Circuit arrangement of a lighting device and lighting device with such a circuit arrangement

Description

[0001] The present invention relates to a circuit arrangement of a lighting device, preferably of a motor vehicle, according to the preamble of claim 1.

[0002] Furthermore, the invention relates to a lighting device of a motor vehicle with a housing and a light exit opening formed in the housing and closed by a cover plate, and with a circuit arrangement of the type mentioned above. The lighting device is designed such that the light emitted by the semiconductor light sources, optionally with the cooperation of optical elements of the lighting device, passes through the cover plate to generate at least one lighting function of the lighting device.

[0003] Semiconductor light sources are usually designed as light-emitting diodes (LEDs). For headlight functions (e.g., low beam, high beam, fog light, partial high beam, city light, country road light, motorway light, cornering light), they are preferably designed as high-performance LEDs that emit white light. White light can be generated, for example, by superimposing blue light from an LED chip and yellow light from a fluorescent layer (e.g., phosphor), onto which part of the blue light strikes and is converted into yellow light. Alternatively, so-called RGB LEDs can be used, which generate red, green, and blue light, which is superimposed to produce white or other colored light, resulting in an additive color mixture. For lighting functions (e.g.,For example, daytime running lights, reversing lights, turn signals, side marker lights, tail lights, brake lights, and rear fog lights, the semiconductor light sources are preferably designed as LEDs that emit white, yellow (orange), or red light. Colored light can be generated, for example, by certain LEDs with or without a fluorescent layer. It would also be conceivable to generate colored light using one or more RGB LEDs. It would also be conceivable, for example, to design the semiconductor light sources as laser diodes or OLEDs.

[0004] Connecting several semiconductor light sources in series has the advantage that only one power source is required for the semiconductor light sources. Automotive headlights with several LEDs arranged in a matrix-like manner in several rows and / or columns (so-called LED pixel systems) comprise a buck converter that generates the current for the LEDs, and semiconductor switches arranged in parallel with the LEDs in the bypass circuits to bridge them. The buck converter has a smoothing capacitor to reduce LED current overshoots (so-called current ripple). Current overshoots must not exceed a certain level for reasons of electromagnetic compatibility (EMC). Furthermore, the maximum permissible value of the LED operating current should under no circumstances be exceeded. This can be caused by the discharging of the smoothing capacitor when switching the semiconductor switches or the LEDs.

[0005] A lighting device with a circuit arrangement is known, for example, from EP 1 322 139 A1. There, it is proposed to arrange a passively controlling bypass circuit with a controllable semiconductor switch arranged therein in parallel to each semiconductor light source in a series circuit. The electrical wiring and control of the semiconductor switch ensures that if an electrical connection via one of the semiconductor light sources is interrupted (e.g. due to a defect in the semiconductor light source), the semiconductor switch in the corresponding bypass circuit is controlled so that the electrical connection is closed via the bypass circuit. This ensures that if one semiconductor light source in the series circuit is defective, the other semiconductor light sources in the series circuit continue to be supplied with power. Active control of the semiconductor switches for the targeted control of the light source supplied via the corresponding bypass circuit orHowever, it is not possible to determine the current flowing through the corresponding semiconductor light source.

[0006] A lighting device with a circuit arrangement is furthermore known from DE 10 2006 031 679 A1. There, it is proposed to arrange an actively controllable bypass circuit parallel to each semiconductor light source in a series circuit. An actively controllable semiconductor switch (e.g. a field-effect transistor) is arranged in each of the bypass circuits, by means of which the corresponding semiconductor light source can be bypassed at least temporarily. The semiconductor switches of the bypass circuits are each controlled by means of a PWM signal, so that the controlled semiconductor switch either enables (semiconductor switch closed) or interrupts (semiconductor switch open) a current flow via the corresponding bypass circuit depending on the level of the PWM signal. The duty cycle averaged over time (so-calledDuty Cycle: The proportion of the high level of a PWM signal per period in relation to the duration of the period of the PWM signal determines the size of the current flowing through the bypass circuit and thus the degree of dimming of the corresponding semiconductor light source.

[0007] Finally, DE 10 2016 120 100 A1 discloses a circuit arrangement in which semiconductor switches arranged in the bypass circuits can also be actively controlled. Control is achieved via signal converters, with each semiconductor switch being assigned its own signal converter. A signal converter generates a corresponding bypass control signal from a control signal and applies this to a control input of the corresponding semiconductor switch. Unlike with a PWM signal, the signal converters can reduce the edge steepness of the bypass control signals and thereby reduce or even avoid current peaks in the current flowing through the semiconductor light sources. Here, too, the duty cycle of the bypass control signal, averaged over time, determines the magnitude of the current flowing through the bypass circuit and thus the degree of dimming of the corresponding semiconductor light source.

[0008] A problem with the described prior art according to DE 10 2006 031 679 A1 and DE 10 2016 120 100 A1 is that analog control or regulation of the semiconductor switches is not possible without additional circuitry complexity. The semiconductor switches are therefore operated digitally, i.e. they are constantly switched back and forth between conductive and non-conductive. Individual dimming of the LEDs is only possible with a constantly applied control signal. A particular disadvantage here is that if one of the LEDs is operated in a dimmed state for an extended period, a control signal is permanently required to continuously control the semiconductor switch corresponding to the dimmed LED. The current flowing through the LED can be changed via the duty cycle (the so-called duty cycle: proportion of the high level of a PWM signal per period in relation to the duration of the period) of the control signal.If a 1 A current is to be reduced to 0.1 A, this can be achieved, for example, by a duty cycle of 10%.

[0009] Furthermore, circuit arrangements and lighting devices of the type mentioned above can be found, for example, in EP 2 670 218 A1; DE 10 2016 208 069 A1; US ​​2009 / 174 343 A1 and WO 2015 / 077 812 A2.

