Abstract:
A surge protection circuit, method, computer readable medium, and use, including: at least one first electronic component having a non-linear characteristic, electrically conductively connected between a tapping point, to which a supply potential is appliable, and a node point; at least one second electronic component having a non-linear characteristic, electrically conductively connected between a tapping point, to which a ground potential is appliable, and the node point; a resistor connected between the node point and a control connection; and a monitoring unit to apply a predetermined voltage to the control connection or to output a predetermined current via the control connection and to detect a voltage/potential at the node point in response thereto, the monitoring unit being configured to identify a malfunction in the surge protection circuit when the detected voltage or the detected potential is not related to an expected voltage or expected potential in a predetermined manner.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a surge protection circuit and to a method for testing a surge protection circuit. 
     BACKGROUND INFORMATION 
     In various electronic circuits, for example a controller for a safety unit in utility vehicles, a protection circuit may be used to avoid excessively high voltages on connections of integrated circuits. In this case, it may not be possible to test whether this protection circuit is still functional over the course of time or has lost its function owing to corrosion or other environmental influences. If the protection circuit is no longer functional, this cannot be verified in the prior art and there is only assumed protection against such excessively high voltages on connections of the integrated circuit. In the event of excessively high voltages actually occurring on connections of integrated circuits, this means that the protective function of this protection circuit is no longer ensured, with the result that the integrated circuit may possibly be damaged in this case, despite the provision of the protection circuit. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an improved surge protection circuit and an improved method for testing a surge protection circuit, the surge protection circuit and method providing cost-effective and checkable surge protection, for example for use in controllers. 
     This object may be achieved by a surge protection circuit and a method according to the main claims. 
     The present invention provides a surge protection circuit which has the following features:
         at least one first electronic component having a non-linear characteristic, which first electronic component is electrically conductively connected between a tapping point, to which a supply potential can be applied, and a node point;   at least one second electronic component having a non-linear characteristic, which second electronic component is electrically conductively connected between a tapping point, to which a ground potential can be applied, and the node point;   a resistor which is connected between the node point and a control connection; and   a monitoring unit which is configured to apply a predetermined voltage to the control connection or to output a predetermined current via the control connection and to detect a voltage or a potential at the node point in response to this, wherein the monitoring unit ( 230 ) is configured to identify a malfunction in the surge protection circuit when the detected voltage or the detected potential is not related to an expected voltage or an expected potential in a predetermined manner.       

     The present invention also provides a method for testing a surge protection circuit as claimed in one of the preceding claims, wherein the method comprises the following steps:
         applying a predetermined voltage to the control connection or impressing a predetermined current into the control connection;   detecting a voltage or a potential at the node point; and   identifying a malfunction in the surge protection circuit when the detected voltage or the detected potential at the node point is not related to an expected voltage or an expected potential in a predetermined manner.       

     A computer program product having program code which can be stored in a machine-readable storage medium, such as a semiconductor memory, a hard-disk memory or an optical memory, and is used for carrying out the method according to one of the above-described embodiments when the program is executed on a signal-processing system, such as a computer or a corresponding device, is also advantageous. 
     The present invention is based on the knowledge that surge protection can now be realized by using two electronic components which are connected in series, in the case of which a node point between these two components is accessible for the purpose of tapping off or impressing a voltage. Firstly, a corresponding voltage or a corresponding current flow from a control connection can be impressed via this node point by a resistor, it then being possible to test the response of the first and/or second electronic component, wherein the first and second components are connected to the ground potential or to the supply potential. In this way, both the function of the first and of the second component can be monitored, for example when an expected voltages differs from an ascertained voltage at the node point (in each case based on the ground potential), when the predetermined voltage has been applied to the control connection or when the predetermined current has been impressed into the control connection. 
     In relation to the prior art, in the case of which only one component between a first connection, to which a supply potential can be applied, and a second connection, to which a ground potential can be applied, is tested, monitoring in the above manner now advantageously allows the individual components which make up the protection circuit for a further electronic component (for example an integrated circuit) to be tested. The use of non-linear electronic components in this case allows the protective function against excessively high voltages to be realized in an effective manner. 
     In this case, non-linear electronic components are, in particular, electronic components which have a non-linear characteristic of these components in a voltage/current graph. Possible components in this case include, in particular, electronic components such as diodes, zener diodes, transistors, thyristors or similar components which have a non-linear characteristic in a voltage/current graph. In this case, the monitoring unit can itself be part of the integrated circuit which is to be protected against excessively high voltages, for example a microcontroller, a digital signal processor or the like. 
