Abstract:
The present disclosure relates to an energy supply device for providing an output voltage and an output current. The device includes a first operating state, a second operating state, a measuring assembly, and a signal generator. The measuring assembly is configured to sense a current amplitude of the output current of the energy supply device. The signal generator is configured to produce the output voltage and the output current. The signal generator is further configured to reduce a voltage amplitude of the output voltage of the energy supply device in the first operating state to change to the second operating state if the sensed current amplitude falls below a first current threshold value and to increase a voltage amplitude of the output voltage of the energy supply device in the second operating to change to the first operating state if the sensed current amplitude exceeds a second current threshold value.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a 371 national phase filing of International Application No. PCT/EP2015/056303, entitled “ENERGY SUPPLY DEVICE HAVING TRANSITIONS BETWEEN OPERATION AND STAND-BY THAT ARE DEPENDENT ON THE OUTPUT CURRENT”, filed 24 Mar. 2015, which claims priority to German Patent Application No. 10 2014 107 545.5, entitled “ENERGIEVERSORGUNGSGERAT”, filed 28 May 2014. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates to an energy supply device, in particular a power supply unit. 
         [0003]    An energy supply device, such as a power supply unit, is an independent device or a subassembly for supplying energy to devices or subassemblies which require voltages and currents other than those provided by the energy supply network. 
         [0004]    An electrical energy supply device usually operates independently of the load connected to the energy supply device as soon as an input voltage has been applied to the energy supply device. 
         [0005]    If a load connected to the energy supply device changes to stand-by operation, the energy supply device usually still provides the input voltage applied to the power supply to the connected load. If the energy supply for the energy supply device with a connected load is switched off, a switching unit, for example a contactor, is usually connected upstream in order to counteract an increased build-up of voltage at the energy supply device and the load, which are electrically connected to one another, while the energy supply is switched off. 
         [0006]    If switched on again from a switched-off state, for example the stand-by state, auxiliary energy is usually needed to change the energy supply device from its stand-by state to the active state again. Therefore, some energy supply devices have a digital input in order to switch the energy supply device on or off with a fixed level. A control input which is controlled by a controller is required for this purpose. 
         [0007]    The document DE 196 00 962 A1 discloses a switched mode power supply unit having stand-by operation. In order to change over from the stand-by operation to the normal operation, the signal at a connection for opening a switch is turned off, with the result that the output voltages are regulated again via a Zener diode. 
       SUMMARY 
       [0008]    The object on which the disclosure is based is to specify an energy supply device and a method which independently and efficiently changes over the energy supply device between two operating states of the energy supply device. 
         [0009]    This object is achieved by means of the subject matters of the independent patent claims. The figures, the description and the dependent claims relate to advantageous examples of the principles of this disclosure. 
         [0010]    The present disclosure is based on the knowledge that the energy supply device can be independently and efficiently changed over between a first operating state and a second operating state by sensing the current amplitude at the output of the energy supply device. 
         [0011]    According to a first aspect of the disclosure, the object is achieved by means of an energy supply device for providing an output voltage and an output current, the energy supply device having a first operating state and a second operating state. The energy supply device has a measuring assembly for sensing a current amplitude of the output current of the energy supply device, and a signal generator for producing the output voltage and the output current. The signal generator is designed to reduce a voltage amplitude of the output voltage of the energy supply device in the first operating state of the energy supply device in order to change to the second operating state if the sensed current amplitude falls below a first current threshold value. The signal generator is also designed to increase a voltage amplitude of the output voltage of the energy supply device in the second operating state of the energy supply device in order to change to the first operating state if the sensed current amplitude exceeds a second current threshold value. 
         [0012]    The output power and therefore the output voltage and the output current have a higher absolute value in the first operating state than in the second operating state. 
