Abstract:
The invention relates to uninterruptible power supply devices which make it possible to supply emergency power to a load, which is to be supplied, in the event of mains failure. The invention is based on the object of providing a device for supplying uninterruptible power, which device can be operated in a more energy-saving manner and in which the emergency power can be controlled in a rapid and safe manner. To this end, the uninterruptible power supply device has a power transistor which can be rapidly switched and can be used to connect a standby power source to the output connections during emergency power operation. The output current can also be dynamically limited by driving the power transistor, which can be rapidly switched, in a corresponding manner. In addition, the input and output of the UPS device are decoupled using a field effect transistor that acts as a power transistor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of U.S. patent application Ser. No. 10/599,812, with a U.S. filing date of Oct. 10, 2006. U.S. application Ser. No. 10/599,812 is a 371 filing of PCT/EP2005/003481, filed on Apr. 2, 2005 which in turn claims priority of German Application Number 10 2004 018 502.6, filed on Apr. 14, 2004. 
         [0002]    Furthermore, U.S. patent application Ser. No. 10/599,812 is incorporated herein by reference. 
     
    
     FIELD ON THE INVENTION 
       [0003]    The present invention relates to electronics in general, and, more particularly, to a device for supplying uninterruptible power. 
       BACKGROUND OF THE INVENTION 
       [0004]    In order to ensure the functionality of electronic devices and systems, for example private computer networks, even in the event of mains failure, so-called UPS (uninterruptible power supply) systems are used. UPS systems ensure that, in the event of the mains voltage failing, the electronic devices or systems are supplied with emergency power via the UPS system. In other words, a UPS system ensures that, in the event of a fault in the mains supply, the system changes over from mains operation to emergency power operation. As soon as the mains supply starts operating again, the UPS system changes over from emergency power operation to mains operation. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention is based on the object of providing a device for supplying uninterruptible power, which device can be operated with a lower power loss than conventional UPS devices. Another aspect of the invention resides in a measure for limiting the output current during emergency power operation. Yet another aspect of the invention resides in making it easier for a user to connect further electrical or electronic components. 
         [0006]    A device for supplying uninterruptible power (also referred to as UPS device for short) is provided, said device having input connections for connection to a primary power supply device, connections for connecting a standby power source, first output connections for connecting a load, a device for decoupling the input connections from the first output connections in the event of a fault in the primary power supply device, a first controllable switching device for connecting the standby power source to the first output connections in a controlled manner in the event of a fault in the primary power supply device, and a control device which is assigned to the first controllable switching device. In addition, the first controllable switching device has a power transistor which can be rapidly switched. A monitoring device is also provided for the purpose of monitoring the output current flowing through the power transistor which can be rapidly switched. The control device is designed to pulse-width-modulate the power transistor, which can be rapidly switched, on the basis of the current being monitored in order to limit the current which can be provided by the standby power source during emergency power operation. 
         [0007]    It shall be mentioned, at this juncture, that the primary power supply device may be, for example, a DC power supply unit or a supply system which provides alternating voltages. The standby power source may contain one or more rechargeable batteries. However, the standby power source may also contain an AC current source. 
         [0008]    In order to be able to prevent a current from flowing to the standby power source, via the power transistor which can be rapidly switched, during mains operation, a diode is connected in series with the rapid power transistor, said diode being operated in the forward direction during emergency power operation and being operated in the reverse direction during mains operation. 
         [0009]    In order to smooth the output voltage from the UPS device, a capacitor is connected between the first output connections. The capacitor is used, in particular, to smooth the pulse-width-modulated current provided by the power transistor, which can be rapidly switched, during emergency power operation. In addition, the capacitor ensures that, when changing over from mains operation to emergency power operation, the switching delays which occur in the process are compensated for. 
         [0010]    The input and output of the UPS device are generally decoupled using conventional diodes or Schottky diodes. The diodes are connected in such a manner that they forward the input current to the output of the UPS device during mains operation. During emergency power operation, they prevent the emergency current from being able to branch to the input of the UPS device. The disadvantage of conventional diodes or Schottky diodes is that a relatively high power loss, which results from the product of the forward voltage and the supply current, is dropped across these diodes during mains operation. In order to be able to reduce the power loss of the decoupling device during mains operation, a second controllable switching device, preferably a field effect transistor that acts as a power transistor, is connected in parallel with the diode. In the on state, a smaller voltage is dropped across such a field effect transistor than across a conventional diode, with the result that the power loss is considerably reduced in comparison with the use of a diode. Thanks to the reduction in the power loss in the decoupling device, smaller heat sinks may be used, thus resulting in a lower production expenditure on the UPS device. In this case, the monitoring device is designed to monitor an input voltage, the control device disconnecting the second controllable switching device if the input voltage being monitored signals a fault in the primary power supply device. 
