SUPPLY UNIT FOR A BUS

Abstract

The invention relates to a bus node, which can be connected to a building services bus, which bus node comprises a supply unit and a control unit, wherein the supply unit is designed to output a measurement current onto the building services bus, and wherein the control unit is designed to sense and evaluate a bus current on the building services bus and, on the basis of the evaluation, to determine whether an operating current is output onto the building services bus by the supply unit.

Claims

1. A bus subscriber (BT1), that can be connected to a building technology bus (3), comprising: a supply unit (1), and a control unit (4), wherein the supply unit (1) is configured to output a measurement current (I.sub.M) to the building technology bus (3), and wherein the control unit (4) is configured to detect and evaluate a bus current (I.sub.Bus) to the building technology bus (3), and to determine on the basis of the evaluation whether an operating current (I.sub.B) is output to the building technology bus (3) by the supply unit (1).

2. The bus subscriber (BT1) according to claim 1, wherein the control unit (4) is configured to activate the supply unit (1) in accordance with the evaluation, and output the operating current (I.sub.B), or deactivate a current output.

3. The bus subscriber (BT1) according to claim 1, wherein the control unit (4) is configured to determine the number (N) of bus subscribers connected to the building technology bus (3) on the basis of the detected bus current (I.sub.BUS), and to determine whether a total bus current that can be output by the determined number (N) of bus subscribers lies within a bus specification.

4. The bus subscriber (BT1) according to claim 3, wherein the control unit (4) is configured to activate the supply unit (1) in a test phase, in particular, in order to output the measurement current (I.sub.M) to the building technology bus (3).

5. The bus subscriber (BT1) according to claim 4, wherein the control unit (4) is configured to activate the supply unit (1), after the test phase, in order to output an operating current (I.sub.B) to the building technology bus (3) when the total bus current that can be output by the determined number (N) of bus subscribers lies within a bus specification.

6. The bus subscriber (BT1) according to claim 4, wherein the control unit (4) is configured to deactivate the current output to the building technology bus (3) by the supply unit (1) when the total bus current that can be output by the determined number (N) of bus subscribers exceeds the bus specification.

7. The bus subscriber (BT1) according to claim 3, wherein the control unit (4) is configured to determine whether the total bus current that can be output by the determined number (N) of bus subscribers exceeds a threshold value in the range of 150-300 milliamperes, wherein the bus specification comprises the threshold value.

8. The bus subscriber (BT1) according to claim 4, wherein the control unit (4) is configured to receive and evaluate a specific bus signal transmitted over the building technology bus (3) and to initiate the test phase after receiving the specific bus signal, and in particular to activate the supply unit (1) to output the measurement current (I.sub.M).

9. The bus subscriber (BT1) according to claim 1, wherein the supply unit (1) is configured to generate the measurement current (I.sub.M) and the operating current (I.sub.B), that are output to the building technology bus (3).

10. The bus subscriber (BT1) according to claim 4, wherein the control unit (4) is configured to detect the bus current (I.sub.BUS) at a random point in time (t.sub.Rand), within the test phase.

11. A lamp that has a bus subscriber (BT1) according to claim 1

12. A bus system for building technology devices, comprising: a DALI building technology bus (3); and at least two bus subscribers (BT1, BT2) which are connected to the building technology bus (3) and which each have a supply unit (1, 1), wherein the supply units (1, 1) are operated independently, and wherein each of the bus subscribers is configured to output a measurement current (I.sub.M) to the building technology bus (3) generated by the respective supply unit (1, 1), and wherein the at least two bus subscribers (BT1, BT2) are connected to the DALI building technology bus (3) such that the measurement currents (I.sub.M) overlap, in particular such that they are added to one another.

13. The bus system according to claim 12, wherein the bus subscribers (BT1, BT2) each have a control unit (4, 4), which is configured to detect and evaluate a bus current (I.sub.BUS) to the building technology bus (3), in a test phase, and to determine a number (N) of bus subscribers (BT1, BT2) connected to the building technology bus (3) on the basis of the detected bus current (I.sub.BUS).

14. The bus system according to claim 13, wherein each control unit (4, 4) is configured to determine, on the basis of the determined number (N) of bus subscribers, whether a threshold value for a total bus current has been exceeded, when the determined number (N) of bus subscribers (BT1, BT2) outputs an operating current (I.sub.B) to the building technology bus (3) instead of the measurement current (I.sub.M).

15. The bus system according to claim 13, wherein each control unit (4, 4) is configured to deactivate a current output to the building technology bus (3) by the supply unit (1, 1) when the threshold value has been exceeded.

16. The bus system according to claim 12, wherein the bus system does not have a central current supply (101).

17. The bus system according to claim 14, wherein the threshold value for an acceptable total bus current is defined in the range of 150-300 milliamperes.

