Abstract:
A DC-to-DC converter for transporting energy between two networks includes two or more converter circuits connected in parallel, wherein a first semiconductor switch that can be actuated as a function of a voltage drop across the first semiconductor switch is arranged in series to each converter circuit or a second semiconductor switch that can be actuated as a function of a voltage drop across the second semiconductor switch is arranged in series to each converter circuit.

Description:
CROSS REFERENCE 
     This application claims priority to German Patent Application No. 10 2013 101400.3, filed Feb. 13, 2013. 
     TECHNICAL FIELD OF THE INVENTION 
     The invention relates to a DC-to-DC converter for transporting energy between two networks comprising several converter circuits connected in parallel. 
     BACKGROUND OF THE INVENTION 
     Such DC-to-DC converters with several converter circuits, which are also called converter cells, are known from the prior art. In particular, multi-phase DC-to-DC converters that comprise several converter circuits are known, for example, from DE 11 2008 004 030 T5 and DE 10 2009 054 957 A1. DC-to-DC converters are used, for example, in motor vehicles, in order to couple different electric systems to each other. 
     If a fault occurs in one of the converter circuits in a DC-to-DC converter with several converter circuits and this causes a short-circuit current, then this can be detected by the controller of the DC-to-DC converter. After the detection of the short-circuit current, the controller switches off the defective converter circuit. From the moment when the short-circuit current occurs up to the moment when the defective converter circuit is switched off, in the known DC-to-DC converters, time can pass that is long enough to allow an increase of the current through the DC-to-DC converter. This current can be so high that the voltages are applied to the networks coupled via the DC-to-DC converters and the networks become unstable or one of these networks becomes unstable. Thus, the monitoring of the currents flowing through the converter circuits by means of the controller can be too slow to prevent a breakdown of the networks. 
     This is where the present invention comes into play. 
     The invention is based on the problem of quickly switching off a converter circuit of a DC-to-DC converter of the type named above in the event of a short circuit. 
     SUMMARY OF THE INVENTION 
     This problem is solved according to the invention in that a first semiconductor switch that can be actuated as a function of a voltage drop across the first semiconductor switch is arranged in series to each converter circuit and/or a second semiconductor switch that can be actuated as a function of a voltage drop across the second semiconductor switch is arranged in series to each converter circuit. According to whether the first or the second semiconductor switch is present, this switch or each of these switches is used to quickly and safely switch off the defective converter circuit. If both the first and the second semiconductor switches are present, then both can be used to quickly and safely switch off the converter circuit. 
     The DC-to-DC converter can have means for detecting the voltage drop across the first semiconductor switches and/or means for detecting the voltage drop across the second semiconductor switches. In the event of a short circuit in one of the converter circuits, due to the current increase, the voltage across the first or second semiconductor switch also greatly increases, because this has a forward resistance, even if only very small. This voltage increase is detected. The first or second semiconductor switch is thus used not only as a switching element, but also as a measuring resistor for detecting the increase of the current or for detecting the short circuit. 
     The means for detecting the voltage drop can be part of threshold switches. The voltages across the first or second semiconductor switch can be detected with these threshold switches and can be compared with at least one switching threshold. Each threshold switch can have at least one output. An output signal that is dependent on the result of the comparison and can be tapped on the output of the threshold switch can be generated with the threshold switches. If, for example, the voltage across the semiconductor switch is higher than a threshold value, the output signal can have a level that corresponds to a logical one, while a logical zero is generated if the voltage is below the threshold value. 
     Advantageously, the switching thresholds of the threshold switches can be adjusted. For this purpose, the threshold switches can have connections for adjusting the threshold values. The connections for adjusting the switching thresholds of the threshold switches can be connected to the controller. Thus it is possible that the switching thresholds can be adjusted and specified by means of the controller. The switching thresholds can be adapted to changing parameters, for example, by the controller, for example, to a changing temperature of the semiconductor switch. This can be useful because the forward resistance of the semiconductor switch is dependent on the temperature. By adapting the switching thresholds to the changing forward resistance, it can be guaranteed that for the same current through the semiconductor switch, the switching thresholds can be exceeded and/or not reached. 
