Abstract:
Various exemplary embodiments relate to a current driver for controlling a safety control device, including: a clamp circuit connected to a first output configured to clamp the voltage at the first output to a clamp voltage value, wherein the first output is configured to be connected to a high voltage switch; a plurality of medium voltage switches; a plurality of switch drivers, wherein each switch driver is connected to one of the medium voltage switches; a plurality of second outputs wherein each of the plurality of second outputs are configured to be connected across one of a plurality of loads; and a controller configured to control the high voltage switch.

Description:
TECHNICAL FIELD 
     Various exemplary embodiments disclosed herein relate generally to medium-voltage drivers in safety applications. 
     BACKGROUND 
     In safety applications (automobiles are one example), a number of loads may be switched on and off by a corresponding switch. In addition, there may be a common (“central”) switch that allows power to be supplied to all loads. In today&#39;s applications, the switches are all high-voltage devices, which implies high-cost (because large silicon area is required for the realization of the switches). Accordingly there remains a need to improve upon today&#39;s applications in order to reduce cost and/or size. 
     SUMMARY 
     A brief summary of various exemplary embodiments is presented below. Some simplifications and omissions may be made in the following summary, which is intended to highlight and introduce some aspects of the various exemplary embodiments, but not to limit the scope of the invention. Detailed descriptions of an exemplary embodiment adequate to allow those of ordinary skill in the art to make and use the inventive concepts will follow in later sections. 
     Various exemplary embodiments relate to current driver for controlling a safety control device, including: a clamp circuit connected to a first output configured to clamp the voltage at the first output to a clamp voltage value, wherein the first output is configured to be connected to a high voltage switch; a plurality of medium voltage switches; a plurality of switch drivers, wherein each switch driver is connected to one of the medium voltage switches; a plurality of second outputs wherein each of the plurality of second outputs are configured to be connected across one of a plurality of loads; and a controller configured to control the high voltage switch. 
     Various exemplary embodiments relate to a method of controlling a maximum voltage applied to loads, including: controlling the state of a high voltage switch; controlling the state of a plurality of medium voltage switches wherein the medium voltage switches have an associated load; detecting an over voltage situation; and clamping the voltage at the high voltage switch to a clamp voltage value. 
     Various exemplary embodiments relate to a safety control device, including: a clamp circuit connected to a first output configured to clamp the voltage at the first output to a clamp voltage value, wherein the first output is configured to be connected to a high voltage switch; a plurality of second outputs wherein each of the plurality of second outputs are configured to be connected to one of a plurality of medium voltage switches and its associated load; a plurality of switch drivers each connected to one of the plurality of second outputs, wherein each switch driver is configured to be connected to one of the medium voltage switches; and a controller configured to control the high voltage switch. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to better understand various exemplary embodiments, reference is made to the accompanying drawings, wherein: 
         FIG. 1  illustrates a related art load protection system; 
         FIG. 2  illustrates another related art load protection system; 
         FIG. 3  illustrates an embodiment of a load protection system; and 
         FIG. 4  illustrates another embodiment of a load protection system. 
     
    
    
     To facilitate understanding, identical reference numerals have been used to designate elements having substantially the same or similar structure and/or substantially the same or similar function. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a related art load protection system. Such load protections systems  100  may be found in various applications and systems. The load protection system may include a control device  110 , a high power switch M 0 , a plurality of loads Load_ 1  to Load_n, and plurality of high voltage switches M 1  to Mn. 
     The high voltage switch M 0  may be connected to a power source such as a battery. A diode D 1  may be included to ensure that current does not flow between BAT and GND terminals when the Battery is connected with wrong polarity to these terminals. 
     The loads Load_ 1  to Load_n are connected to the high power switch M 0 . The loads Load_ 1  to Load_n are substantially parallel to one another. Each of the loads Load_ 1  to Load_n are then connected to their respective high voltage switches M 1  to Mn. The high voltage switches M 1  to Mn may then be connected to ground. 