18. The bus system according to claim 16, wherein the independently operable decentralized supply units (1, 1) of the at least two bus subscribers (BT1, BT2) provide the total bus current.

19. A bus system for building technology devices, comprising: a DALI building technology bus (3), at least two bus subscribers (BT1, BT2), a decentralized current supply for the building technology bus (3), provided by at least two supply units (1, 1) of the at least two bus subscribers (BT1, BT2), wherein the decentralized current supply is configured to output at least a total bus current proportionate to each bus subscriber (BT1, BT2) to the building technology bus (3), and wherein each of the at least two bus subscribers (BT1, BT2) has a control unit (4, 4), which is configured to test whether the total bus current that can be output by the supply units (1, 1) lies within a bus specification.

20. The bus system according to claim 19, wherein the control unit (4, 4) is configured to deactivate a proportionate output of the total bus current by one of the bus subscribers (BT1, BT2) when the test shows that the total bus current, including the proportionate output, lies above the bus specification.

21. The bus system according to claim 19, wherein the at least one control unit (4, 4) is configured to test whether the acceptable total bus current exceeds the bus specification of 250 milliamperes.

22. A process for operating a bus subscriber connected to a building technology bus (3), comprising the steps of: outputting a measurement current (I.sub.M) from a supply unit to the building technology bus (3); using a control unit to detect and evaluate a bus current (I.sub.BUS) to the building technology bus (3); and using the control unit to determine whether an operating current (I.sub.B) is to be output to the building technology bus (3) by the supply unit on the basis of the evaluation.

23. The process as recited in claim 22, wherein at least two bus subscribers (BT1, BT2) are connected to a building technology bus (3), each of which has a supply unit (1, 1), wherein the supply units (1, 1) are operated independently of one another, wherein each of the bus subscribers (BT1, BT2) outputs a measurement current (I.sub.M) generated by the respective supply unit to the building technology bus (3), and wherein the at least two bus subscribers (BT1, BT2) are connected to the building technology bus (3) such that the measurement currents overlap, in particular such that they are added together.

24. The process recited in claim 22, wherein a decentralized current supply for the building technology bus (3) is provided by at least two supply units (1, 1) of at least two bus subscribers (BT1, BT2) wherein the decentralized current supply outputs a total bus current proportionate to each of the bus subscribers (BT1, BT2) to the building technology bus (3), and wherein each of the at least two bus subscribers (BT1, BT2) has a control unit that tests whether the total bus current that can bout output by the supply units lies within a bus specification.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0079] FIG. 1 shows a supply unit according to the prior art.

[0080] FIG. 2 shows an exemplary embodiment of a supply unit according to the invention.

[0081] FIG. 3 shows an exemplary embodiment of a lighting system with a voltage supply system according to the invention.

[0082] FIG. 4 shows an exemplary flow chart for a process according to the invention for operating a voltage supply system.

[0083] FIG. 5 shows an exemplary flow chart of an initializing phase of the process according to the invention pursuant to FIG. 4.

[0084] FIG. 6 shows an exemplary flow chart for a first current draw detection phase of the process according to the invention pursuant to FIG. 4.

[0085] FIG. 7 shows an exemplary flow chart for a slave mode of operation for the process according to the invention pursuant to FIG. 4.

[0086] FIG. 8 shows an exemplary flow chart of a master mode of operation for the process according to the invention pursuant to FIG. 4.

[0087] FIG. 9 shows another exemplary embodiment of a lighting system with a voltage supply system according to the invention.

[0088] FIGS. 10a and 10b shows another exemplary embodiment of a lighting system with a voltage supply system according to the invention.

[0089] FIG. 11 shows, schematically, how a part of a supply unit is utilized in the further exemplary embodiment.

[0090] FIG. 12 shows a process, as it is described in reference to FIG. 9.

[0091] FIG. 13 shows, schematically and by way of example, a process sequence in accordance with the further exemplary embodiment, in the form of a flow chart.

DETAILED DESCRIPTION

[0092] A supply unit 1 according to the prior art is shown in FIG. 1. The supply unit 1 comprises input connections 2, shown as mains line L and the neutral line N. The invention does not exclude the use of a supply unit 1 that also has a protective conductor. The supply unit 1 also has a DALI interface, shown herein as bus 3, which has the lines DA+ and DA. Such DALI supply units supply a bus 3 with a DC voltage, to which DALI operating devices, electronic ballasts, or dimmers, actuators or sensors, are connected as bus subscribers. The supply unit according to FIG. 1 is configured to supply the bus 3 with a current of 240 milliamperes. The supply unit is the only supply in a lighting system according to the prior art. A mains supply voltage of 220 volts to 240 volts is applied to the input connections 2. The mains supply voltage typically has a mains frequency of 50 hertz or 60 hertz. The supply unit is thus configured to output a power of 5 watts. The output voltage is 16 volts, with a tolerance of +/5%. The DALI signal is not SELV.

