Supply circuit and method

Abstract

The invention relates to a supply circuit for lighting means in the automotive field, comprising a current path with at least two loads, in particular lighting means, which are connected to a controllable power source in series between a supply potential terminal and a reference potential terminal. A first control loop between the supply potential terminal and the reference potential terminal comprises a regulating input, to which a signal can be supplied that is derived from a voltage drop along the current path, wherein the first control loop is designed to output, on the basis of the aforementioned signal, a control signal to a control input of the controllable power source. A fault detection circuit with a detection input, which is connected to a first node between the at least two loads, comprises a fault signal output which is coupled to the regulating input of the first control loop. The fault detection circuit is designed to detect a fault, in particular a short-circuit which closes a current path, and generate a fault signal at the fault signal output in response thereto.

Description

[0001] SUPPLY CIRCUIT AND METHOD

[0002] This application claims priority from German patent application DE 10 2024 100 916 . 0 of January 12, 2024, the disclosure of which is hereby incorporated in its entirety by reference. The present invention relates to a power supply circuit, particularly for the automotive sector, and to a method for supplying a plurality of loads connected in series between a supply potential terminal and a reference potential terminal with a controllable current source.

[0003] BACKGROUND

[0004] In the automotive sector, the respective supply voltages and currents for a variety of different lighting devices in different applications must be provided by appropriately configured supply circuits. The necessary currents and voltages are supplied by the internal vehicle electrical system from an alternator or a rechargeable battery.

[0005] The usual supply voltage is between 6 V and 24 V, depending on the application and the vehicle, but nowadays it can also be higher because the consumers in the vehicle require ever greater power. For motor vehicles, especially passenger cars, a voltage of 12 V (or 24 V) is specified, which is provided by the alternator or the battery. For trucks and buses, higher voltages in the range of 24 V, 42 V or even 48 V are often provided. Depending on the application and consumer, the voltage provided by the on-board network is then transformed down to the required voltage for the consumer.

[0006] In practice, however, the increasing number of simultaneously operated devices, as well as legal requirements, is leading to ever-increasing current and power consumption. Furthermore, some devices, particularly lighting, are becoming more complex and comprise a multitude of individual components, such as LEDs, which are connected in series. These are sometimes susceptible to fluctuations in the supply line, increasing the risk of failure of individual elements in a line.

[0007] If some of these fail, the voltage in the string can rise, a so-called short-close condition, so that the remaining LEDs must now withstand the slightly higher voltage. In the worst case, this results in a cascade, so that all components in the string are also damaged due to excessive current flow or the existing voltage spikes.

[0008] Conversely, in a so-called short-open situation, i.e., if an LED fails, for example, the connection can be interrupted, meaning that the subsequent components are no longer supplied with sufficient current. Especially in series circuits, this situation means that if one component fails, the other LEDs will also no longer function.

[0009] At the same time, changes in the voltage in the vehicle electrical system also lead to a change in the voltages applied to the consumers, unless special converters are connected upstream for this purpose. This may be the case for some consumers, but for lighting applications such as indicators, low beam, high beam and parking lights, this is not usually the case; these are operated directly with voltage from the vehicle electrical system. Likewise, if the vehicle is left idle for a long time, the battery can discharge slightly over a longer period. This increases the risk that the voltage in the vehicle electrical system will be below the desired voltage in the initial phase. It is also possible that the voltage supplied by the vehicle electrical system will drop due to increased consumption.

[0010] Static loads, in particular, place increasing strain on both the alternator within the vehicle and the battery, as the required power can reach into the kilowatt range. The increased power consumption can therefore lead to a drop in voltage, meaning that other loads can no longer be adequately supplied with energy. This is particularly important for system-critical applications, such as vehicle-related lighting, as these must continue to operate even in the event of overvoltage or undervoltage, or at least be brought into a safe operating state.

[0011] All of these circumstances are of particular importance for safety-relevant and system-critical applications in vehicles. For example, lighting that is mandatory for vehicles must continue to function flawlessly even when there are different voltages on the vehicle electrical system, particularly in the event of an overvoltage or undervoltage, or even a fault in individual LEDs. The failure of individual elements within a string in particular should be reliably recognized and detected. This is particularly true when the supply voltage changes. This means that even when both circumstances occur, operation must be guaranteed or the lighting must be brought into a safe state.

[0012] There is therefore a need to provide supply circuits, particularly in the automotive sector, in which undervoltages and, if necessary, overvoltages can be reliably detected and suitable measures can be taken.

[0013] SUMMARY OF THE INVENTION

[0014] This problem is solved by the subject matter of the independent patent claims. Further developments and embodiments of these patent claims are specified in the subclaims.

[0015] As already mentioned at the beginning, depending on the application, it is necessary to reliably detect the various fault types and take appropriate measures. These measures include generating appropriate fault signals as well as shutting down or adjusting the supply current to the remaining loads.

[0016] In this respect, four possible faulty operating states would have to be detected. First, the failure of loads, which can lead to either a short open or a short close. The former means that no current flows through the load; in the latter case, the load is short-circuited, resulting in a low-resistance short circuit.

[0017] The other possible fault conditions are overvoltage and undervoltage, where the voltage supply to the loads rises above a value or falls below a value that is tolerable. Overvoltage and undervoltage also occur when a load in a string fails after one of the above cases, because then the supply voltage for the loads further down in a string either rises (in the short close case) or falls (in the short open case).