     The outputs of the threshold switches can be connected directly to a control input of the first or second semiconductor switch whose voltage drop is detected with the threshold switch. 
     Alternatively, it is possible that the outputs of the threshold switches are connected via a bistable multivibrator to a control input of the first or second semiconductor switch whose voltage drop is detected with the threshold switch. 
     The bistable multivibrators can be RS flip-flops. The output of each RS flip-flop can be connected to the control input of one of the first or second semiconductors. A reset input can be connected to the output of the threshold switch that detects the voltage drop of the first or second semiconductor switch whose control input is connected to the RS flip-flop. 
     The set inputs of the RS flip-flops can be connected to the controller. 
     According to the invention, the set inputs of the RS flip-flops can be dominant. Therefore, the semiconductor switches can be forced closed by the controller, even if the voltage across this semiconductor switch has exceeded the switching threshold for opening the semiconductor switch. 
     The reset inputs of the RS flip-flops can also be connected to the controller. Thus, the controller can also cause the semiconductor switch to open. 
     These aspects are merely illustrative of the innumerable aspects associated with the present invention and should not be deemed as limiting in any manner. These and other aspects, features and advantages of the present invention will become apparent from the following detailed description when taken in conjunction with the referenced drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference is now made more particularly to the drawings, which illustrate the best presently known mode of carrying out the invention and wherein similar reference characters indicate the same parts throughout the views. 
         FIG. 1  a simplified circuit diagram of a DC-to-DC converter according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. For example, the invention is not limited in scope to the particular type of industry application depicted in the figures. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention. 
     The DC-to-DC converter shown in  FIG. 1  has n converter circuits, of which a first converter circuit Z 1  and an n-th converter circuit Zn are shown. The converter circuits can have, in principle, any converter topology. 
     Shown in the figure are converter circuits with buck and boost topology. Converter circuits of this topology have a first controllable switching element M 11 , Mn 1  that is designed as a high-side switch and lies between a connection A 1 , An and a point SW 1 , SWn. The point SW 1 , SWn is also connected to a storage inductor L 1 , Ln and to a low-side switch M 12 , Mn 2 . The other connection of the storage inductor L 1 , Ln is connected to the connection E 1 , En. The other connection of the low-side switch M 12 , Mn 2  is connected to a ground connection M 1 , Mn. A capacitor C 1 , Cn is arranged between the connection E 1 , En and the ground connection M 1 , Mn. Outside of the converter switches Z 1 , Zn, the ground connections M 1 , Mn are each connected to ground via a third controllable switching element M 1   m , Mnm, wherein the source connections are connected to the ground connections and the drain connections of the third controllable switching elements M 1   m , Mnm are connected to ground. The gate connections are connected to a controller C of the DC-to-DC converter. 
     The third controllable switching elements M 1   m , Mnm are used as inverse-polarity protection for BN 14  and BN 48 . 
     The converter circuits are connected in parallel between the networks with the potentials BN 48  and BN 14  that have a common ground potential. 
     Connected in series to each converter circuit Z 1 , Zn, a first semiconductor switch M 14 , Mn 4  and a second semiconductor switch M 15 , Mn 5  are connected, wherein the first semiconductor switches M 14 , Mn 4  connect the connections A 1 , An of the converter circuits Z 1 , Zn to the potential BN 48  and the second semiconductor switches M 15 , Mn 5  connect the connections E 1 , En of the converter circuits Z 1 , Zn to the potential BN 14 . The source connections are connected to the terminals or to the connections of the converter circuits. 
     The DC-to-DC converter furthermore has threshold switches X 11 , X 12 , Xn 1 , Xn 2 , with the voltage drop across each of the first semiconductor switches M 14 , Mn 4  or second semiconductor switches M 15 , Mn 5  being fed to each of these threshold switches that compare these voltages with switching thresholds that are fed to the threshold switches X 11 , X 12 , Xn 1 , Xn 2  via connections for setting the switching thresholds. The connections for adjusting the switching thresholds are connected to the controller C. 