[0010] Based on the described prior art, the present invention is based on the object of designing and developing a circuit arrangement of the type mentioned at the outset in such a way that a longer-term dimmed operation of at least one semiconductor light source in a series circuit of several semiconductor light sources is possible without the need for a permanent control signal.

[0011] To achieve this object, a circuit arrangement having the features of claim 1 is proposed. In particular, based on the circuit arrangement of the type mentioned at the outset, it is proposed that the configurable current sink is configurable by selecting and equipping the respective bypass circuit with a respective voltage regulator and a respective ohmic resistor, so that the current component flowing through the bypass circuit is permanently set without the need for a control signal, and the configurable current sink comprises a series circuit of the voltage regulator and the ohmic resistor, wherein the voltage regulator is designed to regulate a voltage applied across the ohmic resistor in such a way that the current component flowing through the bypass circuit is set from the applied voltage divided by a resistance value of the ohmic resistor,wherein an input terminal of the voltage regulator is connected to an anode of the at least one semiconductor light source, an output terminal of the voltage regulator is connected to a first contact of the ohmic resistor, and a voltage regulator terminal of the voltage regulator is connected to a second contact of the ohmic resistor, which is connected to a cathode of the at least one semiconductor light source.

[0012] The circuit arrangement according to the invention is optimized for the operating case of a constant dimming value of one or more semiconductor light sources in a series circuit. The dimming values ​​of individual semiconductor light sources in the series circuit can differ from one another. A particular advantage is that the circuit arrangement no longer requires a control signal to control a semiconductor switch arranged in the bypass circuit, since the circuit is self-regulating. The semiconductor light sources that have a bypass circuit are dimmed in analogue rather than digital mode. This advantageously extends the service life of the semiconductor light sources. Since PWM control is omitted, no current overshoots occur. Additional electrical components for current smoothing, e.g. in the form of a smoothing capacitor, are not required.The circuit arrangement according to the invention can be implemented more cost-effectively overall and offers advantages in terms of EMC compatibility. Particularly with low currents (e.g., in the range < 100 mA) and with RGB LEDs, the analog dimming proposed by the invention for individual or all semiconductor light sources in the series circuit can be advantageous. A dimmed semiconductor light source shines less brightly and / or in a different color. The current flowing through the bypass circuit into the current sink is preferably converted into heat.

[0013] The current sink can be configured by equipping the bypass circuit with appropriate electrical and / or electronic components. Depending on the selected and installed components of the current sink circuit arrangement in the bypass circuit, the portion of the current flowing through the current sink, and thus also the current flowing through the corresponding semiconductor light source, is permanently adjusted without the need for a control signal or without a control signal having to be continuously present.

[0014] The current sink comprises a series connection of a voltage regulator and a resistance. The voltage regulator comprises an input terminal, an output terminal, and a voltage regulator terminal (adjust). The input is connected to the anode of the semiconductor light source, and the output is connected to a first contact of the resistance. The second contact of the resistance is connected to the cathode of the semiconductor light source. The voltage regulator terminal is also connected to the cathode. The voltage regulator is designed to regulate a voltage between the output and the voltage regulator terminal to a predeterminable value, e.g., 1.25 V. The resistance is preferably a reference resistor, by means of which the current sink can be adjusted. The regulated voltage of the voltage regulator is applied to the resistance. A current I BP = regulated voltage U / resistance value R ref flows through the resistance and thus through the bypass circuit, e.g.,I = 1.25 V / R ref [Ω]. This current component therefore does not flow through the semiconductor light source and results in corresponding dimming. The degree of dimming is fixed by the choice of the voltage regulator and the reference resistor. With a given voltage regulator, the degree of dimming is defined primarily by the reference resistor and remains constant over an extended period even without a control signal, since the current sink in the bypass circuit regulates itself.

[0015] In one embodiment, which, however, is not the subject of the invention, it is proposed that the current sink comprises an adjustable transistor, preferably in the form of a power transistor. The transistor is preferably of the npn type. Preferably, the collector terminal of the transistor is connected to the anode of the semiconductor light source and the emitter terminal of the transistor is connected to the cathode of the semiconductor light source. It is conceivable that the current sink comprises a first ohmic resistor in a collector-emitter path of the transistor, in particular between the emitter terminal of the transistor and the cathode of the semiconductor light source. Preferably, the first ohmic resistor is a reference resistor by means of which the current sink can be configured, i.e. by means of which the collector-emitter current flowing through the bypass circuit can be adjusted.Alternatively or additionally, a corresponding resistor could also be arranged between the collector terminal of the transistor and the anode of the semiconductor light source.

[0016] In one embodiment, which, however, is not the subject of the invention, it is proposed that the current sink comprise an element for specifying, in particular for regulating, a static reference voltage applied to the first ohmic resistor, by which the current flowing through the collector-emitter path of the transistor can be statically adjusted. Preferably, the element for specifying the reference voltage comprises an adjustable shunt regulator.

[0017] The current sink can comprise a series connection of the shunt regulator and a second ohmic resistor. Preferably, a base terminal of the transistor is connected between a cathode terminal of the shunt regulator and a first terminal contact of the second ohmic resistor, a collector terminal of the transistor is connected to a second terminal contact of the second ohmic resistor, an emitter terminal of the transistor is connected to a reference terminal of the shunt regulator and to a first terminal contact of the first ohmic resistor, and an anode terminal of the shunt regulator is connected to a second terminal contact of the first ohmic resistor. The collector terminal of the transistor is connected to the anode of the semiconductor light source, and the anode terminal of the shunt regulator is connected to the cathode of the semiconductor light source.

