Abstract:
The invention relates to a relay controller for controlling an excitation current of a relay, wherein the relay controller is designed, upon the energization of the relay by means of a switch, to control the excitation current through the excitation winding of the relay in such a way that through the excitation winding there flows firstly a pull-in current and, after a pull-in time has elapsed, through the excitation winding there flows a holding current that is lower than the pull-in current, and wherein the relay controller is designed, upon the switching-off of the relay by means of the switch, to feed a commutation current that flows through the excitation winding to the commutation device through the first terminal and through the second terminal of the relay controller.

Description:
PRIORITY 
       [0001]    This application is a Continuation in Part of U.S. patent application Ser. No. 12/465,678, which was filed on May 14, 2009. The U.S. patent application Ser. No. 12/465,678 claimed benefit of German Patent Application 102008023626.8, which was filed on May 15, 2008. The entire contents of the prior filed applications are hereby incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to a relay controller for driving an excitation winding of a relay, and a relay device for switching loads. 
         [0003]    When relays are used, high-side or low-side switches that connect an excitation winding of the relay to the operating voltage are used. In this case, the term high-side or low-side identifies the position of the switch relative to the load, which in this case is the excitation winding of the relay. A high-side switch is connected by one terminal to a battery, and a low-side switch is connected by one terminal to a reference potential, usually earth. A relay with a high-side switch is illustrated in  FIG. 1 . The current through the excitation winding is limited by the coil resistance of the excitation winding for example in automotive applications. The disadvantages of such arrangements are the high current consumption after switch-on, the high costs of the excitation winding and the high inductance of the excitation winding. The high inductance of the excitation winding, which arises as a result of the many windings with a thin wire having a high impedance, makes it more difficult for commutation of the relay to be effected, and a slow drop-out of the relay operating contacts of the relay is the consequence. The slow drop-out of the secondary side of the relay can enable sparking to occur at the relay operating contacts of the relay. This sparking considerably impairs the service life of the relay. 
         [0004]    A current-saving relay driving system reduces the current after the pull-in of the relay armature, that is to say shortly after switch-on, in order thus to reduce the power consumption of the switched-on relay. Such a circuit arrangement for the operation of a relay is disclosed in DE4410819. In DE4410819, a switch T1 bridges a holding resistor R4, which sets the holding current of the excitation winding of the relay. As a result of the bridging of the resistor R4, a higher pull-in current is available at the first moment of switching on the excitation winding. 
         [0005]    For commutation purposes, a commutation voltage has to be applied counter to the current direction via the excitation winding; the higher said commutation voltage, the more rapidly the energy of the excitation winding is reduced and the faster the commutation becomes. A diode reverse-connected across the excitation winding can be used for commutation purposes, such that the commutation current can flow through the then conducting diode, as is illustrated in  FIG. 3 . The diode has the disadvantage that a forward-biased diode permits only a low commutation voltage across the excitation winding, with the result that the commutation takes place slowly. As is illustrated in  FIG. 3 , a zener diode can also be used for commutation purposes, said zener diode being connected to the excitation winding of the relay in such a way that the commutation current can flow through the zener diode undergoing breakdown. A zener diode has the disadvantage of a very high power loss. Moreover, a high proportion of energy is drawn from the battery and converted in addition to the energy in the winding in the switch. 
         [0006]    As illustrated in  FIG. 3 , a resistor can also be used for commutation purposes, such that the commutation current can flow through the resistor connected in parallel with the excitation coil. A resistor permits a high voltage on the excitation winding. The higher the voltage on the excitation winding is chosen to be, the more rapidly the excitation current decreases. The relay contacts open more rapidly in the case of a high commutation voltage at the excitation coil than in the case of a low commutation voltage. Rapid opening of the relay contacts reduces erosion of the relay contacts. A resistor has the disadvantage that a high voltage pulse arises shortly after turn-off, which pulse can only be controlled with expensive high-voltage semiconductor switches. A resistor has the further disadvantage that current flows through the resistor when a relay is switched on. 
         [0007]    In automobiles, in particular, in which the petrol consumption is directly dependent on the current requirement of the electronics used, solutions which reduce the current consumption of the electronics and hence the CO 2  emissions of the automobile, are inexpensive to manufacture and have a long service life are becoming important. 