     The threshold switches X 11 , X 12 , Xn 1 , Xn 2  deliver a level with a value of a logical one when the voltage drop across the first semiconductor switch M 14 , Mn 4  or second semiconductor switch M 15 , Mn 5  is greater than the set threshold value. Otherwise, they deliver a logical zero to their output. 
     The outputs of the threshold switches X 11 , X 12 , Xn 1 , Xn 2  are connected to reset inputs R of RS flip-flops RS-FF 11 , FS-FF 12 , RS-FFn 1 , RS-FFn 2 . Additional reset inputs R are also connected to the controller. The RS flip-flops RS-FF 11 , RS-FF 12 , RS-FFn 1 , RS-FFn 2  can be reset by a logical one on the reset input, so that a logical zero is output on the outputs Q of the RS flip-flops RS-FF 11 , RS-FF 12 , RS-FFn 1 , RS-FFn 2 . The reset can be realized both by the controller C and also by the threshold switch X 11 , X 12 , Xn 1 , Xn 2  connected to each reset input R, as long as a logical zero is applied to the dominant set inputs S of the RS flip-flops RS-FF 11 , RS-FF 12 , RS-FFn 1 , RS-FFn 2 . The set inputs S are connected to the controller C. The controller C can therefore set the RS flip-flop RS-FF 11 , RS-FF 12 , RS-FFn 1 , RS-FFn 2  connected to a threshold switch X 11 , X 12 , Xn 1 , Xn 2  at any time and also despite an exceeding of a switching threshold detected by this threshold switch X 11 , X 12 , Xn 1 , Xn 2 , so that a logical one is applied on the output Q of the RS flip-flop RS-FF 11 , RS-FF 12 , RS-FFn 1 , RS-FFn 2 . 
     The outputs Q of the RS flip-flops are connected to the gate connections of the first and second semiconductor switches M 14 , Mn 4 , M 15 , Mn 5 . If a logical one is applied to the output Q of an RS flip-flop RS-FF 11 , RS-FF 12 , RS-FFn 1 , FS-FFn 2 , then the semiconductor switch M 14 , Mn 4 , M 15 , Mn 5  connected to this RS flip-flop RS-FF 11 , RS-FF 12 , RS-FFn 1 , RS-FFn 2  is closed. If, in contrast, a logical zero is applied, then the first or second semiconductor switch is opened. 
     The preferred embodiments of the invention have been described above to explain the principles of the invention and its practical application to thereby enable others skilled in the art to utilize the invention in the best mode known to the inventors. However, as various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by the above-described exemplary embodiment, but should be defined only in accordance with the following claims appended hereto and their equivalents. 
     LIST OF REFERENCE SYMBOLS 
     
         
         Z 1  Converter circuit 
         Zn Converter circuit 
         E 1 , En Inputs of the converter circuits (in buck mode, these are outputs, in boost mode, these are inputs) 
         A 1 , An Outputs of the converter circuits (in buck mode, these are inputs, in boost mode, these are outputs) 
         M 1 , Mn Ground connections of the converter circuits 
         M 11 , Mn 1  First controllable switching elements of the converter circuits 
         M 12 , Mn 2  Second controllable switching elements of the converter circuits 
         L 1 , L 2  Coils of the converter circuits 
         C 1 , Cn Capacitors of the converter circuits 
         M 1   m , Mnm Third controllable switching elements 
         M 14 , Mn 4  First semiconductor switches 
         M 15 , Mn 5  Second semiconductor switches 
         X 11 , Xn 1  Threshold switches 
         X 12 , Xn 2  Threshold switches 
         RS-FF 11 , RS flip-flops 
         RS-FFn 1   
         RS-FF 12 , RS flip-flops 
         RS-FFn 2   
         BN 48  Electric system 
         BN 14  Electric system