[0018] The adjustable shunt regulator sets a regulated reference voltage, e.g. any value between 2.5 V and 36 V, with high precision and keeps it constant. The reference voltage is applied to the first resistor, which serves as the reference resistor, and sets a defined resulting collector-emitter current I BP in the bypass circuit. The current I BP results from the regulated voltage V ref / resistance R ref , e.g. I BP = 2.5 V / R ref [Ω]. This current component I BP therefore does not flow through the semiconductor light source and dims it accordingly. The degree of dimming is predetermined by the choice of electrical or electronic components. With a predetermined shunt regulator or reference voltage predetermined by it, the degree of dimming is defined in particular by the reference resistor and remains constant over an extended period of time even without a control signal.

[0019] In one embodiment, which, however, is not the subject of the invention, it is proposed that the current sink comprise a circuit for adjusting the collector-emitter current through the bypass circuit, by means of which the current flowing through the collector-emitter path of the transistor can be adjusted. Here, too, the collector-emitter current flowing through the bypass circuit is adjusted, thus dimming the corresponding semiconductor light source for an extended period of time, even without a continuously applied control signal.

[0020] The collector-emitter current adjustment circuit can be configured to adjust the current flowing through the collector-emitter path of the transistor between 0% and 100% of the current supplied by the current source of the series circuit. This means that the collector-emitter current, and thus also the current flowing through the corresponding semiconductor light source, can be adjusted to a desired value by the circuit.

[0021] For example, if a first group of semiconductor light sources for a white daytime running light and a second group of semiconductor light sources for a yellow or orange indicator light are arranged in a series circuit, it is conceivable that the semiconductor light sources of the two groups must be operated with different currents, even though they are arranged in a common series circuit. This can be achieved by ensuring that the current supplied by the current source corresponds to the current required by the semiconductor light sources with the higher operating current, and that a portion of the current supplied by the current source for the semiconductor light sources with the lower operating current flows through the corresponding bypass circuits assigned to the semiconductor light sources into the current sink, so that a lower operating current flows through these semiconductor light sources.

[0022] Furthermore, in situations in which the turn signal is activated, the daytime running lights can be dimmed or switched off completely. This can be achieved by part of the current supplied by the power source in the semiconductor light sources for the daytime running lights flowing through the corresponding bypass circuits assigned to the semiconductor light sources into the current sink, so that less or no operating current flows through these semiconductor light sources for the daytime running lights. The temporary dimming of the semiconductor light sources for the daytime running lights can be achieved by the circuit for adjusting the collector-emitter current controlling the transistor arranged in the bypass circuit. The degree of dimming is configured by equipping the current sink with corresponding electrical and / or electronic components, e.g.by a predetermined reference voltage applied to a reference resistor and setting a corresponding current flow in the bypass circuit.

[0023] In one embodiment, which is not the subject of the invention, it is proposed that the circuit for adjusting the collector-emitter current comprises an operational amplifier whose output voltage or a voltage proportional thereto is applied to a base terminal of the transistor, wherein an input voltage of the operational amplifier is a difference between an externally adjustable reference voltage and a voltage of a digital signal that represents an on (low level of the digital signal) or off (high level of the digital signal) of the bypass circuit. The digital signal can also be omitted, in which case the second input of the operational amplifier should then be permanently at the low level. The reference voltage can be used to adjust the current flowing through the bypass circuit in an analog manner.Whether the set current actually flows through the bypass circuit or not is determined by the level or digital signal applied to the second input. The reference voltage at the input of the operational amplifier can be used to adjust the output voltage of the operational amplifier and thus ultimately the collector-emitter current in the bypass circuit over the long term. A constantly applied control signal, especially a PWM signal, is not required for this.

[0024] When the digital signal is low, the operational amplifier can generate the drive signal at its output, causing the transistor to turn on, allowing a collector-emitter current to flow through the bypass circuit. When the digital signal is high, no drive signal would be present at the operational amplifier's output, meaning the drive signal would not turn on the transistor.

[0025] According to an advantageous embodiment of the invention, it is proposed that the series connection of semiconductor light sources comprises a first semiconductor light source emitting red light, a second semiconductor light source emitting green light, and a third semiconductor light source emitting blue light, wherein at least two of the red, green, and blue semiconductor light sources each have bypass circuits of the at least one bypass circuit (18) connected in parallel. The red, green, and blue semiconductor light sources can be part of an RGB light-emitting diode (LED). The light emitted by the individual semiconductor light sources overlaps to form the light of a specific color emitted by the RGB LED. The color of the light is determined by the brightness of the individual semiconductor light sources.One or more RGB LEDs can, in turn, be part of a vehicle light, emitting light of a specific color to achieve a specific lighting function. By operating the individual red, green, and blue semiconductor light sources with specified (possibly different) operating currents, different brightnesses of the semiconductor light sources and thus a specific color of the light emitted by the RGB LED can be set.

[0026] According to another advantageous embodiment of the invention, it is proposed that the at least two semiconductor light sources connected in series comprise a first group of semiconductor light sources for generating a first lighting function and a second group of semiconductor light sources for generating a second lighting function, and that a respective bypass circuit is connected in parallel to at least one of the groups. The first group of semiconductor light sources serves, for example, to generate a white daytime running light, and the second group of semiconductor light sources serves, for example, to generate a yellow / orange flashing light. The semiconductor light sources of one of the groups can have a lower operating current than the semiconductor light sources of the other group. For example, the semiconductor light sources for generating the flashing light can have a lower operating current than the semiconductor light sources for generating the daytime running light.The current supplied by the power source preferably corresponds to the higher operating current of the semiconductor light sources used to generate the daytime running lights. Each semiconductor light source used to generate the turn signal is assigned a bypass circuit through which a portion of the current supplied by the power source can flow, allowing the lower operating current to flow through the corresponding semiconductor light sources.

[0027] The present invention also relates to a lighting device of a motor vehicle having the features of claim 4. In particular, it is proposed that the lighting device of the type mentioned at the outset has a circuit arrangement according to the invention.

