converter HBC consists of a series circuit comprising a first (SW_Buck) and a second (D_B) converter switch, forming a half-bridge HB, a converter inductor L2, a converter capacitor C_B, and a trapezoidal capacitor C_TR.

[0208] Features of the embodiment according to Figure 8:

[0209] • Low-side converter switch: The first converter switch SW_Buck is implemented as a low-side switch, i.e., it is referenced to the negative potential of the circuit ground PW_GND.

[0210] • High-side converter diode: The second converter switch D_B is implemented as a high-side freewheeling diode, i.e., it is referenced to the positive potential of the intermediate circuit voltage U_ZK. • High-side glow-prevention transistor: The

[0211] The glow suppression transistor SW_AG is provided in the current path of the operating current l_LED for the load 5 and is designed as a high-side switch, i.e., it is referenced to the positive potential of the output capacitor C_PFC_Out.

[0212] • Level shifter CP: Since the glow suppressor transistor SW_AG is a high-side switch, a level shifter CP is required to control the transistor. In this embodiment, the level shifter is implemented as a charge pump CP. The charge pump CP consists of diodes D4 and D7, capacitor C3, resistor R2, capacitor C1, diode D10, resistor R7, and the switch SW_CP. The control signal CPC, output by the control circuit CTRL, is a square wave. This square wave is output at a specific frequency, thereby operating the charge pump. At this frequency, capacitor C1 is charged, and when the half-bridge switches, capacitor C3 is charged from capacitor C1. With each subsequent switch of the half-bridge, the potential across capacitor C3 is raised to the corresponding positive potential of the intermediate circuit voltage.This results in a charge on capacitor C3 that is so large that the potential across this capacitor is higher than the positive potential of the intermediate circuit voltage. This allows the glow suppression transistor SW_AG to be effectively switched on.

[0213] • Diode D11 for overvoltage protection. Diode D11 is connected between the source terminal of the glow suppression transistor SW_AG and ground potential GND to protect the glow suppression transistor SW_AG from overvoltage.

[0214] The circuit arrangement also includes a shunt resistor for measuring the operating current l_LED. A measurement path 7 with resistors R1 and R15 and the switch SW_mU allows the measurement of the output voltage. The switch SW_mU is controlled by the control signal SC from the control unit CTRL. A Y-capacitor C_Y is connected between the positive output LED+ and the ground terminal PE.

[0215] The CTRL control unit outputs the control signals PFCC, BC, SC and CPC to control the various functions of the circuit arrangement.

[0216] This embodiment is characterized by the combination of a low-side converter switch with a high-side glow-prevention transistor and a charge pump (CP) for driving the glow-prevention transistor. This combination achieves efficient and cost-effective glow suppression, suitable for LED drivers with high voltage requirements.

[0217] Figure 9 shows a seventh embodiment of a basic circuit with a buck converter having a bottom-mounted converter transistor, a top-mounted glow suppressor transistor, and a cascaded bootstrap circuit for driving this glow suppressor transistor. The circuit arrangement serves to operate a load 5, which is represented as an LED module with a number of series-connected LEDs LED1 to LEDN. The circuit arrangement is designed as a non-insulating LED driver and includes an input stage ES and a buck converter HBC.

[0218] The input stage ES receives an input voltage UN at input terminals L and N. This input voltage UN is rectified by a bridge rectifier BR and passed to a switched-mode converter PFC, which operates as a power factor correction (PFC) converter. The PFC consists of a converter inductor L_PFC, a converter diode D_PFC, a converter switch SW_PFC, an input capacitor C_PFC_ln, and an output capacitor C_PFC_Out. The PFC generates a stabilized DC link voltage U_ZK at the output of the input stage ES. An auxiliary power supply AUX provides power to the control unit CTRL. The control unit CTRL outputs the control signals PFCC, BC, SC, and Opto_C to control the circuit arrangement. The PFCC control signal controls the power factor correction, BC controls the buck converter, SC controls the measurement path transistor, and Opto_C controls the optocoupler.

[0219] The buck converter HBC converts the DC link voltage U_ZK into a suitable operating current l_LED for the load 5. The buck converter HBC consists of a series circuit comprising a first (SW_Buck) and a second (D_B) converter switch, forming a half-bridge HB, a converter inductor L2, a converter capacitor C_B, and a trapezoidal capacitor C_TR.

