Short-circuit fault detection lighting device for a motor vehicle headlight

Description

[0001] The invention relates to a short-circuit fault-detecting lighting device for a motor vehicle headlight, comprising a voltage input and a terminal for connection to ground potential, and a power train supplied via the voltage input, which power train comprises a number of light sources to be monitored, wherein the light sources are configured to emit the light of the lighting device and the light sources are connected in series with one another within the power train.

[0002] Until now, it has been common practice in the automotive industry to only test lighting devices intended for headlights for a specific type of failure, namely that in which the failure of one or more light sources results in an interruption of the electrical connection that can normally be made by the light source. It is generally known that, for example, incandescent lamps, halogen lamps, xenon lamps and also semiconductor components such as LEDs typically become non-conductive in the event of a failure, i.e. that no current is conducted via the light source. If several light sources are connected in series and one of the light sources fails, this results in the light source becoming non-conductive, which in turn causes the entire light source chain to fail and thus also puts functioning, series-connected light sources out of operation.

[0003] However, a second type of fault can also occur: a light source failure resulting in a short circuit. This type of fault was rare in the past, which is why the automotive industry has not implemented any special measures to detect light source short circuits. Until now, only the aforementioned type of fault has been tested, by inferring the functionality of a lighting device based on the loss of current (due to the failure-related electrical non-conduction of the light source).

[0004] US 2018 / 0049301 A1 relates to a device for detecting LED failures. US 10,178,734 B1 relates to an LED lighting circuit for detecting individual LED faults. DE 10 2008 008 217 A1 relates to a circuit arrangement for detecting a short circuit in LEDs. AT 515546 B1 relates to an LED arrangement with a monitoring circuit for short-circuit monitoring.

[0005] It has been found that the use of modern light sources is increasingly associated with errors of the second type, i.e., short-circuit faults. In these cases, the light source affected by the short circuit generally ceases to emit light. However, the other light sources arranged upstream or downstream in series can continue to be supplied with power. Such failures adversely alter the light pattern emitted by the lighting device. One object of the invention is therefore to create a lighting device that is as reliable as possible, which allows the operation of the lighting device to be monitored and measures such as error routines to be initiated.

[0006] This object is achieved with a lighting device of the type mentioned at the outset, which according to the invention has an auxiliary branch with transistors arranged therein and connected in series with one another, wherein each light source of the power branch is assigned one of the transistors, and thus a monitoring pair is formed, consisting of a light source to be monitored and a transistor assigned to the monitoring, wherein each transistor is coupled to the cathode and anode of the light source in such a way that the voltage drop across the light source during normal operation is used to switch the transistor on, and in the event of a short circuit in the light source, the voltage drop caused by the short circuit leads to the transistor and thus the auxiliary branch being blocked, wherein an error detection device coupled to the auxiliary branch is provided, which is designed toIn case of blocking of the auxiliary line, to issue an error signal and / or to trigger an error routine.

[0007] Therefore, if a light source in a light source string is short-circuited due to a fault, only the string voltage will decrease if the power source is supplied via a current source. However, monitoring using transistors can detect the short-circuit fault and, if necessary, report it back despite continued operation (thus avoiding a total failure or shutdown of the power string). The light sources can be LED light sources, for example. The expression "for connection to ground potential" does not mean that the respective connection must necessarily be connected to ground potential. It is clear to the specialist that only a corresponding voltage difference between the voltage input and the connection for connection to ground is required to electrically operate the lighting device. The reference potentials themselves are fundamentally irrelevant.This means the connection does not have to be grounded, but rather it should be possible to connect to ground. The number of light sources is at least 2, 3, or 4, for example, but can also be significantly higher and can be determined by the specialist depending on the specific application.

[0008] According to the invention, the error detection device is designed to carry out an error routine in which the operation of the light sources is automatically switched off in the event of an error being detected. For this purpose, both the power train and the auxiliary train extend between the voltage input and the ground connection, and the error detection device is designed as a main switch which is arranged in series with the power train and is coupled to the auxiliary train in such a way that when the auxiliary train is switched on, the main switch is electrically conductive and when the auxiliary train is blocked, it is electrically blocked. In this way, for example,It can be prevented that a strong reduction in the light intensity of the lighting device, caused by the failure of several light sources in the power train due to a short circuit in one light source, goes unnoticed and thus even falls below the legal minimum requirement for the lighting device, which also entails an increased risk to all road users.