         [0011]    It shall be mentioned, at this juncture, that a fault in the primary power supply device is understood as meaning impermissible voltage fluctuations, but in particular total failure of the primary power supply device. 
         [0012]    If the standby power source is a rechargeable battery, a charging device which charges the standby power source during mains operation and can be controlled by the control device is connected between the input connections and the chargeable standby power source. The charging device is assigned a rectifier if the primary power supply device provides an alternating current. The rectifier may be advantageously connected between the input connections and the decoupling device. If the rectifier is provided at another location, the second controllable switching device needs to be in the form of a bidirectional switch. 
         [0013]    In order to be able to increase the performance of the UPS device, a current-limited supply output which is operational both during mains operation and during emergency power operation is provided in parallel with the first output connections. The supply output is connected to the first output connections via a current limiter. The current limiter may have a rectifier which can be connected if the input voltage is an alternating voltage. The current limiter is also connected in series with a diode which passes a current to the current-limited supply output but blocks a current coming from the supply output. This prevents feedback from the UPS device. 
         [0014]    Depending on the customer&#39;s wishes, external devices, for example state signaling devices, may be operated in conjunction with the current-limited supply output. To this end, the UPS device has at least one third controllable switching device which is preferably a relay, for example a changeover relay, and is intended to connect and disconnect at least one state signaling device. The state signaling device can be connected to a respective second output connection which is assigned to the third controllable switching device, a third output connection which is assigned to the third controllable switching device being arranged at a predetermined distance from the current-limited supply output. This makes it possible to use a predefined contact bridge to short-circuit the current-limited supply output to the third output connection. This makes it possible for relays and state signaling devices to be wired in a simple and safe manner, and incorrect wiring is prevented. 
         [0015]    A device for supplying uninterruptible power according to the characterizing part has a parallel circuit comprising a diode and a second controllable switching device which form the decoupling device. A monitoring device is also provided for the purpose of monitoring an input voltage. The control device of the UPS device disconnects the second controllable switching device if the input voltage being monitored signals a fault in the primary power supply device. 
         [0016]    The second controllable switching device may be a power transistor, in particular a field effect transistor. As already mentioned further above, the advantage of the use of a field effect transistor that is connected in parallel with the diode can be seen in the fact that the power loss can be reduced during mains operation. 
         [0017]    A device for supplying uninterruptible power is also disclosed, which device has a current-limited supply output which is connected in parallel with the first output connections. 
         [0018]    This makes it possible to improve the performance of the UPS device since electrical devices, for example state signaling devices, can be connected in a simple and safe manner. 
         [0019]    At least one second controllable switching device is preferably provided for the purpose of connecting and disconnecting at least one state signaling device which can be connected to a respective second output connection that is assigned to the second switching device. At least one third output connection which is assigned to the second switching device is also arranged at a predetermined distance from the current-limited supply output. 
         [0020]    This makes it possible to use a predefined contact bridge to short-circuit the current-limited supply output to the at least one third output connection. Arranging the current-limited supply output in a well-defined manner with respect to the third output connections makes it possible for the second switching device to be wired in a simple and safe manner. The second controllable switching device is a relay, preferably a changeover relay. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The single FIGURE shows a device for supplying uninterruptible power. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    The single FIGURE shows a device for supplying uninterruptible power (UPS), which is referred to below as UPS device for short. The UPS device is generally provided with the reference symbol  10 . On the input side, the UPS device  10  has two input terminals  90 ,  91  to which a primary power supply device  230  is connected, said power supply device providing a DC voltage U E  in the present example. The primary power supply device  230  may be a 24 V power supply unit or a 24 V power system. On the output side, the UPS device  10  has two output terminals  100  and  101  to which a load  220  to be supplied is connected. A decoupling device  20  is connected between the input terminal  90  and the output terminal  100 . The decoupling device  20  has a parallel circuit comprising a diode and a field effect transistor  24  which is operated as a power transistor. The cathode connection is connected to the output terminal  100 , whereas the anode connection of the diode  21  is connected to the input connection  90 . The source connection S of the field effect transistor  22  is connected to the anode connection of the diode  21 , whereas the drain connection D of the field effect transistor  22  is connected to the cathode connection of the diode  21 . The gate connection G of the field effect transistor  22  is connected to a control and monitoring device  30 ,  31 . The control and monitoring device  30 ,  31  is designed in such a manner that it switches on the field effect transistor  22 , via the gate connection G, during mains operation and switches it off during emergency power operation. On the input side, the control and monitoring device  30 ,  31  is connected to the source connection S and to the drain connection D of the field effect transistor  22  in order to be able to monitor and evaluate the input voltage of the UPS device  10 . The control and monitoring device  30 ,  31  drives the gate connection G of the field effect transistor  22  on the basis of the input voltage being monitored in order to reduce the power loss during mains operation. To this end, the field effect transistor  22  is switched on using the control and monitoring device  30 ,  31  during mains operation, thus bridging the diode  21 . 