[0028] Further features and advantages of the present invention are explained in more detail below with reference to the figures. They show: Figure 1 shows a lighting device according to the invention in accordance with a preferred embodiment; Figure 2 shows a circuit arrangement according to the invention in accordance with a first preferred embodiment; Figure 3 shows a circuit arrangement according to the invention in accordance with a second preferred embodiment; Figure 4 shows a semiconductor light source with bypass circuit of a circuit arrangement according to the invention in accordance with Figure 2 or Figure 3 ; Figure 5 shows a first embodiment of a bypass circuit of a circuit arrangement according to the invention according to Figure 2 or Figure 3 ; Figure 6 shows an embodiment not belonging to the invention of a bypass circuit of a circuit arrangement according to Figure 2 or Figure 3 ; Figure 7 shows an embodiment not belonging to the invention of a bypass circuit of a circuit arrangement according to Figure 2 or Figure 3 ; and Figure 8 shows a circuit arrangement known from the prior art.

[0029] In Figure 1 A lighting device according to the invention is shown in the form of a motor vehicle headlight. It would also be conceivable to implement the lighting device as any motor vehicle light, for example, a rear light or a side light. The motor vehicle light can be arranged in a separate housing or in the same housing as a motor vehicle headlight.

[0030] In Figure 1The motor vehicle headlight is designated in its entirety by the reference numeral 101. The headlight 101 comprises a housing 102, which is preferably made of plastic. In a light exit direction 103, the headlight housing 102 has a light exit opening which is closed by a transparent cover plate 104. The cover plate 104 is made of colorless plastic or glass. The plate 104 can be designed without optically effective profiles as a so-called clear plate. Alternatively, the plate 104 can be provided, at least in some regions, with optically effective profiles (e.g., cylindrical lenses or prisms) which scatter the light passing through it, preferably in a horizontal direction. The headlight 101 is intended for installation on an attachment side of a motor vehicle. Two of the headlights 101 shown, which are arranged on different attachment sides of the motor vehicle, form a motor vehicle lighting arrangement.The headlights 101 installed on different mounting sides are preferably designed to be mirror-symmetrical to one another with regard to their general geometric external appearance.

[0031] In the example shown, two light modules 105, 106 are arranged inside the headlight housing 102. The light modules 105, 106 are arranged fixedly or movable relative to the housing 102. A dynamic cornering light function can be realized by a relative movement of the light modules 105, 106 to the housing 102 in the horizontal direction. Moving the light modules 105, 106 around a horizontal axis, i.e., in the vertical direction, allows headlight range control. Of course, more or fewer than the two light modules 105, 106 shown can also be provided in the headlight housing 102. One or more of the light modules 105, 106 can be designed to generate different light distributions, for example a low beam, a high beam and a partial high beam or parts thereof (e.g. a low beam basic light, a low beam spot, a high beam basic light, a high beam spot, etc.).It is conceivable that the light distributions of the light modules 105, 106 of headlights 101 arranged on different sides of the motor vehicle complement each other to form the resulting light distribution of the lighting arrangement.

[0032] A control unit 107 can be arranged in a control unit housing 108 on the outside of the headlight housing 102. Of course, the control unit 107 can also be arranged at any other location on the headlight 101. In particular, a separate control unit can be provided for each of the light modules 105, 106, wherein the control units can be an integral part of the light modules 105, 106. Of course, the control unit 107 can also be arranged remotely from the headlight 101, for example, in the engine compartment of the motor vehicle. The control unit 107 is used to control and / or regulate the light modules 105, 106 or subcomponents of the light modules 105, 106, such as light and / or radiation sources of the light modules 105, 106 or actuators (e.g. electromagnets, electric motors, piezo actuators) to realize a movement of the light modules 105, 106 relative to the housing 102. The control of the light modules 105, 106 orof the subcomponents by the control unit 107 takes place via connecting lines 110, which are shown in . Figure 1 are represented merely symbolically by a dashed line. The light modules 105, 106 can also be supplied with electrical energy via the lines 110. The lines 110 are led from the interior of the headlight 101 through an opening in the headlight housing 102 into the control unit housing 108 and there connected to the circuit of the control unit 107. If control units are provided as an integral component of the light modules 105, 106, the lines 110 and the opening in the headlight housing 102 can be omitted. The control unit 107 comprises a plug element 109 for connecting a connecting cable to a higher-level control unit (e.g. in the form of a so-called body controller unit) and / or an energy source (e.g. in the form of the vehicle battery).

[0033] Finally, it is conceivable that one or more lighting modules 111 for generating one or more lighting functions are also arranged in the housing 102. In the case of a light mounted on the front of a motor vehicle, the lighting functions can be, for example, daytime running lights, indicator lights, position lights, parking lights, parking lights, or the like. In the case of a rear light, the lighting functions can also include a tail light, a brake light, a reversing light, a rear fog light, or the like. In the case of a light mounted on the side of the vehicle, the lighting function is, for example, a side marker light.

[0034] One or more of the light modules 105, 106 and / or the luminaire module 111 can be semiconductor light sources 16 (cf. Figure 2 or Figure 3) for emitting the light for the light distribution of the headlight 101 or for the lighting function. The emitted light passes through the cover plate 104—optionally with the assistance of optical elements (not shown) of the lighting device 101—to generate at least one lighting function of the lighting device 101. The optical elements can include, for example, light guides, auxiliary optics, focusing optics, lenses, reflectors, and / or beam diaphragms.

[0035] The semiconductor light sources 16 are preferably designed as light-emitting diodes (LEDs). However, a different design of the semiconductor light sources 16 would also be conceivable, for example, as laser diodes and / or as OLEDs. Several semiconductor light sources 16 are arranged in a common series circuit 12 in a circuit arrangement 10 according to the invention and have a common current source 14 for generating a constant current. The current source 14 comprises, for example, a buck converter.

