Patent Publication Number: US-8537507-B2

Title: MEMS-based switching systems

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to switching systems. Particularly, example embodiments of the present invention are related to micro-electromechanical system (MEMS) based switching systems, including motor starters and current-interrupting devices. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to an example embodiment of the present invention, a device for controlling an electrical current may include control circuitry, a micro electromechanical system (MEMS) switch in communication with the control circuitry, the MEMS switch responsive to the control circuitry to facilitate the interruption of the electrical current, a Hybrid Arcless Limiting Technology (HALT) arc suppression circuit disposed in electrical communication with the MEMS switch configured to receive a transfer of electrical energy from the MEMS switch in response to the MEMS switch changing state from closed to open, the HALT arc suppression circuit including a capacitive portion, and a variable resistance arranged in parallel electrical communication with the capacitive portion of the HALT arc suppression circuit. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  depicts an exemplary arc-less micro-electromechanical system switch (MEMS) based switching system, according to an example embodiment; 
         FIG. 2  depicts an exemplary arc-less micro-electromechanical system switch (MEMS) based switching system under a fault condition, according to an example embodiment; 
         FIG. 3  depicts an exemplary arc-less micro-electromechanical system switch (MEMS) based switching system under a fault condition, according to an example embodiment; 
         FIG. 4  depicts an exemplary arc-less micro-electromechanical system switch (MEMS) based switching system under a fault condition, according to an example embodiment; 
         FIG. 5  depicts an exemplary arc-less micro-electromechanical system switch (MEMS) based switching system, according to an example embodiment; 
         FIG. 6  depicts an exemplary arc-less micro-electromechanical system switch (MEMS) based switching system under a fault condition, according to an example embodiment; 
         FIG. 7  depicts an exemplary arc-less micro-electromechanical system switch (MEMS) based switching system under a fault condition, according to an example embodiment; 
         FIG. 8  depicts an exemplary arc-less micro-electromechanical system switch (MEMS) based switching system under a fault condition, according to an example embodiment; and 
         FIG. 9  depicts an exemplary arc-less micro-electromechanical system switch (MEMS) based switching system, according to an example embodiment. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Example embodiments of the present invention present innovations which significantly reduce the complexity, cost, and size of micro electromechanical system (MEMS) based motor starters and current-interrupting devices while providing efficient absorption of energy under fault conditions. The use of MEMS switches provide fast response time, thereby facilitating reduction in the let-through energy of an interrupted fault. A Hybrid Arcless Limiting Technology (HALT) circuit connected in parallel with the MEMS switches provides capability for the MEMS switches to be opened without arcing at any given time regardless of current or voltage, and the inclusion of metal-oxide varistors (MOV) in novel configurations provides for relatively efficient energy absorption under fault conditions. 
       FIG. 1  illustrates an exemplary arc-less micro-electromechanical system switch (MEMS) based switching system  100 , according to an example embodiment. Presently, MEMS generally refer to micron-scale structures that for example can integrate a multiplicity of functionally distinct elements, for example, mechanical elements, electromechanical elements, sensors, actuators, and electronics, on a common substrate through micro-fabrication technology. It is contemplated, however, that many techniques and structures presently available in MEMS devices will in a relatively short amount of time be available via nanotechnology-based devices, for example, structures that may be smaller than 100 nanometers in size. Accordingly, even though example embodiments described throughout this document may refer to MEMS-based switching devices, it is submitted that the inventive aspects of the present invention should be broadly construed and should not be limited to micron-sized devices. 
     For example, according to some example embodiments, MEMS switching devices may include cantilever beam structures. The cantilever beam structures are electrostatically operated via a gate control voltage. Current flows through the cantilever from a drain terminal to a source terminal. MEMS switching devices in general are distinguished from transistors and other switches by their mechanical/moving parts and small size. A plurality of other types of MEMS switches may be applicable to example embodiments; for example, suitable devices should include contacts/switches small enough that they can not dissipate energy through contact arcing (e.g., as a typical relay/electromechanical switch would). These MEMS devices are distinguished from small mechanical switches by (1) the size scales of the structure (beams are 50-100 um in length/width &amp; the contact gaps are on the order of 1 um) &amp; (2) they are electrostatically controlled (i.e., versus electromagnetic control). 
