Abstract:
A device for protecting electronic components against overvoltages of a supply voltage is provided, which device includes at least one semiconductor transistor which is switchable by a trigger circuit when a predetermined overvoltage value is reached, thereby converting electrical energy to thermal energy.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a device for protecting electronic components against overvoltages of the supply voltage, and in particular, but without limitation, relates to protection of electronic components used in electronic systems in motor vehicles.  
         BACKGROUND INFORMATION  
         [0002]    It is generally known that inductive loads, such as coils and the like, produce direct or indirect overvoltages. A particularly harmful overvoltage occurs, for example, in the case of a poor contact or momentary battery disconnection during generator operation (load dump). In the automotive sector, for example, overvoltages of up to 80 V can occur within a 400 ms period in the case of a 12 V supply voltage. These transients can destroy various electronic circuits, in the motor vehicle, such as integrated circuits, unless they are effectively protected against such overvoltages.  
           [0003]    It is possible to prevent overvoltages of the electrical system of a motor vehicle from destroying the electronic components by designing the corresponding components according to the maximum voltage peaks that occur. However, this is extremely expensive and uneconomical.  
           [0004]    It would therefore be advantageous to provide a protective device to protect components designed for normal operation against overvoltages of the generator supply voltage. Currently, Zener diodes are used in conjunction with the generator, that permit only slight voltage variations even when the current varies greatly.  
           [0005]    This approach has the disadvantage that the voltage present at the Zener diode has a wide tolerance range and is greatly dependent on the temperature present at the component. During a transition to a higher vehicle system voltage (as is being planned for mass production), for example, this tolerance and temperature dependency thus becomes too great for practical application.  
         SUMMARY OF THE INVENTION  
         [0006]    The device according to an embodiment of the present invention has the advantage over known approaches that it is suitable for high vehicle system voltages and is reasonably inexpensive to produce, and that the device may be positioned to prevent polarity reversal. The device also has a low tolerance and a low temperature coefficient of the response threshold.  
           [0007]    According to an embodiment of the present invention, the device includes at least one semiconductor transistor which is switchable by a trigger circuit upon reaching predetermined overvoltage values, thereby converting electrical energy to thermal energy and protecting electronic components against system voltage overvoltages.  
           [0008]    By switching the overvoltages of the system voltage in a defined manner via the at least one semiconductor transistor, the load dump energy is converted to heat by the semiconductor component and the internal resistor of the supply voltage source, thus protecting the connected electronic components against damage by the original load dump energy.  
           [0009]    According to an embodiment, the trigger circuit and the semiconductor transistor are provided as integrated circuits on a single chip.  
           [0010]    According to another embodiment, the semiconductor transistor is electrically connectable in series to a Zener diode. The Zener diode stabilizes the voltage and coverts electrical overvoltage energy to thermal energy.  
           [0011]    According to another embodiment, the semiconductor transistor and the Zener diode are provided as integrated circuits on two separate chips. In this case, the two chips may be either stacked or arranged side-by-side and then electrically interconnected.  
           [0012]    According to another embodiment, the device is at least partially surrounded by at least one heat removal apparatus. This makes it possible to remove the heat generated in the semiconductor components from the components and to discharge it to the environment.  
           [0013]    According to a further embodiment, at least one heat removal apparatus is designed as a metal body, a casting compound, for example an epoxy compound, and/or a metal receptacle. The one or more heat removal apparatuses may be placed into direct contact with the corresponding semiconductor components.  
           [0014]    According to a further embodiment, the semiconductor transistor is designed as a MOSFET transistor, for example, a vertical power MOSFET transistor, having an integrated trigger circuit.  
           [0015]    According to a further embodiment, the semiconductor transistor is designed as a vertical bipolar transistor having an integrated trigger circuit.  
           [0016]    According to a further embodiment, the electrical connections of the device are designed as soldered connections and/or direct die bonding connections.  
           [0017]    According to a further embodiment, the Zener diode is connected in series to a rectifier diode. This makes it possible to prevent the component from being damaged in the event of a polarity reversal, for example by using an n + -p-n semiconductor component.  
           [0018]    According to a further embodiment, the Zener diode and the rectifier diode are integrated into a three-layer semiconductor element.  