         [0013]    The transition of the energy supply device from the first operating state to the second operating state causes a reduction in the output voltage of the energy supply device by 30% to 80%, for example, or by 50%, for example. The signal generator reduces the voltage amplitude of the output voltage of the energy supply device from 24 V to 10-12 V, for example, in order to change from the first operating state to the second operating state. 
         [0014]    The signal generator reduces the output current of the energy supply device by 5-20% or more below the rated current in order to change from the first operating state to the second operating state. 
         [0015]    The measuring assembly repeatedly records the current amplitude of the output current at intervals of time. The signal generator compares the sensed current amplitude with the first and second current threshold values which can be or are stored in a memory of the signal generator. 
         [0016]    The energy supply device is a power supply unit, for example. 
         [0017]    The energy supply device according to the disclosure achieves the advantage that a transition between the first operating state and the second operating state of the energy supply device is automatically effected. 
         [0018]    In one advantageous example of the energy supply device, the first operating state is an active state, and the second operating state is an energy-saving state, in particular a stand-by mode or a sleep mode. In the active state, the output voltage and the output current are each set to a value which allows operation of the electrical device connected to the energy supply device, whereas, in the energy-saving state, the output voltage and the output current are each set to a value which restricts operation of the electrical device connected to the energy supply device. 
         [0019]    This achieves the advantage that energy can be automatically saved. 
         [0020]    In one advantageous example of the energy supply device, the second current threshold value is the first current threshold value or a further current threshold value. In a converted form, the first current threshold value is 5%-20% or more below the amplitude of the output current in the first operating state, for example. 
         [0021]    If the first current threshold value is equal to the second current threshold value, a transition of the energy supply device from its second operating state to the first operating state is effected if the first current threshold value is exceeded again, for example. 
         [0022]    If the absolute value of the second current threshold value is higher than that of the first current threshold value, a transition of the energy supply device from its second operating state to the first operating state is effected only if the second current threshold value has been reached or exceeded. 
         [0023]    If the absolute value of the second current threshold value is lower than that of the first current threshold value, a transition of the energy supply device from the second operating state to the first operating state is already effected if the second current threshold value has been reached or exceeded. For example, the second current threshold value is lower than the first current threshold value in order to also enable a transition of the energy supply device from its second operating state to the first operating state for an electrical load which is connected to the energy supply device and whose load current and load voltage are below a minimum load current and a minimum load voltage. 
         [0024]    The second current threshold value achieves the advantage that, if the second current threshold value is exceeded by the load current of a load connected to the energy supply device, the energy supply device changes from the second operating state to the first operating state automatically without the use of an additional energy source. 
         [0025]    In one advantageous example of the energy supply device, the first current threshold value or the second current threshold value or the further current threshold value is settable or prestored. Depending on the load connected to the energy supply device, the first current threshold value and the second current threshold value can be set or prestored current threshold values can be used to change the energy supply device from its first operating state to its second operating state and vice versa. 
         [0026]    This achieves the advantage that the energy supply device can be used in a flexible manner, in particular for consumers having different load currents and load voltages, and the automatic transition from the first operating state to the second operating state and vice versa is not lost in the process. 
         [0027]    In one advantageous example of the energy supply device, the signal generator is designed to compare the sensed current amplitude with the first current threshold value or the second current threshold value or the further current threshold value. The signal generator repeatedly compares the sensed current amplitude with the current threshold values at predetermined times. The predetermined times are preferably given at times after expiry of equidistant intervals of time which are in the seconds range, for example. The current amplitude is sensed by the measuring assembly after expiry of 30, 20, 10 or 5 seconds in each case, for example, and is then compared with the first current threshold value or the second current threshold value or the further current threshold value by the signal generator. 
         [0028]    This achieves the advantage that the energy supply device automatically changes over between the first operating state and the second operating state as soon as the load current falls below or exceeds the current threshold value. 