     As illustrated in  FIG. 1 , the arc-less MEMS based switching system  100  is shown as including MEMS based switching circuitry  101  and arc suppression circuitry  102 , where the arc suppression circuitry  102  may consist or include Pulse assisted turn ON (PATO) circuitry and a Hybrid Arcless Limiting Technology (HALT) circuit, which is operatively coupled to the MEMS based switching circuitry  101 . In certain embodiments, the MEMS based switching circuitry  101  may be integrated in its entirety with the arc suppression circuitry  102  in a single package, for example. In other embodiments, only certain portions or components of the MEMS based switching circuitry  101  may be integrated with the arc suppression circuitry  102 . 
     The MEMS based switching circuitry  101  may include one or more MEMS switches  111 . Additionally, the arc suppression circuitry  102  may include a balanced diode bridge  103  and a pulse circuit  104 . Further, the arc suppression circuitry  102  may be configured to facilitate suppression of an arc formation between contacts of the one or more MEMS switches  111  by receiving a transfer of electrical energy from the MEMS switches in response to the MEMS switches changing state from closed to open. It may be noted that the arc suppression circuitry  102  may be configured to facilitate suppression of an arc formation in response to an alternating current (AC)  113  or a direct current (DC; not illustrated for clarity). 
     In the illustrated example embodiment, MEMS switch  111  is depicted as being a simple switch with two contacts, but it should be understood that MEMS switch  111  is a switch including at least three contacts. For example, although not illustrated, the MEMS switch  111  may include a first contact configured as a drain, a second contact configured as a source, and a third contact configured as a gate. Furthermore, as illustrated in  FIG. 1 , a voltage snubber circuit  105  may be coupled in parallel with the MEMS switch  111  and configured to limit voltage overshoot during fast contact separation as will be explained in greater detail hereinafter. 
     In certain example embodiments, the snubber circuit  105  may include a snubber capacitor  114  coupled in series with a snubber resistor  115 . The snubber capacitor  114  may facilitate improvement in transient voltage sharing during the sequencing of the opening of the MEMS switch  111 . Furthermore, the snubber resistor  115  may suppress any pulse of current generated by the snubber capacitor  114  during closing operation of the MEMS switch  111 . In certain other example embodiments, the voltage snubber circuit  114  may include a metal oxide varistor (MOV) (not shown here; see  516 ,  FIG. 5 ). 
     In accordance with further aspects of the present technique, a load  112  may be coupled in series with the MEMS switch  111  and a voltage source  113 . In addition, the load  112  may also include a load inductance and a load resistance, where the load inductance is representative of a combined load inductance and a bus inductance viewed by the MEMS switch  111 . Reference numeral  106  is representative of a load current that may flow through the load  112  and the MEMS switch  111 . 
     Further, as noted with reference to  FIG. 1 , the arc suppression circuitry  102  may include a balanced diode bridge  103 . In the illustrated example embodiment, a balanced diode bridge  103  is depicted as having a first branch  131  and a second branch  132 . As used herein, the term “balanced diode bridge” is used to represent a diode bridge that is configured such that voltage drops across both the first and second branches  131  and  132  are substantially equal. The first branch  131  of the balanced diode bridge  103  may include a first diode D 1   128  and a second diode D 3   127  coupled together to form a first series circuit. In a similar fashion, the second branch  132  of the balanced diode bridge  103  may include a third diode D 2   130  and a fourth diode D 4   129  operatively coupled together to form a second series circuit. 
     In one embodiment, the MEMS switch  111  may be coupled in parallel across midpoints of the balanced diode bridge  103 . The midpoints of the balanced diode bridge may include a first midpoint located between the first and second diodes  128 ,  127  and a second midpoint located between the third and fourth diodes  130 ,  129 . Furthermore, the MEMS switch  111  and the balanced diode bridge  103  may be tightly packaged to facilitate minimization of parasitic inductance caused by the balanced diode bridge  103  and in particular, the connections to the MEMS switch  111 . It may be noted that, in accordance with exemplary aspects of the present technique, the MEMS switch  111  and the balanced diode bridge  103  are positioned relative to one another such that the inherent inductance between the first MEMS switch  111  and the balanced diode bridge  111  produces a di/dt voltage less than a few percent of the voltage across the drain and source of the MEMS switch  111  when carrying a transfer of the load current to the diode bridge  103  during a MEMS switch  111  turn-off which will be described in greater detail hereinafter. 