[0093] In particular, such a DALI supply unit complies with the DALI standard IEC 62386.

[0094] The disadvantage with the existing DALI system is that it is not possible to connect such DALI supply units 1 in parallel, because the output current cannot exceed a maximum current draw of 250 milliamperes from the bus 3. Communication between the individual DALI supply units is not possible before a stabilized DALI data communication bus has been obtained, such that a later regulation of the DALI supply unit would not prevent the elements in the lighting system A from being operated with excessive current, which would result in damage to these elements, or the destruction thereof.

[0095] The DALI supply unit 1 according to the prior art is too large for numerous applications in lighting technology. A less expensive, modular and more flexible supply of current to the bus 3 for a minimalistic lighting system is therefore desirable.

[0096] Therefore, an alternative approach to supplying a bus with a DC voltage is proposed in accordance with the invention. This should also enable a quasi-communication between supply units 1 connected in parallel. The DALI standardized maximum current draw of a maximum of 240 mA is also not exceeded with the supply units proposed in accordance with the invention. An individual adaptation of existing DALI lighting systems is thus possible, wherein an individual clustering of the lighting system is then possible.

[0097] A supply unit 1 according to the invention is shown in FIG. 2. In addition to the connections 2, 3 shown in FIG. 1, a control unit 4 is provided according to the invention in the supply unit 1. The control unit 4 is configured as a microcontroller, ASIC, FPGA or CPLD, for example. The control unit 4 is connected to the bus 3. A bypass switch 5 is also provided in the supply unit 1. The bypass switch 5 is provided for bypassing the bus 3. For this, the bypass switch 5 has a first switching state I, for connecting the lines DA+ and DA to one another. In a second switching state II, the bypass switch 5 disconnects the current supply lines DA+ and DA from one another. The control unit 4 causes the switching of the switching states of the bypass switch 5. A switching signal is generated by the control unit 4 for this. A current draw from the bus 3, which flows through the supply lines DA+ and DA, can then be detected by means of the bypass switch 5. A measurement element 6 is provided for this in the connection between the supply lines DA+, DA. The control unit 4 is provided for detecting a current drop over a measurement 6, configured as a current measurement resistor, for example, when the bypass switch 5 is activated. Alternatively, the measurement element 6 establishes a galvanic coupling, e.g. by means of coupled coils, or alternatively by means of an optocoupler. The detected current draw from the bus 3 is evaluated in the control unit 4. Depending on the current value, and in comparison with a predefined value I.sub.x for a maximum current draw, e.g. 240 mA according to the DALI standard IEC 62389, a power supply is then provided to the bus 3 by the supply unit 3, and the switch 5 is deactivated, or the power supply is not provided, and the switch 5 is deactivated.

[0098] A storage element 7 is provided according to the invention in the supply unit 1. DALI addresses, DALI lighting groups, DALI lighting scenarios, and/or dimmer values are stored in this storage element 7, which are provided for a specific setting of the lighting system A. When operating device 8 in the lighting system is replaced, the lighting system can then be set by means of the memory 7. All of the relevant data for the elements 8 connected to the lighting system A can thus be stored in the memory 7. These data thus serve as back-up data if operating devices need to be replaced in the lighting system.

[0099] In this manner, fundamental functionalities, e.g. firmware settings or regulations can also be stored in the memory 7. If an operating device is replaced, these data are downloaded from the memory, and are immediately available in the lighting system without elaborate initialization or installation processes. Additional functions such as dimming, group lighting, and emergency lighting scenarios can also be contained in the memory 7.

[0100] A lighting system A according to the invention is shown in FIG. 3. The lighting system A comprises a voltage supply system C, composed of a first supply unit 1 and a second supply unit 1, as is shown, by way of example, in FIG. 2. The bus 3 supplies the elements 8, 8, 8, and 8 with a DC voltage from the supply units 1, 1. Elements 8, 8, 8, and 8 are operating devices for lamps or dimmers or electronic ballasts or sensor elements, or operating devices for actuators in the lighting system A.

[0101] The lighting system A according to FIG. 3 is DALI standardized. The lighting system A is a comparatively small lighting system A, because only four elements are operated therewith. These four lighting elements 8, 8, 8, and 8 can then be interconnected in different patterns, and operated in different clusters. By way of example, a cluster B could be composed of two elements 8 and 8. Such a small cluster B can be operated by means of one of the two supply units 1, 1. A further cluster B can be composed of the elements 8 and 8, and can also be supplied with current by one of the supply units 1, 1. By way of example, a third cluster B can also be formed in which all four lighting elements 8, 8, 8, and 8 are to be operated simultaneously in the lighting system A. In such a cluster B, at least two supply units 1, 1 must be provided in order to generate the necessary current.