[0220] Features of the embodiment according to Figure 9:

[0221] • Low-side converter switch: The first converter switch SW_Buck is implemented as a low-side switch, i.e., it is referenced to the negative potential of the circuit ground PW_GND.

[0222] • High-side converter diode: The second converter switch D_B is designed as a high-side diode, i.e., it is referenced to the positive potential of the intermediate circuit voltage U_ZK.

[0223] • High-side glow-prevention transistor: The

[0224] The glow suppression transistor SW_AG is provided in the current path of the operating current l_LED for the load 5 and is designed as a high-side switch, i.e., it is referenced to the positive potential of the output capacitor C_PFC_Out.

[0225] • Cascaded bootstrap circuit CP: Since the

[0226] Since the glow-prevention transistor SW_AG is a high-side switch, a level shifter is required to control the transistor. In this embodiment, the level shifter is implemented as a cascaded bootstrap circuit CP.

[0227] The switching section of the cascaded bootstrap circuit CP functions as follows: The control unit CTRL outputs the control signal Opto_C. This control signal drives the anode of the optocoupler diode Opto. The output signal of the optocoupler is fed to the input G_AG of the glow suppression transistor.

[0228] The actual bootstrap circuit consists of the following components: capacitor C3, capacitor C4, diode D12, diode D13, and resistor R7. Resistor R7 is connected in series with diode D13 and capacitor C4. Capacitor C4 is connected to the midpoint of the half-bridge HB. Capacitor C3 is connected to the positive output LED+.

[0229] The cascaded bootstrap circuit CP operates as follows: Capacitor C4 is recharged by the oscillation of the midpoint of the half-bridge HB. The midpoint of the half-bridge constantly oscillates between the circuit ground and the positive potential of the DC link voltage. This oscillation charges capacitor C4. Diodes D12 and D13 transfer the potential across capacitor C4 to capacitor C1, which, when the half-bridge switches, is then raised to the positive DC link voltage U_ZK. The potential across C1 is therefore higher than the potential of the DC link voltage U_ZK. This allows the glow suppressor transistor SW_AG to be effectively switched on.

[0230] The diode D11 is connected between the source terminal of the glow suppression transistor SW_AG and the ground potential GND to protect the glow suppression transistor SW_AG from overvoltage.

[0231] The circuit arrangement also includes a shunt resistor (not shown here) for measuring the operating current l_LED. A measurement path 7 with resistors R1 and R15 and the switch SW_mU allows the measurement of the output voltage. The switch SW_mU is controlled by the control signal SC from the control unit CTRL. A Y-capacitor C_Y is connected between the positive output LED+ and the ground terminal PE.

[0232] The CTRL control unit outputs the control signals PFCC, BC, SC, and Opto_C to control the various functions of the circuit arrangement. This embodiment is characterized by the combination of a low-side converter switch with a high-side glow-prevention transistor and a cascaded bootstrap circuit CP for driving the glow-prevention transistor. This combination achieves efficient and cost-effective glow suppression suitable for LED drivers with high voltage requirements. The cascaded bootstrap circuit enables the high-side glow-prevention transistor to be driven without creating an additional current path for glow currents.

[0233] REFERENCE MARK LIST

[0234] UN Input mains voltage L Phase of the mains connection N Neutral conductor of the mains connection PE Ground of the mains connection ES Input stage BR1 Full bridge rectifier U_DC Output voltage of the full bridge rectifier U_IN+ Positive output of the full bridge rectifier

[0235] PW_GND Circuit ground, negative output of the full-bridge rectifier

[0236] L-PFC converter inductance of the first switched-mode converter, which here acts as a power factor correction.