[0018] For LED-based lamps (multiple LEDs connected in series in a string), the voltage required for operation is greater than the sum of the individual forward voltages of the respective lamps. This means that the required operating voltage must be slightly greater than the sum of the individual forward voltages of the diodes connected in series or in a string. However, excessive voltage can damage the LEDs themselves, as well as the controllable power source.

[0019] An increase in power consumption by other consumers or a short-circuit can cause the available operating voltage to drop in the short term, but also in the medium term. Since the diodes are usually connected directly to the operating voltage, i.e., without a step-down converter, this can cause the operating voltage to drop below the sum of the forward voltages, causing the LEDs to shut off.

[0020] Therefore, especially in system-relevant applications, individual or multiple LEDs within the lamp must be bridged and short-circuited in order to maintain operation of at least part of the string. Although the lamp shines less brightly overall this way, functionality can be maintained and the operational safety of the vehicle can be guaranteed. It is also necessary that damaged loads are recognized as such in order to protect the other loads and also to indicate a possible fault. In certain applications, the load string must be brought into a safe state without causing further damage.

[0021] The inventor proposes a novel method and a corresponding arrangement for detecting an LED fault, particularly in the case of undervoltage, where the operating voltage has dropped, and thus providing external fault detection due to the reduced current consumption of the module. In conventional solutions, the voltage drop across the LEDs is usually compared with a reference voltage for fault detection. In this arrangement, the voltage is compared with a variable voltage, thus eliminating the need to generate a reference voltage.

[0022] This concept can be combined with undervoltage detection based on the generation of an internal control signal from the current regulator already present within the supply circuit. Such an electronic control circuit is already present in supply circuits, particularly for lighting, to maintain and regulate the required current. The electronic control circuit, for example, controls a power source to provide the current required to operate the loads.

[0023] The inventor now proposes generating a variable reference voltage from a voltage within the string and feeding this voltage to a detector circuit for fault detection. This eliminates the need for a fixed reference voltage. The signal generated by the detector circuit in response to the variable reference voltage is used as a measure for the electronic control loop. In other words, the signal from the detector circuit is applied to the control loop to control the control loop and, through it, the power source to a safe operating state.

[0024] The signal generated by the detector circuit can expediently be similar to an overvoltage signal, so that the control loop reacts in the same way in both cases. By suitable combination with a detector for generating an undervoltage in the string, part of the string can be switched off in the event of a short-close fault or a reduction in the supply voltage, thus allowing a smaller portion of the loads to continue to receive a supply voltage.

[0025] With the proposed principle, not only can different fault cases be reliably detected, both individually and in combination, but also a suitable measure is taken to either ensure sufficient functionality with the other consumers still present or to achieve a safe state of the circuit.

[0026] The proposed principle significantly reduces the circuit complexity inherent in a current-controlled bypass, thereby lowering the cost of such a supply circuit. Component tolerances, which always occur and must be taken into account to determine the voltage threshold in a voltage-controlled bypass, are not required with the proposed solution. This further reduces complexity. Furthermore, the proposed solution can be easily implemented in existing circuits, eliminating the need for a completely new design to detect the aforementioned faults and implement the appropriate measures.

[0027] In one aspect of the proposed principle, a supply circuit, in particular for lighting devices in the automotive sector, comprises a current path with at least two consumers. These are connected in series with a controllable current source between a supply potential connection and a reference potential connection. The consumers can be lighting devices or other consumers. In this context, it is conceivable in some aspects for the consumers to be of the same construction, so that essentially the same voltage drops across each consumer for a predetermined current. In some other aspects, the consumers also comprise a plurality of individual elements which can themselves be connected in series or in parallel. In the case of lighting devices as consumers, these can be one or more light-emitting diodes.

[0028] According to the proposed principle, a first control loop is also provided, which is connected between the supply potential connection and the reference potential connection. The first control loop comprises a control input to which a signal derived from a voltage drop along the current path can be fed. Furthermore, the first control loop is designed to generate a control signal on the basis of the derived signal and to output this to a control input of the controllable current source. A control output of the first control loop is thus connected to the control input of the controllable current source. In other words, the first control loop in combination with the controllable current source according to the proposed principle serves to adjust the current flowing through the current path accordingly based on a voltage drop along the current path and to regulate it to a setpoint.

[0029] Finally, the supply circuit comprises an error detection circuit with a detection input connected to a first node between the at least two loads. The error detection circuit also has an error signal output coupled to the control input of the first control loop. According to the invention, the error detection circuit is designed to detect a malfunction, in particular a current-closing short circuit, and to generate an error signal at the error signal output in response thereto.

[0030] According to the proposed principle, in contrast to conventional solutions, signals within the current path are used as a criterion for determining whether a load has failed. If this is the case, the current path can be safely shut down. The proposed fault detection is independent of whether an undervoltage is present and a sufficient current supply to the loads in the current path can no longer be guaranteed.

[0031] Particularly in system-critical applications in the automotive sector, for example with lighting devices such as indicators, parking lights or high beams, malfunctions can be reliably detected in this way without the need for complex modifications to the circuits. The lighting device includes the consumers connected in the current path, for example as a result of a series connection of several LEDs arranged one after the other. Using the proposed error detection circuit, errors that occur even in the event of undervoltage can now be detected. With further measures, not only can errors in individual consumers be reliably identified, but overvoltages and undervoltages can also be detected and suitable measures taken.