[0036] For various reasons, it may be necessary to operate one or more of the semiconductor light sources 16 of the series circuit 12 with a lower current than other semiconductor light sources 16 of the series circuit 12. Therefore, the prior art (cf. Figure 8) at least one of the semiconductor light sources 16 of the circuit arrangement 10 has a bypass circuit 18 with a controllable semiconductor switch 20 arranged therein. In the example shown, the Figure 8 The series circuit 12 comprises three semiconductor light sources 16.1, 16.2 and 16.m. Of course, the series circuit 12 can also comprise any other number (between two and very many) of semiconductor light sources 16. The decisive factor for the maximum number of semiconductor light sources 16 in the series circuit 12 is that the current source 14 (in Figure 8 not shown) generates a sufficiently large current I to supply all semiconductor light sources 16.

[0037] In Figure 8Each semiconductor light source 16 has a corresponding bypass circuit 18, so that individual dimming of each semiconductor light source 16 is possible. Of course, it would also be conceivable for only one or some of the semiconductor light sources 16 to have a bypass circuit 18. The bypass circuits 18 are arranged in parallel to the corresponding semiconductor light sources 16 and can bridge them. The semiconductor switches 20 can be designed, for example, as transistors, in particular as power transistors. The semiconductor switches 20 can be controlled by a digital control signal 22, so that they either switch the corresponding bypass circuit 18 through (i.e., bridge the corresponding semiconductor light source 16 so that the entire current supplied by the current source 14 flows via the bypass circuit 18) or interrupt the bypass circuit 18 so that the entire current supplied by the current source 14 flows through the semiconductor light source 16.When a bypass circuit 18 is switched through, at least a portion I BP of the current I supplied by the current source 14 flows, on average over time, via the bypass circuit 18 instead of through the corresponding semiconductor light source 16, so that the current I LED flowing via the semiconductor light source 16 is smaller than the total current I of the current source 14. In this way, it is possible to dim individual or multiple semiconductor light sources 16 in a targeted manner or to switch them off completely.

[0038] In the prior art, the digital control signal 22 for a semiconductor switch 20 is generated from a switching signal 26, for example, by means of a level shifter 24. The switching signal 26 is, for example, a pulse-width modulated (PWM) signal, whose duty cycle determines the degree of dimming of the corresponding semiconductor light source 16. During dimmed operation of one of the semiconductor light sources 16, a switching signal 26 must therefore be continuously present. This is particularly problematic during longer-term dimmed operation of the semiconductor light sources 16. Furthermore, the digital control of the semiconductor switch 20 results in problems with the electromagnetic compatibility (EMC) of the circuit arrangement 10 due to current overshoots (so-called current ripple).

[0039] The circuit arrangement 10 according to the invention has advantages over the prior art, particularly for long-term dimming of semiconductor light sources 16, since the current sink 30 in the bypass circuit 18 is fixedly configured or self-regulating. Thus, no permanently applied control signal 22, in particular no PWM signal, is required. Eliminating a PWM control signal leads to a reduction in current overshoots and an improvement in the EMC properties of the circuit arrangement 10. Furthermore, the analog dimming of the semiconductor light sources 16 reduces the maximum current I LED in a semiconductor light source 16, which extends the service life of the semiconductor light sources 16. Analog dimming can be advantageous, particularly for small currents (<100 mA) and RGB LEDs. The proposed circuit arrangement 10 can be implemented particularly inexpensively.

[0040] In Figure 21 shows a simplified schematic representation of the circuit arrangement 10 according to the invention. This comprises the series circuit 12 of a plurality of semiconductor light sources 16 and bypass circuits 18 connected in parallel to each semiconductor light source 16, in each of which a current sink 30 is arranged. A common current source 14 is provided for the series circuit 12, which preferably comprises a buck converter. Depending on the configuration of the current sink 30, a portion I BP of the current I supplied by the current source 14 flows through the bypass circuit 18 into the current sink 30, where it is preferably converted into heat and the heat is dissipated to the environment. Only the remaining portion I LED of the total current I flows through the semiconductor light source 16. The current sinks 30 can be configured differently, so that different operating currents I LED flow through the individual semiconductor light sources 16.

[0041] In Figure 31 shows an example of a series circuit 12 comprising several semiconductor light sources 16, some of which are provided with parallel current sinks 30. The series circuit 12 has a common current source 14. The example from Figure 3 shows an RGB LED with three individual semiconductor light sources 16 in the form of LED chips for emitting red, green, and blue light. The color of the light emitted by the RGB LED results from a superposition or optical color mixing of the red, green, and blue light emitted by the individual LED chips 16.

[0042] The present invention is based on the idea of ​​using a configurable current sink 30 instead of a parallel semiconductor switch 20 controlled by a PWM signal, in order to dispense with a control signal 22 or a control signal 26. In the case of a fixed configuration of the current sinks 30, this eliminates the need for the control circuit for generating a control signal, in particular a PWM signal. Various known or novel circuits can be used to implement the current sink 30. The aim of the invention is to operate several semiconductor light sources 16 in series (fed from a common current source 14) with a constant, yet different, current I LED , without the need for a constantly applied control signal, in particular a PWM signal.

[0043] Figure 4shows a simplified schematic representation of a semiconductor light source 16 of a circuit arrangement 10 according to the invention with a bypass circuit 18 connected in parallel to the semiconductor light source 16 and a current sink 30 arranged therein. The current sink 30 can be configured, for example, by equipping the bypass circuit 18 with corresponding electrical and / or electronic components. Depending on the selected and installed components of the circuit arrangement 10 for the current sink 30, the portion I BP of the total current I flowing in the bypass circuit 18 and thus also the current I LED flowing via the corresponding semiconductor light source 16 are permanently adjusted without the need for a control signal or without a control signal having to be constantly present.