[0237] PFC-SW Converter switch of the first clocked converter D-PFC Converter diode of the first clocked converter C-PFC Converter capacitance of the first clocked converter PFC First clocked converter, here a power factor correction U_ZK Output voltage of the first clocked converter U_R Positive output of the first clocked converter M2, SW_Buck Switch of the second clocked converter, here a buck converter

[0238] M1 Synchronous switch of the second clocked converter instead of a freewheeling diode

[0239] D_B Freewheeling diode of the second switched-mode converter HB Half-bridge consisting of M1 and M2 or SW_Buck and D_B C_B Converter capacitance of the second switched-mode converter L2 Converter inductance of the second switched-mode converter C_TR Trapezoidal capacitor of the second switched-mode converter HBC Second switched-mode converter, here a buck converter with a half-bridge

[0240] SW_AG Glow prevention switch SN Circuit section connected to the mains input SF Circuit section disconnected from the mains input 7 Measuring path for measuring the output voltage of the circuit arrangement

[0241] LED+ positive output terminal of the circuit assembly LED- negative output terminal of the circuit assembly l_LED current at the output of the circuit assembly LED1-LEDN LEDs as load of the circuit assembly 5 LED module with LEDs LED1 to LEDN arranged on it, which is connected to the output of the circuit assembly

[0242] L+ positive input of the LED module 5

[0243] L- negative input of LED module 5

[0244] CP level converter

Claims

PATENT CLAIMS 1. Circuit arrangement for operating a load (5), comprising: - a first (L) and a second (N) input terminal for inputting an input voltage (UN) - an input stage (ES) for inputting the input voltage (UN) and for outputting an intermediate circuit voltage (U_ZK) at a first (U_R) and second (PW_GND) output of the input stage (ES), - a switched-mode converter (HBC) operating as a buck converter with a series connection of a first (M2, SW_Buck) and a second (M1, D_B) converter switch, which together form a half-bridge (HB), a converter inductor (L2), a converter capacitor (C_B) and a trapezoidal capacitor (C_TR) for converting the DC link voltage (U_ZK) into a suitable operating current (l_LED) for the load (5), - an output with a first (LED+) and a second (LED-) output terminal for connecting the load (5), characterized in that - a glow suppression transistor (SW_AG) is provided in the current path of the operating current (l_LED) for the load (5) of the second clocked converter (HBC), - the glow suppression transistor (SW_AG) is arranged within the circuit such that it divides the circuit arrangement into a circuit part (SN) located at the input (L, N) and a switchable circuit part (SF) located at the output (LED+, LED-), - the first (M2, SW_Buck) and the second (M1 , D_B) converter switches are provided as further glow prevention elements, which interrupt the current paths between the circuit part (SN) located at the first (L) and a second (N) input terminal and the switchable circuit part (SF) located at the output (LED+, LED-), - a Y-capacitor (C_Y) is connected between the switchable circuit part (SF) and an earth connection (PE) of the mains AC voltage (UN), - the converter capacitor (C_B) is entirely located in the switchable circuit section (SF) and is connected between an output terminal of the converter inductor (L2) and an output terminal of the glow suppression transistor (SW_AG), wherein the first (LED+) and the second (LED-) output terminals are electrically isolated and thus switched off from the first (L) and second (N) input terminals in a rest mode of the circuit arrangement by the glow suppression elements (M2, M1 , SW_AG, D_B, SW_Buck), so that almost no glow current can flow through the connected load (5) and also almost no glow current can flow to ground via the connected load (5).

2. Circuit arrangement according to claim 1, characterized in that at least a part of the trapezoidal capacitor (C_TR, C_TR1) is connected between the half-bridge center (HBM) and the switchable circuit part (SF).

3. Circuit arrangement according to claim 1 or 2, characterized in that the first (M2, SW_Buck) and the second (M1 , D_B) converter switches and the glow suppression transistor (SW_AG) are configured to open current paths between the input terminals (L, N) and the output terminals (LED+, LED-).

4. Circuit arrangement according to one of claims 1 to 3, characterized in that it further comprises a converter measurement path (7) consisting of a series connection of two resistors (R_B1 , R_B2 or R1 , R15) which is provided between an output terminal (LED+ or LED-) and the second output of the input stage (PW_GND), wherein a measurement path transistor (Q_S or SW_mU) is provided in the converter measurement path (R_B1 , R_B2 or R1 , R15) as a further glow suppression element to interrupt the converter measurement path when the circuit arrangement is in standby mode.