         [0029]    In one advantageous example of the energy supply device, the signal generator is designed to reduce the voltage amplitude of the output voltage of the energy supply device to a settable first or prestored first voltage amplitude value if the sensed current amplitude falls below the first current threshold value. The first current threshold value is preferably stored or can be stored in a memory of the signal generator. With a reduction in the output voltage, the output current of the energy supply device can be reduced at the same time, with the result that the energy supply device changes from the first operating state to the second operating state automatically, that is to say without an additional energy source. 
         [0030]    This achieves the advantage that the energy supply device automatically saves energy. 
         [0031]    In one advantageous example of the energy supply device, the signal generator is designed to reduce the voltage amplitude of the output voltage of the energy supply device in the first operating state after expiry of a settable or prestored first delay time interval. After a first sensing of a current amplitude below the first current threshold value, the measuring assembly carries out a further sensing of the current amplitude after expiry of the first delay time interval. If the further sensed current amplitude is likewise below the first current threshold value, the signal generator reduces the voltage amplitude of the output voltage of the energy supply device. For example, the first delay interval comprises a period of several seconds, for example 30, 20, 10, 5 or 3 seconds. 
         [0032]    This achieves the advantage that a transition from the first operating state to the second operating state cannot be initiated by random output current fluctuations. 
         [0033]    In one advantageous example of the energy supply device, the signal generator is designed to increase the voltage amplitude of the output voltage of the energy supply device to a settable second or prestored second voltage amplitude value if the sensed current amplitude exceeds the second current threshold value. If the measuring assembly records a sensed current amplitude which exceeds the second current threshold value during operation of the energy supply device in the second operating state, the signal generator increases the voltage amplitude of the output voltage of the energy supply device to a settable second or prestored second voltage amplitude value. 
         [0034]    For example, the voltage amplitude is increased from a value in the range of 8 V to 14 V or 10 V to 12 V in the second operating state to a voltage amplitude having a value of between 20 V and 60 V or between 20 V and 28 V or to 24 V, for example, in the first operating state. 
         [0035]    This achieves the advantage that the energy supply device automatically changes from the second operating state to the first operating state. 
         [0036]    In one advantageous example of the energy supply device, the signal generator is designed to increase the voltage amplitude of the output voltage of the energy supply device immediately or after expiry of a prestored second delay time interval after it has been detected that the second current threshold value of the current amplitude has been exceeded. The prestored second delay time interval comprises, for example, the same period as the first delay time interval. For example, the second delay interval comprises a period of several seconds, for example 30, 20, 10, 5 or 3 seconds. 
         [0037]    It is also conceivable, for example, for the second delay time interval to comprise a shorter period than the first delay time interval, for example 20, 10, 5, 3 or 1 seconds. 
         [0038]    If the voltage amplitude of the output voltage is increased immediately, the voltage amplitude of the output voltage is increased in a period of less than one second, for example. The switching delay is based on the circuit properties of the components of the energy supply device. 
         [0039]    This achieves the advantage that a transition from the second operating state to the first operating state cannot be initiated by random output current fluctuations. 
         [0040]    In one advantageous example of the energy supply device, the measuring assembly has a measuring resistor. The measuring resistor is designed to record the current amplitude of the output current on the basis of a voltage drop across the measuring resistor. For example, the measuring resistor is provided in the form of a measuring shunt. A measuring shunt is a low-value electrical resistor which is used to measure the electrical current. The current which flows through a measuring shunt causes a voltage drop which is proportional to it and is measured. The measuring shunt resistor is connected in parallel with a measuring circuit and then records its voltage drop. Since higher current intensities cannot be directly measured, they are passed through a measuring shunt resistor and the resulting voltage drop is measured. The resistance value of measuring shunt resistors is accordingly in the milli-ohm range or below at several tenths or hundredths of a milli-ohm. 
         [0041]    This achieves the advantage that the current amplitude of the output current can be sensed by the measuring assembly of the energy supply device. 
