CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. national stage application of PCT/EP2007/007607 filed on Aug. 31, 2007, and claims priority to, and incorporates by reference, German Patent Application No. 10 2006 044 879.0 filed on Sep. 22, 2006. 
     
    
     BACKGROUND 
       [0002]    The invention is based on a power supply apparatus. 
         [0003]    Power supply apparatuses, particularly for application in aircraft, are already known which have a regulatory unit and which are provided for the purpose of aligning a current profile with a voltage profile. 
       SUMMARY 
       [0004]    The invention is based on a power supply apparatus, particularly for an aircraft, having a regulatory unit which is provided for the purpose of aligning a current profile with a voltage profile. In this context, “aligning” is to be understood to mean particularly at least approximating the voltage profile to the current profile. 
         [0005]    It is proposed that the power supply unit have at least one active unit having at least one connectable unit. In this context, an “active unit” is to be understood to mean particularly a unit which is provided for the purpose of at least semi-automatically implementing a switching operation. In addition, the “connectable unit” is intended to be understood to mean particularly a unit which can be used to influence the current profile in an operating range. Undesirable differences between the current profile and the voltage profile despite the regulation by the regulatory unit can therefore advantageously be at least counteracted. Furthermore, it is possible to achieve filtering in a further frequency range, particularly between 350-800 Hz, a distortion factor can be improved and it is possible to attain advantageous limiting for an inrush current. 
         [0006]    If the active unit is provided for the purpose of connecting the unit in the range of a zero crossing in the voltage profile, it is possible to at least reduce difference errors particularly in the range of the zero point in the voltage profile or at the zero crossing. In this case, “range of a zero crossing in the voltage profile” is intended to be understood to mean particularly a range below 30%, preferably below 20% and particularly advantageously below 15% of the maximum applied voltage. 
         [0007]    The unit may be formed by various units which appear appropriate to a person skilled in the art, particularly advantageously by a unit which has an at least essentially linear response in at least one operating range, preferably at a zero crossing of the voltage, “essentially” being intended to be understood to mean particularly that the response thereof differs from a theoretically fully linear response by less than 10%. 
         [0008]    In addition, the unit is particularly advantageously formed by a resistor unit, a “resistor unit” being intended to be understood to mean particularly a unit which is provided for the purpose of simulating an ohmic resistor at a zero crossing in at least one operating range, such as a field-effect transistor, and/or preferably has at least one ohmic resistor, which means that the resistor unit is simple to implement particularly in design terms. A resistor unit can advantageously easily be used to achieve the filtering in a further frequency range, to improve the distortion factor, and it is possible to attain advantageous limiting of an inrush current, specifically particularly by virtue of it being possible to dispense with an input resistor for the regulatory unit or to at least reduce the resistance value of said input resistor. 
         [0009]    If the unit has, at least in one range, at least one parameter which is dependent on a temperature value in order to achieve a specific temperature response, it is advantageously possible to achieve desired automatic adjustment to a varying temperature value, and advantageous linearization over the load can be attained. “Specific temperature response” is in this case intended to be understood to mean particularly that the unit is chosen specifically such that its response changes with the temperature value. 
         [0010]    Particularly advantageously, the unit has an NTC (Negative Temperature Coefficient) response, so that as the temperature rises a parameter falls, such as advantageously an electrical resistance, which means that increased safety can be achieved. To attain the NTC response, the unit may have various components which appear suitable to a person skilled in the art, but the unit advantageously has at least one NTC resistor, which allows an appropriate response to be implemented easily and inexpensively in design terms. 
         [0011]    In a further refinement of the invention, it is proposed that the active unit have at least one control unit which is provided for the purpose of initiating a switching operation at least at a particular phase angle, which means that interference effects occurring at particular phase angles can be counteracted specifically. In this case, the control unit may be formed by various units which appear appropriate to a person skilled in the art, such as particularly by phase angle comparators and/or by units which switch at particular times, for which there are particular phase angles, etc. A switching threshold may be coupled to a phase and/or to an amplitude. 
         [0012]    Preferably, the active unit has at least one comparator, which means that a desired switching operation, particularly at a particular phase angle, can be achieved specifically, in a manner which is simple in design terms. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Further advantages can be found in the description of the drawing which follows. The drawing shows an exemplary embodiment of the invention. The drawing, the description and the claims contain numerous features in combination. A person skilled in the art will expediently also consider the features individually and combine them to form appropriate further combinations. 