       SUMMARY 
       [0008]    One aspect of the present invention provides a relay controller and a relay device in which the excitation current of a relay is controlled in current-saving fashion in a simple manner. 
         [0009]    The relay controller for controlling an excitation current of a relay comprises a first terminal, which is connected to an excitation winding of the relay, a second terminal, which is connected to a commutation device of the relay, wherein the relay controller, when the relay is turned on, controls the excitation current through the excitation winding of the relay in such a way that through the excitation winding there flows firstly a pull-in current and, after a pull-in time has elapsed, through the excitation winding there flows a holding current that is lower than the pull-in current, and wherein the relay controller, when the relay is switched off, feeds a commutation current that flows through the excitation winding to the commutation device through the first terminal and through the second terminal of the relay controller. 
         [0010]    The relay controller preferably lies in the freewheeling path of the relay. The relay controller controls the temporal sequence of the pull-in operation of the relay. If the high-side switch or the low-side switch turns the relay circuit off, the relay controller conducts the freewheeling current or the commutation current to the commutation device. The voltages at the terminals of the relay controller remain limited to low values. By contrast, the switch-side terminal of the excitation winding can oscillate freely, its voltage swing preferably being limited by the breakdown voltage of the switch. It is also possible to use mechanical or other inexpensive switches. 
         [0011]    The relay controller can be designed to control the excitation current only after a current that flows, after the switching-on of the switch, through the commutation device into the second terminal energizes the relay controller. For this purpose, the commutation device has to enable the flow of the current switched by the switch to the relay controller. For this purpose, by way of example, the commutation device can be embodied as a resistor. After the switch has been switched on, current firstly flows via the commutation device through the second terminal into the relay controller and thereby starts the latter. At this moment no excitation current can be provided by the relay controller. Once the relay controller is ready for operation, the excitation current can also be provided. 
         [0012]    The relay controller can be designed to detect the current that flows after the energization of the relay through the switch, through the commutation device into the second terminal, in order thus to determine a turn-on instant, wherein this turn-on instant determines the start of the pull-in time. This state can be detected for example by a power-on reset circuit that monitors the internal supply voltage. A power-on reset circuit monitors an internal supply voltage and generates a signal as soon as the internal supply voltage exceeds a specific threshold. After the detection, a capacitor or a counting device can be reset. The start of the relay controller then determines the start of the pull-in time. 
         [0013]    The relay controller can be designed to detect the excitation current. If the excitation current exceeds a threshold, the capacitor or the counting device can be reset. The exceeding of the excitation current threshold then determines the start of the pull-in time. 
         [0014]    The relay controller can have a fifth terminal, wherein a switching on and a switching off of the relay controller can be determined by means of a circuit connected to the fifth terminal. The excitation current of the relay can be switched on or off with a signal via the fifth terminal or can be determined by means of a circuit connected to the fifth terminal. The relay controller can switched be on or off with a signal via the fifth terminal. 
         [0015]    The relay controller can be designed to determine the hold current. After the pull-time has elapsed the pull-in current can be reduced to a lower hold current. The hold current has to be large enough to hold the relay on. For an efficient operating of the relay it is useful to reduce the hold current as much as possible. The relay controller can have a sixth terminal, wherein the excitation current through the excitation winding, the hold-current can be determined by means of a circuit connected to the sixth terminal or with a signal via the sixth terminal 
         [0016]    The device can comprise a temperature sensor circuit comprising a temperature sensor for detecting the temperature of the relay controller. The temperature sensor circuit can be designed to implement measures for reducing the power consumption of the relay controller if a maximum temperature is exceeded. One measure for reducing the power consumption of the relay controller can consist in turning off the current through the excitation winding. 
         [0017]    In one embodiment, the relay controller draws a current from the second terminal during operation. The relay controller thus utilizes the current flowing through the commutation device for its own supply, with the result that there is no need for a further terminal for providing a supply voltage. The current that flows through the commutation device is limited by the relay controller since only the current required for supplying the relay controller flows. 