[0044] In Figure 51 shows an example of a specific implementation of the series circuit 12 or the current sink 30. The bypass circuit 18 comprises a series circuit of a voltage regulator 32 and a nonreactive resistor 34. The voltage regulator 32 has an input terminal V in , an output terminal V out and a voltage regulator terminal Adj. The input V in is connected to the anode A of the semiconductor light source 16, and the output V out is connected to a first contact of the nonreactive resistor 34. The second contact of the nonreactive resistor 34 is connected to the cathode K of the semiconductor light source 16. The voltage regulator terminal Adj is also connected to the cathode K. The voltage regulator 32 is designed to regulate a voltage U between the output V out and the voltage regulator terminal Adj to a predefinable value, e.g. 1.25 V. The nonreactive resistor 34 serves as a reference resistor by means of which the current sink 30 can be configured.The regulated voltage U of the voltage regulator 32 is applied to the reference resistor 34. A current I BP = regulated voltage U / resistance value R ref , e.g. I BP = 1.25 V / R ref [Ω], flows through the reference resistor 34 and thus through the bypass circuit 18. This current component I BP therefore does not flow via the semiconductor light source 16 and leads to a corresponding dimming of the semiconductor light source 16. The degree of dimming is permanently configured by the choice of the electrical or electronic components, in particular the voltage regulator 32 and the reference resistor 34. For a given reference voltage U, it is defined in particular by the reference resistor 34 and is maintained over an extended period even without a control signal, since the circuit of the current sink 30 is self-regulating.

[0045] The voltage regulator 32 can be, for example, an LM317 from National Semiconductor Corp., which is suitable for currents up to 1.5 A. For higher currents, a voltage regulator such as an LM150 (up to 3 A) or LM338 (up to 5 A) can be used. Of course, other voltage regulators 32 can also be used.

[0046] According to the example from Figure 6 , which is not part of the invention, the current sink 30 comprises an adjustable transistor 36, preferably in the form of a power transistor, which is arranged in the bypass circuit 18 with collector terminal C and emitter terminal E. The transistor 36 is preferably of the npn type. Preferably, the collector terminal C of the transistor 36 is connected to the anode A of the semiconductor light source 16, and the emitter terminal E of the transistor 36 is connected at least indirectly to the cathode K of the semiconductor light source 16.

[0047] It is conceivable that the current sink 30 comprises a first ohmic resistor 38 in the bypass circuit 18, in particular between the emitter terminal E of the transistor 36 and the cathode K of the semiconductor light source 16. The first ohmic resistor 38 preferably serves as a reference resistor by which the current sink 30 can be configured, i.e., by which the collector-emitter current I BP can be adjusted by the bypass circuit 18. Alternatively or additionally, a corresponding resistor could also be arranged between the collector terminal C of the transistor 36 and the anode A of the semiconductor light source 16.

[0048] The current sink 30 may include an element 40 for specifying a static reference voltage V ref applied to the first ohmic resistor 38, by which the collector-emitter current I BP of the transistor 36 can be adjusted by the bypass circuit 18. Preferably, the element 40 for specifying the static reference voltage V ref comprises an adjustable shunt regulator.

[0049] A second ohmic resistor 42 can be arranged in series with the shunt regulator 40, which is connected on the one hand to a cathode terminal K of the regulator 40 and on the other hand to the anode A of the semiconductor light source 16 or the collector terminal C of the transistor 36. Preferably, a base terminal B of the transistor 36 is then connected between the cathode terminal K of the shunt regulator 40 and a first connection contact of the second ohmic resistor 42, a collector terminal C of the transistor 36 is connected to a second connection contact of the second ohmic resistor 42, an emitter terminal E of the transistor 36 is connected to the reference terminal V ref of the shunt regulator 40 and to a first connection contact of the first ohmic resistor 38, and an anode terminal A of the shunt regulator 40 is connected to a second connection contact of the first ohmic resistor 38. The shunt regulator 40 provides a regulated reference voltage V ref , e.g.any value between 2.5 V and 36 V, with high precision and keeps it constant. The voltage V ref is applied to the first resistor 38, which serves as a reference resistor, and sets a defined resulting collector-emitter current I BP in the bypass circuit 18. The current I BP results from the regulated voltage V ref / resistance value R ref, e.g. I CE = 2.5 V / R ref [Ω]. This current component I BP therefore does not flow via the semiconductor light source 16 and causes a corresponding dimming of the semiconductor light source 16. The degree of dimming is predetermined by the choice of the electrical or electronic components, in particular by the shunt regulator 40 or the reference voltage V ref predetermined by it and the reference resistor 38. With a predetermined shunt regulator 40 orWith the reference voltage V ref specified by this, the degree of dimming is defined in particular by the resistance value of the reference resistor 38 and is maintained over a longer period of time even without a control signal, since the circuit of the current sink 30 is self-regulating.

[0050] The adjustable shunt regulator 40 can be, for example, a TL431 or TL432 from Texas Instruments Inc., or one of its many variants (e.g., TLVH431, LMV431). Likewise, another adjustable shunt regulator from a different manufacturer can be used (e.g., LT1004 from Analog Devices Inc., TS431 from Taiwan Semiconductor Manufacturing Company, Ltd., TL431 from NXP Semiconductors NV, now nexperia BV).

[0051] The shunt regulator 40 of type TL431 from Texas Instruments is ideally suited as a current sink 30. To calculate the resistance value R ref of the reference resistor 38 for a desired current I BP, the following applies: R ref = V ref I BP . Since the voltage V ref = 2.5 V, the following applies: R ref = 2.5 / I BP . The second resistor 42 must be dimensioned such that sufficient current IB is available for the base terminal B of the transistor 36 and for the shunt regulator 40. The current IB for the transistor 36 can be estimated as IB / β, where β is a current gain factor of the transistor 36. The shunt regulator 40 operates in principle like an adjustable Zener or Z-diode. Using a voltage divider at the reference input, the output voltage V ref can be continuously adjusted between approximately 2.5 V and 36 V.

