Abstract:
A method and system is provided for retrieving information about operational data from a plurality of building systems and service and maintenance information for a plurality of building sites. A customer web portal is provided with a database for storing the operational data and the service information allowing users to more readily generate reports and obtain service related information for a plurality of sites without having to maintain separate database systems at remote locations.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of, and claims the benefit of, prior application Ser. No. 11/731,765, filed on Mar. 29, 2007, which in turn claims priority from German patent application no. 10 2006 014 523.2-33, filed Mar. 29, 2006, the contents of which are incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The invention relates to a circuit arrangement for overtemperature detection in transistors, particularly power transistors. 
       BACKGROUND 
       [0003]    Power transistors are transistors which provide for large current and voltage amplitudes and are thus suitable for directly operating loads with relatively large powers. Power transistors are used, for example, in output stages and switching stages for industrial electronics and motor vehicle engineering. 
         [0004]    In this context, the temperature of a power transistor represents a significant factor for its functional capability. An overtemperature of the power transistor, generated, for example, by a higher ambient temperature or by malfunction such as a short circuit of loads, can lead to it being damaged or destroyed and in addition can also lead to impairment or even destruction of the load. It is essential, therefore, to detect any overtemperature of power transistors in time and reliably in order to be able to take suitable measures such as, for example, switching off the transistor or the load before critical temperature values and thus the damage limit are/is reached. 
         [0005]    To determine the temperature of a semiconductor component, a temperature sensor can be attached to the package of the semiconductor component or to its semiconductor body/chip. It can be inappropriate that the sensor and the actual semiconductor component are two separate components, as a result of which the sensor only detects the temperature externally on the semiconductor component which can deviate considerably from the temperature in the interior of the semiconductor component and, in addition, has an unwanted inertia in the case of rapid temperature changes in the interior of the semiconductor component. It is precisely the temperature in the interior of the semiconductor body, however, which is relevant to the determination of critical operating states. 
         [0006]    There is a general need for a circuit arrangement with a temperature sensor which is integrated into the same semiconductor body like the power transistor, where the temperature sensor reliably provides a voltage dependent on the temperature in the interior of the semiconductor body. 
       SUMMARY 
       [0007]    In one embodiment of the invention a diode structure is additionally integrated into a semiconductor body. The diode structure is fed with a current in its forward direction from a current source. The voltage drop across the diode structure is dependent on the temperature of the diode structure and thus on the temperature of the transistor structure, and can therefore be used for overtemperature detection by an evaluating unit, wherein the protection of the power transistor and of the co-integrated temperature sensor due to undesirable destruction guaranteed by the evaluating unit. 
         [0008]    Using a diode structure integrated into the semiconductor body, which is fed in the forward direction (not in the reverse direction) by a current (not by a voltage) provides for a large signal swing, and due to the fact that a switching element located in the evaluating unit actively produces a short circuit between the bulk of the semiconductor body and the source of the power transistor when this is required due to the operating state of the power transistor or of the evaluating unit, which for the first time enables the arrangement according to at least one embodiment of the invention to be used for overtemperature detection in n-channel LS switches and in p-channel HS switches. 
         [0009]    Further advantages can also be obtained if the (for example separate, particularly external) evaluating unit for detecting the overtemperature and the power transistor structure are thermally decoupled from one another, which has a positive influence on the accuracy and reliability of the evaluating unit, and due to the fact that the influence of the ambient temperature on the power transistor structure and the evaluating unit can be taken into consideration. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The invention can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, instead emphasis being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts. In the drawings: 
           [0011]      FIG. 1  shows the chip-on-chip technology for measuring the temperature; 
           [0012]      FIG. 2  shows the measurement of the leakage current of an integrated diode in the reverse direction at the n-channel HS switch; 
           [0013]      FIG. 3  shows the measurement of the diode voltage of a forward-polarized diode on the exemplary n-channel HS switch; 
           [0014]      FIG. 4  shows an n-channel LS switch and a parasitic diode structure; 
           [0015]      FIG. 5  shows a p-channel HS switch and a parasitic diode structure; 
           [0016]      FIG. 6  is a circuit diagram of a temperature sensor integrated in a semiconductor body, with parasitic diode structure and a separate evaluating unit, taking into consideration the ambient temperature, according to a first embodiment of the invention; 
           [0017]      FIG. 7  is a circuit diagram of a temperature sensor integrated in a semiconductor body, with parasitic diode structure and a separate evaluating unit with voltage/current converters according to a second embodiment of the invention; 
           [0018]      FIG. 8  is a circuit diagram of a temperature sensor integrated in a semiconductor body, with parasitic diode structure and a separate evaluating unit with monitoring of the voltage at the drain terminal of the power transistor structure according to a third embodiment of the invention; and 
           [0019]      FIG. 9  is a circuit diagram of a temperature sensor integrated in a semiconductor body, with parasitic diode structure and a separate evaluating unit with external activation of the measurement according to a fourth embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    To determine the temperature of a semiconductor component  100 , a temperature sensor  101  can be attached to the package of the semiconductor component  100  or to its semiconductor body/chip (see  FIG. 1 ). Sometimes it can be useful that the sensor and the actual semiconductor component are not two separate components, as a result of which the sensor only detects the temperature externally on the semiconductor component which can deviate considerably from the temperature in the interior of the semiconductor component and, in addition, has an unwanted inertia in the case of rapid temperature changes in the interior of the semiconductor component. It is precisely the temperature in the interior of the semiconductor body, however, which is relevant to the determination of critical operating states. 
