The present invention relates to overvoltage protection devices and, more particularly, to an overvoltage protection device module including a varistor device and a thyristor.

It is well known that electrical circuits may experience surges in power that is supplied to the circuit. These power surges may be caused by a wide variety of circumstances, such as equipment failure and/or lightning strikes. Such surges may occur relatively quickly, leaving little time to respond in a fashion to protect electrical equipment connected to the surging line. Accordingly, voltage limiting devices may be used for protection of electrical circuits and/or other electronic equipment.

Thyristors are solid-state semiconductor switching devices that may be employed in voltage limiting devices to protect electrical circuits and/or other electronic equipment. A thyristor may be activated to conduct current between its main terminals when a current pulse is received at a gate terminal of the thyristor. For example, thyristors may be used in power supplies as a sort of circuit-breaker, or "crowbar", to prevent failure in the power supply from damaging more surge sensitive components. However, when the thyristor is in a deactivated or blocking state, the thyristor may be damaged by high-voltage surges, for example, such as those which may result from lightning strikes. More particularly, if the surge current magnitude and duration exceeds the energy dissipating capability of the thyristor, the thyristor may be destroyed.

Accordingly, it is known to suppress such overvoltages using one or more varistors (i.e., voltage-variable non-linear resistors) electrically connected across the main terminals of the thyristors. The electrical resistance of a varistor may switch from a relatively high standby value (for applied voltages of less than a so-called breakover voltage level) to relatively low conducting value (for voltages above the breakover level). More specifically, the varistor has a characteristic clamping voltage such that, responsive to a voltage increase beyond a prescribed voltage, the varistor forms a low resistance shunt path for the overvoltage current that reduces the potential for damage to more sensitive components. Typically, a line fuse may also be provided in a protective circuit, and the line fuse may be blown or weakened by the short-circuit essentially created by the shunt path. Thus, varistors may offer a relatively high degree of non-linearity, switching with negligible delay time (less than 50 nanoseconds), and relatively high energy handling capability. As such, in conventional voltage limiting devices, relatively high overvoltage conditions, such as those generated by lightning, may be limited by the varistor, while relatively lower overvoltage conditions of a relatively greater time duration may be limited by the thyristor.

According to some embodiments of the present invention, a voltage limiting device includes a varistor device having first and second terminals, a thyristor having first and second terminals respectively electrically connected to the first and second terminals of the varistor device, and a triggering circuit electrically connected to a gate terminal of the thyristor. The triggering circuit is configured to monitor a voltage between the first and second terminals of the thyristor, and selectively provide a triggering current to the gate terminal of the thyristor based on the voltage between the first and second terminals of the thyristor.

According to other embodiments of the present invention, a method of operating a voltage limiting device including a varistor device and a thyristor electrically connected to the varistor device is provided. The method includes monitoring a voltage between first and second terminals of the thyristor, and selectively providing a triggering current to a gate terminal of the thyristor. More particularly, the triggering current is selectively provided to the gate terminal of the thyristor when the voltage between the first and second terminals of the thyristor exceeds a desired triggering voltage.

According to embodiments of the present invention, an overvoltage protection device module includes an electronics assembly and a housing. The electronics assembly includes a varistor device, a thyristor electrically connected in parallel with the varistor device, and an inductive coil electrically connected to the thyristor. The housing contains the electronics assembly. Each of the varistor device, the thyristor and the inductive coil is disposed in the housing.

According to some embodiments of the present invention, an overvoltage protection device module includes an electronics assembly and a housing. The electronics assembly includes a varistor device, and a thyristor electrically connected in parallel with the varistor device. The housing contains the electronics assembly. The housing includes: an inner housing formed of polyurethane encapsulating at least a portion of the electronics assembly; and an outer shell formed of polycarbonate surrounding at least a portion of the inner housing and the electronics assembly.

According to further embodiments of the present invention, an overvoltage protection device module includes an electronics assembly and a housing. The electronics assembly includes a varistor device, and a thyristor electrically connected in parallel with the varistor device. The housing contains the electronics assembly. The housing includes: an inner housing formed of a resin encapsulating at least a portion of the electronics assembly; an outer shell surrounding at least a portion of the inner housing and the electronics assembly; a gas chamber defined between the electronics assembly and the inner housing to accommodate thermal expansion of the inner housing.

According to some embodiments of the present invention, a method for forming an overvoltage protection device module includes: placing an electronics assembly in a shell cavity of a shell such that at least a portion of the electronics assembly is contained therein; introducing a liquid filler resin into the shell cavity between the shell and the electronics assembly; and curing the liquid filler resin to form an inner housing between the shell and the electronics assembly, wherein a gas chamber is defined between the inner housing and the electronics assembly.