         [0042]    In one advantageous example of the energy supply device, the signal generator has a transformer with a primary side, to which an input voltage can be applied, and with a secondary side for outputting the output voltage. The transformer of the signal generator has a primary winding which is directly fed with the AC voltage from the energy supply network and the network frequency of the energy supply network. The transformer of the signal generator converts the input voltage, that is to say the AC voltage from the energy supply network, to the required output voltage value(s) and ensures galvanic separation from the mains. 
         [0043]    The secondary AC voltage on the secondary side of the transformer can be converted, by means of a rectifier and a smoothing capacitor, to a DC output voltage which can then be provided at the output of the signal generator. A downstream linear regulator and a buffer capacitor also possibly ensure an output voltage which can be kept constant. 
         [0044]    This achieves the advantage that any desired output voltage can be applied to the energy supply device. 
         [0045]    According to a second aspect of the disclosure, the object is achieved by means of a method for operating an energy supply device, the energy supply device having a first operating state and a second operating state, a measuring assembly for sensing a current amplitude of an output current of the energy supply device and a signal generator for controlling a voltage amplitude of the output voltage of the energy supply device. 
         [0046]    The method comprises sensing a current amplitude of the output current of the energy supply device by means of the measuring assembly; reducing a voltage amplitude of the output voltage of the energy supply device in the first operating state of the energy supply device by means of the signal generator in order to change to the second operating state if the sensed current amplitude falls below a first current threshold value. 
         [0047]    The method also comprises increasing the voltage amplitude of the output voltage of the energy supply device in the second operating state of the energy supply device by means of the signal generator in order to change to the first operating state if the sensed current amplitude exceeds a second current threshold value. 
         [0048]    The output power and therefore the output voltage and the output current are set to a higher absolute value in the first operating state than in the second operating state. If the energy supply device changes from the first operating state to the second operating state, the output voltage of the energy supply device is reduced by 30% to 80%, for example, or by 50%, for example. The voltage amplitude of the output voltage of the energy supply device is reduced from 2.4 V to 10-12 V, for example, in order to change from the first operating state to the second operating state. 
         [0049]    In this case, the output current of the energy supply device is reduced by 5-20% or more below the rated current so that the energy supply device changes from the first operating state to the second operating state. 
         [0050]    The measuring assembly repeatedly senses the current amplitude of the output current at intervals of time. 
         [0051]    The sensed current amplitude is compared with the first current threshold value and with the second current threshold value by the signal generator. The second current threshold value is set to be equal to the second current threshold value, for example, or is prestored. A lower or higher current threshold value can also be set or prestored for the second current threshold value, for example. 
         [0052]    In the case of a lower second current threshold value, a consumer which is connected to the energy supply device and has a load with a low load current and a low load voltage can be detected by the energy supply device. In accordance with the method according to the disclosure, the energy supply device then automatically changes from the second operating state to the first operating state. 
         [0053]    The energy supply device is a power supply unit, for example. 
         [0054]    In the method according to the disclosure, the first operating state is set as an active state, and the second operating state is set as an energy-saving state, in particular a stand-by mode or a sleep mode. In the active state, the output voltage and the output current are each set to a value which allows operation of the electrical device connected to the energy supply device, whereas, in the energy-saving state, the output voltage and the output current are each set to a value which restricts operation of the electrical device connected to the energy supply device. 
         [0055]    The method according to the disclosure achieves the advantage that a transition between the first operating state and the second operating state of the energy supply device is automatically effected. 
         [0056]    In one advantageous example of the method, the sensed current amplitude is compared with the first current threshold value or the second current threshold value or the further current threshold value by the signal generator. The signal generator compares the sensed current amplitude with the current threshold values at predetermined times. For example, the predetermined times are determined by expiry of equidistant intervals of time which are in the seconds range, for example. 
         [0057]    For example, after expiry of 30, 20, 10 or 5 seconds in each case, the current amplitude is sensed by the measuring assembly and is then compared with the first current threshold value or the second current threshold value or the further current threshold value by the signal generator. 