     It is expedient when, according to one embodiment of the present invention, the first electronic component is a diode, in particular when the cathode of the diode is connected to the tapping point to which the supply potential can be applied, and the anode of the diode is connected to the node point. An embodiment of the present invention of this kind provides the advantage of a very simple configuration of the first electronic component, with the result that a cost-effective surge protection circuit can be realized. 
     It is particularly advantageous when the diode is a zener diode. An embodiment of the present invention of this kind provides the advantage of a simple configuration of the first electronic component, wherein the first component is not destroyed in the event of excessively high voltages actually occurring between the supply potential connection and the ground potential connection. Instead, the excessively high voltages can be discharged in a defined manner by a zener diode of this kind, wherein the breakdown voltage of the zener diode allows a large voltage drop in the voltage between the supply potential connection and the ground potential connection. 
     Furthermore, according to a further embodiment of the present invention, the second electronic component can be a diode. An embodiment of the present invention of this kind likewise provides the advantage of a very simple configuration of the second electronic component, with the result that a cost-effective surge protection circuit can be realized. 
     It is further expedient when the diode of the second electronic component is connected to the node point by way of the anode, and the cathode of the diode is connected to the tapping point to which the ground potential can be applied. An embodiment of the present invention of this kind ensures that the second electronic component ensures defined discharge of current in the event of excessively high voltages between the supply potential connection and the ground potential connection from the node point to the ground potential connection, that is to say the tapping point to which the ground potential can be applied. 
     In order to set a defined voltage from which the surge protection circuit discharges current by bypassing the integrated circuit which is to be protected, it is also possible to provide at least a third electronic component having a non-linear characteristic, wherein the third electronic component is electrically conductively connected between the second electronic component and the tapping point to which the ground potential can be applied, in particular wherein the third electronic component is a diode, the anode of the diode being connected to the second electronic component, and the cathode of the diode being connected to the tapping point to which the ground potential can be applied. An embodiment of the present invention of this kind provides the advantage that the voltage dropped across the second electronic component and the voltage dropped across the third electronic component can be summed by the series connection of the second electronic component and the third electronic component, with the result that a breakdown voltage which is relatively high overall can be still realized between the node point and the tapping point, to which the ground potential can be applied, in the case of small breakdown voltages of the second and of the third electronic component. This allows more precise identification of faults in the surge protection circuit than if only a small voltage between the node point and the tapping point, to which the ground potential can be applied, had to be evaluated. 
     As an alternative, the second electronic component used can be a diode, which is a zener diode, in particular wherein the cathode of the zener diode is connected to the node point, and the anode of the zener diode is connected to the tapping point to which the ground potential can be applied. An embodiment of the present invention of this kind provides the advantage of a higher breakdown voltage than when one or more diodes which are connected in series are used as the second electronic component. As a result, the breakdown voltage between the node point and the tapping point, to which the ground potential can be applied, can be realized with a single electronic component, as a result of which the surge protection circuit can be configured in a cost-effective and simple manner. 
     A further embodiment of the present invention provides for the use of a surge protection circuit according to the above description and/or of a method according to the above description in a utility vehicle, in particular for use in a safety controller, in particular for use in an ABS controller. An embodiment of the present invention of this kind ensures correct operation of the utility vehicle or functioning of a safety controller of this kind in a utility vehicle, for example a heavy-goods vehicle or a bus, over a very long period of time since the function of the first and/or second electronic component can be tested, and a fault message can optionally be output, for example at specific time intervals. In this way, a defective component can be identified in good time and replaced. As a result, a high degree of occupant protection or protection of other road users can be achieved in a cost-effective manner. 
     Advantageous exemplary embodiments of the present invention will be explained in greater detail below with reference to the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a block diagram of a utility vehicle which has a exemplary embodiment of the surge protection circuit according to the invention. 
         FIG. 2  shows a circuit diagram of a first exemplary embodiment of the surge protection circuit according to the invention. 
         FIG. 3  shows a circuit diagram of a second exemplary embodiment of the surge protection circuit according to the invention. 
         FIG. 4  shows a flowchart of an exemplary embodiment of the method according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of the exemplary embodiments of the present invention, identical or similar reference symbols will be used for the elements which are illustrated in the various drawings and act in a similar manner, wherein these elements will not be repeatedly described. 