         [0018]    The relay controller can have a third terminal, which is connected to the second reference potential, for example earth. The voltage between the first terminal and the third terminal can be limited by means of a voltage limiting device. The relay controller can thus limit the voltage upon reduction of the current after the pull-in of the armature. If the relay controller is jeopardized by an increased temperature, for example, the voltage limiting device protects the relay controller against high voltages. 
         [0019]    The third terminal can preferably be connected to the reference potential. An internal supply voltage can be established between the second terminal and the third terminal. Between the first terminal and the third terminal, the relay controller can comprise a current source and a second switch for providing an excitation current. 
         [0020]    Between the first terminal and the second terminal, the relay controller can have a first switch for controlling the commutation current. 
         [0021]    The first switch of the relay controller can be a diode. In one embodiment, the cathode of the diode of the first switch is connected to the second terminal of the relay controller. The first switch of the relay controller can be a MOS transistor or a bipolar transistor. 
         [0022]    The relay controller can have an undervoltage sensor between the second terminal and the third terminal, for detecting an undervoltage. 
         [0023]    If the undervoltage sensor detects an undervoltage, the relay controller can reset the pull-in time to a predetermined value. The relay controller can thus indirectly change over to a higher current, or to a maximum possible current, in order that the relay operating contacts remain closed even when there is a low voltage between the first and the second reference potential. 
         [0024]    The relay controller can comprise a second switch provided in parallel with the current source that provides excitation current, said second switch bridging the current source if the undervoltage sensor detects an undervoltage. The relay controller thus provides a maximum possible current in order that the relay operating contacts remain closed even in the case of a low voltage. 
         [0025]    In a further exemplary embodiment, the current source provides only the holding current, and for the pull-in of the relay, the second switch bridges the current source during the pull-in time. 
         [0026]    The relay controller can have a fourth terminal, wherein the pull-in time can be determined by means of a circuit connected to the fourth terminal. 
         [0027]    A relay device for switching loads comprises: a relay, a relay controller comprising at least two terminals for controlling the relay, a commutation device, wherein the commutation device is coupled in parallel with the excitation winding of the relay via a first terminal and a second terminal of the relay controller, a switch, wherein the excitation winding of the relay, the relay controller and the switch are coupled in series. 
         [0028]    In a relay device for switching loads, the relay controller can be integrated with the relay in a housing. The integration of the relay controller into the relay has the advantage that for example the handling and stockkeeping can be greatly simplified. In the case of integration, the relay controller can be coordinated precisely with the relay, with the result that a simplification of the relay controller can be afforded. 
         [0029]    In a relay device for switching loads, the switch can be a high-side switch. 
         [0030]    In a relay device for switching loads, the switch can be a low-side switch. 
         [0031]    In a relay device for switching loads, the commutation device can contain at least one resistor. 
         [0032]    In a relay device for switching loads, the commutation device can contain at least one zener diode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    Embodiments are explained in more detail below with reference to the following drawings. 
           [0034]      FIG. 1  shows a relay with a high-side switch. 
           [0035]      FIG. 2  shows a relay with a low-side switch and a freewheeling diode. 
           [0036]      FIG. 3  shows a relay with a low-side switch and a zener diode. 
           [0037]      FIG. 4  shows a relay with a low-side switch and a resistor. 
           [0038]      FIG. 5  shows a relay with a high-side switch, a commutation circuit and a relay controller. 
           [0039]      FIG. 6  shows a relay with a low-side switch, a commutation circuit and a relay controller. 
           [0040]      FIG. 7  shows a relay controller. 
           [0041]      FIG. 8  shows signal profiles. 
           [0042]      FIG. 9  shows a relay with a commutation circuit and a relay controller. 
           [0043]      FIG. 10  shows a relay with a commutation circuit and a relay controller. 
       
    
    
     DESCRIPTION 
       [0044]      FIG. 1  shows a relay  300  and a high-side switch  210 , which are connected in series between the reference potentials  110  and  120  in a known manner. The voltage between the reference potentials  110  and  120 , the supply voltage Vs, can be a battery voltage for example in an automobile. The high-side switch  210  or the low-side switch switches the supply voltage onto the excitation winding  310  of the relay  300 . The current through the excitation winding  310  can be limited by the coil resistance of the excitation winding  310 . 