         [0058]    Depending on the connected consumers and their loads, that is to say their load voltages and load currents, the first current threshold value or the second current threshold value or the further current threshold value is set or prestored. 
         [0059]    This achieves the advantage that the method according to the disclosure can be applied to consumers having different loads and a transition between the first operating state and the second operating state is effected as soon as the load current falls below the first current threshold value or the load current exceeds the second current threshold value. 
         [0060]    In one advantageous example of the method, the signal generator reduces the voltage amplitude of the output voltage of the energy supply device to a settable first or prestored first voltage amplitude value if the sensed current amplitude falls below the first current threshold value. For example, the first current threshold value is stored in a memory of the signal generator. 
         [0061]    With a reduction in the output voltage, the output current of the energy supply device is reduced at the same time, with the result that the energy supply device changes from its first operating state to the second operating state automatically, that is to say without an additional energy source. 
         [0062]    This achieves the advantage that the energy provided at the output of the energy supply device is automatically reduced by using the method according to the disclosure. 
         [0063]    In one advantageous example of the method, the signal generator reduces the voltage amplitude of the output voltage of the energy supply device in the first operating state after expiry of a settable or prestored first delay time interval. After a first sensing of a current amplitude below the first current threshold value, the measuring assembly records a further current amplitude after expiry of the first delay time interval. If the further sensed current amplitude is also below the first current threshold value, the signal generator reduces the voltage amplitude of the output voltage of the energy supply device. For example, the first delay interval comprises a period of several seconds, for example 30, 20, 10, 5 or 3 seconds. 
         [0064]    This achieves the advantage that a transition from the first operating state to the second operating state cannot be initiated by random output current fluctuations. 
         [0065]    In one advantageous example of the method, the signal generator increases the voltage amplitude of the output voltage of the energy supply device to a settable second or prestored second voltage amplitude value if the sensed current amplitude exceeds the current threshold value or the further current threshold value. If the measuring assembly records a sensed current amplitude which exceeds the second current threshold value during operation of the energy supply device in the second operating state, the signal generator increases the voltage amplitude of the output voltage of the energy supply device to a settable second or prestored second voltage amplitude value. 
         [0066]    For example, the voltage amplitude is increased from a value in the range of 8 V to 14 V or 10 V to 12 V, for example, in the second operating state to a voltage amplitude having a value of between 20 V and 60 V or between 20 V and 28 V, for example, or to 24 V, for example, in the first operating state. 
         [0067]    This achieves the advantage that the energy supply device automatically changes from the second operating state to the first operating state when using the method. 
         [0068]    In one advantageous example of the method, the signal generator increases the voltage amplitude of the output voltage of the energy supply device immediately or after expiry of a prestored second delay time interval after it has been detected that the second current threshold value of the current amplitude has been exceeded. The prestored second delay time interval comprises, for example, the same period as the first delay time interval. 
         [0069]    For example, the second delay interval comprises a period of several seconds, for example 30, 20, 10, 5 or 3 seconds. For example, the second delay time interval comprises a shorter period than the first delay time interval, for example 20, 10, 5, 3 or 1 seconds. 
         [0070]    If the voltage amplitude of the output voltage is increased immediately, the voltage amplitude of the output voltage is increased in a period of less than one second. The switching delay is then based on the circuit properties of the components of the energy supply device which are used when using the method. 
         [0071]    The method according to the disclosure achieves the advantage that a transition from the second operating state to the first operating state cannot be initiated by random output current fluctuations. 
         [0072]    According to a third aspect of the disclosure, the object is achieved by means of a method for operating an energy supply device, the energy supply device having a first operating state and a second operating state. A current amplitude of the output current of the energy supply device is sensed. Furthermore, a voltage amplitude of the output voltage of the energy supply device in the first operating state of the energy supply device is reduced by means of a signal generator in order to change to the second operating state if the sensed current amplitude falls below a first current threshold value; and the voltage amplitude of the output voltage of the energy supply device in the second operating state of the energy supply device is increased by means of the signal generator in order to change to the first operating state if the sensed current amplitude exceeds a second current threshold value. 