[0009] Furthermore, it can be provided that the transistors of the auxiliary branch are designed as npn bipolar transistors, wherein an ohmic resistor is connected in series between the transistors and the coupling between the light source and the transistor in each monitoring pair is achieved by connecting the anode of the light source to the base of the transistor and the cathode of the light source to the emitter of the transistor, wherein those connections which emanate from connection points located between light sources are each provided with a diode which determines the power flow between the power branch and the auxiliary branch, wherein the flow direction of the diodes is connected towards the auxiliary branch in the form of the transistor of the respective monitoring pair, wherein the main switch is designed as a normally-off p-channel MOSFET which is connected on the source side to the voltage input,The drain side is electrically connected to the power string and the gate side is electrically connected to a voltage input-side end of the auxiliary string. This creates a reliable and cost-effective short-circuit fault-detecting lighting device. In a further development, it can be provided that the voltage input-side end of the auxiliary string is connected to the voltage input via an ohmic auxiliary resistor, and a ground-side end of the auxiliary string is connected to the ground connection. A node is formed between the auxiliary string and the ohmic auxiliary resistor, which is connected to the gate of the main switch in such a way that, if the auxiliary string is blocked, the potential of the node is changed such that the main switch is blocked, and if the auxiliary string is conductive, the potential of the node is changed such that the main switch is conductive.

[0010] Alternatively, the transistors of the auxiliary branch can be designed as normally-off MOSFET transistors. In a further development, the transistors of the auxiliary branch can be designed as normally-off n-channel MOSFETs, with an ohmic resistor connected in series between each transistor, and the coupling between the light source and the transistor for each monitoring pair being established by directly connecting the anode of the light source to the gate of the transistor and the cathode of the light source to the drain of the transistor. The cathode connections emanating from connection points located between light sources are each provided with a diode that determines the power flow between the power branch and the auxiliary branch, with the flow direction of the diodes being connected toward the auxiliary branch in the form of the transistor of the respective monitoring pair.wherein the main switch is designed as a normally-off p-channel MOSFET, which is electrically connected on the source side to the voltage input, on the drain side to the power string, and on the gate side to a voltage input-side end of the auxiliary string.

[0011] Furthermore, it can be provided that the voltage input-side end of the auxiliary branch is connected to the voltage input via an ohmic auxiliary resistor and a ground-side end of the auxiliary branch is connected to the ground connection, wherein a node is formed between the auxiliary branch and the ohmic auxiliary resistor, which node is connected to the gate of the main switch in such a way that in the event of the auxiliary branch being blocked, the potential of the node is changed such that the main switch is blocked and in the event of the auxiliary branch being conductive, the potential of the node is changed such that the main switch is conductive.

[0012] Alternatively, it can be provided that the transistors of the auxiliary branch are designed as normally-off p-channel MOSFETs, wherein an ohmic resistor is connected in series between the transistors and the coupling between the light source and the transistor in each monitoring pair is achieved by connecting the anode of the light source to the source of the transistor and the cathode of the light source to the gate of the transistor, wherein those anode connections which emanate from connection points located between light sources are each provided with a diode which determines the power flow between the power branch and the auxiliary branch, wherein the flow direction of the diodes is switched in the direction of the power branch for this purpose, wherein the main switch is designed as a normally-off n-channel MOSFET which is connected on the source side to the ground connection,It is electrically connected on the drain side to the power string and on the gate side to a ground connection-side end of the auxiliary string. The term "anode connections" refers to those connections that lead from the anode of the respective light source to the respective transistor. In a further development, it can be provided that the ground connection-side end of the auxiliary string is connected to the ground connection via an ohmic auxiliary resistor, and a voltage input-side end of the auxiliary string is directly connected to the voltage input. A node is formed between the auxiliary string and the ohmic auxiliary resistor, which is connected to the gate of the main switch in such a way that, if the auxiliary string is blocked, the potential of the node is changed such that the main switch is blocked, and if the auxiliary string is conductive, the potential of the node is changed such that the main switch is conductive.

[0013] Furthermore, the invention relates to a vehicle headlight comprising a lighting device according to the invention.