       FIG. 1  shows a block diagram of a utility vehicle which has an exemplary embodiment of the surge protection circuit according to the invention.  FIG. 1  shows a utility vehicle  100 , for example a heavy-goods vehicle or a bus, which has a controller  110  for the ABS function in order to supply appropriate control signals to the brake units  120  of the wheels of the utility vehicle  100 . In this case, the controller  110  is supplied with electrical energy, for example, by an energy store  130  (for example a battery), wherein this electrical power is delivered between a supply potential connection VCC and a ground potential connection GND. In this case, further components (which are not illustrated in  FIG. 1 ) are also connected to the supply potential connection VCC and the ground potential connection GND. By way of example, a charging socket for charging the energy store  130  can be provided, it being possible to make electrical contact with the two potential connections by the charging socket. 
     If, for example, the energy store  130  is now charged with an excessively high voltage, this excessively high voltage is also applied to the controller  110 , with the result that electronic components of the controller  110  could be damaged. In order to avoid such damage, a surge protection circuit is provided in the prior art, this involving, for example, a zener diode being installed between the supply potential connection VCC and the ground potential connection GND against the direction of flow, a breakdown voltage being exceeded when an excessively high voltage is applied between the supply potential connection and the ground potential connection. In this case, current is therefore discharged in the form of a bypass around voltage-sensitive components of the controller  110 , with the result that the voltage between the supply potential connection under the ground potential connection can be lowered to the maximum or desired value. 
     If, however, this electronic component (for example the zener diode) for ensuring the protective function is now defective, this defect cannot be detected in the prior art, with the result that, for example, the protective function is no longer active, even when the electronic component for ensuring the desired protective function is present. A defect of this kind can be caused, for example, by aging of the electronic component or in the event of an excessively high voltage actually occurring between the supply potential connection and the ground potential connection. 
     In order to then identify such a case of a defect occurring in an electronic component, this ensuring the desired protective function against excessively high voltages between the connection for the supply potential VCC and the connection for the ground potential GND, a first exemplary embodiment of the present invention now proposes using two electronic components between which a node or tapping point is accessible, it being possible to apply or tap off signals at the node or tapping point. A circuit diagram of this first exemplary embodiment of the present invention is illustrated in  FIG. 2 . This option of tapping off signals between the two electronic components which ensure the desired protective function against excessively high voltages between the connection for the supply potential VCC and the connection for the ground potential GND now allows the two electronic components to be checked for correct functioning. 
     According to the circuit diagram (illustrated in  FIG. 2 ) of the first exemplary embodiment of the surge protection circuit  20  according to the invention, a zener diode D 1  and a first diode D 2  and a second diode D 3  are connected in series between the tapping point  200 , to which the supply voltage potential VCC can be applied, and the tapping point  210 , to which the ground potential GND can be applied. A node point  220  is arranged between the zener diode D 1  and the first diode D 2 , the node point being connected to a first output DIO (DIO=Digital Input/Output) of a monitoring unit  230  via a resistor R 1 , wherein this first output DIO serves as the control connection for the subsequent monitoring of the surge protection circuit. In this case, the zener diode D 1  is connected up in such a way that the anode of the zener diode is connected to the node point  220 , while the cathode of the zener diode is connected to the tapping point  200  to which the supply potential can be applied. The anode of the first diode D 2  is connected to the node point  220 , whereas the cathode of the first diode D 2  is connected to the anode of the second diode D 3 , and the cathode of the second diode D 3  is connected to the tapping point  210  to which the ground potential GND can be applied. In this case, the monitoring unit  230  is likewise connected to the tapping point  200  to which the supply potential VCC can be applied, and to the tapping point  210  to which the ground potential GND can be applied, and can furthermore also contain yet further components of the controller, such as integrated circuits of a microcontroller μC, in order to implement, for example, the ABS function of the utility vehicle  100 . The monitoring unit  230  can therefore be part of the microcontroller μC. Furthermore, the monitoring unit  230  is also configured to read a voltage between the node point  220  and a ground potential GND, for example via an analog input AD. 
     The zener diode D 1  has, for example, a breakdown voltage of 3.7 or 4.2 V when a supply voltage between VCC and GND of 5 V is intended to be applied. The first diode D 2  and the second diode D 3  can have, for example, a flux voltage of 0.7 V when a current flows through these diodes, with the result that current begins to flow through the series circuit comprising the first and second diodes only starting from a common flux voltage of 1.4 V. 