[0032] In addition to the fault detection circuit, in some aspects, this can also be combined with an overvoltage detection circuit. In some aspects, an overvoltage detection circuit is thus provided in the supply circuit according to the proposed principle, which is designed to detect a voltage above a threshold voltage at the supply potential terminal. The overvoltage detection circuit comprises an output coupled to the control input of the first control loop.

[0033] This means that an overvoltage can be reliably detected and, to protect against it, the regulated power source can be switched off or regulated down to such an extent that the overvoltage can cause no further damage. From the perspective of a consumer, an overvoltage is to be assessed in a similar way to a consumer in the event of a short-close fault. In this case, one consumer in a string is short-circuited with a low resistance, so that a higher voltage drops across all the other consumers. Although this is not an overvoltage on the supply line, it has the same effect for all the other consumers and is reliably detected by the proposed fault detection circuit.

[0034] In some aspects, this situation is exploited by connecting the error signal output of the error detection circuit to the output of the overvoltage detection circuit. Both inputs are thus equally routed to the control input of the first control loop.

[0035] In a further aspect, the error detection circuit comprises a controlled path, in particular in the form of a transistor. A control input of the controlled path forms the detection input. Optionally, in the case of a transistor as the controlled path, the base of the transistor is coupled to the detection input, and the collector of the transistor forms the error signal output.

[0036] In another aspect of the proposed principle, the control input of the first control loop is connected to a node in the current path. This node is located between the controllable current source and the reference potential terminal.

[0037] In some aspects, the aforementioned voltage drop can result from a drop across a reference load arranged in the current path. In particular, this reference load can be connected between the controllable current source and the reference potential terminal. In this context, it is expedient if the reference load is a linear component, which means that the voltage drop changes essentially linearly with the current flow through the component. It would also be expedient if the component showed only a slight temperature dependence. Other current-voltage waveforms are also conceivable, but again increase the complexity of the circuit.

[0038] In a further aspect, the first control loop comprises a controllable voltage divider connected between the supply potential terminal and the reference potential terminal. A tap in the voltage divider is connected to a control input of the controllable current source. By adjusting the voltage divider, a different signal can be tapped at the tap and fed to the control input of the controllable current source. The controllable voltage divider is thus also coupled to the control input for setting a voltage division.

[0039] In some aspects, the controllable voltage divider comprises a controlled path, in particular with a transistor, whose control input is coupled to the control input. In other words, in some aspects, the controllable voltage divider can comprise a constant resistor and a variable resistor, wherein the variable resistor is adjustable by a signal at the control input. Thus, a variable signal is also present at the tap of the controllable voltage divider, which signal is coupled to the control input of the controllable

[0040] power source is supplied.

[0041] In some aspects, the proposed supply circuit further comprises a bridging circuit that is connected between the supply potential terminal and a first node between the at least two loads. The bridging circuit is designed to bridge at least one load between the supply potential terminal and the node in response to a bridging signal at a control input. This allows at least one load to be effectively removed from the current path depending on the bridging signal. Accordingly, no voltage is then dropped across this load during operation, so that a higher voltage is available for the other loads.In addition, the supply circuit further comprises a second control loop configured to generate the bypass signal at the control input of the bypass circuit by evaluating a detected voltage between the control signal for the control input of the controllable current source and a potential in the current path. In this context, the potential can also be a voltage signal if the aforementioned potential is compared to a reference potential.

[0042] With the second control loop and the bypass circuit, undervoltages on the supply line can also be detected and corrected or their impact reduced by selectively switching off loads. This way, loads are selectively removed from the line, allowing the remaining loads to continue operating at a reduced voltage.

[0043] It should be noted in this context that, in the present application, the terms "potential" and "voltage" or "signal" can be considered synonymous when the potential is meaningfully considered against a reference. This arises from the fact that a voltage is the difference between two potentials.

[0044] A further aspect relates to the second control loop. In some aspects, this has a first input connected to the control input of the controllable current source and a second input connected to a node in the current path between the controllable current source and the at least two consumers. A control signal can therefore be fed to the input of the second control loop, which signal results from the signal of the controllable current source, i.e. the signal internal to the first control loop, and a second signal. This can, for example, be derived from a potential tapped from a node in the current path. In particular, in some aspects, this arrangement provides control of the second control loop by means of a voltage drop in the controllable current source.This is advantageous because, in such a case, the internal signals used for the first control loop are also used to control the second control loop, reducing circuit complexity. In some aspects, the controllable current source comprises an adjustable linear regulator. In this context, the voltage sensed by the second control loop may thus result from the control signal and a potential in the current path. This corresponds to a voltage across the connection of the linear regulator to the supply potential and its control input.

[0045] In a further aspect, the second control loop comprises a controlled path. This is connected with one connection to the control input of the bridging circuit and with the other connection to a node in the current path between the controllable current source and the at least two consumers. A signal derived from the control signal can also be fed to the control input of this controlled path. According to this principle, the second control loop thus controls the control input of the bridging circuit by evaluating a portion of the voltage or potential at the node between the controllable current source and the at least two consumers and the control signal or a signal derived therefrom. On the basis of the evaluation, a control signal is generated and output to the control input of the bridging circuit.