         [0045]      FIGS. 2 to 4  show different known embodiments of a commutation device. The commutation devices  410 ,  420 ,  430  shown can also be employed with high-side switches. In  FIG. 2 , the commutation device  400  is embodied as a diode  410 . If the low-side switch, here embodied as an NMOS transistor  221 , is switched on, an excitation current flows through the excitation winding  310 . On account of the inductive properties of the excitation coil, the excitation current continues to flow until the energy stored in the excitation winding has been dissipated. After the NMOS transistor  221  has been turned off, the excitation current flows through a freewheeling path or through the commutation device  400 , which is configured in such a way that the energy of the excitation winding is dissipated. After the NMOS transistor  221  has been turned off, the excitation current flows through the now conducting diode. The potential of the second terminal of the excitation winding is approximately 0.7 to 1.3 volts above the first reference potential  110 . On account of the low diode voltage across the excitation winding, the energy of the excitation winding is dissipated only slowly, with the result that the commutation operation lasts a long time and the opening of the relay operating contacts lasts a long time, whereby much erosion can be produced at the relay operating contacts. Faster opening of the relay contacts can be achieved by means of commutation devices that permit a higher voltage on the excitation winding. Embodiments of such commutation devices are shown in  FIG. 3  and  FIG. 4 . The zener diode  420  from  FIG. 3  permits higher voltage on the excitation winding  310 , such that the energy of the excitation winding  310  can be rapidly dissipated and, as a consequence of this, the relay operating contacts open rapidly. A further advantage of the zener diode  420  is that it can easily be integrated into the NMOS transistor. During the commutation, current can still be drawn from the supply voltage Vs, this current leading to additional losses. 
         [0046]    A resistor  430  as commutation device  400  in accordance with  FIG. 4  has the advantages that during commutation no commutation current is drawn from the supply voltage Vs, and that it permits a high voltage for the commutation of the excitation winding  310 . The dimensioning of the resistor  430  is costly, however, since the voltage for commutation must not damage the NMOS transistor. Since the price of NMOS transistors increases with the ability of the transistors to withstand high voltages, an economic limit is placed on the dimensioning of the resistor  430 . The additional current that flows via the resistor when the relay is turned on is likewise disadvantageous. 
         [0047]      FIG. 5  shows an arrangement comprising a relay  300 , a commutation device  400 , an NMOS transistor  211  as high-side switch and a relay controller  500 . A first terminal of the NMOS transistor  211  is connected to the first reference potential  110  and a second terminal of the NMOS transistor  211  is connected to the first terminal  311  of the excitation winding  310  of the relay  300  and to a first terminal of the commutation device  400 . The second terminal  312  of the excitation winding  310  is connected to the first terminal  501  of the relay controller  500 . A second terminal of the commutation device  400  is connected to the second terminal  502  of the relay controller  500 . The third terminal  503  of the relay controller  500  is connected to the second reference potential  120 . If this arrangement is used in an automobile, then the first reference potential  110  can be provided by the battery and the second reference potential  120  can be provided by the earth terminal of the automobile. The NMOS transistor  211  is only one exemplary embodiment of a high-side switch  210 ; the high-side switch  210  can also be embodied as a PMOS transistor, PNP or NPN transistor, or as a relay operating contact of a relay. The high-side switch  210  can also be connected to a plurality of arrangements comprising relay  300  and relay controller  500 . 
         [0048]    An arrangement comprising a low-side switch is possible analogously to this and is shown in  FIG. 6 . In such an arrangement, the third terminal  503  of the relay controller  500  is connected to the first reference potential  110 , thus resulting in an arrangement which arises from the mirroring of the high-side arrangement about a horizontal axis. The description of the function of a relay  300  with a relay controller  500  with a high-side switch  210 ,  211  is analogously also applicable to the arrangement comprising a low-side switch. 
         [0049]    If the high-side switch  211  is switched off, the entire arrangement is without current and the relay is switched off. In other words, the switch  320  of the relay  300  is open, with the result that no current can flow through the terminals  321 ,  322  of the relay  300 . This state corresponds, in  FIG. 8 , to the states before the instant t 1  is reached. 
         [0050]      FIG. 8   a  shows a switching voltage Vsw between the terminal of the excitation winding  311  and the third terminal  503  of the relay controller. 