5. Circuit arrangement according to one of the preceding claims, characterized in that the trapezoidal capacitor (C_TR) is divided into two partial capacitances (C_TR1 , C_TR2), wherein the first partial capacitance (C_TR1 ) is from The midpoint of a half-bridge (HBM) from the first (M2, SW_Buck) and a second (M1 , D_B) converter switch is connected to the output-side connection of the glow suppression transistor (SW_AG), and the second partial capacitance (C_TR2) is connected from the midpoint of the half-bridge (HBM) to the input-side connection of the glow suppression transistor (SW_AG).

6. Circuit arrangement according to claim 5, characterized in that the first partial capacitance (C_TR1 ) has a capacitance value of OpF to 4.7nF, preferably from 33pF to 560pF, and the second partial capacitance (C_TR2) has a capacitance value of OpF to 1 nF, preferably from 33pF to 330pF.

7. Circuit arrangement according to one of the preceding claims, characterized in that - the first converter switch (M2) is located on the high side of the half bridge and conducts during a magnetization phase of the converter inductance (L2) and - the second converter switch (M1) is located on the low side of the half bridge and conducts during a demagnetization phase of the converter inductance (L2) and is implemented either as an actively controlled semiconductor switch or as a diode, - the glow suppression transistor (SW_AG) is connected in the current path of the operating current (l_LED) for the load (5) between the second (LED) output terminal and the second (PW_GND) output of the input stage (ES), - the Y capacitor (C_Y) is connected between the second (LED) output terminal and the earth terminal (PE) of the AC mains voltage (UN).

8. Circuit arrangement according to one of the preceding claims 1 to 6, characterized in that - the first converter switch (SW_Buck) is located on the low side of the half-bridge and conducts during a magnetization phase of the converter inductance (L2), and - the second converter switch (D_B) is located on the high side of the half bridge and conducts converter inductance (L2) during the demagnetization phase and is implemented either as an actively controlled semiconductor switch or as a diode, - the glow suppression transistor (SW_AG) is connected in the current path of the operating current (l_LED) for the load (5) between the first (U_R) output of the input stage (ES) and the first (LED+) output terminal, - the Y capacitor (C_Y) is connected between the first (LED+) output terminal and the earth terminal (PE) of the AC mains voltage (UN).

9. Circuit arrangement according to one of the preceding claims, characterized in that the glow suppression transistor (SW_AG) is either a MOSFET, or that the glow suppression transistor (SW_AG) is a bipolar transistor or a Darlington transistor or an IGBT, and a diode (D_AG) is connected in parallel to the bipolar transistor or Darlington transistor or IGBT.

10. Circuit arrangement according to claim 9, second option, characterized in that it has a control circuit (CTRL) which controls the glow-prevention transistor (SW_AG), wherein a control current of the glow-prevention transistor (SW_AG) is set by the control circuit (CTRL) such that it is substantially proportional to the current through the load (5), wherein the control current of the glow-prevention transistor (SW_AG) is known to the control circuit (CTRL) and is taken into account when measuring the current through the load (l_LED) by means of a shunt (SHT).

11. Circuit arrangement according to claim 10, characterized in that the control circuit (CTRL) controls the glow suppression transistor (SW_AG) such that it is just in saturation.

12. Circuit arrangement according to one of the preceding claims, characterized in that the input stage (ES) comprises either a rectifier or a switched-mode converter or a switched-mode converter (PFC) operating as a power factor correction.

13. Circuit arrangement according to one of the preceding claims, characterized in that in each current path between the circuit part (SN) located at the input (L, N) and the one at the output (LED+, LED-) A glow suppression element (SW_mU, SW_CP, Q_S) is switched on the unlockable circuit part (SF) that contributes to a visible glow current.

14. Circuit arrangement according to one of claims 1 to 13, characterized by a level shifter (CP) for controlling the glow suppression transistor (SW_AG), wherein the level shifter (CP) is deactivated in the idle mode of the circuit arrangement, and wherein the level shifter (CP) comprises one or more glow suppression elements (C1 , SW_CP, D4, D7, D10) connected in series to reduce the glow current caused by the level shifter (CP) in idle mode.

15. Circuit arrangement according to one of claims 1 to 14, characterized in that a diode (D11 ) is provided between the source terminal of the glow suppression transistor (SW_AG) and an earth potential (PW_GND) to protect the glow suppression transistor (SW_AG) from overvoltage.

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