[0046] In this context, the controlled path can comprise a transistor whose base or gate terminal is coupled to the control input of the controllable current source and the reference potential terminal, in particular via a further voltage divider. In this case, the signal derived from the control signal would be a signal divided by the voltage divider, which is fed to the base or gate terminal. A bipolar transistor as the controlled path would in this case be connected in a common base circuit.

[0047] In a further aspect, the bypass circuit has a controlled path connected between the supply potential terminal and the first node. In some aspects, the bypass signal can be fed to the control input. The controlled path can thus be used to short-circuit the load to be bypassed via the bypass signal and thus effectively remove it from the current path. In this context, the controlled path of the bypass circuit can also comprise a transistor in a common collector circuit.

[0048] According to the principle presented here, the bridging circuit can not only bridge a single consumer from a large number of consumers connected in series, but can also gradually bridge several consumers connected in series in order to provide sufficient current for the remaining consumers. Accordingly, in some aspects it is provided that several nodes are arranged between each two consumers. These nodes are connected to the bridging circuit. The bridging circuit is then designed to bridge, i.e. short-circuit, the at least one consumer and at least one further consumer depending on a bridging signal at a control input.

[0049] In other words, the bridging circuit is designed to apply the supply potential in the current path to the node that was selected accordingly by the bridging signal and enabled by the bridging circuit. In some aspects, the controlled paths are implemented with bipolar transistors. In other aspects, field-effect transistors are also used, at least in part, although combinations of field-effect transistors and bipolar transistors are also possible. Another aspect relates to a method for supplying a plurality of loads that are connected in series with a controllable current source between a supply potential terminal and a reference potential terminal.

[0050] A voltage drop along the current path is detected and a control signal is generated from the voltage drop to control a current through the current path. The current through the current path is controlled using the control signal. Furthermore, a further signal from the current path is detected and evaluated. An error signal is generated based on the further signal and a signal at one of the supply potential terminals and the reference potential terminal. This allows the current source to be switched off if necessary, since the error signal is applied to a circuit provided for current control as a new control signal to switch off the current through the current path.

[0051] In some further aspects, in the step of generating an error signal, the further signal is also compared to a threshold value, wherein the threshold value is derived from a base-emitter voltage or a base-collector voltage of a transistor. Likewise, in some aspects, the bypass signal can be derived from a drain-gate voltage.

[0052] In some aspects, the further signal and the voltage drop are two different signals, wherein the further signal forms a potential at a node in the current path between the at least two loads.

[0053] BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Further aspects and embodiments according to the proposed principle will become apparent with reference to the various embodiments and examples which will be described in detail in conjunction with the accompanying drawings.

[0055] Figure 1 shows a first block diagram of a supply circuit according to some aspects of the proposed principle; Figure 2 shows a first block diagram of a supply circuit according to some aspects of the proposed principle;

[0056] Figure 3 shows a detailed circuit diagram of a supply circuit according to some aspects of the proposed principle.

[0057] DETAILED DESCRIPTION

[0058] The following embodiments and examples show various aspects and their combinations according to the proposed principle. The embodiments and examples are not always true to scale. Likewise, various elements can be shown enlarged or reduced in size to emphasize individual aspects. It goes without saying that the individual aspects and features of the embodiments and examples shown in the figures can be combined with one another without thereby impairing the inventive principle. Some aspects have a regular structure or shape. It should be noted that in practice slight deviations from the ideal shape can occur without, however, contradicting the inventive idea.

[0059] Furthermore, the individual figures, features, and aspects are not necessarily shown in the correct size, and the proportions between the individual elements may not always be correct. Some aspects and features are emphasized by being shown enlarged. However, terms such as "top", "above", "below", "below", "larger", "smaller", and the like are correctly represented with reference to the elements in the figures. This makes it possible to infer such relationships between the elements from the illustrations.

[0060] Figure 1 shows a first block diagram of a supply circuit 1 for a current path 10 according to the proposed principle. In the present exemplary embodiment, the power supply circuit comprises a current path 10 between a supply potential connection 1 and a ground potential connection 2. The current path 10 comprises two series-connected loads 11 and 12, for example lighting devices in the form of light-emitting diodes or the like, as well as a controllable current source 14. This is used to control the current to a necessary setpoint for the power supply of the two loads 11 and 12 in the current path 10. For this purpose, a first control circuit 20 is provided, the control connections of which are led to two nodes 103 and 104 for detecting a voltage across these two nodes. In the present exemplary embodiment, node 104 is at ground potential, and node 103 is arranged between the controllable current source 14 and the load 12.The first control loop 20 detects the signal falling across a reference load (this can include the current source) and generates a control signal for the control input 141 of the controllable current source 14. This allows the current flow of the controllable current source 14 through a consumer 11 and 12 to be adjusted. Depending on the implementation, it can be assumed that the signal falling across the controllable current source changes independently of a specific relationship that is taken into account by the control.

[0061] According to the proposed principle, the supply circuit additionally comprises an error detection circuit 50. This is connected on the one hand to a node 102 which is arranged between two consumers and on the other hand to the supply potential connection 1. An error signal output 51 is connected to a corresponding input 21 of the first control loop. The error detection circuit 50 then monitors the consumers for possible damage or failure. The so-called short-open case is particularly important here, since in such a fault case the failed consumer becomes high-impedance. Accordingly, a different voltage is dropped across the other consumer, so that the risk of damage or failure also increases. The error detection circuit 50 therefore uses a variable signal from the current path itself to identify such an error.However, a short-close condition can also be detected and treated with the error detection circuit 50. This merely requires a slight modification of the design.