         [0021]    To determine the internal temperature of a semiconductor component, diode structure may be provided in the same semiconductor body in which the semiconductor component is integrated, the diode structure being connected to a supply voltage. 
         [0022]      FIG. 2  shows an example of an n-channel HS switch (HS=High Side; LS=Low Side). The arrangement according to  FIG. 2  comprises a power transistor structure  102  integrated in a semiconductor body and an evaluating unit  103 , electrically connected to the former, for overtemperature detection of the power transistor structure  102 . In addition to the power transistor structure  102 , a reverse-biased bipolar diode structure  104  is also integrated in the semiconductor body, which is fed from a current source  107  located in the separate evaluating unit  103  via an additional body or bulk terminal  105  on the semiconductor body by a reference current  106  in the reverse direction of the diode structure  104 . The diode structure  104  can be formed, e.g., by the bulk drain diode always present in a MOSFET. The usual short circuit between source and bulk does not exist in this and the following embodiments. 
         [0023]    The measuring voltage  108  dropped accordingly across the diode structure  104  and dependent on the temperature of the diode structure  104  and thus on the temperature of the semiconductor body and thus, in turn, on the temperature of the power transistor structure  102  is compared with a comparison voltage  109  in the evaluating unit  103  in order to generate from this a signal  110  identifying an overtemperature. In this arrangement, the voltage  109  of a voltage source  112 , present at one input of a comparator  111 , is compared with the voltage  108  at the body terminal  105  of the diode structure  104 . If the voltage at the body terminal  105  of the diode structure  104  exceeds the permanently preset value of the reference voltage source  112 , the signal state at the output of the comparator  111  changes and generates the signal  110  identifying an overtemperature of the power transistor. In this way, the diode structure  104  is used as temperature sensor for the temperature of the power transistor structure  102 , the diode structure  104  being operated in the reverse direction with an impressed current. 
         [0024]    This makes use of the fact that the reverse current of the diode structure, detected by an evaluating unit, is exponentially dependent on the temperature so that the temperature in the semiconductor body can be inferred from the reverse current. If the reverse current of the diode structure  104  exceeds the current  106  predetermined by the current source  107 , the voltage at the body terminal  105  changes and the voltage drop across the diode structure  104  drops. In consequence of this process, the comparator  111  generates the overtemperature signal  110  as described. However, this reverse current exhibits a significant, that is to say analyzable, amount only at high temperatures due to the exponential characteristic, so that the signal deviation of such a diode structure temperature sensor is small. 
         [0025]    Although it is possible to partially compensate for this disadvantage by constructing the diode structure with the greatest possible area, this runs counter to the general demand for the highest possible degree of miniaturization of semiconductor components. In addition, diode structures always have a barrier layer capacitance in which a charge is stored. This stored charge can cause a current which may be greater than the reverse current used for temperature detection which unacceptably influences the measurement result. 
         [0026]    Furthermore, the power transistor structure can also be arranged as p-channel LS switch in the arrangement according to  FIG. 2 . The aforementioned disadvantages with regard to temperature range, signal deviation also exist in this case. 
         [0027]    For determining the internal temperature of a semiconductor component, a diode structure may be provided in the same semiconductor body in which the semiconductor component is integrated, the diode structure being operated by an impressed current in its forward direction. The circuit arrangement according to  FIG. 3  again comprises a power transistor structure  102  integrated in a semiconductor body and an evaluating unit  103  electrically connected to the former, for detecting overtemperature of the power transistor structure  102  which is only used for representing the basic principle in this case. In addition to the power transistor structure  102 , a bipolar diode structure  104  is again also integrated in the semiconductor body, which diode structure is fed from the current source  107  located in the separate evaluating unit  103  via the additional body terminal  105  at the semiconductor body via the reference current  106  in the forward direction of the diode structure  104  compared with  FIG. 2 . 
         [0028]    The voltage  108  correspondingly dropped across the diode structure  104 , which is dependent on the temperature of the diode structure  104  and thus on the temperature of the semiconductor body and thus, in turn, on the temperature of the power transistor structure  102  is again compared with a comparison voltage  109  in the evaluating unit  103  in order to generate from this, analogously to the circuit arrangement in  FIG. 2 , a signal  110  identifying an overtemperature. Apart from the exemplary embodiment of the power transistor structure  102  as n-channel HS switch, the power transistor structure  102  in  FIG. 3  can also be constructed as p-channel LS switch. 