     In one embodiment, the MEMS switch  111  may be integrated with the balanced diode bridge  103  in a single package or optionally, the same die with the intention of minimizing the inductance interconnecting the MEMS switch  111  and the diode bridge  103 . 
     Additionally, the arc suppression circuitry  104  may include a pulse circuit  102  coupled in parallel electrical communication with the balanced diode bridge  103 . The pulse circuit  102  may be configured to detect a switch condition and initiate opening of the MEMS switch  111  responsive to the switch condition. As used herein, the term “switch condition” refers to a condition that triggers changing a present operating state of the MEMS switch  111 . For example, the switch condition may result in changing a first closed state of the MEMS switch  111  to a second open state or a first open state of the MEMS switch  111  to a second closed state. A switch condition may occur in response to a number of actions including but not limited to a circuit fault or switch ON/OFF request. 
     The pulse circuit  102  may include a pulse switch  124  and a pulse capacitor  123  series coupled to the pulse switch  124 . Further, the pulse circuit may also include a pulse inductance  126  and a first diode  125  coupled in series with the pulse switch  124 . The pulse inductance  126 , the diode  125 , the pulse switch  124  and the pulse capacitor  123  may be coupled in series to form the pulse circuit  102 , where the said components may be configured to facilitate pulse current shaping and timing. 
     Additionally, Arc suppression circuitry  104  may include Hybrid Arcless Limiting Technology (HALT) specific circuitry  108 . The circuitry  108  may include a HALT capacitance  121  (i.e., capacitive portion or capacitor) and a HALT switch  122 . The HALT capacitance  121  and the HALT switch  122  may be coupled in series to form the HALT-specific circuitry  108 . It is noted that although  FIG. 1  illustrates the Pulse inductance  126  in series with the HALT-specific circuitry  108 , example embodiments are not so limited. For example, a separate HALT inductance may be coupled in series with the HALT capacitance  121  and switch  122 , and the entire HALT-specific circuitry  108  may further be coupled in parallel across the pulse inductance  126  and pulse capacitance  123 . 
     In accordance with aspects of the present invention, the MEMS switch  111  may be rapidly switched (for example, on the order of picoseconds or nanoseconds) from a first closed state to a second open state while carrying a current albeit at a near-zero voltage. This may be achieved through the combined operation of the load circuit  112 , and pulse circuit  102  including the balanced diode bridge  103  coupled in parallel across contacts of the MEMS switch  111 . 
     As further illustrated, the system  100  may include a variable resistance bank comprising a plurality of variable resistors  133 ,  134  couple in parallel electrical communication with the MEMS based switching circuitry  101 . The variable resistors  133 ,  134  may be any suitable variable resistors, including but not limited to Metal-Oxide varistors (MOV). The variable resistors  133 ,  134  may be rated and configured to absorb electrical energy transferred directly from the MEMS based switching circuitry  101  in the event of a fault. For example, a MEMS based switching system  200  under a fault condition is illustrated in  FIG. 2 . 
     As illustrated, the system  200  is substantially similar to the system  100 . Therefore, exhaustive description of the arrangement and operation of each component is omitted herein for the sake of brevity. 
     As illustrated, the system  200  is under a fault condition where fault current  201  is transferred to the variable resistors  133 - 134  and a fault current  203  flows across contacts of the MEMS switch  111 . In response to this fault, HALT-specific circuitry  108  may be initiated through activation of HALT switch  122  to aid in clearing the fault and initiating a HALT current  204 . This is illustrated in  FIG. 3 . 
     As illustrated, the system  300  of  FIG. 3  is substantially similar to the system  100 . Therefore, exhaustive description of the arrangement and operation of each component is omitted herein for the sake of brevity. 
     As described above, the HALT switch  122  has been activated thereby transferring electrical energy from the MEMS based switching circuitry  101  to the HALT specific circuitry  108  as illustrated with currents  301 - 303 . Upon electrical energy transfer, the fault is cleared by opening the MEMS switch  111 , which is illustrated in  FIG. 4 . 