           [0014]    In the drawing, 
           [0015]      FIG. 1  shows a schematic illustration of a power supply apparatus according to the invention, and 
           [0016]      FIG. 2  shows a voltage profile. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]      FIG. 1  shows a schematically illustrated power supply apparatus for an aircraft having a regulatory unit  10  which is provided for the purpose of aligning a current profile with a voltage profile  12  ( FIGS. 1 and 2 ). The regulatory unit  10  is connected to an AC (Alternating Current) current source—not shown in more detail—by means of the connections  24 ,  26  and, following the connection, has an NTC resistor  28  in order to limit an inrush current. The NTC resistor  28  is followed by a bridge rectifier  30  in the regulatory unit  10 . In addition, the regulatory unit  10  comprises a buffer capacitor  32  for a switch  34  in the regulatory unit  10 , said switch being switched by a PFC (Power Factor Correction) chip  36  in the regulatory unit  10 . In addition, the regulatory unit  10  has an electronic unit  38  which is coupled to the PFC chip  36  and has an inductor and an auxiliary coil for storing energy, a diode  40  for rectification which is connected downstream of the electronic unit  38 , and a capacitor  42  which is connected downstream of the diode  40 . In addition, the regulatory unit  10  has resistors  44 ,  46  for voltage feedback which are connected downstream of the diode  40  and in parallel with the capacitor  42 , with a path  48  coupled between the resistors  44 ,  46  being routed to the PFC chip  36 . The task of the regulatory unit  10  is to produce a current which follows the sinusoidal shape of the voltage as exactly as possible. This applies both to the sinusoidal shape of the current and to the phase between current and voltage. This means that the regulatory unit  10  is provided for the purpose of more or less simulating a resistive load. 
         [0018]    Besides the regulatory unit  10 , the power supply apparatus has an active unit  14  having a connectable unit  16  which is formed by an ohmic NCT resistor. The active unit  14  is connected downstream of the switch  34  in series at the docking points identified by A and B or is integrated into the current path of the switch  34 . Referring to  FIGS. 1 and 2 , the active unit  14  has a control unit  22  which is formed by a comparator and which is provided for the purpose of comparing a voltage applied downstream of the bridge rectifier  30  with a reference voltage U ref  which is between 5% and 15%, preferably approximately 10%, of the maximum voltage or approximately 15 V, and hence connecting the unit  16  in a range  18  of a zero crossing  20  in the voltage profile  12  by means of a switch  50  at a particular phase angle. Starting from a connection  52  downstream of the bridge rectifier  30 , a path  54  to the control unit  22  has a resistor  56  connected upstream of it and a resistor  58  connected downstream of it, the second resistor  58  being grounded. 
         [0019]    Above the reference voltage U ref , the switch  50  is closed. Once the reference voltage U ref  is undershot, the control unit  22  opens the switch  50  and the current from the switch  34 , which is controlled by the PFC chip  36 , flows via the unit  16 , and this affects the clock frequency of the PFC chip  36  by virtue of a soft characteristic curve being achieved and the clock frequency being lowered as a result. In addition, the connection affects the sinusoidal current of the asynchronous generator by virtue of an actual ohmic resistor being present. When the sinusoidal input voltage rises above the reference voltage U ref  again, the unit  16  is shorted by the switch  50  again and is therefore inoperative. 
         [0020]    When the AC current source is switched on or when the system is started up, the switch  50  is open. The current accordingly flows through the unit  16  formed by the NTC resistor and is limited to a known value. After a certain time when the system has been initiated, the switch  50  closes and the unit  16  formed by the NTC resistor is shorted. At this time, the capacitor  42  holds a charge and, without the active unit  14  and without the NTC resistor  28 , would have resulted in a high inrush current, so that the deactivation of the unit  16  formed by the NTC resistor has no consequences. As a result of the active unit  14 , the NTC resistor  28  can advantageously be provided with small dimensions or even eliminated completely, which means that losses and resultant heating can at least be reduced. 
         [0021]    The design of the unit  16  as an NTC resistor means that malfunctions and overheating can be avoided in the event of the switch  50  failing.
A power supply device, particularly for an airplane, has a control unit that is provided to match a current path to a voltage curve. An embodiment relates to a rectifier with power factor correction in the form of a step-up converter with switchable (startup) current limitation.