         [0029]    The disadvantageous effect is here that for such an arrangement of the diode structure  104  according to  FIG. 3 , in the case of an n-channel LS switch, the corresponding supply voltage is not constantly applied to the drain terminal of the power transistor structure  102  but that, due to, e.g., switching processes of the power transistor structure, the voltage  108  dropped across the diode structure  104  in dependence on the temperature is subject to large voltage swings. An additional disadvantageous factor is that, for the arrangement according to  FIG. 3 , in the case of a p-channel HS switch, ground potential is not constantly applied to the drain terminal of the power transistor structure  102  but, due to, e.g., switching processes of the power transistor structure, the voltage  108  dropped across the diode structure  104  in dependence on temperature is also subject to large voltage swings. It is also a disadvantageous factor that the opening of the bulk-source short circuit produced by the diode structure  104  also being integrated no longer guarantees the dielectric strength of the power transistor. At a high voltage between drain and source of the power transistor structure  102 , this can lead to a voltage breakdown which takes place at a lower voltage than defined by the voltage class of the power transistor structure which is specified with the bulk short circuited with the source. In addition, the high voltage between source and drain produces a high voltage between collector and emitter of an NPN transistor formed from two individual diode structures. 
         [0030]    The circuit diagram according to  FIG. 4  shows a power transistor  1 , constructed as n-channel LS switch, including a parasitic diode structure  8 , which is always present when MOS technology is used, which is located in the reverse direction between bulk terminal  15  and drain terminal  9 . The parasitic diode structure  8  can be formed by the bulk-drain diode always present in MOS transistors. 
         [0031]    Compared with  FIG. 3 , the arrangement according to  FIG. 4  thus additionally takes into consideration the parasitic diode structure  8  which always exists in MOS transistors but which was neglected in the preceding figures. In this arrangement, a power transistor structure  7  is connected with its drain terminal  9  via an external load resistor  10  to a positive supply potential  11  and with its source terminal  12  to ground potential, as a result of which a load current  13 , flowing into the drain terminal  9  of the power transistor structure  7 , can be generated in dependence on a voltage, not designated in greater detail here, on the gate terminal of the power transistor structure  7 . Furthermore, the co-integrated diode structure  2  (e.g. the bulk-source diode which must not be short circuited in the present case) is connected in series opposition to the parasitic diode structure  8  (e.g. the bulk-drain diode) and the diode structures  2  and  8  are connected in parallel with the load path of the power transistor structure  7 . A bulk-source diode structure  2  is operated in the forward direction with an impressed current  14  as a result of which a voltage  16  dropped across the diode structure  2  is generated. 
         [0032]    This voltage  16  is not equal to the load path voltage of the power transistor structure  7  and is used for overtemperature detection of the power transistor. Furthermore, the voltage across the load path at drain  9  is compared with a preset voltage value  17  of a reference voltage source  18 . In the present case, this comparison takes place via a comparator  19 , to the inverting input of which the preset comparison voltage  17  is applied and the non-inverting input of which is connected to the drain terminal  9  of the power transistor structure  7  of the semiconductor body  1 . The comparator  19  can suitably have a switching characteristic with hysteresis. 
         [0033]    If the voltage present at the drain terminal  9  of the power transistor structure  7  exceeds the value of the comparison voltage  17 , the state of the signal at the output of the comparator  19  changes and short circuits the diode structure  2  via a transistor structure  49 . A short circuit of the diode structure  2  also takes place due to the switching-through of the transistor structure  49  if then a control signal “OFF” is activated, this control signal “OFF” and the output of the comparator  19  being linked via an OR gate  63  preceding the gate of the transistor structure  49 . 
         [0034]    It has an advantageous effect that the bulk-source diode (co-integrated diode structure  2 ) can be used as sensor element for the temperature measurement without reducing the dielectric or break-down strength of the power transistor. This is achieved by the fact that the bulk-source short circuit of the power transistor is only temporarily opened for a permissible range of the voltage, predetermined by the reference voltage  17 , at the drain of the power transistor which is below the hazard limit for the effects mentioned above. It also has an advantageous effect that no current flow generated by the impressed current  14  takes place at the source and the drain output of the power transistor if this is switched off (active “OFF” signal). It also has an advantageous effect that a temperature measurement is now possible with the power transistor switched on and thus a low load path voltage between drain and source of the power transistor (voltage at drain  9  lower than reference voltage  17 ). A further possible embodiment is obtained from specifying a maximum permissible voltage at the load path for the temperature measurement, which can also be monitored by measuring the operating voltage, for example in bridge circuits. 
         [0035]    The circuit diagram of  FIG. 5  shows the basic principle of an arrangement with a power transistor constructed as p-channel HS switch, including the parasitic diode structure  8 , which is always present when using MOS technology, which is located in the reverse direction between drain terminal  9  and bulk terminal  15  (parasitic drain-bulk diode), and the diode structure  2  (source-bulk diode). The evaluating unit also shown corresponds to that of  FIG. 4  and is only slightly less adapted to the changed application. 
         [0036]    The arrangement according to  FIG. 5  again comprises the parasitic diode structure  8 . The power transistor structure  7  is now connected with its drain terminal  9  to ground via an external load resistor  10  and connected to a positive supply potential  11  with its source terminal  12 , as a result of which a load current  13  flowing from the drain terminal  9  of the power transistor structure  7  is generated in dependence on the voltage at the gate terminal. Furthermore, the co-integrated diode structure  2  (source-bulk diode) is connected in series opposition to the parasitic diode structure  8  (drain-bulk diode) and the diode structures  2  and  8  are connected in parallel with the load path of the power transistor structure  7 . 