[0102] The clustering takes place, for example, during the installation or planning of the lighting system A. In order not to have to specify the clustering at such an early stage, a flexible, modular and modifiable structure can be obtained by means of supply units 1, 1 that can be connected in parallel.

[0103] The number of supply units 1, elements 8, and clusters B, is merely exemplary, and not limited to the numbers given, according to the invention.

[0104] In order to be able to operate this lighting system A according to the DALI standard, it must be ensured that the current draw never exceeds a predefined value I.sub.x for a maximum current draw, but that all of the elements 8 are supplied with sufficient power. It must also be ensured that the supply is provided within the waiting period of 600 milliseconds. This is enabled by a process for operating the voltage supply system C, as is depicted by way of example in FIGS. 4 to 8.

[0105] A further exemplary embodiment of a lighting system is shown in FIG. 9, which has supply units 1, 1 connected in parallel. The supply units 1, 1 are each preferably disposed inside a bus subscriber BT1, BT2 here. Other bus subscribers BTx, BTy, BTz, which may differ from the bus subscribers BT1, BT2, and in particular do not need to include a supply unit, are likewise shown in FIG. 9.

[0106] The supply units 1, 1 are also supplied via the input connections 2, 2, and connected to a bus 3. As illustrated, a control unit 4, 4 is provided in each of the bus subscribers, each of which can activate the supply units 1, 1, respectively. An activation signal, for example, can be output at a control input SE1 or SE2 of the supply units 1, 1 by the respective control unit 4, 4.

[0107] According to the exemplary embodiment in FIG. 9, the bus 3 is then supplied with electricity by the at least two supply units 1, 1 of the at least two bus subscribers BT1, BT2, which function as decentralized, independent current supplies. It is understood thereby that other bus subscribers BTx, BTy, BTz can also be configured in a manner analogous to the bus subscribers BT1, BT2, such that the decentralized, independent current supply comprises more than the supply units 1, 1. The supply units 1, 1 of the at least two bus subscribers BT1, BT2 then supply current to the bus 3, such that the current supply no longer needs to take place centrally, through a correspondingly sized central bus supply unit.

[0108] The supply units 1, 1 can therefore be smaller than the central bus supply unit. The supply units 1, 1 can also be assigned to the bus subscribers in another manner. A bus subscriber can thus not include a supply unit 1, 1, while another bus subscriber can include more than one supply unit 1, 1.

[0109] Another incentive for the decentralized current supply is that a central bus supply unit is relatively expensive, and is only justified when used with a large number of bus subscribers. With a small number of bus subscribers, it is more economical to use smaller and less expensive current supplies, as mentioned in the introductory portion of this application.

[0110] The bus system illustrated in FIG. 9 is thus equipped with at least two supply units 1, 1, which create the decentralized current supply. The bus subscribers BT1, BT2 and/or the supply units 1, 1 are preferably disposed such that the currents that are supplied to the bus 3 can be superimposed to form a total bus current.

[0111] The bus subscribers BT1, BT2 that provide the decentralized current supply for the bus 3, which is preferably a building technology bus, can exhibit an intelligence in the form of control units 4, 4 (preferably IC, ASIC or microcontrollers (C)). The bus subscribers BT1, BT2 can thus each test whether the resulting total bus current to the bus 3 and in particular an expected total bus current falls within a bus specification, in particular a DALI bus specification. This means, e.g., that the control unit 4, 4 tests whether a threshold value for a current, e.g. a threshold value for a maximum acceptable total bus current of, e.g. 150 to 350 milliamperes, preferably 250 milliamperes, has been exceeded when the at least two supply units 1, 1 output an operating current, in addition to or instead of a measurement current, to the bus 3.

[0112] If it has been determined that the threshold value has been reached or exceeded, thus exceeding the acceptable total bus current, the intelligence, i.e. the control units 4, 4 in the bus subscribers BT1, BT2, takes measures for reducing the ultimately resulting total bus current.

[0113] In a specific configuration, the intelligence tests the bus current applied to the bus 3 in a training or test phase. This means that at least one of the control units 4, 4 detects and evaluates the current applied to the bus 3 in a defined time period, which begins, e.g. when the control units 4, 4 receive a signal, and has a predefined length (e.g. stored in a memory accessible to the control unit 4, 4). Each bus subscriber BT1, BT2 determines whether the contribution of its respective decentralized supply unit 1, 1 is necessary regarding the maximum total bus current.

[0114] The sequence is preferably:

[0115] Each bus subscriber BT1, BT2 that has a decentralized current supply has at least one current source, e.g. in a supply unit 1, 1, which can deliver a constant current at at least two different current levels.

[0116] A first current level output by the supply unit 1, 1 is a measurement current I.sub.M. This measurement current I.sub.M is output by the supply units 1, 1 in the test phase. This measurement current I.sub.M can be relatively low, e.g. 10-25 milliamperes.

