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 bridging circuit is connected between the supply potential terminal and a first node between the at least two loads in order to bridge at least one load in response to a bridging signal. A first control loop between the supply potential terminal and the reference potential terminal comprises a control 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 second control loop is designed to generate the bridging signal for the bridging circuit in evaluation of a detected voltage between the control signal and a potential in the current path.

Description

[0001] SUPPLY CIRCUIT AND METHOD

[0002] This application claims priority from German patent application DE 10 2024 100 914 . 4 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 can now also be higher because the consumers in the vehicle require ever greater power. A voltage of 12 V (or 24 V) is usually specified for motor vehicles, particularly passenger cars, and 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 operating devices, as well as legal requirements, leads to ever-increasing current and power consumption. If the alternator's output is no longer sufficient, the supply voltage in the vehicle's electrical system may drop slightly, either over a longer period or only sporadically. A similar effect can occur with sudden peaks in power consumption, i.e., when devices are added or the alternator's output drops and the battery cannot compensate for this.

[0007] Changes in the voltage in the vehicle electrical system also lead to a change in the voltages applied by consumers, unless special converters are connected upstream. 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 not used 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.

[0008] This is particularly important for safety-relevant and system-critical applications. For example, lighting devices that are mandatory for the vehicle must function flawlessly even under varying voltages in the vehicle electrical system, particularly in the event of overvoltage or undervoltage. Accordingly, it is necessary to detect such deviations from the nominal voltage early on in order to be able to take appropriate measures automatically.

[0009] Static consumers in particular place increasing strain on both the alternator in the vehicle and the battery, as the power required can reach into the kilowatt range. The increased power consumption can therefore lead to a drop in voltage, meaning that other consumers can no longer be supplied with sufficient energy. This is particularly important for system-critical applications, for example vehicle-related lighting, as these must still be operated in the event of an overvoltage or undervoltage, or at least be put into a safe operating state. There is therefore a need, particularly in the automotive sector, to provide supply circuits in which undervoltages and, where appropriate, overvoltages can be reliably detected and suitable measures can be taken.

[0010] SUMMARY OF THE INVENTION

[0011] 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.

[0012] As already mentioned at the beginning, depending on the application, the voltage required for operation, especially for lamps, may be greater than the sum of the individual forward voltages of the respective lamps. Since lamps based on light-emitting diodes are increasingly being used in this area, this means that the required operating voltage must be greater than the sum of the individual forward voltages of the diodes connected in series or in a string.

[0013] A sudden increase in power consumption or even excessive power consumption overall can cause the available operating voltage to drop in the short or medium term. As the diodes are usually connected directly to the operating voltage, i.e. without a step-down converter, this can result in the operating voltage falling below the sum of the forward voltages, causing the LEDs to switch off. Therefore, particularly in system-relevant applications, individual or multiple LEDs within the lamp must be bridged and short-circuited in order to at least maintain operation of part of the string. Although the lamp shines less brightly overall this way, its functionality can be retained, thus ensuring the operational reliability of the vehicle.

[0014] The inventor proposes a new method and a corresponding arrangement that reliably detects this undervoltage drop and thus bypasses unnecessary loads. At the same time, this circuit is particularly easy to implement and provides a cost-effective alternative to conventional detector circuits.

[0015] Previous detector circuits use either the operating voltage level, a so-called voltage-controlled bypass, or the current consumption within the load, a so-called current-controlled bypass, as the criterion for deciding whether to bypass loads. Both solutions are more complex and therefore expensive due to the necessary detector circuitry.

[0016] The inventor now proposes a different solution based on generating an internal control signal from the current regulator that is 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. Such an electronic control circuit controls, for example, a current source to provide the current required to operate the loads. The inventor now proposes using the signals within the control circuit as a criterion for determining whether and to what extent the loads need to be bypassed in order to maintain the required current for the remaining loads even in the event of an undervoltage.With the proposed principle, not only can the undervoltage as such be reliably detected, but also a selection of the consumers to be bridged is made in order to ensure sufficient functionality with the other consumers still present.