         [0037]    In this arrangement, the source-bulk diode structure  2  is operated with the impressed current  14  in the forward direction, as a result of which the voltage  16  dropped across the diode structure  2  is generated. This voltage  16  is used for overtemperature detection of the power transistor. Furthermore, the voltage at the drain terminal  9  of the power transistor is compared with the preset voltage value  17  of the reference voltage source  18 . In the present case, this comparison is made via the comparator  19 , to the positive input of which the preset comparison voltage  17  is applied and the negative input of which is connected to the drain terminal  9  of the power transistor structure  7 . The comparator  19  can suitably have a switching characteristic with hysteresis. 
         [0038]    If the voltage across the load path exceeds the value of the comparison voltage  17 , the state of the signal at the output of the comparator  19  changes and short circuits the diode structure  2  via the transistor structure  49 . A short circuit of the diode structure  2  due to the switching-though of the transistor structure  49  also occurs when the control signal “OFF” is activated, this control signal “OFF” and the output of the comparator  19  being linked via the NOR gate  68  preceding the gate terminal of the transistor structure  49 . This again results in the same advantageous effects as in the arrangement from  FIG. 4 . The operating voltage can also be monitored again, e.g. in bridge circuits, in order to prevent the maximum permissible load path voltage possibly being exceeded whilst the bulk-source short circuit is opened at the same time. 
         [0039]    The circuit arrangement according to  FIG. 6  comprises a power transistor structure  7  integrated in a semiconductor body  1  and an evaluating unit  3 , which is electrically connected to the former but is spatially separate and thermally decoupled from it, for overtemperature detection of the power transistor structure  7 . In the power transistor structure  7 , which, in the present case, is an n-channel MOS field effect transistor but could equally be a bipolar transistor, IGBT, thyristor etc., a bipolar diode structure  2  is co-integrated in the semiconductor body  1  in addition to the power transistor structure  7 , which diode structure is fed from a current source  5  located in the separate evaluating unit  3  via an additional body or bulk terminal  15  at the semiconductor body  1  by a reference current  14  in the forward direction of the diode structure  2 . The voltage  16  correspondingly dropped across the diode structure  2 , dependent on the temperature of the diode structure  2  and thus on the temperature of the power transistor structure  7 , is compared with a comparison voltage  22  in the evaluating unit  3  in order to generate from it a signal  20  identifying an overtemperature. In this way, the diode structure  2  (the bulk-source diode in the case shown) is used as temperature sensor for the temperature of the power transistor structure  7 , the diode structure  2  being operated in the forward direction with an impressed current. 
         [0040]      FIG. 6  also comprises the parasitic bulk-drain diode structure  8  which is always present when MOS technologies are used, and forms a bipolar transistor together with the diode structure  2 . A device of comparator  65  and reference voltage source  64  for monitoring the load path voltage at the drain  9  is also contained therein. 
         [0041]    The circuit arrangement according to  FIG. 6  additionally contains a monitoring circuit with a reference voltage source  64  for generating a reference voltage  67 , a comparator  65  (possibly with hysteresis) and an MOS field effect transistor  66 . In this arrangement, the non-inverting input of the comparator  65  is connected to the drain terminal  9  of the power transistor structure  7  and the reference voltage  67  is present at the inverting input of the comparator  65 . The output of the comparator  65  is connected to the gate of the transistor  66 . The drain terminal of the transistor  66  is connected to the body terminal  15  of the semiconductor body  1  and the current source  5  whilst the source terminal of the transistor  66  is connected to ground. 
         [0042]    The monitoring circuit has the purpose of monitoring the amplitude of the voltage at the drain terminal  9  of the power transistor structure  7  and comparing it with the preset reference voltage  67 . In this way, an excessive voltage at the drain terminal  9  of the power transistor structure  7  is detected which, with the bulk-source short circuit being opened at the same time and the dielectric strength of the semiconductor structure  1  thus being reduced, can lead to its destruction. The reference voltage  67  can be selected to be very low so that temperature detection is only carried out when the load path, represented by the resistor  10 , via the power transistor structure  7  is connected. The reference voltage  67  can also assume higher values as long as its value is below the critical maximum load path voltage leading to a destruction, which is reduced by the source-bulk short circuit being opened. 
         [0043]    If then the voltage to ground, present at the drain terminal  9 , exceeds the value of the reference voltage  67 , for example because the load path is not connected, the gate of the transistor  66  is driven via the output of the comparator  65  and the diode structure  2  is short circuited via the transistor  66  as a result of which the current used for overtemperature detection (largely) does not flow through the diode structure  2  but (largely) flows through the source-drain path of the transistor  66 . In this case, however, the signal  20  cannot be used as a measure of an overtemperature detection since the voltage  16  dropped across the short circuited diode structure  2  is then always very low independently of the actual temperature of the power transistor structure  7  and the voltage  16  is thus always lower than the voltage  22  used for the comparison and for detecting an overtemperature. 