[0062] In particular, the error detection circuit 50 is designed to compare the signal from the current path with a reference. In a preferred implementation, this reference is derived directly from a base-emitter voltage or a base-collector voltage, for example. The error detection circuit comprises a controlled path (not shown here) or a switch which, based on the variable signal and one of the above-mentioned voltages, i.e., from physical parameters, generates a signal for shutdown at the error signal output 51. In this embodiment, this is done via the controlled switch which, in the event of an error, i.e., when a voltage or potential at node 102 increases, sets the error signal output 51 to a high potential and thus causes the current source to be switched off via the first control loop.

[0063] The supply circuit according to the proposed principle further comprises a bypass circuit 40 which is connected in parallel to the first consumer 11 between the node 101 and the supply potential 100. The bypass circuit comprises a controllable switch 401 with the aid of which the first consumer 11 is effectively bypassed depending on the respective switch position. Thus, the bypass circuit 40 can bypass the consumer 11 depending on a signal at the bypass input and thus apply the potential at the supply potential connection 1 directly to the second consumer 12. In this context, further elements can also be implemented in series or parallel to the switch of the bypass circuit 40; here, for example, a resistor has been implemented later in series with the switch of the bypass circuit in order to create a smoother transition.Since a voltage drop across the first consumer 11 is thus avoided, the voltage at node 101 increases.

[0064] A second control circuit 30 is provided for controlling the bypass circuit 40, the output 301 of which is connected to the bypass input of the bypass circuit 40. The control signal of the first control circuit 20 is then supplied to the second control circuit at node 201, and a second terminal 303 is connected to node 103. The second control circuit 30 thus detects a voltage from the potential node 103 and the control signal for the controllable current source 14 at point 201.

[0065] During normal operation of the arrangement, the controllable current source 14 regulates the current through the two consumers 11 and 12. If the supply voltage between terminals 1 and 2 changes, the potential at node 103 also changes and thus the voltage drop across the controllable current source 14. This is detected by the first control circuit, which then supplies a change in a control signal to the control input 141 in order to keep the current through the two consumers at a constant value. This control takes place both for slightly increasing and for slightly decreasing supply voltages.

[0066] However, if the existing supply voltage drops below a certain value, namely below the sum of all voltages across consumers 11 and 12 and source 14, this is referred to as undervoltage. In this case, the control still attempts to control, but even when the controllable current source is at maximum output, the voltage remains too low. This can lead, for example, to the control in the first control circuit 20 regulating right up to the stop and the controllable current source switching through completely. Regardless of the possible success, this state is undesirable and signals a condition in which an adequate power supply to the two consumers can no longer be guaranteed due to the supply voltage being too low. The same effect also occurs in the event of a fault, if, for example, consumer 11 fails with a short open, a high-impedance failure.In both cases, the power source is regulated down to reduce the total current consumption below a certain level and thus signal a failure to a higher-level control unit; that is the basic idea.

[0067] To prevent this, the second control loop 30 is provided. This loop detects the control signal 141 and the potential at node 103 and generates a derived signal, for example, the voltage across these two.

[0068] The second control loop 30 is now set up in such a way that when a control signal is present at the control input 141, which is usually present in the normal state, no additional control takes place because, for example, the voltage drop between node 103 and the control input 141 is sufficiently high. However, when there is an undervoltage, this potential difference changes and is detected by the second control loop 30. Depending on this, a control signal is generated at the output 301 and fed to the bypass circuit 40. This then closes the bypass circuit so that there is no longer any voltage drop across the consumer 11, but rather the voltage is fully applied to node 101. As a result, the voltage between node 101 and the reference potential connection 2 rises again, so that the second consumer 12 is again supplied with a sufficient supply voltage.At the same time, this also affects the control in the first control loop 20, so that the controllable current source 14 again controls the linear operation.

[0069] If the supply voltage rises above the sum of the voltages across loads 11 and 12, the bridging in circuit 40 can be reset so that when the supply voltage is sufficient, both loads are powered again. This control can be instantaneous or with hysteresis so that very short fluctuations have little or no effect on the control in circuits 20 and 30. In a further embodiment, the bridging circuit is first throttled (this works when the bridging circuit is implemented with a controlled path), after which the control loop begins to limit the current again as the voltage rises.

[0070] The advantage of this principle lies in the use of signals already present internally in the current path for detecting faults in the loads as well as for overvoltage and undervoltage. For undervoltage, the control signal generated in the first control loop at control input 141 is used for evaluation in the second control loop 30. In the event of a fault, one or more potentials in the current path are also evaluated separately.

[0071] In this way, it is possible, for example, to either bridge cascaded loads in a series or to connect them into the current path in order to achieve a gradual switching off or switching on of individual loads in a current path. Figure 2 shows a corresponding embodiment based on the proposed principle. In this case, the circuit comprises several series-connected loads 11, 12 and 13, which can represent, for example, individual light-emitting diodes, LEDs, but also chains or arrays of light-emitting diodes.