[0017] The circuit complexity present in a current-controlled bypass is significantly reduced by the proposed principle, thereby reducing the costs of such a supply circuit. Component tolerances that always occur and have to be taken into account in a voltage-controlled bypass to determine the voltage threshold are not required with the proposed solution. This further reduces complexity. The proposed solution can also be easily implemented in existing circuits, meaning that a completely new design for detecting undervoltages and taking the corresponding measures is not necessary. In one aspect of the proposed principle, a supply circuit, particularly 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 loads can be lamps or other loads. In this context, it is conceivable in some aspects for the loads to be of the same construction, so that essentially the same voltage drops across each load for a given current. In some other aspects, the loads also comprise several individual elements, which in turn can be connected in series or in parallel. In the case of lamps as loads, this can be one or more light-emitting diodes.

[0018] The proposed supply circuit further comprises a bridging circuit which is connected between the supply potential connection 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 connection 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 as a function of 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.

[0019] 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 control it to a setpoint.

[0020] Finally, the supply circuit further comprises 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 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 above-mentioned potential is viewed against a reference potential. It should be mentioned in this context that in the present application the terms potential and voltage or signal can be viewed as synonymous if the potential is meaningfully viewed against a reference. This results from the fact that a voltage is a difference between two potentials.

[0021] According to the proposed principle, in contrast to conventional solutions, signals within the control loop for current control through the current path are used as a criterion for determining whether an undervoltage is present and thus a sufficient current supply to the loads in the current path is no longer guaranteed. If this is the case, the second control loop—evaluated by the second control loop—activates the bypass circuit to selectively remove loads from the current path without restricting the functionality of the other loads.

[0022] Particularly in system-critical applications in the automotive sector, for example with lighting devices such as indicators, parking lights, or even high beams, the functionality of the respective lighting device can be maintained in this way even in the event of undervoltage. The lighting device includes the loads connected in the current path, for example as a result of a series connection of several LEDs arranged one behind the other. Using the proposed bypass circuit and the evaluation of the internal current regulation, the LEDs that can be operated with the maximum available current and the remaining supply voltage can now be supplied accordingly, even in the event of undervoltage.

[0023] In this context, the bridging circuit may, in some aspects, also be arranged at nodes in the current path between one or more loads.

[0024] In one 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.

[0025] 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.

[0026] 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.

[0027] 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 can be adjusted 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 fed to the control input of the controllable current source.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] In a further aspect, the bridging circuit has a controlled path that is connected between the supply potential connection and the first node. In a further aspect, the bridging circuit comprises an adjustable current source that is addressed by the second control loop. This makes it possible to provide additional current for the other loads, enabling a seamless current transition between the node for the supply potential and the node in the current path. This adjustable current source can, among other things, be a controlled path that is addressed by the second control loop. This not only allows control in the event of an undervoltage, but also allows the bridging path to be continuously reduced when the supply voltage rises again.

[0032] In some aspects, the bypass signal can be fed to the control input. The controlled path can thus short-circuit the load to be bypassed via the bypass signal, effectively removing 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.

[0033] 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.

[0034] In other words, the bypass circuit is designed to apply the supply potential in the current path to the node that has been selected by the bypass signal and enabled by the bypass 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.

[0035] Another aspect relates to a method for supplying a plurality of consumers which are connected in series between a supply potential terminal and a reference potential terminal with a controllable current source.

[0036] 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 by means of the control signal. Furthermore, the control signal and another signal from the current path are evaluated. From this, a bridging signal is generated depending on the evaluation of the control signal and the other signal. This allows at least one consumer in the current path to be bypassed in response to the generated bridging signal, if required.

[0037] In some further aspects, the step of generating a bypass signal also includes comparing the control signal with a threshold value, wherein the threshold value is derived from the further signal. Finally, in some aspects, the bypass signal may be derived from a drain-gate voltage.