[0117] Each bus subscriber BT1, BT2 is assigned to a point in time, e.g. by a (local) pseudo-random generator, at which it tests/measures the total current capacity currently available at the bus 3. The bus subscribers BT1, BT2 can form a maximum load to the bus 3 for this. The bus subscriber BT1, BT2, or the control unit 4, 4 can then detect which current is applied to the bus 3. It is important during the test phase that the respective bus subscriber BT1, BT2, or the supply units 1, 1 only activate the current source that outputs the measurement current I.sub.M, thus, that which supplies the lower constant current (e.g. 10 mA, in comparison with 50 mA in, e.g., a total current maximum load of 250 mA).

[0118] When a bus subscriber BT1, BT2 tests which total bus current is being employed, it can determine, when the level of the measurement current I.sub.M is known, the number of decentralized current supplies, or bus subscribers BT1, BT2 outputting a measurement current I.sub.M to the bus 3. The bus subscriber BT1, BT2 can then conclude whether a bus current set by the bus 3 lies within or beyond the bus specifications, in particular the DALI specifications when a second, larger and/or additional current source is activated, which provides an operating current I.sub.B. The bus subscriber knows which operating current is output by each bus subscriber BT1, BT2. The larger current source alternatively or additionally delivers the operating current I.sub.B, which can preferably be 10-70 milliamperes, and ideally can be 15, 25, 40, 50, 65, 75, 90, 105, 125 or 140 milliamperes.

[0119] It can thus be concluded whether the bus subscriber that is currently assessing/measuring/testing must actually deliver a contribution with the decentralized current supply. If this is not the case, the testing bus subscriber BS1, BS2 shuts off, or deactivates the output of a current provided by the supply unit 1, 1 to the bus 3.

[0120] After all of the bus subscribers BT1, BT2 have completed the test phase, the bus system is configured, and if applicable, only a sub-group of the bus subscribers BT1, BT2 output their operating current I.sub.B with the decentralized current supply after the test phase when actually in operation.

[0121] After completion of the training phase, all of the bus subscribers BT1, BT2 that have determined that they must deliver a contribution each activate the operating current I.sub.B, and a total current is obtained that lies in the acceptable range of the total current. The operating current I.sub.B can be output alternatively to or in addition to the measurement current I.sub.M.

[0122] It is also possible to repeat the test phase, e.g. if certain bus parameters are lacking that are prerequisites for the measurement. The starting point for the test phase does not need to be defined by the bus subscribers BT1, BT2, e.g. it can be defined externally, by a bus signal from a bus master. The test phase can also be initiated automatically by the bus subscribers BT1, BT2, e.g. starting after a predetermined point in time, or within a predetermined time period, starting when the bus subscriber BT1, BT2 is supplied with a supply voltage.

[0123] A lighting system 100 is shown In FIG. 10a for a better comparison with a lighting system according to the prior art. A bus supply unit 102 is supplied with power by a supply voltage source 101, in particular an AC voltage. The bus supply unit 102 supplies the bus 103 with the bus voltage, or bus current I.sub.BUS. The bus supply unit 102 is configured specifically for supplying the bus 103, and in particular, is configured as a DALI bus supply unit.

[0124] Moreover, bus subscribers 104, 105, 106 are shown, each of which can likewise be supplied with power by a voltage supply 107, 108, 109. The voltage supplies 107, 108, 109 operate the bus subscribers 104, 105, 106, and are used for operating bus subscribers, e.g. equipment 110 such as lamps, sensors, actuators, etc. Each of the bus subscribers 104, 105, 106 has an operating device BG1, BG2, BG3, which converts the supply voltage supplied by the voltage supplies 107, 108, 109 for the corresponding equipment 110, and can also communicate with the bus 103 in order to receive commands transmitted by the bus 103, and activate the equipment 110 accordingly.

[0125] FIG. 10b, by comparison, shows a design according to the further exemplary embodiment of the invention shown in FIG. 9, in which the bus subscribers BT1, BT2, and an additional bus subscriber BT3, are supplied with power by a voltage supply 107, 108, 109, wherein the bus subscribers BT1, B2, BT3 each have, in addition to operating devices BG1, BG2, BG3, a supply unit 1, 1, 1, which then supply the bus 3. A central bus supply unit 102 is thus unnecessary for supplying the bus 3 with power. The main reason for this configuration is that, as stated above, the costs for bus systems increase quickly due to the bus supply unit 102, when the bus system is small. Furthermore, the central bus supply unit 102 must also be wired accordingly. The central bus supply unit 102 normally provides a current source for this, which has a maximum output of 250 mA.