[0014] The invention is explained in more detail below with reference to an exemplary and non-limiting embodiment, which is illustrated in the figures. Figure 1 a schematic representation of a first embodiment of the invention, Figure 2 a schematic representation of a second embodiment of the invention, Figure 3 a schematic representation of an embodiment not according to the invention, Figure 4 a schematic representation of an embodiment not according to the invention, Figure 5 a schematic representation of a fifth embodiment of the invention, and Figure 6 a schematic representation of a sixth embodiment of the invention.

[0015] In the following figures, unless otherwise stated, the same reference symbols denote the same features.

[0016] Figures 1 to 6 show a short-circuit fault-detecting lighting device 1 for a motor vehicle headlight, comprising a voltage input SE and a terminal ME for connection to ground potential. The lighting device 1 further comprises a power train LS supplied via the voltage input SE, which power train LS comprises a number of light sources 2 to be monitored. The light sources 2 are configured to emit the light of the lighting device 1, and the light sources 2 are connected in series with one another within the power train LS.

[0017] The lighting device 1 further comprises an auxiliary branch HS with transistors 3 arranged therein and connected in series. Each light source 2 of the power branch LS is assigned one of the transistors 3. This forms a monitoring pair P1, P2, P3, or P4, respectively, which consists of a light source 2 to be monitored and a transistor 3 assigned to monitor the same. For clarity, only the light source and the transistor of the first monitoring pair P1 are provided with a reference symbol.

[0018] In each monitoring pair, transistor 3 is coupled to the cathode and anode of the associated light source 2 in such a way that the voltage drop across light source 2 during normal operation is used to turn on transistor 3. In the event of a short circuit in light source 2, however, the voltage drop caused by the short circuit is used to block transistor 3 and thus interrupt the current flow of the auxiliary branch HS. In addition, a fault detection device 6 is provided which is coupled to the auxiliary branch HS and is designed to generate a fault signal SF (see Fig. 3 and 4 ) or to trigger an error routine FR (see remaining figures).

[0019] The embodiments according to Figures 1 , 2 , 5 and 6have in common that the error detection device 6 is set up to carry out an error routine FR, in which the operation of the light sources 2 is automatically switched off in the event of an error being detected. For this purpose, it is provided that both the power line LS and the auxiliary line HS extend between the voltage input SE and the ground connection ME and the error detection device 6 is designed as a main switch 4. This main switch 4 is arranged in series with the power line LS and coupled to the auxiliary line HS in such a way that when the auxiliary line HS is switched on, the main switch 4 is electrically conductive and when the auxiliary line HS is blocked, it is electrically blocked.

[0020] In the embodiments according to Fig. 5 and 6It is also provided that the transistors 3 of the auxiliary branch HS are designed as npn bipolar transistors. An ohmic resistor is connected in series between each transistor 3. For each monitoring pair P1, P2, P3 or P4, the coupling between light source 2 and transistor 3 is achieved by connecting the anode of light source 2 to the base of transistor 3 and the cathode of light source 2 to the emitter of transistor 3. Those connections which originate from connection points P located between light sources 2 are each provided with a diode 7 which determines the power flow between the power branch LS and the auxiliary branch HS. This means that the forward direction of diode 7 is selected such that the power flow in one direction is correspondingly determined.For this purpose, the forward direction of diodes 7 is oriented toward the auxiliary branch HS, namely toward transistors 3 of the respective monitoring pair P1, P2, P3, P4. The main switch 4 is designed as a normally-off p-channel MOSFET, which is electrically connected on the source side (S4) to the voltage input SE, on the drain side (D4) to the power branch LS, and on the gate side (G4) to a voltage input-side end of the auxiliary branch HS. Figure 6 differs from Figure 5 by using so-called double diodes 7', which are available at particularly low cost.

[0021] Furthermore, in the embodiment according to Figures 5 and 6provided that the voltage input-side end of the auxiliary branch HS is connected to the voltage input SE via an ohmic auxiliary resistor 5 and a ground-side end of the auxiliary branch HS is connected to the ground connection ME, wherein a node K is formed between the auxiliary branch HS and the ohmic auxiliary resistor 5, which node K is connected to the gate G4 of the main switch 4 in such a way that if the auxiliary branch HS is blocked, the potential of the node K is changed such that the main switch 4 is blocked and if the auxiliary branch HS is conductive, the potential of the node K is changed such that the main switch 4 is conductive.

[0022] The embodiments according to Figures 1 to 4 have in common that the transistors 3 of the auxiliary branch HS are designed as self-blocking MOSFET transistors.