         [0044]    The effect, which can be reproduced quantitatively, that the voltage occurring at a diode structure operated in the forward direction with the impressed current depends on the temperature of this diode structure is utilized in such a manner that due to the conductance of the diode structure, which rises with temperature, the voltage dropped across the diode structure with a constant impressed current is reduced. The forward voltage of a diode structure changes linearly with about −2 mV per degree Celsius (.degree. C.). 
         [0045]    The diode structure  2  used for temperature measurement is co-integrated into the semiconductor body  1  in such a manner that, in operation, it is essentially subject to the same heating as the power transistor structure  7  itself and thus can be used as a measure of the operating temperature of the power transistor structure  7  and thus for overtemperature detection of the power transistor structure  7 . The additional, externally accessible body or bulk terminal  15  is provided at the semiconductor body  1  for the purpose of feeding the current  14  into the diode structure  2  and for measuring the voltage  16  dropped across this diode structure  2  (in the case of an external evaluating circuit as in the present case). 
         [0046]    In the circuit arrangement according to  FIG. 6 , the diode structure  2  is connected in the forward direction between body and ground. A further diode structure  8  is located between body (and thus body terminal  15 ) and drain terminal  9  of the power transistor structure  7 , this being the parasitic bulk-drain diode structure always present. In this arrangement, the power transistor structure  7  is connected with its drain terminal  9  with a positive supply potential  11  via an external load resistor  10  and with its source terminal  12  to ground potential as a result of which a load current  13  flowing into the drain terminal  9  of the power transistor structure  7  can be generated. 
         [0047]    As already explained, the circuit arrangement according to  FIG. 6  comprises a current source  5  for generating the impressed current  14  for the diode structure  2  and additionally a first embodiment of a comparison circuit  4  for comparing the voltage  16  dropped across the diode structure  2  with a preset comparison voltage  22 . In the present case, the comparison circuit  4  consists of a comparator  19 , to the positive input of which a preset comparison voltage  22  generated by a circuit  21  is applied and the negative input of which is connected to the terminal  15  of the semiconductor body  1  and to which voltage  16  dropped across the diode structure  2  is thus applied. The comparator  19  can suitably have a switching characteristic with hysteresis. 
         [0048]    In this arrangement, the circuit  21  is constructed in such a manner that the comparison voltage  22  generated by it is temperature-dependent, in such a manner that an increase in temperature of the evaluating unit  3 , and thus an increase in temperature of the circuit  21 , leads to an increase in the comparison voltage  22  generated from it. 
         [0049]    An increase in temperature of the evaluating unit  3  occurs, for example, if the ambient temperature increases at which the evaluating unit  3  and correspondingly also the semiconductor body  1  are operated. This is the case, for instance, in applications in a motor vehicle where semiconductor bodies and circuits used in the engine compartment are heated to a different degree by radiation of engine heat in dependence on the operating state and weather-related external temperatures. In this manner, the limit value of the overtemperature to be determined can be automatically adapted to the prevailing ambient temperatures, for example reduced, in order thus to take into account, for example, the circumstance that a value of the overtemperature which is critical or damaging for the operation is lower at high ambient temperatures than at low ambient temperatures. 
         [0050]    The prerequisite for taking the ambient temperature into consideration with sufficient accuracy is that the semiconductor body  1  and the evaluating unit  3  are thermally decoupled but are placed so close to one another spatially that the same ambient temperature is applied to them. However, thermally decoupling also means, in particular, that the two are not so close that the heat dissipation of the power transistor influences the ambient temperature in the area of the evaluating circuit. In applications in which this ambient temperature is generated, for example by a heat-radiating source such as a motor vehicle engine, this ambient temperature changes very rapidly with distance from the source and a spatially more separate arrangement of the semiconductor body  1  and the evaluating unit  3  would not achieve the desired effect. 
         [0051]    According to  FIG. 6 , the circuit  21  for generating the comparison voltage  22  comprises an MOS field effect transistor  39 , an MOS field effect transistor  40 , a bipolar transistor  41  and a bipolar transistor  42  and a resistor  23 , a resistor  43  and a resistor  46 . The transistor  39  is a p-channel MOS field effect transistor and connected with its source terminal to a positive supply potential  47  and to the source terminal of the transistor  40  which is also of the p-channel type. The drain terminal of the transistor  39  is connected to the gate terminal of the transistor  39  and to the collector terminal of the transistor  41 ; similarly, there is a connection between the gate terminal of the transistor  39  and the gate terminal of the transistor  40 . The drain terminal of the transistor  40  is connected to the collector terminal of the transistor  42  which, in turn, is connected to the base terminal of the transistor  42  and to the base terminal of the transistor  41 . Furthermore, the emitter terminal of the transistor  42  is connected to the resistor  46  and the emitter terminal of the transistor  41  is connected to the resistor  46  via the resistor  43 . The two resistors  46  and  23  represent a voltage divider, the comparison voltage  22  dropped across the resistor  23  being applied to the positive input of the comparator  19 . 
         [0052]    With a rising ambient temperature acting on the evaluating unit  3  and thus on the components contained in this evaluating unit  3 , linearly increasing currents through a first resistor  23 , a second resistor  43  and a third resistor  46  are generated in the circuit  21 . As a result, a voltage drop  22  rising linearly with the temperature is generated at the first resistor  23 , which, in the present embodiment, is used as comparison voltage  22  for later comparison by the comparator  19  with the voltage  16  dropped across the diode structure  2 , applied to the negative input of the comparator  19 . 