[0038] BRIEF DESCRIPTION OF THE DRAWINGS

[0039] 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.

[0040] Figure 1 shows a first block diagram of a supply circuit according to some aspects of the proposed principle;

[0041] Figure 2 shows a first block diagram of a supply circuit according to some aspects of the proposed principle;

[0042] Figure 3 shows a detailed circuit diagram of a supply circuit according to some aspects of the proposed principle.

[0043] DETAILED DESCRIPTION

[0044] 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.

[0045] 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.

[0046] 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 therein 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 dropping across the controllable 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 load 11 and 12 to be adjusted. Depending on the implementation, it can be assumed that the signal dropping across the controllable current source changes independently of a specific relationship that is taken into account by the control.

[0047] The supply circuit according to the proposed principle further comprises a bridging circuit 40 which is connected in parallel to the first consumer 11 between a node 101 and the supply potential 100. The bridging circuit comprises a controllable current source as a switch 401, with the aid of which the first consumer 11 is effectively bridged depending on the respective switch position. Thus, the bridging circuit 40 can bridge the consumer 11 depending on a signal at the bridging input and thus apply the potential at the supply potential connection 1 directly to the second consumer 12. Since a voltage drop across the first consumer 11 is thus avoided, the voltage at node 101 increases.

[0048] 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.

[0049] 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.

[0050] 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 loop 20 regulating right up to the stop and the controllable current source switching on 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 second control loop 30 is provided to prevent this.This detects the control signal 141 on the one hand and the potential at node 103 on the other hand and generates a derived signal from this, for example the voltage across these two.

[0051] The second control loop 30 is now set in such a way that when a control signal is normally present at the control input 141 in the normal state, no additional control takes place because, for example, the voltage drop between the intermediate node 103 and the control input 141 is sufficiently high.

[0052] In the event of an undervoltage, however, this potential difference changes and is detected by the second control circuit 30. Depending on this, a control signal is generated at output 301 and fed to the bypass circuit 40. This then closes the bypass circuit, so that no more voltage drops across the load 11, but rather it is fully present at node 101. As a result, the voltage between node 101 and the reference potential terminal 2 rises again, so that the second load 12 is again supplied with a sufficient supply voltage.

[0053] If the supply voltage rises above the sum of the voltages across loads 11 and 12, the bypass in circuit 40 can be reset so that, once the supply voltage is sufficient, both loads are again powered. This control can be instantaneous or hysteresis-based, so that very short fluctuations have little or no effect on the control in circuits 20 and 30.

[0054] If the switches in the bypass circuit 40 are replaced by controllable paths, an additional current is provided during the bypassing, which also affects the control in the first control loop 20. This allows the first control loop to be maintained within a reasonable control range for a longer period.

[0055] The advantage of this principle lies in the fact that the signals already present internally, in particular the control signal generated in the first control loop at control input 141, can be used for evaluation in the second control loop 30. This allows existing component tolerances to be compensated, which would otherwise have to be taken into account to determine the required threshold. Furthermore, this principle can also be applied to current paths with multiple loads and multiple nodes between the individual loads.

[0056] 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) or chains or arrays of light-emitting diodes.

[0057] 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.

[0058] 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 current sources 401 and 402 of the bypass circuit 40. Thus, in the event of an undervoltage, control is such that, depending on the extent of the undershoot, only the first consumer 11 is bypassed by the controlled current source 401 by means of a suitable switching signal. This means that only the two consumers 12 and 13 are still supplied with current from the current source 14. If the first control loop of the controllable current source 14 is now controlled in a non-linear mode or .If the control system 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 thereto, the second controlled source 402 is controlled accordingly in order to bypass the second consumer 12.

[0059] 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.

[0060] Figure 3 shows a concrete embodiment of the proposed principle using a circuit diagram. The design includes an electrical circuit

[0061] 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 2 .9 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

[0062] 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.