         [0051]      FIG. 8   b  shows an output voltage Vro between the first terminal  501  of the relay controller  500  and the third terminal  503  of the relay controller. 
         [0052]      FIG. 8   c  shows an excitation current Irel that flows into the terminal  311  of the excitation winding through the excitation winding  310 . 
         [0053]      FIG. 8   d  shows a supply current Irs of the relay controller that flows into the second terminal  502  of the relay controller  500 . 
         [0054]      FIG. 9  shows an arrangement comprising a relay  300 , a commutation device  400  and a relay controller  500 . The first terminal  311  of the excitation winding  310  of the relay  300  is connected to a reference voltage  110 . The second terminal  312  of the excitation winding  310  is connected to the first terminal  501  of the relay controller  500 . A second terminal of the commutation device  400  is connected to the second terminal  502  of the relay controller  500 . The third terminal  503  of the relay controller  500  is connected to the second reference potential  120 . If this arrangement is used in an automobile, then the first reference potential  110  can be provided by the battery and the second reference potential  120  can be provided by the earth terminal of the automobile.  FIG. 9  shows a fifth terminal  505  to switch on or off the relay controller.  FIG. 8  shows a sixth terminal to determine the hold current of the relay controller. 
         [0055]      FIG. 10  shows an arrangement comprising an excitation winding connected to the second reference potential  120 , which can provided by the earth terminal, is possible analogously to the embodiment shown in  FIG. 9 . In such an arrangement, the third terminal  503  of the relay controller  500  is connected to the first reference potential  110 , thus resulting in an arrangement which arises from the mirroring of the arrangement of  FIG. 9  about a horizontal axis. The description of the function of this embodiment is analogously and also applicable to the arrangement shown in  FIG. 9 . 
         [0056]    The instants t 1  to t 5  in  FIG. 8  describe instants at which the state of the arrangement changes, the high-side switch  210 ,  211  being switched off until t 1 . If the high-side switch  210 ,  211  is closed at the instant t 1 , then the switching voltage Vsw rises almost to a supply voltage Vs. The supply voltage Vs is the voltage between the first  110  and the second  120  reference potentials. Assuming that the internal resistance of the high-side switch  210 ,  211  is low, the voltage drop across the high-side switch  210 ,  211  can be disregarded. A supply current Irs then flows into the relay controller  500  via the commutation device  400 . With the aid of the supply current, the relay controller  500  starts and, with the aid of a switch or a current source, provides the excitation current Irel at the first terminal  501  of the relay controller  500 . 
         [0057]    After the relay controller  500  has started, the start instant of the pull-in time can be determined and defined. The excitation current Irel rises continuously, and the relay operating contact  320  of the relay  300  closes before the excitation current Irel has reached the magnitude of the predetermined pull-in current of the relay  300 . The output voltage Vro remains for as long at a low level which can correspond to a minimum drain voltage of a MOS transistor or a minimum collector voltage of a bipolar transistor. 
         [0058]    In addition to a current source that can be embodied as a current source transistor, a second switch that can be embodied as a switching transistor is also possible in order to minimize the output voltage further. The excitation current can be detected, in which case the exceeding of a threshold can determine a start instant of the pull-in time. If the predetermined pull-in current has been reached, the excitation current Irel rises further until it is limited by the sum of the resistances if the pull-in current is provided by a switch. If the pull-in current is provided by a current source, the excitation current Irel does not rise further. 
         [0059]    The output voltage Vro settles to a value given by the supply voltage Vs, the pull-in current and the internal resistance of the excitation winding  310 . Independently of this, the potential at the second terminal  502  of the relay controller  500  assumes a value given by the internal resistance of the commutation device  400 , the supply voltage Vs and the supply current Irs. 
         [0060]    At the instant t 2 , after the pull-in time has elapsed, the relay controller  500  switches the excitation current from the value of the pull-in current to a predetermined value of a holding current. The holding current can be chosen such that it is lower than the pull-in current, but high enough that the relay operating contact  320  of the relay  300  remains closed. 
         [0061]    The instant t 2  can be determined by a predetermined pull-in time. The instant t 2  can also be determined by the relay controller  500  detecting the instant at which the excitation current has reached the value of the pull-in current and permitting a predetermined pull-in time to elapse after this instant. 