[0126] In the configuration shown in FIG. 10b, each bus subscriber BT1, BT2, BT3 has its own supply unit 1, 1, 1, each of which can output an operating current I.sub.B to the bus 3. If numerous bus subscribers BT1, BT2, BT3 with such supply units 1, 1, 1 are then added to the system and connected to the bus 3, they can collectively output their operating currents I.sub.B to the bus 3, or they can detect the bus current I.sub.BUS at the bus 3, and adjust their own contribution to the total bus current.

[0127] The fundamental idea is thus to determine The measurement current I.sub.M output by the bus subscribers BT1, BT2, BT3 (only) during the test phase has a predefined level. Thus, by way of example, a total bus current of 100 mA can be output to the bus 3, and detected by a bus subscriber BT1, BT2, BT3, when the measurement current is 10 mA, and 10 bus subscribers are connected to the bus 3. If a bus subscriber BT1, BT2, BT3 then determines that a bus current of 10 mA is applied to the bus, the control unit 4, 4 of the bus subscriber BT1, BT2, BT3 can then determine that with a respective measurement current I.sub.M of 10 mA, 10 bus subscribers BT1, BT2, BT3 can participate in the decentralized current supply.

[0128] during the test or training phase, what current is available at the bus 3. The bus subscribers BT1, BT2, BT3, or their control units 4, 4 thus detect the current applied to the bus 3 within the test phase, and can decide on the basis of this, whether they will output the operating current I.sub.B by means of their own supply units 1, 1, 1, thus increasing the current feed to the bus 3.

[0129] The bus subscriber BT1, BT2, BT3 detects the bus current I.sub.BUS applied to the bus 3 within the test phase at a random point in time. In particular, the bus subscriber BT1, BT2, BT3 can have a (not shown) random generator, which establishes the random point in time within the test phase or training phase. It is also possible for a randomly generated number to be stored in the bus subscriber BT1, BT2, BT3, which defines a point in time within the test phase. In particular, each bus subscriber BT1, BT2, BT3 can detect the start of the test phase in that, for example, a specific signal is received via the bus 3, indicating the start of the test phase. This signal can be transmitted in particular by a bus master.

[0130] If the bus subscriber BT1, BT2, BT3 then detects a current applied to the bus 3, it knows that when all of the bus subscribers were to output an operating current I.sub.B of, e.g., 50 mA to the bus, this would violate the bus specifications. These specify, e.g., that only 250 mA are to be applied to the bus 3 according to the DALI standard. In this regard, the bus specification has at least one threshold value for the maximum acceptable total bus current. If each of the bus subscribers BT1, BT2, BT3 were to output an operating current I.sub.B of 50 mA to the bus, this would result in a bus current of 500 mA. In order to avoid this, the bus subscriber BT1, BT2, BT3 adjusts its current output to the bus 3.

[0131] Thus, another bus subscriber BT1, BT2, BT3, e.g. bus subscriber BT2, can then detect a bus current of 90 mA to the bus at another random point in time, and thus likewise determine that with new bus subscribers, the bus specification would be violated by the operating current output to the bus following the test phase.

[0132] This process is then carried out until, e.g., a bus subscriber BTx has determined that there is only a bus current of, e.g. 50 mA or less at the bus. If this is the case, the bus subscriber BTx determines that with an output of the operating current I.sub.B after the test phase by all of the remaining bus subscribers, a bus specification will not be violated, because with a respective operating current of 50 mA, the threshold value for the maximum total bus current of 250 mA is not exceeded.

[0133] It should also be noted that the supply units of the bus subscribers can also be integrated in operating device of the bus subscribers. This has been depicted for bus subscriber BT3.

[0134] The process is also illustrated in FIG. 11. It can be seen herein that in the test phase, first all bus subscribers with a supply unit output the measurement current I.sub.M to the bus, such that there is first a current I.sub.BUS at the bus 3 that corresponds to the measurement current I.sub.M multiplied by the number of bus subscribers N. As explained above, it is then checked by the bus subscriber, at a random point in time, whether or not it should provide an operating current after the test phase. If this is not the case, it no longer outputs a measurement current I.sub.M to the bus 3. This results in a drop in the bus current I.sub.BUS.

[0135] A bus subscriber testing at another point in time would thus detect a modified bus current I.sub.BUS, and the control unit of the bus subscriber would then carry out the evaluation on the basis of the modified bus current I.sub.BUS. Lastly, at least one bus subscriber determines that the remaining number of bus subscribers, e.g. N3, can each output an operating current I.sub.B to the bus 3, without violating the bus specifications, or exceeding the threshold value for the maximum total bus current. After completion of the test phase, these remaining bus subscribers then each make their operating current I.sub.B available to the bus 3, such that the bus current I.sub.BUS increases as a whole to the extent of the superimposed, and summed operating currents, e.g. N3*I.sub.B.