     As illustrated, the system  400  of  FIG. 4  is substantially similar to the system  100 . Therefore, exhaustive description of the arrangement and operation of each component is omitted herein for the sake of brevity. 
     As described above, the MEMS switch  111  is opened, thereby clearing the fault and allowing electrical energy to be absorbed through the snubber circuitry  105  and the varistors  133 ,  134  as illustrated with currents  401 - 402 . 
     Reference is now made to  FIG. 5 , where an alternative MEMS based switching system  500  is illustrated. 
     As illustrated in  FIG. 5 , the arc-less MEMS based switching system  500  is shown as including MEMS based switching circuitry  501  and arc suppression circuitry  502 , where the arc suppression circuitry  502  may consist or include Pulse assisted turn ON (PATO) circuitry and a Hybrid Arcless Limiting Technology (HALT) circuit, which is operatively coupled to the MEMS based switching circuitry  501 . As described with reference to system  100 , in certain embodiments, the MEMS based switching circuitry  501  may be integrated in its entirety with the arc suppression circuitry  502  in a single package, for example. In other embodiments, only certain portions or components of the MEMS based switching circuitry  501  may be integrated with the arc suppression circuitry  502 . 
     The MEMS based switching circuitry  501  may include one or more MEMS switches  511 . Additionally, the arc suppression circuitry  502  may include a balanced diode bridge  503  and a pulse circuit  504 . Further, the arc suppression circuitry  502  may be configured to facilitate suppression of an arc formation between contacts of the one or more MEMS switches  511  by receiving a transfer of electrical energy from the MEMS switches in response to the MEMS switches changing state from closed to open. It may be noted that the arc suppression circuitry  502  may be configured to facilitate suppression of an arc formation in response to an alternating current (AC)  513  or a direct current (DC; not illustrated for clarity). 
     In the illustrated example embodiment, MEMS switch  511  is depicted as being a simple switch with two contacts, but it should be understood that MEMS switch  511  is a switch including at least three contacts. For example, although not illustrated, the MEMS switch  511  may include a first contact configured as a drain, a second contact configured as a source, and a third contact configured as a gate. Furthermore, as illustrated in  FIG. 5 , a voltage snubber circuit  505  may be coupled in parallel with the MEMS switch  511  and configured to limit voltage overshoot during fast contact separation as will be explained in greater detail hereinafter. 
     In certain example embodiments, the snubber circuit  505  may include a snubber capacitor  514  coupled in series with a snubber resistor  515 . The snubber capacitor  514  may facilitate improvement in transient voltage sharing during the sequencing of the opening of the MEMS switch  511 . Furthermore, the snubber resistor  515  may suppress any pulse of current generated by the snubber capacitor  514  during closing operation of the MEMS switch  151 . As further illustrated, the voltage snubber circuit  505  may include a metal oxide varistor (MOV)  516 . 
     In accordance with further aspects of the present technique, a load  512  may be coupled in series with the MEMS switch  511  and a voltage source  513 . In addition, the load  512  may also include a load inductance and a load resistance, where the load inductance is representative of a combined load inductance and a bus inductance viewed by the MEMS switch  511 . Reference numeral  506  is representative of a load current that may flow through the load  512  and the MEMS switch  511 . 
     Further, as noted with reference to  FIG. 5 , the arc suppression circuitry  502  may include a balanced diode bridge  503 . In the illustrated example embodiment, a balanced diode bridge  503  is depicted as having a first branch  531  and a second branch  532 . As used herein, the term “balanced diode bridge” is used to represent a diode bridge that is configured such that voltage drops across both the first and second branches  531  and  532  are substantially equal. The first branch  531  of the balanced diode bridge  503  may include a first diode D 1   528  and a second diode D 3   527  coupled together to form a first series circuit. In a similar fashion, the second branch  532  of the balanced diode bridge  503  may include a third diode D 2   530  and a fourth diode D 4   529  operatively coupled together to form a second series circuit. 