         [0073]    The output power and therefore the output voltage and the output current are set to a higher absolute value in the first operating state than in the second operating state. 
         [0074]    If the energy supply device changes from the first operating state to the second operating state, the output voltage of the energy supply device is respectively reduced by 30% to 80%, for example, or by 50%, for example. The voltage amplitude of the output voltage of the energy supply device is reduced from 24 V to 10-12 V, for example, in order to change from the first operating state to the second operating state. 
         [0075]    In this case, the output current of the energy supply device is reduced by 5-20% or more below the rated current, for example, in order to change from the first operating state to the second operating state. 
         [0076]    The current amplitude of the output current is repeatedly sensed at intervals of time. The sensed current amplitude is compared with the first current threshold value and the second current threshold value. The second current threshold value is set to be equal to the second current threshold value, for example, or is prestored. A lower or higher current threshold value can also be set or prestored for the second current threshold value, for example. 
         [0077]    In accordance with the method according to the disclosure, the energy supply device automatically changes from the second operating state to the first operating state. In the method according to the disclosure, the first operating state is set as an active state, and the second operating state is set as an energy-saving state, in particular a stand-by mode or a sleep mode. 
         [0078]    In the active state, the output voltage and the output current are each set to a value which allows operation of an electrical device connected to the energy supply device, whereas, in the energy-saving state, the output voltage and the output current are each set to a value which restricts operation of the electrical device connected to the energy supply device. 
         [0079]    This achieves the advantage that a transition between the first operating state and the second operating state is automatically effected. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0080]    Examples of the principles of this disclosure are illustrated in the drawings and are described in more detail below. 
           [0081]    In the drawings: 
           [0082]      FIG. 1  shows a schematic illustration of an energy supply device; 
           [0083]      FIG. 2  shows a schematic illustration of a measuring assembly of the energy supply device; 
           [0084]      FIG. 3  shows a schematic illustration of a signal generator of the energy supply device; 
           [0085]      FIG. 4  shows a schematic illustration of the energy supply device with a connected consumer; 
           [0086]      FIG. 5  shows a schematic diagram for the sequence of the method for operating the energy supply device; and 
           [0087]      FIG. 6  shows a schematic illustration of the time against the output voltage and the output current of the energy supply device. 
       
    
    
     DETAILED DESCRIPTION 
       [0088]      FIG. 1  shows a schematic illustration of an energy supply device  100  having a measuring assembly  101  for sensing a current amplitude of the output current of the energy supply device  100  and having a signal generator  103  for producing the output voltage and the output current of the energy supply device  100 . 
         [0089]    The measuring assembly  101  is schematically illustrated with further details in  FIG. 2 . The measuring assembly  101  has a measuring resistor  201  and repeatedly senses the current amplitude of the output current of the energy supply device  100  (see  FIG. 1 ) at intervals of time. The measuring assembly  101  senses the current amplitude of the output current on the basis of a voltage drop UA-UM across the measuring resistor  201 , UA denoting the output voltage at the output of the measuring assembly and UM denoting the voltage across the measuring resistor  201 . 
         [0090]    The measuring resistor  201  is provided in the form of a measuring shunt, as illustrated in  FIG. 2 . The current which flows through a measuring resistor  201  causes a voltage drop UA-UM which is proportional to it and is measured. The measuring resistor  201  is connected in parallel with a measuring circuit  203 , the voltage drop across the measuring resistor  201  being used to measure the current amplitude. The resistance value of the measuring resistor  201  is, for example, in the milli-ohm range or below at several tenths or hundredths of a milli-ohm. 