[0023] In the embodiment according to Figure 1the transistors 3 of the auxiliary branch HS are designed as normally-off n-channel MOSFETs, wherein an ohmic resistor 8 is connected in series between the transistors 3, and for each monitoring pair P1, P2, P3, P4 the coupling between light source 2 and transistor 3 is effected by the anode of light source 2 being directly connected to the gate of transistor 3 and the cathode of light source 2 being connected to the drain of transistor 3, wherein those cathode connections which emanate from connection points P located between light sources 2 are each provided with a diode which determines the power flow between power branch LS and auxiliary branch HS, wherein the flow direction of the diodes is connected in the direction of the auxiliary branch HS in the form of transistor 3 of the respective monitoring pair P1, P2, P, P4, wherein the main switch 4 is designed as a normally-off p-channel MOSFET which is connected on the source side to the voltage input SE,is electrically connected on the drain side to the power string LS and on the gate side to a voltage input end of the auxiliary string HS. In detail, in the embodiment according to , Fig. 1It can be provided that the voltage input-side end of the auxiliary branch HS is connected to the voltage input SE via an ohmic auxiliary resistor 5 and a ground-side end of the auxiliary branch HS is connected to the ground connection ME, wherein a node K is formed between the auxiliary branch HS and the ohmic auxiliary resistor 5, which node K is connected to the gate G4 of the main switch 4 in such a way that if the auxiliary branch HS is blocked, the potential of the node K is changed such that the main switch 4 is blocked and if the auxiliary branch HS is conductive, the potential of the node K is changed such that the main switch 4 is conductive. In this way, the power branch LS is automatically switched off as soon as a short circuit in a light source 2 occurs.

[0024] In Fig. 2the transistors 3 of the auxiliary branch HS are designed as normally-off p-channel MOSFETs, wherein an ohmic resistor is connected in series between the transistors 3 and for each monitoring pair P1, P2, P3, P4 the coupling between light source 2 and transistor 3 is effected by the anode of light source 2 being connected to the source of transistor 3 and the cathode of light source 2 being connected to the gate of transistor 3, wherein those anode connections which emanate from connection points P located between light sources 2 are each provided with a diode which determines the power flow between power branch LS and auxiliary branch HS, wherein the flow direction of the diodes is switched in the direction of the power branch LS for this purpose, wherein the main switch 4 is designed as a normally-off n-channel MOSFET which is connected on the source side to the ground connection ME,is electrically connected on the drain side to the power string LS and on the gate side to a ground connection-side end of the auxiliary string HS. In detail, it can be provided that the ground connection-side end of the auxiliary string HS is connected to the ground connection ME via an ohmic auxiliary resistor 5, and a voltage input-side end of the auxiliary string HS is directly connected to the voltage input SE, wherein a node K is formed between the auxiliary string HS and the ohmic auxiliary resistor 5, which is connected to the gate G4 of the main switch 4 in such a way that, if the auxiliary string HS is blocked, the potential of the node K is changed such that the main switch 4 is blocked, and if the auxiliary string HS is conductive, the potential of the node K is changed such that the main switch 4 is conductive.

[0025] The embodiments according to Fig. 3 and 4have in common that the transistors 3 of the auxiliary branch HS are designed as normally-off p-channel MOSFETs, with an ohmic resistor being connected in series between each transistor 3, and with each monitoring pair the coupling between light source 2 and transistor 3 is achieved by connecting the anode of light source 2 to the source of transistor 3 and the cathode of light source 2 to the gate of transistor 3, with those anode connections which originate from connection points P located between light sources 2 each being provided with a diode which determines the power flow between power branch LS and auxiliary branch HS, with the flow direction of the diodes being switched in the direction of the power branch LS,wherein a ground connection-side end of the auxiliary branch HS is connected to the ground connection ME via an ohmic auxiliary resistor 5, and a voltage input-side end of the auxiliary branch HS is directly connected to the voltage input SE, wherein a node K is formed between the auxiliary branch HS and the ohmic auxiliary resistor 5, and the fault detection device 6 is electrically connected to this node K and thus detects a potential change of the node K caused by blocking or conducting the auxiliary branch HS and outputs an error signal as a function thereof.