     In one embodiment, the MEMS switch  511  may be coupled in parallel across midpoints of the balanced diode bridge  503 . The midpoints of the balanced diode bridge may include a first midpoint located between the first and second diodes  528 ,  527  and a second midpoint located between the third and fourth diodes  530 ,  529 . Furthermore, the MEMS switch  511  and the balanced diode bridge  503  may be tightly packaged to facilitate minimization of parasitic inductance caused by the balanced diode bridge  503  and in particular, the connections to the MEMS switch  511 . It may be noted that, in accordance with exemplary aspects of the present technique, the MEMS switch  511  and the balanced diode bridge  503  are positioned relative to one another such that the inherent inductance between the first MEMS switch  511  and the balanced diode bridge  511  produces a di/dt voltage less than a few percent of the voltage across the drain and source of the MEMS switch  511  when carrying a transfer of the load current to the diode bridge  503  during a MEMS switch  511  turn-off which will be described in greater detail hereinafter. 
     In one embodiment, the MEMS switch  511  may be integrated with the balanced diode bridge  503  in a single package or optionally, the same die with the intention of minimizing the inductance interconnecting the MEMS switch  511  and the diode bridge  503 . 
     Additionally, the arc suppression circuitry  504  may include a pulse circuit  502  coupled in parallel electrical communication with the balanced diode bridge  503 . The pulse circuit  502  may be configured to detect a switch condition and initiate opening of the MEMS switch  511  responsive to the switch condition. As used herein, the term “switch condition” refers to a condition that triggers changing a present operating state of the MEMS switch  511 . For example, the switch condition may result in changing a first closed state of the MEMS switch  511  to a second open state or a first open state of the MEMS switch  511  to a second closed state. A switch condition may occur in response to a number of actions including but not limited to a circuit fault or switch ON/OFF request. 
     The pulse circuit  502  may include a pulse switch  524  and a pulse capacitor  523  series coupled to the pulse switch  524 . Further, the pulse circuit may also include a pulse inductance  526  and a first diode  525  coupled in series with the pulse switch  524 . The pulse inductance  526 , the diode  525 , the pulse switch  524  and the pulse capacitor  523  may be coupled in series to form the pulse circuit  502 , where the said components may be configured to facilitate pulse current shaping and timing. 
     Additionally, Arc suppression circuitry  504  may include Hybrid Arcless Limiting Technology (HALT) specific circuitry  508 . The circuitry  508  may include a HALT capacitance  521  (i.e., capacitive portion) and a HALT switch  522 . The HALT capacitance  521  and the HALT switch  522  may be coupled in series to form the HALT-specific circuitry  508 . It is noted that although  FIG. 5  illustrates the Pulse inductance  526  in series with the HALT-specific circuitry  508 , example embodiments are not so limited. For example, a separate HALT inductance may be coupled in series with the HALT capacitance  521  and switch  522 , and the entire HALT-specific circuitry  508  may further be coupled in parallel across the pulse inductance  526  and pulse capacitance  523 . 
     In accordance with aspects of the present invention, the MEMS switch  511  may be rapidly switched (for example, on the order of picoseconds or nanoseconds) from a first closed state to a second open state while carrying a current albeit at a near-zero voltage. This may be achieved through the combined operation of the load circuit  512 , and pulse circuit  502  including the balanced diode bridge  503  coupled in parallel across contacts of the MEMS switch  511 . 
     As further illustrated, the system  500  may include a variable resistance bank comprising a plurality of variable resistors  533 ,  534  couple in parallel electrical communication with the HALT capacitance  521 . The variable resistors  533 ,  534  may be any suitable variable resistors, including but not limited to Metal-Oxide varistors (MOV). The variable resistors  533 ,  534  may be rated and configured to absorb electrical energy transferred directly from the MEMS based switching circuitry  501  in the event of a fault once the HALT switch  522  is activated. For example, a MEMS based switching system  600  under a fault condition is illustrated in  FIG. 6 . 
     As illustrated, the system  600  is substantially similar to the system  500 . Therefore, exhaustive description of the arrangement and operation of each component is omitted herein for the sake of brevity. 