Further features, advantages and details of the present invention will be appreciated by those of ordinary skill in the art from a reading of the figures and the detailed description of the preferred embodiments that follow, such description being merely illustrative of the present invention.

Figure 1 is a top, front perspective view of an overvoltage protection device module according to some embodiments of the present invention.

Figure 2 is a bottom, rear perspective view of the overvoltage protection device module of Figure 1.

Figure 3 is an exploded, perspective view of the overvoltage protection device module of Figure 1, wherein an inner housing of the overvoltage protection device module is not shown.

Figure 4 is a perspective view of an electronic assembly and a film each forming a part of the overvoltage protection device module of Figure 1.

Figure 5 is a cross-sectional view of the overvoltage protection device module of Figure 1 taken along the line 5-5 of Figure 1.

Figure 6 is a cross-sectional view of the overvoltage protection device module of Figure 1 taken along the line 6-6 of Figure 5.

Figure 7 is a cross-sectional view of a varistor device forming a part of the overvoltage protection device module of Figure 1.

Figure 8 is a schematic diagram illustrating an overvoltage protection circuit which may be employed in an overvoltage protection device module according to some embodiments of the present invention.

Figure 9 is a schematic diagram further illustrating the overvoltage protection circuit of Figure 8 and related methods of operation according to some embodiments of the present invention.

Figure 10 is a schematic diagram illustrating an alternate overvoltage protection circuit and related methods of operation according to further embodiments of the present invention.

Figure 11 is a graph illustrating an exemplary variation of the desired triggering voltage as a function of temperature as may be provided by overvoltage protection circuits in accordance with some embodiments of the present invention.

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. In the drawings, the relative sizes of regions or features may be exaggerated for clarity. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

It will be understood that when an element is referred to as being "coupled" or "connected" to another element, it can be directly coupled or connected to the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly coupled" or "directly connected" to another element, there are no intervening elements present. Like numbers refer to like elements throughout.

In addition, spatially relative terms, such as "under", "below", "lower", "over", "upper" and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "under" or "beneath" other elements or features would then be oriented "over" the other elements or features. Thus, the exemplary term "under" can encompass both an orientation of over and under. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

As used herein the expression "and/or" includes any and all combinations of one or more of the associated listed items. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

As used herein, the term "wafer" means a substrate having a thickness which is relatively small compared to its diameter, length or width dimensions.

With reference to Figures 1-10, an integrated overvoltage protection device module 100 according to embodiments of the present invention is shown therein. The module 100 includes an electronics assembly 105 (see, e.g., Figures 3 and 4) and a housing assembly 170 (Figures 1-3, 5 and 6). The electronics assembly 105 includes a positive pole plate 110, a negative pole plate 112, a varistor device 120, an inductive coil 130, a thyristor 140 and a triggering circuit assembly 150. The housing assembly 170 encapsulates the electronics assembly 105.

The module 100 may be used to protect personnel against touch and accessible voltages used, for example, in rail traction systems, as well as to protect telecommunications and/or other electronic equipment from overvoltages. For example, the overvoltage protection device module 100 may be installed between the current return path and electrical equipment and/or other conductive structures adjacent to the rails in a rail traction system. In the case of overvoltage, the overvoltage protection device module 100 may provide a durable conductive path between the overloaded area and a substation. More particularly, overvoltages with a time duration of more than about 3 milliseconds may be limited by the thyristor 140, while higher overvoltages with a time duration of less than a few milliseconds (such as overvoltages generated by lightning) may be limited by the varistor device 120.

The positive pole plate 110 includes a body portion 110a and a terminal portion 110b. A terminal bore 110c extends through the terminal portion 110b. A pair of coil bores 110d, a plurality of thyristor bores 110e, and a varistor device bore 110f extend through the body portion 110a. A slot 110g is formed in a lateral edge and the bottom of the pole plate 110 between the terminal portion 110b and the body portion 110a. In order to not weaken the plate 110, the slot 110g does not extend the full width of the plate 110.

The positive pole plate 110 may be formed of any suitable electrically conductive material. According to some embodiments, the pole plate 110 is formed of a corrosion resistant alloy. According to some embodiments, the pole plate 110 is formed of aluminum or aluminum alloy. The positive pole plate 110 may be formed by any suitable method, such as casting, molding and/or machining.

The negative pole plate 112 includes a body portion 112a and a terminal portion 110b. A terminal bore 112c is formed in the terminal portion 112b. A thyristor bore 112d and a varistor device bore 112e are formed in the body portion 112a. The negative pole plate 112 may be formed of the same materials and using the same methods as described above with regard to the positive pole plate 110.