           [0019]    According to a further embodiment, the device may be provided in an electronic system of a motor vehicle to protect the system components against overvoltages of the motor vehicle electrical system. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 a  shows a circuit diagram of the device according to a first exemplary embodiment of the present invention.  
         [0021]    [0021]FIG. 1 b  shows a circuit diagram of the device according to a second exemplary embodiment of the present invention.  
         [0022]    [0022]FIG. 1 c  shows a circuit diagram of the device according to a third exemplary embodiment of the present invention.  
         [0023]    [0023]FIG. 2 shows a detailed circuit diagram of the device according to the first exemplary embodiment shown in FIG. 1 a.    
         [0024]    [0024]FIG. 3 a  shows a circuit diagram of a Zener diode and a rectifier diode connected in series.  
         [0025]    [0025]FIG. 3 b  shows a schematic cross-sectional view of the rectifier diode shown in FIG. 3 a.    
         [0026]    [0026]FIG. 4 a  shows a schematic representation of the device having heat removal apparatuses according to the third exemplary embodiment shown in FIG. 1 c.    
         [0027]    [0027]FIG. 4 b  shows a schematic representation of a further geometric arrangement of the device in conjunction with heat removal apparatuses according to the third exemplary embodiment shown in FIG. 1 c.    
         [0028]    [0028]FIG. 5 shows a schematic cross-sectional view of the geometric arrangement of a device having heat removal apparatuses according to the first or second exemplary embodiment shown in FIGS. 1 a  and  1   b , respectively.  
         [0029]    [0029]FIG. 6 shows a schematic cross-sectional view of a further geometric arrangement of the device having heat removal apparatuses according to the first or second exemplary embodiment shown in FIGS. 1 a  and  1   b , respectively. 
     
    
     DETAILED DESCRIPTION  
       [0030]    [0030]FIGS. 1 a  and  2  illustrate block diagrams of an exemplary circuit of a device  1  for protecting electronic components against overvoltages of generator voltage V Gen  according to a first embodiment of the present invention.  
         [0031]    A vertical power MOSFET transistor  2  is advantageously electrically connected to supply voltage source V Gen , a trigger circuit  3  being connected to supply voltage source V Gen  and MOSFET transistor  2 . FIG. 2 shows a detailed illustration of trigger circuit  3  which activates or switches MOSFET transistor  2  when the overvoltage of supply voltage source V Gen  reaches a predetermined voltage value.  
         [0032]    A Zener diode  4  is also advantageously connected in series to MOSFET transistor  2 . Thus, when trigger circuit  3  activates MOSFET transistor  2  upon reaching a predetermined overvoltage value, semiconductor components  2 ,  4  and the internal resistor of supply voltage source V Gen  convert electrical overvoltage energy (load dump energy), according to the first exemplary embodiment, into thermal energy on the basis of the current flow and may also discharge it to the environment.  
         [0033]    [0033]FIG. 1 b  shows a block diagram of a circuit of device  1  according to a second exemplary embodiment of the present invention. In contrast to the first exemplary embodiment, additional Zener diode  4  is connected in series between voltage source V Gen  and MOSFET transistor  2 . The overvoltage energy is reduced, i.e. the energy is converted, in the same manner as in the first exemplary embodiment described above.  
         [0034]    [0034]FIG. 1 c  shows a block diagram of a circuit of device  1  according to a third exemplary embodiment of the present invention, without a series-connected Zener diode  4  being provided and with only semiconductor component  2  serving as the energy conversion component upon activation by trigger circuit  3 .  
         [0035]    To prevent Zener diode  4  from being destroyed in the first and second exemplary embodiments according to FIGS. 1 a  and  1   b , Zener diode  4  may be connected in series to a rectifier diode  5 , as illustrated in FIG. 3 a . Rectifier diode  5  may be designed with a layer structure, including an n + -doped layer  52 , a p-doped layer  53  and an n-doped layer  54  and is activatable via two metallization layers  50 ,  51 .  
         [0036]    [0036]FIGS. 4 a  and  4   b  show two different geometric embodiments of protective device  1  according to the third exemplary embodiment illustrated in FIG. 1 c,  trigger circuit  3  and MOSFET transistor  2  being advantageously integrated on a common chip  20 .  