         [0053]    In this way, an increase of the ambient temperature acting on the evaluating unit  3 , by increasing the comparison voltage  22 , leads to a reduction in the difference between the voltage  16  at the diode structure  2  and the comparison voltage  22  as a result of which the limit value for detection of an overtemperature of a power transistor structure  7  is reached earlier. The heating of the semiconductor body  1 , and thus of the power transistor structure  7 , necessary for reaching the overtemperature is less for high ambient temperatures. At low ambient temperatures, a greater range of heating of the power transistor structure  7  is thus permitted (temperature swing) than is the case at high ambient temperatures. 
         [0054]    Corresponding to the circuit arrangements according to  FIG. 4  and  FIG. 5 , the voltage  16  at the diode structure  2  and a comparison voltage  22  are again compared by the comparator  19 . The comparison voltage  22  and the impressed current  14  are selected in such a manner that the voltage  16  dropped across the diode structure  2  at permissible operating temperatures of the semiconductor body  1  is greater than the comparison voltage  22  preset in the evaluating unit  3 . If the voltage  16  dropped across the diode structure  2  exceeds the value of the comparison voltage  22  with increasing temperature of the semiconductor body  1 , and if the voltage  16  is thus lower than the comparison voltage  22 , the state of the signal  22  at the output of the comparator  19  changes and thus indicates that an overtemperature of the power transistor structure  7  has been reached. In this case, as stated above, the limit value of the overtemperature to be determined is not preset but is dependent on the ambient temperature acting on the circuit arrangement  21 . 
         [0055]    The circuit arrangement according to  FIG. 7  again contains a semiconductor body  1  and an external, thermally decoupled evaluating unit  3 . The structure of the power transistor structure  7  and of the diode structures  2  and  8  is identical with that shown in  FIG. 6 . In contrast to the embodiments described above, the voltages used for detecting an overtemperature are first converted into corresponding currents, namely voltage  16  into current  25  and comparison voltage  28  into current  26 , for the purpose of the evaluation. 
         [0056]    This is achieved by a voltage/current converter  24  for converting a voltage  16  dropped across the diode structure  2  into a current  25  and by a voltage/current converter  27  for converting a comparison voltage  28  into a current  26 . In this arrangement, the voltage/current converters  24  and  27  are initially reproduced as abstract circuit blocks in  FIG. 7 . The current  25  generated by the voltage/current converter  24  and the current  26  generated by the voltage/current converter  27  are subtracted at a node  29  and, if necessary, converted into a voltage. The resultant current or the resultant voltage, respectively, are again evaluated by a using a comparator  19  (for example by a comparison with zero). 
         [0057]    If the first current  25  generated by converting the voltage  16  measured at the diode structure  2  falls below the value of the second current  26  generated by converting the comparison voltage  28  due to a temperature increase, the state of the signal at the output  20  of the comparator  19  changes and thus indicates that an overtemperature of the power transistor structure  7  has been reached. The limit value of the overtemperature to be determined can be selected freely by suitably choosing the preset comparison voltage  28 . 
         [0058]      FIG. 8  shows a development of the circuit arrangement shown in  FIG. 7 , with voltage/current converter  24  and voltage/current converter  27 . In this arrangement, the voltage/current converter  24  contains an operational amplifier  30 , an MOS field effect transistor  31 , an MOS field effect transistor  35  and a resistor  32  across which a voltage  33  proportional to the voltage  16  dropped across a diode structure  2  is dropped. In the voltage/current converter  24 , the gate terminals of the two transistors  31  and  35  are connected to the output of the operational amplifier  30 , the source terminals of the transistors  31  and  35  also being connected to one another and being connected to the positive supply potential  34 . The drain terminal of the transistor  31  is connected to ground via the resistor  32 . The voltage  33  dropped across the resistor  32  is fed back to the non-inverting input of the operational amplifier  30 , at the inverting input of which the voltage across the diode structure  2  is present. The operational amplifier  30  corrects the voltage  33  across the resistor  32  in such a manner that it is equal to the voltage across the diode structure  2 . The current through the source/drain path of the transistor  31  is thus equal to the ratio of voltage  33  to the value of the resistor  32 . Accordingly, the current through the source-drain path of the transistor  35 , forming the output current, is then proportional to the current through the source/drain path of the transistor  31  and proportional to the voltage across the diode structure  2 , the output current thus becoming lower with increasing temperature of the semiconductor body  1 . 
         [0059]    The drain terminal of the second transistor  35  is connected to a node  29  so that the current  25  from the voltage/current converter  24  acting as current source flows into the node  29 , a current  26  flowing off again via the voltage/current converter  27  acting as current sink so that the difference between the two currents can be evaluated by the comparator  19  (for example by comparison with a fixed threshold or zero). The voltage/current converter  27  is that from the circuit  21 , explained in  FIG. 6 , for generating an ambient-temperature-dependent reference voltage. Accordingly, the circuit  21  again contains the transistor  39 , transistor  40 , transistor  41  and transistor  42 , resistor  43  and resistor  45 . In addition, an MOS field effect transistor  36 , an MOS field effect transistor  37  and an MOS field effect transistor  38  are provided in the exemplary embodiment according to  FIG. 9 . 