According to some embodiments, the pole plates 110, 112 have a specific heat of at least about 900 Joules/(kg-°K). According to some embodiments, the positive pole plate 110 has a thermal mass of at least about 1750 Joules/K. According to some embodiments, the positive pole plate 110 has a thickness of between about 19.5 and 20.5 mm. According to some embodiments, the negative pole plate 112 has a thermal mass of at least about 198 Joules/K. According to some embodiments, the negative pole plate 112 has a thickness of between about 7.5 and 8.5 mm.

The varistor device 120 can be any suitable varistor device. According to some embodiments, the varistor device 120 is an overvoltage protection device as disclosed in U.S. Patent No. 6,430,020 to Atkins et al. , titled "Overvoltage Protection Device Including Wafer of Varistor Material," the disclosure of which is incorporated herein by reference, and/or a Strikesorb™ overvoltage protection device as sold by Raycap Corporation of Greece.

An exemplary varistor device 120 is illustrated in Figure 7. The varistor device 120 includes a housing 122, an electrode member 124, a spring clip 126a, a cap 126, an insulator ring 127, O-rings 127a, 127b, a varistor wafer 128, and spring washers 129. According to some embodiments, the housing 122 is an integral, unitarily formed housing. The housing 122 includes an endwall 122a and a sidewall 122b defining a cavity 122c and an opening 122d communicating with the cavity 122c. A terminal post 122e extends from the endwall 122a. The electrode member 124 may also be an integral member that is unitarily formed. The electrode member 124 includes a head 124a and a shaft 124b. The cap 126 and the insulator ring 127 are mounted in the cavity 122c to secure the head 124a in the cavity 122c. A collar portion of the insular ring 127 extends up through a hole in the cap 126. The shaft 124b extends up through the hole in the cap 126 and a hole in the insulator ring 127. The spring washers load the electrode head 124a against the wafer 128.

According to some embodiments, the housing 122 and the electrode member 124 are formed of metal. According to some embodiments, the housing 122 and the electrode member 124 are formed of aluminum or aluminum alloy. According to some embodiments, the insulator ring 127 is formed of an electrically insulative polymeric material having a high melting temperature such as polycarbonate. According to some embodiments, the varistor wafer 128 is formed of a metal oxide varistor (MOV) material.

The housing 122 is electrically connected with and mechanically secured to the positive pole plate 110 by the terminal post 122e, which may threadily engage the bore 110f. The shaft 124b of the electrode member 124 is electrically connected with and mechanically secured to the negative pole plate 112 by a bolt 125 that extends through the bore 112e. Notably, the external surface of the endwall 122e of the housing 122 may abut the positive pole plate 110, providing a substantial contact area therebetween.

The inductive coil 130 may be any suitable inductive coil device. Suitable inductive coils may include air cored coils, iron cored coils, or ferrite cored coils. The coil 130 has a positive terminal 132 and a negative terminal 134. The coil 130 is electrically connected and mechanically secured to the positive pole plate 110 by the terminal 132, which extends through the slot 110g and is held to the underside of the plate 110 by bolts 136. An electrolytic tin coating may be applied to the terminal 132.

The thyristor 140 may be any suitable thyristor device. Suitable thyristor devices may include power thryistor modules or hockey puck thyristors. The thyristor 140 has a first main terminal 142 and a second main terminal 144. According to some embodiments of the present invention and as described hereinafter, the first main terminal 142 may be a positive terminal, and the second main terminal 144 may be a negative terminal. The positive terminal 142 is directly electrically connected to the negative terminal 134 of the coil 130 by a bolt 143. The negative terminal 144 of the thyristor 140 is directly electrically connected to the negative pole plate 112 and to the electrode member shaft 124b of the varistor device 120 by a bolt 145 that extends through the bore 112e and an aluminum spacer 148 provided between the plate 112 and the terminal 144. The thyristor 140 has mounting bores and is secured to the positive pole plate 110 by bolts 146 that extend through the mounting bores and into the bores 110e. The thyristor 140 further includes a gate terminal 149. The thyristor 140 is configured to conduct current in one direction when an appropriate control or trigger signal is applied to the gate terminal 149. A thermally conductive paste may be provided between the bottom of the thyristor 140 and the plate 110 to enhance contact and heat transfer therebetween.

The triggering circuit assembly 150 includes a printed circuit board (PCB) 152, a positive terminal tab 155, a negative terminal tab 156, a jumper cable 157, and a capacitor 154. The terminals 155, 156 may be metal (e.g., tin coated copper) sheets that are welded to the PCB 152. The terminal 155 overlies the thyristor positive terminal 132 and is secured thereto by the bolt 143. The terminal 156 overlies the thyristor negative terminal 144 and is secured thereto by the bolt 145. The PCB 152 is thereby flexibly or displaceably mounted or suspended over the thyristor 140. The jumper cable 157 is received in a connector socket or otherwise connected to the gate terminal 149 of the thyristor 140. The construction and operation of the triggering circuit assembly 150 is described in more detail below.