     As illustrated, the system  600  is under a fault condition. Generally, if a system is under a fault condition, it may be desirable to clear a fault quickly or immediately. As current is high (or at least non-zero) a relatively large amount of energy may be trapped inside the motor  512 . Thus, in response to this fault, HALT-specific circuitry  508  may be initiated through activation of HALT switch  522  to aid in clearing the fault. This is illustrated in  FIG. 7 . 
     As illustrated, the system  700  of  FIG. 7  is substantially similar to the system  500 . Therefore, exhaustive description of the arrangement and operation of each component is omitted herein for the sake of brevity. 
     As described above, the HALT switch  522  has been activated thereby transferring electrical energy from the MEMS based switching circuitry  501  to the HALT specific circuitry  508 , where fault current  601  is transferred to the variable resistors  533 - 534 , and a fault current  602  flows across contacts of the MEMS switch  511 . 
     Upon electrical energy transfer, the fault is cleared by opening the MEMS switch  511 , which is illustrated in  FIG. 8 . 
     As illustrated, the system  800  of  FIG. 8  is substantially similar to the system  500 . Therefore, exhaustive description of the arrangement and operation of each component is omitted herein for the sake of brevity. 
     As described above, the MEMS switch  511  is opened, thereby clearing the fault and allowing electrical energy to be absorbed through the snubber circuitry  505  and the varistors  533 ,  534  as illustrated with currents  801 - 802 . 
     As shown above, varistors  533 ,  534  absorb fault energy stored in an inductive load in response to a fault condition. As the varistors are in parallel communication with a capacitive portion  521  of the HALT circuitry  508 , the varistors may be of a relatively smaller voltage rating when compared to the varistors  133 ,  134  due to the difference in applied voltage. Further, because of the relatively smaller voltage seen across the varistors  533 ,  534  during a protective energy transfer operation, a relatively smaller voltage appears across the diode bridge  503 , the MEMS switch  511 , the HALT switch  522 , and the PATO switch  524 . Due to this smaller voltage during the protective energy transfer operation, the diode bridge  503 , the MEMS switch  511 , the HALT switch  522 , and the PATO switch  524  may be rated for a relatively lower voltage, resulting in smaller practicable size and cost. 
     Reference is now made to  FIG. 9 , which illustrates a block diagram of an exemplary soft switching system  900 , in accordance with aspects of the present invention. As illustrated in  FIG. 9 , the soft switching system  900  includes switching circuitry  12 , detection circuitry  70 , and control circuitry  72  operatively coupled together. The detection circuitry  70  may be coupled to the switching circuitry  12  and configured to detect an occurrence of a zero crossing of an alternating source voltage in a load circuit (hereinafter “source voltage”) or an alternating current in the load circuit (hereinafter referred to as “load circuit current”). The control circuitry  72  may be coupled to the switching circuitry  12  and the detection circuitry  70 , and may be configured to facilitate arc-less switching of one or more switches in the switching circuitry  12  responsive to a detected zero crossing of the alternating source voltage or the alternating load circuit current. In one embodiment, the control circuitry  72  may be configured to facilitate arc-less switching of one or more MEMS switches comprising at least part of the switching circuitry  12 . 
     In accordance with one aspect of the invention, the soft switching system  900  may be configured to perform soft or point-on-wave (PoW) switching whereby one or more MEMS switches in the switching circuitry  903  may be closed at a time when the voltage across the switching circuitry  903  is at or very close to zero, and opened at a time when the current through the switching circuitry  903  is at or close to zero. By closing the switches at a time when the voltage across the switching circuitry  903  is at or very close to zero, pre-strike arcing can be avoided by keeping the electric field low between the contacts of the one or more MEMS switches as they close, even if multiple switches do not all close at the same time. Similarly, by opening the switches at a time when the current through the switching circuitry  903  is at or close to zero, the soft switching system  900  can be designed so that the current in the last switch to open in the switching circuitry  903  falls within the design capability of the switch. As alluded to above and in accordance with one embodiment, the control circuitry  901  may be configured to synchronize the opening and closing of the one or more MEMS switches of the switching circuitry  903  with the occurrence of a zero crossing of an alternating source voltage or an alternating load circuit current, or in the event of a fault. 
     As described above, example embodiments of the present invention present innovations which significantly reduce the complexity, cost, and size of MEMS-based motor starters while providing efficient absorption of energy under fault conditions. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.