[0072] The current path 10 further comprises a controllable current source 14 and a linear component 15, which is arranged between the nodes 105 and 104 of the current path 10. A measurable voltage thus drops across the component 15 and serves as an input signal for the first control circuit 20. Between the individual consumers 11, 12 and 13, taps 101 and 102 are provided, which are connected to the bridging circuit 40 and two switching elements 401 and 402 arranged therein. Depending on the switch position of the two switching elements 401 and 402, the consumer 11 alone or two of the three consumers, namely 11 and 12, can be selectively bridged. Accordingly, depending on the switch position, the supply potential is applied either to all consumers or only to consumers 12 and 13 or only to consumer 13.

[0073] The bypass circuit 40 is controlled by a second control circuit 30. Its inputs 303 are connected, on the one hand, to a node 103 between the last consumer 13 and the controllable current source 14, and to a node 201 for detecting the control signal of the first control circuit 20. Operation is similar to that in Figure 1, with the difference that the second control circuit now has two switching stages in order to be able to operate the two controlled switching elements 401 and 402 of the bypass circuit 40.

[0074] Thus, in the event of an undervoltage, control is carried out in such a way that, depending on the extent of the undershoot, only the first consumer 11 is bypassed by a suitable switching signal on the controlled path 401. This means that only the two consumers 12 and 13 are still supplied with current by the current source 14. If control of the first control loop of the controllable current source 14 continues in non-linear operation or if the control reaches saturation again, this is again detected by the second control loop 30 by evaluating the voltage signal between the nodes 201 and 103 and, in response, the second controlled path 402 is controlled accordingly in order to bypass the second consumer 12.

[0075] In this way, loads can be selectively added to or removed from the current path independently of the control signal at input 141 of the controllable current source, in order to still supply the remaining loads with sufficient current. Here, too, a suitable bypass signal is generated in the second control loop 30 by evaluating the internal signals at control input 141 and at node 103.

[0076] The supply circuit also includes an error detection device 50. This is connected on the input side to each of the nodes 101, 102 and 103. The error signal output 51 is led to an error signal input 203, to which the signal at node 105 or a signal derived therefrom is ultimately fed. The error detection device compares the variable signals at the nodes 101, 102, 103 with one another and / or with a signal derived from the supply potential. In this way, various error cases of the consumers 11, 12 and 13 can be reliably detected and either passed on externally as an error signal, or the first control loop can be controlled using the error signal. Depending on the position and type of error that has occurred, several measures are possible in the first control loop.For example, in the event of a fault, the current of the controllable power source can be reduced to reduce overloading of the remaining loads while still maintaining their operating state. Alternatively, the power can be completely shut off. Together with the bypass circuit 40 and the second control loop 30, various faults are detected in this way, and various countermeasures are taken. By using the signals already present internally, i.e., in the first control loop or in the current path, the complexity of the circuit is reduced.

[0077] Figure 3 shows a concrete embodiment of the proposed principle using a circuit diagram. The design comprises a circuit 10 with a first load element consisting of two series-connected light-emitting diodes 11 and 11' and a second load element consisting of two series-connected light-emitting diodes 12 and 12'. The respective operating voltages of these light-emitting diodes are in the range of 1.5 V, so that a voltage of approximately 6 V to 6.5 V drops across the entire string of four light-emitting diodes. Between the two first light-emitting diodes 11 and

[0078] A first node 102 is provided between the first and second LEDs 11 and 12. A second node 103 is arranged downstream of the second LEDs 12 and 12 and upstream of the adjustable current source 14. The adjustable current source 14 comprises a field-effect transistor as a current-regulating element, the drain terminal of which is connected to the node 103 and the source terminal of which is connected to the input 105. The gate terminal of the transistor of the current source 14 forms the control input 141 via a resistor.

[0079] The transistor of the current source 14 therefore represents a linear regulator which is controlled via a control signal at the input 141. The node 141 is also at the same potential as the node 201 which forms the control output of the first control loop 20. The first control loop comprises a controlled path made up of two elements RI and R2 which are connected in series and form a voltage divider. The element RI is designed as a constant resistor and is connected between the supply potential connection 1 for the potential VBat and the control output 201. The second element R2 is formed by a controlled path, here in the form of a small-signal transistor TI. The latter is connected with its collector connection to the node 202 and its emitter connection to the ground potential VG and the connection 2. The capacitor CI is also provided in parallel between the collector and the ground connection.The base terminal of the small-signal transistor TI forming the controlled path R2 is connected, on the one hand, to node 202, i.e., to the collector terminal, via a second capacitor C2, and, on the other hand, to the ground potential terminal VG, via a capacitor C3. The base terminal of the transistor TI forms the control input for the controlled path R2. The base terminal is also connected, via resistors R3 and R4, to node 105 in the current path. A resistance element 15 is also provided between node 105 and the ground potential terminal 2 and the potential Vg.

[0080] In a normal operating state, the controllable current source 14 is controlled in such a way that the controlled path R2 evaluates the voltage drop across element 15 via its control input, i.e., its base terminal, and uses this to adjust the resistance, i.e., the voltage drop across the collector-emitter path of the small-signal transistor TI, of the controlled path R2. This results in a certain voltage division across the controlled path comprising the elements RI and R2, which in turn is fed as a control signal to the field-effect transistor of the current source 14 for current control.

[0081] The supply circuit also includes overvoltage protection. This comprises a path arranged between the supply line and node 203 in the first control loop. The path includes two series-connected resistors R16 and R15, which form part of the error detection circuit 50. They are also connected to ground with another resistor in series. To detect an overvoltage, a Zener diode ZI is provided after the resistor R15, which is connected via a resistor R7 to node 203 of the first control loop.