[0136] A concrete design for a supply unit 1, 1 is shown schematically in FIG. 12. In particular, the supply unit 1 has a first current source I.sub.1 and a second current source I.sub.2. The first current source I.sub.1 can provide the measurement current I.sub.M, for example, while the second current source I.sub.2 can provide the operating current I.sub.B. Switches S1, S2, S3 are likewise shown, which are activated by the control unit 4. A measuring resistor R.sub.Shunt is connected in series to the switch S3, with which the control unit 4 can detect a voltage V.sub.Shunt.

[0137] At the start of the test phase, switch S2 is activated, and switch S1 is connected to the current source I.sub.1, such that the current source I.sub.1 outputs the measurement current I.sub.M to the bus 3. After a random period, which can be established by a random generator, as explained above, switch S3 is activated, and a voltage that reflects the current at the bus, or a current, is measured at the measuring resistor R.sub.Shunt. Because all of the bus subscribers output the same measurement current I.sub.M to the bus, the detected bus current thus corresponds to a multiple of a measurement current I.sub.M, and the number of bus subscribers can therefore be determined. If the maximum number of bus subscribers is exceeded, i.e. the number of bus subscribers that can output an operating current I.sub.B to the bus without violating the bus specifications is exceeded, switch S2 is deactivated, and the current sources I.sub.1, I.sub.2 are deactivated.

[0138] Otherwise, switch S2 remains active, and after a predetermined period, i.e. after the test phase, switch S1 is switched to the current source I.sub.2, thus outputting an operating current I.sub.B to the bus.

[0139] As a matter of course, the test phase can also be automated, e.g. taking place after a predetermined period following the initiation of a current supply by the bus subscribers.

[0140] The process carried out by a bus subscriber according to the invention is shown in a flow chart in FIG. 13.

[0141] The test phase starts in step S130. The start of the test phase can be indicated by a bus signal, as explained above, or it can start after a specific time following the voltage supply to the bus subscriber that has been stored in the bus subscriber. The length of the test phase in particular is also stored in the bus subscriber.

[0142] In step S131, the supply unit 1, 1 outputs the measurement current I.sub.M to the bus 3.

[0143] The control unit then detects the bus current I.sub.BUS applied to the bus 3 in step S132, at a random point in time t.sub.Rend, preferably lying between 0 and 65.5 ms after the start of the test phase.

[0144] In step S133, the control unit 4 determines the number of bus subscribers connected to the bus 3 on the basis of the detected bus current I.sub.BUS. In step S134, the control unit 4 of the bus subscriber then determines whether a threshold value for the total bus current has been reached on the basis of the determined number or the detected bus current I.sub.BUS, if all of the bus subscribers in the determined number were to output the operating current I.sub.B. The threshold value thus represents a criterion, according to which it is determined whether the bus specifications have been violated.

[0145] If the bus specifications have been violated, or a violation thereof occurs, the bus subscriber deactivates a current output to the bus 3 in step S135.

[0146] Otherwise, the bus subscriber switches to outputting the operating current I.sub.B in step S136 after completion of the test phase.

[0147] An exemplary embodiment of a process flow chart for a process according to the invention for operating a voltage supply system C is described in FIG. 4. The voltage supply system C is constructed like that in FIG. 3, by way of example, and comprises at least two supply units 1, 1.

[0148] An initialization phase of the process according to the invention is initiated in step S1. The initialization phase is explained in greater detail in reference to FIG. 5. A simultaneous switching of the bypass switch 5 to the first switching state I by two supply units 1, 1 is prevented in particular in phase S1.

[0149] Following the initialization phase, a first current draw detection phase S2 takes place. This current draw detection phase S2 is explained in greater detail in reference to FIG. 6.

[0150] The result of the current draw detection phase S2 is a comparison result, showing how much greater the detected current draw from the bus 3 is than a predefined value I.sub.x for a maximum current draw, e.g. the maximum acceptable current of 240 milliamperes in the operation of a lighting system A in accordance with the DALI standard. If the current draw is greater than the predefined value I.sub.x in the lighting system (yes case), then the master mode operation S4 is initiated. In the no case, the slave mode operation S3 is initiated for the respective supply unit 1. Subsequently to the slave mode of operation S3 or the master mode of operation S4, a time period check S5 takes place, in which it is checked whether the bypass switch 5 of one of the supply units 1, 1 is switched to the switching state I for more than a maximum acceptable time T.sub.x. If this is the case, the process begins anew. If this is not the case, the operation continues to run as it is.

[0151] The process according to FIG. 4 is preferably completed before completion of a start-up procedure waiting period of 600 milliseconds. Thus, prior to completion of a stabilization of the DALI bus 3, a quasi-communication between the supply units 1 is created, and a stable operation of the lighting system 1 is ensured.