         [0060]    A current, which is proportional to the current  48  through the source-drain path of the transistor  39  flows through the source-drain path of the transistor  38 , the source and gate terminals of which are in each case connected to the source and gate terminals of transistor  40 , in the manner of a current mirror, just like it does through the source-drain path of transistor  40 , so that a current rising linearly with the ambient temperature of the evaluating unit  3 , which is defined by the ratio of the voltage  44  dropped across the resistor  43  and the resistance value of the resistor  43 , is provided. 
         [0061]    The current provided by the transistor  38  is then mirrored by means of a (further) current mirror consisting of transistors  36  and  37 , in such a manner that the current  26  flowing off from the node  29  is generated. Due to the current  48  being mirrored twice in the voltage/current converter  27 , the current  26  is thus produced which also rises linearly with the ambient temperature of the evaluating unit  3 . 
         [0062]    From the current  25 , depending linearly on the voltage  16  at the diode structure  2  and becoming lower with rising temperature of the semiconductor body  1 , the current  26  becoming greater with ambient temperature is subtracted at the node  29 . The node  29  is connected to the comparator  19  so that the difference produced by subtracting the currents  25  and  26  at the comparator  19  is a measure of whether the operating temperature of the power transistor structure  7  integrated in the semiconductor body  1  is permissible or not, the relevant limit value being dependent on the ambient temperature represented by the current  26 . 
         [0063]    If the current  25  drops below the current  26  (for example in the case of the zero-point comparison: current  25 −current  26 &lt;0), the state of the signal  20  at the output of the comparator  19  changes and thus indicates that an overtemperature of the power transistor  7  has been reached. The heating of the power transistor structure  7  necessary for reaching the overtemperature is thus less at higher ambient temperatures of semiconductor body  1  and evaluating unit  3 . 
         [0064]    According to the embodiment, a greater heat range of the power transistor structure  7  (temperature swing) is permitted at the same time at low ambient temperatures of the semiconductor body  1  and the evaluating unit  3  than is the case at higher ambient temperatures. A significant advantage consists in that, due to the use of identical materials and possibly identical dimensions in the resistors  32  and  43 , the absolute accuracy tolerances of these resistors compensate for the temperature dependences reducing the measuring accuracy and thus allow the absolute accuracies to be distinctly increased. 
         [0065]    The circuit arrangement according to  FIG. 8  also contains a monitoring circuit  52  with a reference voltage source for generating a reference voltage  50 , a comparator  51  (possibly with hysteresis) and an MOS field effect transistor  49 . In this arrangement, the non-inverting input of the comparator  51  is connected to the drain terminal  9  of the power transistor structure  7  and a reference voltage  50  is present at the inverting input of the comparator  51 . The output of the comparator  51  is connected to the gate of the transistor  49 . The drain terminal of the transistor  49  is connected to the body terminal  15  of the semiconductor body  1  and the current source  5  while the source terminal of the transistor  49  is connected to ground. 
         [0066]    It is the purpose of the monitoring circuit  52  to monitor the magnitude of the voltage at the drain terminal  9  of the power transistor structure  7  and to compare it with a preset reference voltage  50 . In this way, an excessive voltage at the drain terminal  9  of the power transistor structure  7  is detected which, with the bulk-source short circuit being opened at the same time and the dielectric strength of the semiconductor structure  1  thus being reduced, can lead to its destruction. The reference voltage  50  can be selected to be very low in order to carry out temperature detection only when the load path, represented by the resistor  10 , is connected via the power transistor structure  7 . The reference voltage  50  can also assume higher values as long as its value is below the critical maximum load path voltage leading to a destruction, which is reduced by opening the source-bulk short circuit. 
         [0067]    If then the voltage to ground, present at the drain terminal  9 , exceeds the value of the reference voltage  50 , for example because the load path is not connected, the gate of the transistor  49  is driven via the output of the comparator  51  and the diode structure  2  is short circuited via the transistor  49  as a result of which the current used for overtemperature detection (largely) does not flow through the diode structure  2  but (largely) flows through the source-drain path of the transistor  49 . With the load path switched off, the current at the drain terminal  9  is very low in any case. In this case, however, the signal  20  cannot be used as a measure of overtemperature detection since then the voltage  16  dropped across the short circuited diode structure  2  is always very low independently of the actual temperature of the power transistor structure  7  and the current  25  is thus always lower than the current  26  used for the comparison and for detecting an overtemperature. For the case of restoring the source-bulk short circuit with an excessive voltage at the drain  9 , it is then no longer possible to monitor the temperature. This state is obtained, for example, with a very high load (short circuit) or a normal switching-off process. Since the temperature monitoring is used in any case for switching off the switch with an excessive temperature and to prevent further power input, this behavior does not have a disadvantageous effect. The dielectric strength of the power transistor, which, in the normal case, is present due to the bulk-source short circuit with the technology used, which is no longer given by using the co-integrated diode structure  2  in the present case, is restored by short circuiting the diode structure  2  via the transistor  49  with excessive voltage values at the drain. 