         [0091]    The signal generator  103  (see  FIG. 1 ) is electrically connected to the measuring assembly  101 .  FIG. 3  shows a schematic illustration of the signal generator  103  which comprises a transformer  300 . The transformer  300  has a primary side  301 , to which an input voltage U ein  is applied, and a secondary side  303  which then provides a nominal output voltage U nom . 
         [0092]    The transformer of the signal generator has, on its primary side  301 , a primary winding  305  which is directly fed with the input voltage U ein , that is to say the AC voltage from the energy supply network and the network frequency of the energy supply network, and has, on its secondary side  303 , a secondary winding  307  which provides the output voltage U nom . The transformer  300  of the signal generator  103  converts the input voltage U ein , that is to say the AC voltage from the energy supply network, to the required output voltage value(s) U nom  and ensures galvanic separation from the mains. 
         [0093]    The secondary AC voltage on the secondary side  303  of the transformer  300  can be converted, by means of a rectifier and a smoothing capacitor (not illustrated in  FIG. 3 ), to a DC output voltage which can be provided at the output of the signal generator  103 . A downstream linear regulator and a buffer capacitor (not illustrated in  FIG. 3 ) also possibly provide an output voltage J, which can be kept constant. 
         [0094]      FIG. 4  shows a schematic illustration of the energy supply device  100 , to the output  405  of which a consumer  401  is connected. A capacitor  403  is connected in parallel with the consumer  401 . The capacitor  403  provides a backup capacitance which provides a predetermined minimum power with a minimum load current and a minimum load voltage. Interposing the backup capacitance ensures that a consumer  401  connected to the energy supply device  100  exceeds a current threshold value, in particular the second current threshold value, with the result that the energy supply device  100  changes to its active state in order to automatically supply the connected consumer  401  with energy. 
         [0095]    The connected consumer  401  may be an electrical device, a motor, a PLC consumer (programmable logic controller), an industrial installation, a device which can be mounted on top-hat rails, a control cabinet or another electrical consumer. The connected consumer can be operated with DC voltage or with AC voltage. 
         [0096]      FIG. 5  shows a schematic diagram for the sequence of the method  500  for operating an energy supply device  100 . The method  500  for operating the energy supply device  100  first of all comprises sensing  501  a current amplitude of the output current  601  of the energy supply device  100  by means of the measuring assembly  101 . The sensed current amplitude of the output current  601  is then compared with settable or prestored current threshold values. After comparing  503  with a first current threshold value I 1  and a second current threshold value I 2 , either the output voltage  603  is reduced  505  or the output voltage  603  is increased  507  depending on the result of the comparison  503 . 
         [0097]    If the energy supply device  100  is in its first operating state  605 , its active state, in which the consumer(s)  401  connected to the energy supply device  100  are supplied with energy, the energy supply device  100  changes from its first operating state  605  to its second operating state  607  if a current threshold value which is below a first current threshold value I 1  is sensed  501 . This transition is effected by reducing  505  the voltage amplitude of the output voltage  603  of the energy supply device  100  to a settable or prestored output voltage value U low . The second operating state  607  is an energy-saving state which is operated with the reduced output voltage U low . 
         [0098]    If the energy supply device  100  is in its second operating state  607 , the energy-saving state, the energy supply device  100  changes from its second operating state  607  to its first operating state  605  if a current threshold value which is above a second current threshold value I 2  is sensed  501 . This transition is effected by increasing  507  the voltage amplitude of the output voltage  603  of the energy supply device  100  to a settable or prestored output voltage value U nom . The first operating state  605  is the active state which is operated with the nominal output voltage U nom . 
         [0099]      FIG. 6  shows a schematic illustration of the output voltage and the output current of the energy supply device. In its first operating state  605 , the energy supply device  100  provides an output voltage value U nom  and an output current value I nom  at its output or is increased to these values, with the result that connected consumers  401  can be supplied with energy. The temporal profile of the amplitude of the output current  601  and the temporal profile of the amplitude of the output voltage  603  are illustrated both in the first operating state  605  and in the second operating state  607  in  FIG. 6 . 