         [0062]    The energy difference arising from the difference of the pull-in current and of the holding current of the excitation current can be dissipated via the commutation device  400  by the excess excitation current being conducted through the first  501  to the second  502  terminal of the relay controller  500  to the commutation device  400 . A current resulting from the difference of the supply current Irs and of the excess excitation current then flows from the second terminal  502  of the relay controller  500 . While the excitation current decreases, a voltage that can be higher than the supply voltage Vs is established by the commutation device at the first terminal  501  and second terminal  502  of the relay controller  500 . This voltage can be limited by a voltage limiting circuit, which can be within or outside the relay controller  500  and can be e.g. a zener diode. 
         [0063]    Once the energy difference arising from the difference of the pull-in current and of the holding current of the excitation current has been dissipated, the instant t 3  has been reached. The output voltage Vro settles to a value given by the supply voltage Vs, the holding current and the internal resistance of the excitation winding  310 . 
         [0064]    Depending on the magnitude of the supply voltage Vs, conditions in which the relay controller  500  cannot provide a sufficient excitation current can arise in this or a preceding state. An undervoltage sensor circuit  570  detects if the supply voltage is too low to provide a sufficient excitation current, and initiates measures for increasing the excitation current. One measure is to bridge the current source by means of a switch having a low voltage drop. 
         [0065]    Depending on the magnitude of the supply voltage Vs, conditions in which the power consumption of the relay controller  500  exceeds the permissible power consumption can arise in this or a preceding state. An increased power consumption can occur in the current source that provides the excitation current. The relay controller  500  can have a temperature sensor circuit  560  that initiates measures for reducing the power consumption of the relay controller  500  if a maximum temperature is reached. One measure is to reduce the excitation current. If this measure is unsuccessful, the excitation current can be completely turned off. 
         [0066]    The relay is switched off by the high-side switch  210 ,  211  being switched off. In  FIG. 8 , the high-side switch is switched off at the instant t 4 . Since no excitation current can flow through the high-side switch  210 ,  211 , the excitation current flows through the commutation device  400 . As a result of the voltage drop thus caused across the commutation device  400 , the switching voltage Vsw becomes negative. The negative switching voltage Vsw can be limited by a zener diode of the high-side switch  210 ,  211 . In the case of mechanical switches, the voltage can remain unlimited. The voltage then reaches the value resulting from the product of the commutation resistance and the commutation current. Once the energy of the excitation coil  310  has been dissipated, the instant t 5  has been reached in that the device is deenergized. 
         [0067]      FIG. 7  shows an exemplary embodiment of a relay controller  500 . A current controller  510  is connected to the first terminal  501  and the third terminal  503  of the relay controller  500 . A voltage limiting circuit  530  is connected to the first terminal  501  and the third terminal  503  of the relay controller  500 . A freewheeling controller  520  is connected to the first  501  and the second  502  terminal of the relay controller  500 . A circuit for generating a supply voltage  550 , a temperature sensor circuit  560  and an undervoltage sensor circuit  570  are connected to the second  502  and the third  503  terminal of the relay controller. A time controller  540  is designed to control the current controller  510 . A fourth terminal  504  of the relay controller  500  can be formed, at which means for influencing the time controller  540  can be provided. One means for influencing a time controller  540  is a capacitor connected to the fourth terminal  504  of the relay controller  500 . One exemplary embodiment of a current controller  510  contains an NMOS transistor or an NPN transistor, the drain or collector of which is connected to the first terminal  501  of the relay controller  500  and which is controlled in such a way that it provides a constant current. The current controller  510  can also contain an NMOS transistor or an NPN transistor, the drain or collector of which is connected to the first terminal  501  of the relay controller  500  and which is switched in such a way that the output voltage Vro becomes as low as possible. One exemplary embodiment of a voltage limiting circuit  530  contains a zener diode, the cathode of which is connected to the first terminal  501  of the relay controller. The voltage-limiting effect of the zener diode can be amplified by a circuit. One exemplary embodiment of a freewheeling controller  520  can contain a diode, the cathode of which is connected to the second terminal  502  of the relay circuit. Instead of a diode, the freewheeling circuit  520  can contain a transistor.