         [0023]    The UPS device  10  also has two input terminals  190  and  191  to which a standby power source  60  is connected. As in the present example, the standby power source  60  may be a rechargeable battery. In this case, a charging unit  50  which charges the rechargeable battery  60  during mains operation is connected between the input terminal  90  and the connection terminal  190 . The charging unit  50  is a device which is known per se and automatically detects when the rechargeable battery  60  has been charged. The charging device  50  is likewise driven, using the control and monitoring device  30 ,  31 , in such a manner that the rechargeable battery  60  is not charged during emergency power operation. It shall be mentioned, at this juncture, that the charging device  50  provides a plurality of functions. It is thus used, first of all, to limit the charging current of the rechargeable battery  60 . It also adapts the charging voltage to the requirements of the rechargeable battery  60  during charging. Charging is ended when, for example, the primary power supply device  230  has to provide a maximum load current. Battery charging is likewise switched off when the rechargeable battery  60  has been charged. 
         [0024]    A further switching device  40  is connected in series with a diode  70  between the connection terminal  190  and the output terminal  100 . The switching device  40  contains a power transistor  42  which can be rapidly switched and is in the form of a field effect transistor  42  that is illustrated together with the production-dictated inverse diode  41 . In this embodiment variant, the drain connection D is connected to the connection terminal  190 , while the source connection S of the field effect transistor  42 , which can be rapidly switched, is connected to the anode connection of the diode  70 . The cathode connection of the diode  70  is connected to the output terminal  100 . The gate connection G of the field effect transistor  42 , which can be rapidly switched, is connected to an output of the control and monitoring device  30 ,  31 . The diode  70  is connected in such a manner that it is forward-biased during emergency power operation and is reverse-biased during mains operation so that charging of the rechargeable battery  60  during mains operation is prevented using the switching device  40 . A capacitor  80  which smoothes, in particular, the voltage provided by the rechargeable battery  60  during emergency power operation is connected between the output terminals  100  and  101 . Together with the diode  70 , the switching device  40  is used not only to decouple the rechargeable battery  60  from the output terminals  100  and  101  but also to limit the emergency current during emergency power operation. To this end, the emergency current, that is to say the current of emergency power operation which flows through the field effect transistor  42 , is monitored and evaluated by the control and monitoring device  30 ,  31 . Depending on the emergency current measured, the field effect transistor  42  which can be rapidly switched is pulse-width-modulated via the gate electrode G, thus making it possible to reduce the current. 
         [0025]    At this juncture, it shall be briefly pointed out that it is irrelevant to the invention whether the standby power source  60 , which can also be referred to as a standby voltage source in an equivalent manner, is an internal part of the UPS device  10  or, as illustrated in the FIGURE, can be externally connected. 
         [0026]    According to another aspect of the invention, a current-limited supply output  130  is provided in parallel with the output terminals  100  and  101 . The supply output  130  is connected to the output terminal  100  via a diode  180  and a current limiter  110 . The cathode connection of the diode  180  is connected to the supply output  130 , whereas the anode connection of the diode  180  is connected to the output of the current limiter  110 . This avoids feedback from the UPS device  10  via the supply output  130 . 