     The control device  110  may include a controller  112  and a plurality of low side drivers (LS-drivers)  114 . The controller  112  may detect problems in the system that require power to be removed from the system. The controller may include a gate driver (GD) and a change prep (CP). When the controller  112  senses such problem, it opens the switch M 0  to remove power from the loads Load_ 1  to Load_n. The LS-drivers  114  each may be connected to one of the high power switches M 1  to Mn. The LS-drivers  114  may control the high power switches M 1  to Mn to turn power on and off to the loads Load_ 1  to Load_n. 
     The switches M 0  to Mn may be operated in the linear region, i.e., the transistors may operate as a switch. This may be done for power dissipation reasons, because if one or more switches do not operate in the linear region, too much power dissipation in the switches may cause thermal issues in the application or worst case even destroy the switches. 
     A problem arises with the related art protection system. For example in automotive applications, the supply voltage may reach high-levels (up to 40V in automotive). Because of this all switches M 0  to Mn need to be realized with devices that can withstand at least 40V. This makes the switches M 0  to Mn expensive. 
       FIG. 2  illustrates another related art load protection system. The difference between  FIG. 1  and  FIG. 2  is the relative location of the loads Load_ 1  to Load_n and switches M 1  to Mn to one another. In  FIG. 1 , the loads Load_ 1  to Load_n are in between switch M 0  and switches M 1  to Mn. In  FIG. 2 , the loads Load_ 1  to Load_n are in between the switches M 1  to Mn and ground. The LS-drivers in  FIG. 1  become instead high side drivers (HS-drivers) in  FIG. 2 . The embodiment of  FIG. 2  is less common and more expensive, but it does have the benefit of being able to control for individual load ground shorts. Otherwise the embodiment of  FIG. 2  has the same elements and functions the same as the embodiment in  FIG. 1 . 
     A solution to the problem described above involves operating the central switch M 0  in a linear mode when the operating voltage is below a specified operating value, and when the operating voltage is above the specified operating value, operating the switch in a saturation mode and clamping the gate voltage of the central switch M 0  to a clamping voltage. In automotive application, the specified operating value may be about 18V and the clamping voltage may be about 29 V. Various other values may be used depending up the specified system and its requirements and operating environment. Thermal issues may not occur because the switch does not carry current when the supply voltage is higher than the operating voltage range. 
       FIG. 3  illustrates an embodiment of a load protection system. The load protection system may include a control device  310 , a high power switch M 0 , a plurality of loads Load_ 1  to Load_n, and plurality of medium voltage switches M 1  to Mn. 
     The high voltage switch M 0  may be connected to a power source such as a battery. A diode D 1  may be present to ensure that current does not flow back into the battery. 
     The loads Load_ 1  to Load_n are connected to the high power switch M 0 . The loads Load_ 1  to Load_n are substantially parallel to one another. Each of the loads Load_ 1  to Load_n are then connected to their respective medium voltage switches M 1  to Mn. The medium voltage switches M 1  to Mn may then be connected to ground. 
     The control device  310  may include a controller  312  and a plurality of LS-drivers  314 . The controller  312  may detect problems in the system that require power to be removed from the system. When the controller  312  senses such a problem, it opens the switch M 0  to remove power from the loads Load_ 1  to Load_n. Further, the controller  312  may include a clamp circuit. The clamp circuit may clamp the voltage through the high power switch M 0  to a clamping voltage. The clamp circuit will be described further below. The LS-drivers  314  each may be connected to one of the medium power switches M 1  to Mn. The LS-drivers  314  may control the medium power switches M 1  to Mn to turn power on and off to the loads Load_ 1  to Load_n. 
     Because the clamp circuit will reduce the maximum voltage seen by the medium voltage switch M 1  to Mn, the medium voltage switches may be designed to accommodate a lower applied voltage. This has the advantage of being lower cost and allowing for smaller switching devices. 