[0026] In the embodiment according to Figure 3It is also provided that the error detection device comprises an auxiliary transistor 10, which is switched on depending on the potential of the node, wherein the auxiliary transistor 10 is connected to an electrical control unit (ECU) via a temperature-dependent resistor 9, wherein the electrical control unit (ECU) detects the switching state of the auxiliary transistor 10 and outputs an error signal depending thereon. The temperature-dependent resistor 9 can, for example, originate from an existing lighting device monitoring system, e.g., a temperature monitoring system. For example, it is common practice to attach the light sources 2 to a heat sink and to detect the temperature of the heat sink via a temperature-dependent resistor 9 connected to an ECU. The current can be controlled depending on the measured temperature. For example,It should be provided that from a temperature of 110°C, the actual current is reduced compared to the nominal current and, for example, at a temperature of 130°C, only reaches half the nominal current in order to prevent or at least slow down further heating. Such a temperature monitoring device can be part of the present lighting device and thus combined with short-circuit detection by using the temperature-dependent resistor and the ECU already provided for temperature monitoring. If a short circuit is detected, the auxiliary transistor 10 switches off and ensures that the temperature-dependent resistor (e.g. in the form of an NTC) provided for temperature measurement, for example of a circuit board or a heat sink, is used for a second purpose beyond temperature measurement – ​​namely, switched to "open load" – which can trigger error routines in the downstream ECU.

[0027] In Fig. 4 It is provided that the error detection device 6 comprises an auxiliary transistor 10 which is switched on as a function of the potential of the node K, wherein the switching state of the auxiliary transistor 10 is used to output a binary error signal.

[0028] The invention further relates to a vehicle headlight not shown in the figures.

[0029] The invention is not limited to the embodiments shown, but is defined by the entire scope of the claims. Individual aspects of the invention or the embodiments may also be taken up and combined with one another. Any reference symbols in the claims are exemplary and serve only to facilitate the readability of the claims, without limiting them.

Claims

1. Short-circuit fault-detecting lighting device (1) for a motor vehicle headlight, comprising - a voltage input (SE) and a connector (ME) for connection to earth potential, - a power line (LS) which is supplied via the voltage input (SE) and comprises a number of light sources (2) to be monitored, this number being at least two, the light sources (2) being set up to emit the light of the lighting device (1) and the light sources (2) being connected in series with one another within the power line (LS), wherein the lighting device (1) further comprises - has an auxiliary line (HS) with transistors (3) arranged therein and connected in series with one another, one of the transistors (3) being assigned to each light source (2) of the power line (LS), and thus a monitoring pair (P1, P2, P3, P4), consisting of a light source (2) to be monitored and a transistor (3) assigned for monitoring, each transistor (3) being coupled to the cathode and anode of the light source (2) in such a way that the voltage dropping across the light source (2) during normal operation is used for this purpose, the transistor (3) is switched through, and in the event of a short circuit of the light source (2), the voltage dip caused by the short circuit leads to a blocking of the transistor (3) and thus of the auxiliary line (HS), the short-circuit fault-detecting lighting device (1) furthermore having a fault detection device (6) which is coupled to the auxiliary line (HS) and is set up to output a fault signal (SF) or to trigger a fault routine (FR) in the event of the auxiliary line being blocked, characterized in that the fault detection device (6) is set up for carrying out a fault routine (FR) in which the operation of the light sources (2) is switched off automatically in the event of a fault being detected, it being provided for this purpose that both the power line (LS) and the auxiliary line (HS) extend between the voltage input (SE) and the connector (ME) and the fault detection device (6) is designed as a main switch (4) which is arranged in series with the power line (LS) and is coupled to the auxiliary line (HS) in such a way that the main switch (4) conducts electrically when the auxiliary line (HS) is switched through and blocks electrically when the auxiliary line (HS) is blocked.

2. Lighting device (1) according to claim 1, wherein the transistors (3) of the auxiliary line (HS) are designed as npn bipolar transistors, wherein an ohmic resistor is connected in series between the transistors (3) in each case and for each monitoring pair (P1, P2, P3, P4), the coupling between light source (2) and transistor (3) is effected by the anode of the light source (2) being connected to the base of the transistor and the cathode of the light source (2) being connected to the emitter of the transistor (3), wherein those connections which originate from connection points (P) located between light sources (2), are each provided with a diode (7) which determines the power flow between the power line (LS) and the auxiliary line (HS), the flow direction of the diodes (7) being connected for this purpose in the direction of the auxiliary line in the form of the transistor (3) of the respective monitoring pair (P1, P2, P3, P4), wherein the main switch (4) is designed as a self-locking p-channel MOSFET which is electrically connected on the source side (S4) to the voltage input (SE), on the drain side (D4) to the power line (LS) and on the gate (G4) to a voltage input end of the auxiliary line (HS).