         [0037]    In FIG. 4 a , chip  20 , on which trigger circuit  3  and MOSFET transistor  2  are integrated, is provided in a container  13 , which may be a highly conductive metal receptacle  13 , for the purpose of removing the heat generated in the semiconductor component. Chip  20  is connected to metal receptacle  13  and leads  14  via soldered connections  15 . A casting compound  12 , advantageously an epoxy compound, is also provided in metal receptacle  13  and brought into contact with chip  20  for heat removal purposes.  
         [0038]    [0038]FIG. 4 b  shows a further embodiment of a single-chip arrangement in which trigger circuit  3  and MOSFET transistor  2  are integrated on a single chip  20 . Chip  20  is thermally contacted on the bottom with a highly thermally conductive metal body  10 , for example a metal plate  10 , via a soldered connection  15 .  
         [0039]    Leads  14 , in turn, are attached to the corresponding components via soldered connections  15 .  
         [0040]    This arrangement is completely surrounded by a casting compound  12 , which may be provided in a metal receptacle  13 . This also ensures efficient heat removal from the semiconductor component to the materials surrounding it or to the environment.  
         [0041]    Chips  20  may include solderable metal plating on both the front and back for soldered connection to leads  14 .  
         [0042]    [0042]FIG. 5 shows a schematic cross-sectional view of a device according to the present invention based on the first or second exemplary embodiment of the present invention illustrated in FIGS. 1 a  and  1   b , respectively.  
         [0043]    In this exemplary embodiment, the device is designed as a dual-chip arrangement, i.e., trigger circuit  3  and MOSFET transistor  2  are provided together on a single chip  20 , and additional Zener diode  4  is integrated on an additional, separate chip  21 .  
         [0044]    In this exemplary embodiment, both chips  20 ,  21  are provided in a stacked arrangement, the corresponding electrical connections between chips  20 ,  21  being established by soldered connections  15 . Semiconductor chips  20 ,  21  may also be interconnected by direct die bonding.  
         [0045]    For the purpose of removing the heat generated in semiconductor components  2  and  4 , chip  20  may be thermally connected to a metal body  10  on top and to a metal receptacle  13  at the exposed surfaces of the bottom.  
         [0046]    For the purpose of heat removal, chip  21  also comes into contact with metal receptacle  13  on the bottom. Within metal receptacle  13 , the arrangement is further surrounded by a casting compound  12 .  
         [0047]    A further exemplary embodiment of the dual-chip arrangement is illustrated in FIG. 6. Once again, trigger circuit  3 , MOSFET transistor  2  and additional Zener diode  4  are attached to, or integrated into, two mechanically separate chips  20 ,  21 . In the exemplary embodiment according to FIG. 6, both chips  20 ,  21  are mounted side-by-side on a correspondingly shaped metal body  11  and interconnected by soldered connections  15  or directly by direct die bolding. A correspondingly shaped metal body  10 , which is may be configured as a metal plate, is again provided for heat removal purposes on the surface of both chips  20 ,  21 . The device described above is surrounded by a casting compound  12  and is again located in a metal receptacle  13  via which the dissipated heat is discharged to the environment.  
         [0048]    In the dual-chip arrangement, leads  14  are soldered onto the chips, i.e. the metal plates, via soldered connections  15  to establish an electrical connection.  
         [0049]    In contrast to the conventional approaches, the protective device according to the present invention is usable even at higher motor vehicle system voltages. This device is also economical to produce, easy to assemble due to the compact bipolar component, and thermally isolatable from a rectifier.  
         [0050]    Although the present invention was described above on the basis of one preferred exemplary embodiment, it is not limited thereto, but may be modified in many different ways.  
         [0051]    For example, a dual-chip arrangement is also implementable by integrating power MOSFET transistor  2  and trigger circuit  3  on mechanically separated chips. Depending on the cost of producing the power MOSFET transistor and the assembly costs, the single-chip arrangement (power MOSFET transistor with trigger circuit), a dual-chip arrangement (power MOSFET transistor with trigger circuit and Zener diode or power MOSFET transistor and trigger circuit on two separate chips) or a triple-chip arrangement (power MOSFET transistor, trigger circuit and Zener diode on separate chips) may be more economical to produce.