[0152] The initialization phase S1 of the process according to the invention according to FIG. 4 is illustrated in detail in FIG. 5. For this, the voltage supply system A is first activated in step S11. The bypass switch 5 is then switched to the first switching state I in step S12. The bus supply line DA+ is connected in this manner to the bus supply line DA. Subsequently, completion of an activation waiting period T.sub.Einschalt is waited for in step S13. This is necessary to ensure that the supply unit 1 is in stable operation for a correct detection of the current draw by the control unit 4. In the subsequent step S14, the supply unit 1 waits for the completion of a random waiting period T.sub.Zufall. This random waiting period T.sub.Zufall is different for each supply unit in the voltage supply system C, thus preventing simultaneous current draw detection by two different supply units 1. In this manner, the detection of a misleading current draw by another supply unit 1 is prevented.

[0153] A first current draw detection phase S2 according to FIG. 4 is shown in FIG. 6. For this, a current draw from the bus 3 is detected in step S21. The bypass switch 5 remains activated for this (see initialization phase S1). The control unit 4 detects the current draw through the measuring element 6. In the subsequent step S22, a comparison is made between the current draw and a predefined value I.sub.x for the maximum current draw by the control unit 4. If the detected current draw I is less than or equal to the predefined value I.sub.x, the first current draw detection phase S2 is completed.

[0154] If the detected current draw I is greater than the predefined value I.sub.x, the supply unit 1 is deactivated in step S23. The current draw from the bus 3 is subsequently detected again in step S24. Following this, a comparison S25 takes place again, corresponding to the previous comparison S22. If the detected current draw I is less than or equal to the predefined value I.sub.x, the supply unit 1 is operated in the slave mode of operation S3, and the detection phase S2 is completed. If the detected current draw I is greater than the predefined value I.sub.x, the first current draw detection phase S2 is completed, but the supply unit 1 is operated in the master mode S4.

[0155] The slave mode of operation S3 according to FIG. 4 is described in greater detail in FIG. 7. The slave mode of operation S3 is activated when the current draw detected in step S25 or step S22 is less than the predefined value I.sub.x. The bypass switch 5 is then deactivated in step S31 in that it is switched to the switching state II. The DA+ line of the bus 3 is thus disconnected from the DA line of the bus 3. The detection of a voltage U of the bus 3 then takes place in step S32. If a comparison S33 shows that the voltage is lower than a reference voltage U.sub.x, e.g. 9 V, it is assumed that there is no other supply unit 1 in the voltage supply system C. If the comparison shows that the voltage is higher than 9 V, for example, then completion of a random period T.sub.Zufall is waited for in step S34. The bypass switch 5 is then switched back to the activated state I (see step S35). The current draw from the bus 3 is again detected in accordance with steps S36 and S37. The detected current draw is again compared here with the value I.sub.x, wherein if it falls below the value I.sub.x, a switching to the master mode takes place in accordance with S4.

[0156] If the current draw is less than the value I.sub.x, it is assumed that no other supply unit 1 is active in the voltage supply system C, and the bypass switch 5 can be switched back to state II in accordance with step S38. After waiting for completion of a master mode waiting period T.sub.Master in step S39, the supply unit 1 is switched off (see step S40). The slave mode S3 is then terminated.

[0157] The master mode of operation S4 according to FIG. 4 is shown in greater detail in FIG. 8. First, completion of a master mode waiting period T.sub.Master is waited for in step S41. Subsequently, detection of the current draw takes place in steps S42 and S43. In this manner, it is determined whether the current draw lies below the value I.sub.x. Moreover, each supply unit 1 terminates the slave mode S3 in this phase, because a current draw has been detected that is higher than the value I.sub.x, and the current draw from the bus 3 must thus be reduced.

[0158] As soon as the current draw is less than the value I.sub.x, the bypass switch 5 is switched to the deactivated state I in accordance with step S44. This is followed by the detection of the voltage to the bus 3 in accordance with steps S45 and S46, in a manner similar to that in steps S33 and S32. If the voltage is greater than a reference voltage U.sub.x, it is assumed that there is only one master supply unit 1 in the lighting system A, and this assumes the role of the main supply. If it has been determined in step S46 that the voltage is lower than the reference voltage U.sub.x, then there are other supply units 1, 1 running in the master mode in the lighting system 1. Completion of a random waiting period T.sub.Zufall is then waited for (S47), and the bypass switch 8 is switched back to the switching state I in accordance with step S48. A current draw detection is repeated in step S49. If the current draw is greater than the value I.sub.x, the master mode in accordance with step S4 is reinstated.

[0159] With the process steps described in FIGS. 4 to 8, it is ensured that the maximum current draw never exceeds a value I.sub.x, and the lighting system A can be adapted to its respective clustering B, B, B.

[0160] All of the features that are shown, depicted, or claimed herein can be combined arbitrarily with one another.