         [0100]    At a time t 0 , a consumer  401  connected to the energy supply device  100  is switched off, with the result that the amplitude of the output current  601  is reduced to a first current threshold value I 1  or to a value below the latter until a time t 1 , while the amplitude of the output voltage  603  has remained constant at the output voltage value U nom . The energy supply device  100  changes over from its first operating state  605  to the second operating state  607  only after expiry of the first delay interval  609  which corresponds to a period t 1 -t 0 . This results in the amplitude of the output voltage being reduced to the output voltage value U low  and the amplitude of the output current being reduced to the second current threshold value I 2  between the times t 1  and t 2 . 
         [0101]    For example, the amplitude of the output voltage is reduced from 24 V to 8 V to 16 V or 10-12 V, for example, while the amplitude of the output current is reduced by 5-20% below the amplitude of the rated current. 
         [0102]    The remaining output current I 2  is repeatedly measured at equidistant intervals of time in the second operating state  607 . As long as the amplitude of the output current does not exceed the second current threshold value I 2 , the energy supply device  100  remains in its second operating state  607 . Only if a consumer  401  having a load is connected to the energy supply device  100  at a time t 3  is the amplitude of the output current  601  through the consumer  401  increased until a time t 4 , whereas the amplitude of the output voltage  603  is kept constant at the output voltage value U low . Connecting the consumer  401  having a backup capacitance can also result in a current peak in the amplitude of the output current  601  (not illustrated). In both cases, the increase in the amplitude of the output current is evaluated as the end of the second operating state  607 . Consequently, at the time t 4 , that is to say after expiry of a second delay interval  611  which comprises the period t 4 -t 3 , the amplitude of the output current  601  is increased to the output current I nom  and the amplitude of the output voltage is increased to the nominal output voltage U nom    603  until the time t 5 . 
         [0103]    At the time t 5 , the energy supply device provides an output voltage U nom  and an output current I nom  which can be used to operate the connected consumer  401 . The output voltage U nom  is, for example, 24 V or more. For example, 60 V for the output voltage U nom  are not exceeded in order to avoid exceeding a safety range. The output current I nom  is in a range between 40 A and 80 A, for example. 
         [0104]    All features explained and shown in connection with individual examples of the principles of this disclosure can be provided in a different combination in the subject matter according to the disclosure in order to simultaneously achieve their advantageous effects. 
         [0105]    The scope of protection of the present disclosure is given by the claims and is not restricted by the features explained in the description or shown in the Figures. 
       LIST OF REFERENCE NUMBERS 
       [0000]    
       
           100  Energy supply device 
           101  Measuring assembly 
           103  Signal generator 
           201  Measuring resistor 
           203  Measuring circuit 
           300  Transformer 
           301  Primary side 
           303  Secondary side 
           305  Primary winding 
           307  Secondary winding 
           401  Consumer 
           403  Capacitor 
           405  Output 
           500  Method 
           501  Sensing 
           503  Comparing 
           505  Reducing 
           507  Increasing 
           601  Output current 
           603  Output voltage 
           605  First operating state 
           607  Second operating state 
           609  First delay interval 
           611  Second delay interval 
         I 1  First current threshold value 
         I 2  Second current threshold value 
         I nom  Amplitude of the output current in the first operating state 
         U nom  Amplitude of the output voltage in the first operating state 
         U low  Amplitude of the output voltage in the second operating state 
         U A  Output voltage at the output of the measuring assembly 
         U M  Voltage across the measuring resistor 
         U A -U M  Voltage drop 
         U ein  Input voltage 
         t 0  Time 
         t 1  Time 
         t 2  Time 
         t 3  Time 
         t 4  Time 
         t 5  Time