       FIG. 4  illustrates another embodiment of a load protection system. The load protection system may include a control device  410 , a high power switch M 0 , and a plurality of loads Load_ 1  to Load_n. 
     The high voltage switch M 0  may be connected to a power source such as a battery. A diode D 1  may be included to ensure that current does not flow between BAT and GND terminals when the Battery is connected with wrong polarity to these terminals. 
     The loads Load_ 1  to Load_n are connected to the high power switch M 0 . The loads Load_ 1  to Load_n are substantially parallel to one another. Each of the loads Load_ 1  to Load_n are then connected to their respective medium voltage switches M 1  to Mn. The medium voltage switches M 1  to Mn may then be connected to ground. In this embodiment the medium voltage switches M 1  to Mn may be implemented in the control device  410 . 
     The control device  410  may include a controller  412 , a plurality of LS-drivers  414 , a clamp circuit  416 , and a plurality of medium voltage switches M 1  to Mn. The controller  412  may detect problems in the system that require power to be removed from the system. When the controller  412  senses such a problem, it opens the switch M 0  to remove power from the loads Load_ 1  to Load_n. Further, the controller  412  may include a clamp circuit  416 . The clamp circuit  416  may clamp the voltage through the high power switch M 0  to a clamping voltage. The clamp circuit may include a zener diode  418  with a breakdown voltage, while the clamp voltage becomes the breakdown voltage plus the forward voltage of a diode. The clamp circuit  416  may also be any other type of clamp circuit that is capable of clamping the voltage to a desired clamp voltage. 
     The LS-drivers  414  each may be connected to one of the medium power switches M 1  to Mn. The LS-drivers  414  may control the medium power switches M 1  to Mn to turn power on and off to the loads Load_ 1  to Load_n. In this case, the medium power switches M 1  to Mn are shown as part of the control device. This may now be possible because the use of medium voltage switches M 1  to Mn reasonably allows for the switches to be implemented in the control device. Further, the control device may have diodes across the outputs of the control device that are connected to the loads Load_ 1  to Load_n. 
     While the switches M 0  to Mn are all depicted as NMOS devices, which is the most common implementation, other device types such as PMOS or bipolar switches may be used as well. 
     The control device  310  and  410  may be implemented on a single integrated circuit (IC). Further, in the description above, specific voltage values were described. Other values may be used as well. The relationship between the high voltage and the medium voltage may be such that they lead to significant differences in the design of the high voltage switch M 0  versus the medium voltage switches M 1  to Mn. The use of medium voltage switches M 1  to Mn leads to greatly reduced cost and size of the devices. Further, it may lead to the medium voltage switches M 1  to Mn being implemented in the control device and implemented on a single IC. 
     The load protection system may be used in automotive application areas, for example, antilock braking system, electronic stability program, electronic power steering, electronic parking brake, etc. Further, the load protection system may be applied in other systems that require load and safety protection. 
     It should be apparent from the foregoing description that various exemplary embodiments of the invention may be implemented in hardware and/or firmware. Furthermore, various exemplary embodiments may be implemented as instructions stored on a machine-readable storage medium, which may be read and executed by at least one processor to perform the operations described in detail herein. A machine-readable storage medium may include any mechanism for storing information in a form readable by a machine, such as a personal or laptop computer, a server, or other computing device. Thus, a tangible and non-transitory machine-readable storage medium may include read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash-memory devices, and similar storage media. 
     It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the invention. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in machine readable media and so executed by a computer or processor, whether or not such computer or processor is explicitly shown. 
     Although the various exemplary embodiments have been described in detail with particular reference to certain exemplary aspects thereof, it should be understood that the invention is capable of other embodiments and its details are capable of modifications in various obvious respects. As is readily apparent to those skilled in the art, variations and modifications can be effected while remaining within the spirit and scope of the invention. Accordingly, the foregoing disclosure, description, and figures are for illustrative purposes only and do not in any way limit the invention, which is defined only by the claims.