[0052] Following the example of Figure 7, which is not part of the invention, the current sink 30 or the current I BP flowing through the bypass circuit 18 can be adjusted not only via the installed electrical and / or electronic components, but also via the specification of a corresponding control signal, in particular an externally adjustable reference voltage REF in . For this purpose, the current sink 30 has a circuit for adjusting the collector-emitter current I BP. The circuit can control the transistor 36 so that it switches on or off, and can use a variable reference voltage to adjust the collector-emitter current I BP that flows through the bypass circuit 18 when the transistor 36 switches on. The adjustment of the collector-emitter current I BP and thus also the dimming of the corresponding semiconductor light source 16 takes place here for a longer period of time even without a constantly applied control signal, in particular without a PWM signal.

[0053] The circuit for adjusting the collector-emitter current I BP is designed to adjust the collector-emitter current I BP between 0% and 100% of the total current I supplied by the current source 14. The circuit for adjusting the collector-emitter current I BP comprises, for example, an operational amplifier 44, whose output voltage applied to its output V out or a voltage proportional thereto is applied to the base terminal B of the transistor 36. An input voltage of the operational amplifier 44 is given by a difference between the reference voltage REF in and a voltage HI_LO of a digital signal, which represents a switching on (low level of the digital signal) or blocking (high level of the digital signal) of the transistor 36. The reference voltage is preferably applied to the non-inverting input '+' of the operational amplifier 44 and the voltage of the digital signal HI_LO is applied to the inverting input '-' of the operational amplifier 44.An operating voltage is applied to terminals +Ub and -Ub of the operational amplifier 44.

[0054] The digital signal HI_LO can also be omitted, in which case the inverting input '-' of the operational amplifier 44 must then be permanently at the low level, so that the transistor 36 switches on and the current I BP flowing through the bypass circuit 18 can be adjusted in analog form using the applied reference voltage REF in. The reference voltage REF in is preferably proportional to the collector-emitter current I BP in the bypass circuit 18. Whether or not the set current I BP actually flows through the bypass circuit 18 is determined by the level applied to the inverting input '-' of the operational amplifier 44. The output voltage V out of the operational amplifier 44 and thus ultimately the collector-emitter current I BP in the bypass circuit 18 can be adjusted over the long term using the reference voltage REF in.The magnitude of the set current I BP can also depend on other electrical components of the circuit for adjusting the collector-emitter current I BP . These additional components include, for example, a first resistor 46 (for level adjustment) between the output V out of the operational amplifier 44 and the base terminal B of the transistor 36, a second resistor 48 between the emitter terminal E of the transistor 36 and the inverting input "-" of the operational amplifier 44, and / or a capacitor 50 between the output V out and the inverting input "-" of the operational amplifier 44. The circuit for adjusting the collector-emitter current I BP operates like a linear current regulator with an operational amplifier. A constantly applied control signal, in particular a PWM signal, is not required.

[0055] Coming back to the Figure 3In the embodiment of the circuit arrangement 10 according to the invention shown, the series circuit 12 of the semiconductor light sources 16 comprises a first semiconductor light source 16.1 emitting red light, a second semiconductor light source 16.2 emitting green light, and a third semiconductor light source 16.3 emitting blue light, wherein two of the semiconductor light sources 16 can each be bridged by a bypass circuit 18 connected in parallel to the corresponding semiconductor light source 16 and having a current sink 30 arranged therein. The red, green, and blue semiconductor light sources 16.1, 16.2, 16.3 can be part of an RGB light-emitting diode (LED). The light emitted by the individual semiconductor light sources 16.1, 16.2, 16.3 is superimposed to form the light of a specific color emitted by the RGB LED. The color of the light is determined by the brightness of the individual semiconductor light sources 16.1, 16.2, 16.3.One or more RGB LEDs can, in turn, be part of a motor vehicle light that emits light of a specific color for a specific lighting function (e.g., daytime running light, reversing light, indicator light, side marker light, tail light, brake light, rear fog light). By operating the individual red, green, and blue semiconductor light sources 16.1, 16.2, 16.3 with specified (possibly different) operating currents, different brightnesses of the semiconductor light sources 16.1, 16.2, 16.3 and thus a specific color of the light emitted by the RGB LED can be set.

[0056] In the example of Figure 3A bypass circuit 18 with a current sink 30 is connected in parallel to the green semiconductor light source 16.2 and to the blue semiconductor light source 16.3. The aim of the invention is to operate a plurality of semiconductor light sources 16 in series (supplied from a common current source 14) with a constant, but different, current I LED (or in this example I red , I green and I blue ) so that the RGB LED emits light of a desired color. The current source 14 must therefore supply at least the maximum current of a semiconductor light source 16 (here I ≥ I red ). If the current source 14 supplies the maximum current I = I red of the red semiconductor light source 16, a bypass circuit 18 can be dispensed with for the red semiconductor light source 16.1 (cf. Figure 3). However, if the current source 14 supplies a current I that is greater than the operating current I red of the red semiconductor light source 16.1 (I > I red ), a bypass circuit 18 with a current sink 30 arranged therein must also be provided for the red semiconductor light source 16.1.

[0057] For the green and blue semiconductor light sources 16.2, 16.3 with a lower operating current (I green < I and I blue < I) compared to the current I of the current source 14, the current I LED through the semiconductor light sources 16 must be reduced to the respective operating current I green , I blue via the parallel current sink 30. For this purpose, the current sinks 30 are adjusted such that a current component I SP1 or I BP2 of the total current I flows via the bypass circuit 18 into the current sink 30. This results in the following: I red = I , I green = I − I BP 1 , and I blue = I − I BP 2 .

[0058] A numerical example shows the following: I red = I = 30 mA , I green = I − I BP 1 = 30 mA − 20 mA = 10 mA , and I blue = I − I BP 2 = 30 mA − 12 mA = 18 mA .