[0082] This additional path provides overvoltage protection. In the event of an overvoltage on supply potential line 1 (i.e., an excessively high potential VBat), the Zener diode ZI becomes conductive and switched through. This pulls the base terminal of the controlled path R2 to a higher potential, so that the collector-emitter path of transistor TI becomes low-impedance. Accordingly, the signal at node 201 and at control input 141 decreases (both nodes are pulled to ground or Vg via transistor TI).

[0083] This blocks the field-effect transistor of the controllable current source 14, and damage to this transistor due to excessive current flow through the current path 10 is avoided altogether. In other words, the drain-gate voltage across this transistor, i.e., the voltage across nodes 103 and 141, is increased. At the same time, in the event of an overvoltage, no voltage is applied to the base of transistor T2; T2 blocks.

[0084] The resistors R16 and R15 advantageously also form part of the error detection circuit 50 according to the invention, so that assemblies for the overvoltage protection and the error detection circuit can be used together. In particular, a node between the resistors R16 and R15 is connected to the emitter of a transistor T4, which forms a controlled path. The transistor T4 is a PNP transistor and its collector is connected to the node 203 via the resistor R7. The base of the transistor T4, together with the resistor R14, forms the input of the error detection circuit for the error detection signal. For this purpose, the input is connected to the node 102.

[0085] During normal operation of the circuit, the potential at the base is quite high, in most cases even higher than the emitter voltage, so that the transistor T4 is blocked. In the event of a fault, simulated here by the additional resistor 110, a larger voltage drops across the upper part of the path, so the potential or voltage at the base of the transistor T4 drops. If this now drops below the emitter voltage, the transistor T4 becomes conductive and applies the supply potential to the node 203 via R16 and R7. The node is thus pulled upwards and the transistor T1 regulates in such a way that the node 202, i.e. the control output of the first control loop, is pulled towards ground or Vg.

[0086] Similarly, a short circuit in one of the two LEDs 12 and 12' can also be detected if this also leads to a voltage increase at node 102. In a further aspect, the detection circuit is supplemented with a complementary component, e.g., with an NPN transistor as an additional controlled path. This allows both short-open and short-close cases to be reliably detected and transmitted as a signal to the first control circuit.

[0087] The supply circuit according to the proposed principle further comprises a second control loop 30. This second control loop also comprises a controlled path consisting of a common-base bipolar transistor T2. For this purpose, the base terminal of the transistor T2 is connected via a voltage divider to the ground potential terminal 2 and the potential Vg, on the one hand, and to the control input 141, on the other hand. In the present exemplary embodiment, the voltage divider with its two resistors R9 and RI0 is designed such that half of the signal at the control input 141 is applied to the base of the transistor T2.

[0088] The emitter of transistor T2 is connected to node 103, the collector forms the output 301 of the second control loop 30 and is connected to the control input 401 of the bypass circuit 40. The bypass circuit 40 also includes a controlled path in the form of a bipolar transistor T3, which has its emitter connected between the supply potential terminal 1 for the supply potential VBat and its collector connected to node 102 via a further resistor R12. The base terminal of transistor T3 is connected to the control input 401 of the bypass circuit 40 via a resistor R11 and is connected to the supply potential terminal 1 via a resistor R13.

[0089] In the event of an undervoltage, the voltage drop across the individual diodes 11, 12, and 12' creates a situation in which the current through the LED string is reduced. This is typically compensated for by the control signal at the input of the current source 141 through the first control loop. The decreasing voltage at node 105 increases the control signal at the control input 141, thereby opening the field-effect transistor further.

[0090] In the event of undervoltage, however, this compensation is no longer sufficient, so that the field-effect transistor is driven into saturation. The control signal becomes so high that the drain-gate voltage drops to its minimum value; the current source transistor is in saturation. The increasing control signal at the gate, i.e., the decreasing drain-gate voltage, is evaluated as the base-emitter voltage of transistor T2 in the second control loop 30. In particular, the control signal at input 141 is fed to the base of transistor T2 as a divided voltage signal.

[0091] The transistor T2 becomes increasingly conductive and thus pulls the base of the transistor T3 of the controlled path of the bypass circuit 40 also into a conductive state, i.e. towards ground. The operating point of the controlled path and of the transistor T3 can be set by selecting the two resistors 11 and 13. When the bypass circuit 40 is conductive, the supply potential VBat less the voltage drop across the controlled path with the transistor T3 and resistor R12 is applied to the node 102. This applied voltage is greater than the voltage drop across the two diodes 12 and 13, so that current can flow again, even if the current regulator 14 is no longer operated in saturation.

[0092] The solution presented, particularly in Figure 3, has the advantage that the individual controlled paths, in particular the bypass circuit and the second control loop, do not operate digitally, but essentially linearly over a longer range. As a result, bypassing of diodes 11 and 12 does not occur suddenly, but rather over a short voltage range.