3. Lighting device (1) according to claim 2, wherein the voltage input-side end of the auxiliary line (HS) is connected to the voltage input via an ohmic auxiliary resistor (5) and a ground-side end of the auxiliary line is connected to the connector (ME), wherein a node (K) is formed between the auxiliary line (HS) and the ohmic auxiliary resistor (5), which is connected to the gate (G4) of the main switch (4) in such a way that when the auxiliary line (HS) is blocked, the potential of the node (K) is changed in such a way that the main switch (4) blocks and when the auxiliary line (HS) conducts, the potential of the node (K) is changed in such a way that the main switch (4) conducts.

4. Lighting device (1) according to claim 1, wherein the transistors (3) of the auxiliary line (HS) are designed as self-locking MOSFET transistors.

5. Lighting device (1) according to claim 4, wherein the transistors (3) of the auxiliary line (HS) are designed as self-locking n-channel MOSFETS, wherein an ohmic resistor (8) is connected in series between the transistors (3) in each case and, for each monitoring pair (P1, P2, P3, P4), the coupling between the light source (2) and the transistor (3) is effected by the anode of the light source (2) being directly connected to the gate of the transistor (3) and the cathode of the light source (2) being connected to the drain of the transistor (3), wherein those cathode connections which are made between light sources (2) and transistors (3) are connected in series, which emanate from connection points (P) located between light sources (2) are each provided with a diode defining the power flow between the power line (LS) and the auxiliary line (HS), the direction of flow of the diodes for this purpose being in the direction of the auxiliary line (HS) in the form of the transistor (3) of the respective monitoring pair (P1, P2, P, P4), the main switch (4) being designed as a self-locking p-channel MOSFET which is electrically connected on the source side to the voltage input (SE), on the drain side to the power string and on the gate side to a voltage input end of the auxiliary string.

6. Lighting device (1) according to claim 5, wherein the voltage input-side end of the auxiliary line (HS) is connected to the voltage input (SE) via an ohmic auxiliary resistor (5) and a ground-side end of the auxiliary line (HS) is connected to the connector (ME), wherein a node (K) is formed between the auxiliary line (HS) and the ohmic auxiliary resistor (5), which is connected to the gate (G4) of the main switch (4) in such a way that when the auxiliary line (HS) is blocked, the potential of the node (K) is changed in such a way that the main switch (4) blocks and when the auxiliary line (HS) conducts, the potential of the node (K) is changed in such a way that the main switch (4) conducts.

7. Lighting device (1) according to claim 4, wherein the transistors (3) of the auxiliary line (HS) are designed as self-locking p-channel MOSFETS, wherein an ohmic resistor is connected in series between the transistors (3) and the coupling between light source (2) and transistor (3) takes place for each monitoring pair, in that the anode of the light source (2) is connected to the source of the transistor (3) and the cathode of the light source (2) is connected to the gate of the transistor (3), wherein those anode connections which emanate from connection points (P) located between light sources (2) are each provided with a diode defining the power flow between the power line (LS) and the auxiliary line (HS), the direction of flow of the diodes being switched in the direction of the power line (LS) for this purpose, wherein the main switch (4) is designed as a self-locking n-channel MOSFET which is electrically connected on the source side to the connector (ME), on the drain side to the power line (LS) and on the gate side to an end of the auxiliary line (HS) on the earth connection side.

8. Lighting device (1) according to claim 7, wherein the end of the auxiliary line (HS) on the earth connection side is connected to the connector (ME) via an ohmic auxiliary resistor (5) and an end of the auxiliary line (HS) on the voltage input side is connected directly to the voltage input (SE), wherein a node (K) is formed between the auxiliary line (HS) and the ohmic auxiliary resistor (5), which is connected to the gate (G4) of the main switch (4) in such a way that, if the auxiliary line (HS) is blocked, the potential of the node (K) is changed in such a way that the main switch (4) blocks and, if the auxiliary line (HS) conducts, the potential of the node (K) is changed in such a way that the main switch (4) conducts.

9. Vehicle headlamp comprising a lighting device according to one of the preceding claims 1 to 8.