         [0068]    In the circuit arrangement according to  FIG. 9 , a further embodiment of a circuit for overtemperature detection of a power transistor structure  7  with a monitoring circuit  52 , extended with respect to  FIG. 8 , and a further embodiment of the voltage/current converter  27  is provided. Semiconductor body  1  and voltage/current converter  24  correspond to those shown in  FIG. 8 . 
         [0069]    The monitoring circuit  52  contains an inverter  53 , an OR gate  54  and an MOS field effect transistor  49 . A logical input signal is fed in at a terminal  55  of the evaluating unit  3  in order to be able to activate and deactivate the evaluating circuit  3  from the outside. Compared with the embodiment according to  FIG. 8 , the output of the comparator  51  is not connected directly to the gate terminal of the transistor  49  but initially to a first input of the OR gate  54 . The terminal  55  is connected to the input of the inverter  53 , the output of which is connected, in turn, to a second input of the OR gate  54 , the output of the OR gate  54  being coupled to the gate terminal of the transistor  49 . 
         [0070]    The logic level H (power transistor structure  7 : “ON”) at terminal  55  of the evaluating unit  3  stands for the case in which the temperature detection and the monitoring of the voltage at the drain terminal  9  is to be activated, wherein this level can be generated, for example, by a load connected via the power transistor structure  7 . The logic level H at the terminal  55  is converted into the logic level L by the inverter  53  and applied to the second input of the OR gate  54 . If the output signal of the comparator  51  has the logic level L, that is to say the voltage at the drain terminal  9  of the power transistor structure  7  is below the preset reference voltage  50 , the temperature detection is carried out as described above. 
         [0071]    If the output signal of the comparator  51  has the logic level H, that is to say the voltage at the drain terminal  9  of the power transistor structure  7  is above the preset reference voltage  50  and thus in a range which could result in the destruction of the semiconductor body  1 , the diode structure  2  is again short circuited via the transistor  49 , driven by the output signal from the OR gate  54 . Such a case is, for example, that of an avalanche in which a bipolar transistor formed from the two diode structures  2  and  8 , which is already active, forms the weak point. The temperature is therefore monitored only in the switched-through state of the power transistor structure  7  and/or when the voltage drops below the maximum permissible load path voltage predetermined by the voltage  50 . 
         [0072]    If the logic level L (power transistor structure  7 : “OFF”) is present at terminal  55  of the evaluating unit  3 , temperature detection is deactivated. In this event, the logic level L at terminal  55  is first converted into the logic level H via the inverter  53  and applied to the second input of the OR gate  54 . Independently of the value of the level present at the first input of the OR gate  54  (from output of the comparator  51 ), a signal with the logic level H is thus generated in every case at the output of the OR gate  54  and the diode structure  2  is again short circuited via the transistor  49 . As stated above, the signal  20  cannot be used for overtemperature detection in all cases in which the diode structure  2  is short circuited via the transistor  49 . 
         [0073]      FIG. 9  also shows a further embodiment of the voltage/current converter  27  from  FIG. 7  which has a supply potential  47 , a resistor  56 , a resistor  61 , a bipolar transistor  57 , a bipolar transistor  58 , a bipolar transistor  59  and a bipolar transistor  60 . In this arrangement, the transistor  57  is connected with its collector terminal to the supply potential  47  via the resistor  56 . The base terminal of the transistor  57  is connected to the base terminal of the transistor  58  and to the collector terminal of the transistor  57 . The collector terminal of the transistor  58  is connected to the node  29  at which the current  25  from the voltage/current converter  24  and the current  26  into the voltage/current converter  27  are subtracted from one another for the purpose of evaluation by the comparator  19  and thus for generating the signal  20 . Furthermore, the emitter terminal of the transistor  57  is connected to the collector terminal of the transistor  59 , the emitter terminal of the transistor  58  is connected to the collector terminal of the transistor  60 , the emitter terminal of the transistor  57  is connected to the base terminal of the transistor  60  and the emitter terminal of the transistor  58  is connected to the base terminal of the transistor  59 . The emitter terminal of the transistor  59  is connected directly to ground; the emitter terminal of the transistor  60  is connected to ground via the resistor  61 . The limit value of the overtemperature is again dependent on the ambient temperature at the evaluating unit  3 . Similarly, by suitably using resistor components of the same material for the resistors  32  and  61  in the voltage/current converters  24  and  27 , the absolute accuracy tolerances of these resistors and thus different temperature dependences reducing the measuring accuracy are again compensated for and the absolute accuracy of the overtemperature detection is thus distinctly increased. 
         [0074]    The exemplary embodiments do not show start-up circuits which could be necessary under some circumstances when switching on the circuit arrangement but which do not have any significance for the basic function of the circuit arrangement and have therefore been omitted for the sake of clarity. The expert can however easily use known start-up circuits for the respective purpose. 
         [0075]    While the invention disclosed herein has been described in terms of several different embodiments, there are numerous alterations, permutations, and equivalents which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and compositions of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.