[0093] In particular, hysteresis effects can be generated so that short-term voltage fluctuations on supply line 1 have no influence on the circuit, but only when the required supply voltage falls below the required level for a longer and continuous period does bridging by transistor T3 and resistor R12 occur. Resistor R12 also serves as a current limiter. Transistor T3 has a greater current carrying capacity than the small-signal transistors in control loops 30 and 20. In particular, the power dissipation of the transistor should be selected such that current source 14 does not provide more than the maximum possible current through transistor T3, even in saturation mode. LIST OF REFERENCE SYMBOLS

[0094] 1 supply potential connection

[0095] 2 Reference potential connection

[0096] 10 Current path

[0097] 11 , 12 , 13 Consumers , LEDs

[0098] 11 ' 12 ' LEDs

[0099] 14 controllable power source

[0100] 20 first control loop

[0101] 30 second control loop

[0102] 40 Bridging circuit

[0103] 50 Error defective ions circuit

[0104] 51 Error signa laus gang

[0105] 101 102 , 103 knots

[0106] 104 105 knots

[0107] 141 St your entrance

[0108] 201 Rege lice gang

[0109] 203 Error signal input

[0110] 301 Rege laus gang

[0111] 303 Control input

[0112] 401 switching element

[0113] CI , ... C3 capacitor

[0114] RI , ... R16 resistor

[0115] TI, T2, T3, T4 transistor ZI Zener diode

Claims

PATENT CLAIMS 1. Supply circuit, in particular for lighting devices in the automotive sector, comprising: a current path with at least two consumers, in particular lighting devices, which are connected in series with a controllable current source between a supply potential connection and a reference potential connection; a first control loop, which is connected between the supply potential connection and the reference potential connection, with a control input to which a signal derived from a voltage drop along the current path can be fed; wherein the first control loop is designed to output a control signal to a control input of the controllable current source on the basis of which signal;an error detection circuit having a detection input connected to a first node between the at least two consumers and comprising an error signal output coupled to the control input of the first control loop, wherein the error detection circuit is designed to detect a malfunction, in particular a current-opening short circuit, and in response thereto to generate an error signal at the error signal output; 2. Supply circuit according to claim 1, wherein the control input of the first control loop is coupled to a node in the current path which is arranged between the controllable current source and the reference potential terminal. 3 . Supply circuit according to one of the preceding claims, in which the voltage drop along the current path results from a drop across a reference load which is connected between the controllable current source and the reference potential terminal. 4 . Supply circuit according to one of the preceding claims , in which the first control loop comprises a controllable voltage divider between the supply potential terminal and the reference potential terminal , and comprises a tap which is connected to the control input of the adjustable current source and wherein the controllable voltage divider is coupled to the control input for setting a voltage division. 5 . Supply circuit according to claim 4, wherein the controllable voltage divider comprises a controlled path, in particular with a transistor, the control input of which is coupled to the control input.

6. Supply circuit according to one of the preceding claims, further comprising an overvoltage detection circuit which is designed to detect a voltage above a threshold voltage at the supply potential terminal and comprises an output coupled to the control input of the first control loop.

7. Supply circuit according to claim 6, wherein the error signal output is connected to the output of the overvoltage detection circuit. 8 . Supply circuit according to one of the preceding claims, wherein the error detection circuit comprises a controlled path, in particular in the form of a transistor, wherein a control input of the controlled path forms the detection input; and optionally the base of the transistor is coupled to the detection input and the collector of the transistor forms the error signal output.

9. Supply circuit according to one of the preceding claims, further comprising: a second control loop which is designed to generate the bridging signal at the control input of the bridging circuit by evaluating a detected voltage between the control signal and a potential in the current path. a bridging circuit which is connected between the supply potential connection and a node, in particular the first node between the at least two consumers, for bridging at least one consumer between the supply potential connection and the node in response to a bridging signal at a control input; 10. Supply circuit according to claim 9, wherein the second control loop is connected with a first input to the control input of the controllable current source and with a second input to a node in the current path between the controllable current source and the at least two consumers.

11. Supply circuit according to claim 9 or 10, wherein the voltage detected by the second control loop between the control signal and a potential in the current path is a voltage detectable via a linear regulator and its control input.

12. Supply circuit according to one of claims 9 to 11, in which the second control loop comprises a controlled path which is connected with one connection to the control input of the bridging circuit and with the other connection to a node in the current path between the controllable current source and the at least two consumers, and whose control input can be supplied with a signal derived from the control signal; and optionally the controlled path comprises a transistor whose base or gate connection is coupled to the control input of the controllable current source and the reference potential connection, in particular via a voltage divider.

13. Supply circuit according to one of the preceding claims, in which the bridging circuit has a controlled path which is connected between the supply potential terminal and the first node and to whose control input the bridging signal can be fed.

14. Supply circuit according to one of claims 9 to 13, wherein the bridging circuit is connected to a further node between two of the at least two consumers and is designed to bridge the at least one consumer and at least one further consumer in response to the bridging signal at the control input.

15. A method for supplying a plurality of consumers in a current path, which are connected in series between a supply potential terminal and a reference potential terminal with a controllable current source, comprising the steps of: Detecting a voltage drop along the current path; Generating a control signal from the voltage drop to control a current through the current path; Controlling a current through the current path using the control signal; detecting another signal from the current path; Generating an error signal based on the further signal and a signal at a connection consisting of a supply potential terminal and a reference potential terminal; Applying the error signal as a new control signal to switch off the current through the current path.

16. The method of claim 15, wherein the step of generating an error signal comprises the step of comparing the further signal with a threshold value, the threshold value being derived from a base-emitter voltage or a base-collector voltage of a transistor.

17. A method according to claim 15 or 16, wherein the step of detecting the further signal and the voltage drop represent two different signals, the further signal forming a potential at a node in the current path between the at least two loads.

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