     The surge protection circuit  20  according to the exemplary embodiment illustrated in  FIG. 2  therefore comprises at least two diodes which are connected in series and one resistor R 1  which can be switched by the monitoring unit  230  in the microcontroller μC and which, according to the circuit diagram from  FIG. 2 , has a value of 1 kΩ, and an analog feedback system due to the option of voltage tapping at the node point  220 . If the resistor R 1 , which is situated between the node point  220  of the two diodes D 1  and D 2 , the switchable resistor R 1  and the analog input AC of the μC (that is to say the monitoring unit  230 ) on the one hand and the control connection DIO on the other, at the control input DIO is set to high (that is to say to the level of the supply potential VCC), the diode D 2  or the two diodes D 2  and D 3 , which is/are connected to GND, can be tested by analog feedback via the AD input (that is to say by reading a voltage between the node point  220  and the ground potential GND). In this case, the voltage at the node point  220  should drop to 1.4 volts due to the flux voltages of the diodes D 2  and D 3 , with the result that, at a value which differs from this expected value for the voltage at the node point  220 , a fault in the diode D 2  or one of the diodes D 2  or D 3  can be identified. The remaining voltage up to the supply potential VCC is dropped across the resistor R 1  in this case. 
     Similarly, the zener diode D 1 , which is connected to the tapping point  200  to which the supply potential VCC can be applied, can be tested by connecting the resistor R 1  to GND. For example, setting the potential of the control connection DIO to the value of the ground potential GND allows the connection state of the zener diode D 1  to be tested. In the case of this test, the voltage at the node point  220  should drop to a value which corresponds firstly to the difference between the voltage between the supply potential VCC and the ground potential GND and secondly the breakdown voltage of the zener diode Z 1 . The remaining voltage up to ground potential is dropped across the resistor R 1  in this case. If the voltage value which is detected at the node point  220  differs from the expected voltage value in the above-mentioned case of testing the application of ground potential GND to the control connection, it can likewise again be concluded that there is a fault, in this case in the zener diode D 1 . 
       FIG. 3  shows a circuit diagram of a second exemplary embodiment of the present invention of a surge protection circuit. In this case, the circuit topology of the surge protection circuit  20  corresponds to the circuit topology from  FIG. 2  of the surge protection circuit  20 , with the difference that, instead of the first diode D 2  and/or the second diode D 3  as the second component, a further zener diode D 2  is used as the second component. The polarity of this further zener diode D 2  is such that the anode of the zener diode is connected to the tapping point  210  to which the ground potential GND can be applied, and the anode of the zener diode is connected to the to the node point  220 . An exemplary embodiment of the present invention of this kind provides the advantage over the circuit topology illustrated in  FIG. 2  that only one component has to be used, and at the same time a sufficiently high breakdown voltage can be achieved, this leading to a sufficiently high voltage, which can be tapped off, at the node point  220 , with the result that faults can be reliably identified in the first and/or second electronic component. 
     As an alternative, it is also possible to set the first electronic component in the form of the zener diode D 1  by a series circuit of two diodes, wherein the two diodes would be connected in accordance with the polarity from  FIG. 2 , that is to say against the polarity of the zener diode D 1  from  FIGS. 2 and 3 . 
       FIG. 4  shows a flowchart of an exemplary embodiment of the present invention as a method  40  for testing a surge protection circuit  20 . The method uses a surge protection circuit, as has been described above. The method  40  comprises a step of applying  410  a predetermined voltage to the control connection or impressing a predetermined current into the control connection. The method further comprises a step of detecting  420  a voltage at the node point, and a step of identifying  430  a malfunction in the surge protection circuit when the detected voltage between the node point and the ground potential is not related to an expected voltage at the node point in a predetermined manner. 
     The background to the present invention is therefore that, for example, overvoltage protection by a zener diode cannot be tested for freedom from faults over the service life of controllers. An important aspect of the present invention was therefore that of removing the inability to monitor the surge protection, as a result of which the controllers with an untestable surge protection of this kind cannot actually be used for increasing the safety requirements in a utility vehicle. 
     According to the solution proposed here, the surge protection circuit can now be part of an internal computer supply voltage unit. The structural configuration of the surge protection circuit comprises standard components. By virtue of the approach proposed here, surge protection during operation can be tested for existence or efficacy. At the same time, only low hardware costs have to be taken into account for implementing the approach presented here. 
     The described exemplary embodiments are selected only by way of example and can be combined with one another. 
     The list of reference symbols is as follows:
       100  Utility vehicle     110  Controller     120  Brake unit     130  Energy store, battery     20  Surge protection circuit     200  Tapping point to which the supply potential can be applied     210  Tapping point to which the ground potential can be applied     220  Node point     230  Monitoring unit   D 1  Zener diode   D 2  First diode, zener diode   D 3  Second diode   R 1  Resistor   DIO Control connection   AD Analog input     40  Method for monitoring a surge protection circuit     410  Application step     420  Detection step     430  Identification step