[0059] The current sinks 30, which are connected in parallel to the green and blue semiconductor light sources 16.2, 16.3, respectively, must therefore be adjusted to draw 20 mA and 12 mA, respectively. The current I SP1 and I SP2 flowing through the bypass circuits 18 is adjusted by designing the respective current sink 30 according to one of the previously described examples or by another suitable design of the current sink 30.

[0060] Returning to the example of Figure 2It is proposed that the series circuit 12 of the semiconductor light sources 16 comprises a first group of semiconductor light sources 16 for generating a first light function (e.g. the semiconductor light sources 16.1 and 16.2) and a second group of semiconductor light sources 16 for generating a second light function (e.g. the semiconductor light source(s) 16.m), wherein at least the semiconductor light sources 16 of one of the groups can each be bridged by a bypass circuit 18 connected in parallel to the corresponding semiconductor light source 16 and having a current sink 30 arranged therein. The groups can each comprise one or more semiconductor light sources 16. In the example of Figure 2 The semiconductor light sources 16 of both groups are each bridged by a parallel bypass circuit 18 with a current sink 30 arranged therein. However, it would be conceivable to bridge only the semiconductor light sources 16 of one of the groups.

[0061] The first group of semiconductor light sources 16.1, 16.2 serves, for example, to generate a white daytime running light, and the second group of semiconductor light sources 16.m serves, for example, to generate a yellow / orange flashing light. The semiconductor light sources 16.m of one of the groups have a lower operating current than the semiconductor light sources 16.1, 16.2 of the other group. For example, the semiconductor light sources 16.m for generating the flashing light can have a lower operating current than the semiconductor light sources 16.1, 16.2 for generating the daytime running light. The current I supplied by the current source 14 and flowing through the series circuit 12 preferably corresponds to the higher operating current of the semiconductor light sources 16.1, 16.2 for generating the daytime running light, so that a bypass circuit 18 with a current sink 30 arranged therein could be dispensed with in these semiconductor light sources 16.1, 16.2.In the example shown, all semiconductor light sources 16 of the series circuit 12 each have a parallel-connected bypass circuit 18 with a current sink 30 arranged therein. This is useful, for example, if the current source 14 supplies a current I that is greater than the operating current I LED of all semiconductor light sources 16.

[0062] During operation of the semiconductor light sources 16 from Figure 2the current sinks 30 are set such that a current I BP flows through the bypass circuits 18, resulting in a current corresponding to the operating current I LED flowing through the semiconductor light sources 16. The operating current I LED1 , I LED2 of the semiconductor light sources 16.1, 16.2 of the first group is greater than the operating current I LEDm of the semiconductor light source(s) 16.m of the second group. This means that the current sinks 30 are set such that the current I BP1 , I BP2 flowing through the bypass circuits 18 of the first group of semiconductor light sources 16.1, 16.2 is greater than the current I BPm flowing through the bypass circuit(s) 18 of the second group of semiconductor light sources 16.m.

Claims

1. Circuit arrangement (10) of a lighting device (101), preferably of a motor vehicle, the circuit arrangement (10) comprising at least two semiconductor light sources (16) connected in series and connected to a common current source (14) and comprising at least one bypass circuit (18), a bypass circuit (18) of the at least one bypass circuit (18) being connected in parallel to at least one semiconductor light source (16) of the at least two semiconductor light sources (16) connected in series, by means of which bypass circuit the at least one semiconductor light source (16) can be bridged, in each of the at least one bypass circuit (18) a configurable current sink (30) being arranged, which is designed to receive a current component (IBP) of a current (I) generated by the current source (14), so that an operating current (ILED) flows through the at least one semiconductor light source (16), to which the bypass circuit (18) is connected in parallel, which operating current is lower than the current (I) generated by the current source (14), characterized in that the configurable current sink (30) is configurable by selecting and equipping the relevant bypass circuit (18) with a relevant voltage regulator (32) and a relevant ohmic resistor (34), so that the current component (IBP) flowing through the bypass circuit (18) is permanently set without the need for a control signal, and the configurable current sink (30) comprises a series circuit of the voltage regulator (32) and the ohmic resistor (34), the voltage regulator (32) being designed to regulate a voltage (U) applied across the ohmic resistor (34) in such a way that the current component (IBP) flowing through the bypass circuit (18) results from the applied voltage (U) divided by a resistance value of the ohmic resistor (34), an input terminal (Vin) of the voltage regulator (32) being connected to an anode (A) of the at least one semiconductor light source (16), an output terminal (Vout) of the voltage regulator (32) being applied to a first contact of the ohmic resistor (34) and a voltage regulator terminal (Adj) of the voltage regulator (32) being applied to a second contact of the ohmic resistor (34) which is connected to a cathode (K) of the at least one semiconductor light source (16).

2. Circuit arrangement (10) according to claim 1, characterized in that the at least two semiconductor light sources (16) connected in series comprise a first semiconductor light source (16.1) emitting red light, a second semiconductor light source (16.2) emitting green light, and a third semiconductor light source (16.3) emitting blue light, and a bypass circuit (18) of the at least one bypass circuit (18) is connected in parallel to at least two of the first, second, and third semiconductor light sources (16).

3. Circuit arrangement (10) according to claim 1, characterized in that the at least two semiconductor light sources (16) connected in series comprise a first group of semiconductor light sources (16.1, 16.2) for generating a first light function and a second group of semiconductor light sources (16.m) for generating a second light function, and a relevant bypass circuit (18) of the at least one bypass circuit (18) is connected in parallel to at least one group of the first group of semiconductor light sources (16.1, 16.2).

4. Lighting device (101) of a motor vehicle, wherein the lighting device (101) has a housing (102) having a light exit opening formed in the housing (102) and closed by a cover plate (104) and a circuit arrangement (10) according to any of the preceding claims, wherein the lighting device (101) is designed such that the light emitted by the semiconductor light sources (16) passes through the cover plate (104), optionally with the cooperation of optical elements of the lighting device (101), for generating at least one light function of the lighting device (101).