         [0027]    The UPS device  10  preferably also has a changeover relay whose exciter circuit, which is symbolically illustrated, bears the reference symbol  120 , while the output circuit of the changeover relay is labeled using the reference symbol  122 . On the output side, the exciter circuit  120  of the changeover relay is connected to the control and monitoring device  30 ,  31 . In the present example, the output circuit  122  has three connections  140 ,  160  and  170 . A respective light-emitting diode  200  and  210  can be connected to the connections  160  and  170  in order to signal the state of the UPS device  10 . For example, the light-emitting diode  200  signals that the UPS device  10  is operating with mains operation, while lighting-up of the light-emitting diode  210  can signal that the UPS device  10  is operating with emergency power operation. The further connection contact  140  of the output circuit  122  is arranged at a firmly prescribed distance from the supply output  130 . A correspondingly defined insertable jumper  150  can be used to short-circuit the supply output  130  to the output terminal  140  of the output circuit  122 . This makes it possible for the output circuit  122  of the changeover relay to be supplied, in a fault-free and safe manner, either with the input voltage U E  during mains operation or via the rechargeable battery  60  during emergency power operation. The method of operation of a changeover relay is generally known, with the result that it is possible to dispense with a detailed description. 
         [0028]    As already mentioned, the field effect transistor  42  is also used to limit the load current during emergency power operation. If the control and monitoring device  30 ,  31  detects that the current through the field effect transistor  42  is becoming too large, the power switch  40  is switched off. After a short pause, the field effect transistor  42  is switched on again. The switch-on and switch-off cycle depends on the magnitude of the monitored current through the drain-source path of the field effect transistor  42 , which is monitored and evaluated by the control and monitoring device  30 ,  31 . The control and monitoring device  30 ,  31  ensures, in conjunction with the field effect transistor  42 , that, during emergency power operation, high short-circuit currents can be limited in a considerably faster and more reliable manner than is the case when using relays, for example. In order to prevent the rechargeable battery  60  from being charged during mains operation, the diode  70  is provided since field effect transistors cannot block inverse voltages, as is symbolically indicated using the inverse diode  41 . Thanks to the dynamic current limitation with the aid of the control and monitoring device  30 ,  31  and the field effect transistor  42 , the output characteristic curve of the UPS device  10  can be adapted to the conventional output characteristic curve of power supplies and a peak current can be limited early and reliably. 
         [0029]    The method of operation of the UPS device  10  will be explained briefly below. 
         [0030]    For the sake of simpler explanation, it shall be assumed that a DC voltage U E , for example a 24 V DC voltage, is applied to the input terminals  90  and  91 . The input voltage is tapped off, monitored and evaluated by the control and monitoring device  30 ,  31  at the source connection S and drain connection D of the field effect transistor  22 . As long as the input voltage U E  is within a prescribed tolerance range, the UPS device  10  operates with mains operation. This means that the field effect transistor  22  is held in the on state via the gate connection G. If the rechargeable battery  60  has not been fully charged, the charging device  50  is used to charge the rechargeable battery  60 . During mains operation, the field effect transistor  42  which is required for current limitation is held in the off state using the control and monitoring device  30 ,  31 . The diode  70  which is connected in series with the field effect transistor  42  prevents an undesirable flow of current to the rechargeable battery  60  via the field effect transistor  42 . As soon as the control and monitoring device  30 ,  31  detects a disturbance in the input voltage U E  (this may be undesirable voltage fluctuations or the complete failure of the primary power supply device  230 ), the field effect transistor  22  is switched off via the gate connection G so that the input terminals  90 ,  91  and the output terminals  70 ,  100  and  101  are decoupled. At the same time, the field effect transistor  42  is switched on using the control and monitoring device  30 ,  31  so that the load  220  which is connected to the output terminals  100  and  101  is now supplied with emergency power via the rechargeable battery  60 . During emergency power operation, the control and monitoring device  30 ,  31  monitors the current flowing through the field effect transistor  42  in order to limit said current if necessary. As already mentioned, the output current of the field effect transistor  42  is limited by the control and monitoring device  30 ,  31  pulse-width modulating the output current via the gate connection G, i.e. the switch-on and switch-off cycle of the field effect transistor  42  determines the output current of the latter. 
         [0031]    As already mentioned, the control and monitoring device informs the exciter circuit  120  of the changeover relay of the change from mains operation to emergency power operation so that the respective state can be indicated to the user using the light-emitting diode  200  or  210 . 
         [0032]    It shall be pointed out, at this juncture, that additional relays or else changeover relays can be connected to the control and monitoring device  30 ,  31 . The corresponding output connections of the respective output circuits are arranged at defined distances from the supply output  140  in order to make it possible, in a simple and fault-protected manner, to connect the relays or the output circuits of the relays in parallel using the insertable jumper  150 .