[0063] 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 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.

[0064] 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 connection, 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 made up of 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. In addition, node 203 is connected to the supply potential connection 1 for the potential VBat via a path consisting of resistor R7, a zener diode ZI and resistor R8.

[0065] 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. The signal at node 201 and at control input 141 decreases accordingly (both nodes are pulled to ground via transistor TI).

[0066] 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.

[0067] 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.

[0068] 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 acts as a current source and is connected with its emitter between the supply potential terminal 1 for the supply potential VBat and with its collector via a further resistor R12 to the node 102. The base terminal of the current source transistor T3 is connected via a resistor R11 to the control input 401 of the bypass circuit 40 and on the other hand is connected via a resistor R13 to the supply potential terminal 1.

[0069] In the event of an undervoltage fault, 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 current source 141 through the first control loop. The decreasing voltage at node 105 increases the control signal at control input 141, thereby opening the field-effect transistor further.

[0070] In the event of a fault, 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 the 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.

[0071] The transistor T2 becomes increasingly conductive and thus pulls the base of the transistor T3 in the controlled path of the bypass circuit 40 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.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 period of time.

[0072] Resistor R12 also serves as a current limiter. Transistor T3 has a higher current carrying capacity than the small signal transistors in control loops 30 and 20. In particular, the transistor's current carrying capacity should be selected so that current source 14 does not provide more than the maximum possible current through transistor T3, even in saturation mode.

[0073] LIST OF REFERENCE SYMBOLS

[0074] 1 supply potential connection

[0075] 2 Reference potential connection

[0076] 10 Current path

[0077] 11, 12, 13 Consumers, LEDs

[0078] 11', 12' LEDs

[0079] 14 controllable power source

[0080] 20 first control loop

[0081] 30 second control loop

[0082] 40 Bridging circuit

[0083] 101, 102, 103 knots

[0084] 104, 105 knots

[0085] 141 St your entrance

[0086] 201 Rege lice gang

[0087] 301 Rege laus gang

[0088] 303 Control input

[0089] 401, 402 controllable current source

[0090] CI, ... C3 capacitor

[0091] RI, ... R13 resistor

[0092] TI, T2, T3 transistor

[0093] 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 between a supply potential connection and a reference potential connection with a controllable current source; a bridging circuit, which is connected between the supply potential connection and a first node between the at least two consumers or between two nodes with at least one consumer, for bridging at least one consumer between the supply potential connection and the node in response to a bridging signal at a control input; 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 at least part of 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 the control signal; a second control loop is designed to generate the bridging signal to the control input of the bridging circuit by evaluating a detected voltage between the control signal and a potential in the current path; 2. Supply circuit according to claim 1, wherein the control input of the first control loop is connected 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 at least part of 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 coupled to the control input of the controllable 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 1, 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, in which 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.

7. Supply circuit according to one of the preceding claims, in which 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.

8. Supply circuit according to one of the preceding claims, 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 to whose control input a signal derived from the control signal can be fed.

9. Supply circuit according to claim 8, wherein the controlled path comprises 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 voltage divider.

10. 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 connection and the first node or between two nodes in the current path with at least one consumer and whose control input can be supplied with the bridging signal.

11. Supply circuit according to one of the preceding claims, in which 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.

12. 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, comprising the steps of: Detecting a signal corresponding to a voltage drop along the current path; Generating a control signal from the signal for controlling a current through the current path; Controlling a current through the current path using the control signal; evaluating the control signal and another signal from the current path; Generating a bridging signal depending on the evaluation of the control signal and the further signal; Bridging at least one load in the current path in response to the generated bridging signal.

13. A method according to claim 12, wherein the step of generating a bridging signal comprises the step of comparing the control signal with a threshold value, the threshold value being derived from the further signal.

14. The method of claim 12 or 13, wherein the step of generating a bypass signal, wherein the bypass signal is derived from a drain-gate voltage.

Images