With reference to Figures 1-3, 5 and 6, the housing assembly 170 includes a shell 172, an inner housing 174 (not shown in Figure 3), and a barrier film 180. A gas chamber 184 is defined within the film 180 as described below. For the purpose of explanation and clarity, the components of the electronic components assembly 105 are shown in cross-section as solid objects in Figures 5 and 6. However, it will be appreciated that these components may in fact include various subcomponents, etc.

The shell 172 includes two shell parts 171 that define a shell cavity 172a. Opposed slots or end openings 172b communicate with the shell cavity 172a. Additionally, fill holes 172c are provided in one endwall of the shell 172 and communicate with the shell cavity 172a. The shell 172 has a convex top surface 172d. Standoff ribs 172e project inwardly from the bottom walls of the shell parts 171. The shell 172 may be otherwise shaped and constructed. For example, according to some embodiments, the shell includes one piece having the shape and dimensions of the overall shell 172 except that an end wall thereof is separable to serve as a removable cover to permit insertion of the electronic components assembly 105.

The shell 172 may be formed of any suitable rigid material. According to some embodiments, the shell 172 is formed of a UV resistant material. According to some embodiments, the shell 172 has a flame resistance of at least about V-0, 3 mm flammability class UL94 and good electrical isolation properties with comparative tracking index V > 200 (IEC 60112). According to some embodiments, the shell 172 is formed of a thermoplastic material. According to some embodiments, the shell 172 is formed of polycarbonate.

The inner housing 174 is disposed in the shell cavity 172a, An outer surface of the inner housing 174 may contact and be bonded with the inner surface of the shell 172. The inner surface of the inner housing 174 defines an inner housing cavity within the shell cavity 172a. The inner housing 174 has opposed end openings 174a through which the terminal portions 110b, 112b extend. The inner housing 174 forms a seal about and is bonded with the positive pole plate 110 and the negative pole plate 112 adjacent the terminal portions 110b, 112b.

The inner housing 174 may be formed of any suitable electrically insulating material. According to some embodiments, the inner housing 174 is formed of a polymeric resin. According to some embodiments, the inner housing 174 is formed of a water impermeable polymeric material. According to some embodiments, the inner housing 174 is formed of polyurethane.

The film 180 is disposed in the inner housing cavity and surrounds the electronic components 120, 130, 140, 150 and portions of the pole plates 110, 112 interior of the terminal portions 110b, 112b. According to some embodiments, the film 180 directly engages the inner surface of the inner housing 174. The film 180 may include multiple superimposed layers. For example, the film 180 may be concentrically wound. The ends of the film 180 are secured in a closed position by suitable securing members such as pieces of self adhesive tape 182. The film 180 thereby defines a gas chamber 184 within the film 180. A volume of a suitable gas such as air is contained in the gas chamber 184.

The film 180 may be any suitable film. According to some embodiments, the film 180 is a flexible organic film. According to some embodiments, the film 180 may be formed of polyethylene. According to some embodiments, the film 180 has a melting temperature of at least 80 °C. According to some embodiments, the total thickness of the film 180 (i.e., including all of the film layers) is between about 0.3 and 0.5 mm.

The gas chamber 184 may be configured such that the film 180 engages some portions of the electronics assembly 105, such as the positive pole plate 110 and the capacitor 154. However, according to some embodiments, the gas chamber 184 is configured such that a gap is provided between the inner surface of the inner housing 174 and at least the PCB 152. According to some embodiments, the width of the gap at these locations is at least about 85 mm. According to some embodiments, the gap width is at least about 100 mm.

The module 100 may be formed as follows in accordance with embodiments of the present invention. The electronics assembly 105 is assembled by mechanically and electrically coupling the varistor device 120, the coil 130, the thyristor 140 and the triggering circuit assembly 150 to the pole plates 110, 112 and to each other as described above and as shown in Figure 4.

The film 180 is then wrapped around the electronics assembly 105. The self-adhesive tape pieces 182 are installed to form an airtight enclosure. A volume of air (or other suitable gas) is trapped in the film 180 (i.e., between the film 180 and the electronics assembly 105).

The shell 172 may be separately pre-formed. According to some embodiments, the shell parts 171 are injection molded.

The preformed shell parts 171 are mounted on the electronics assembly 105 so that the electronic components 120, 130,140, 150 and the film 180 are contained in the shell cavity 172A. The joint between the opposing open ends of the shell parts 171 may be secured together using a silicone caulk, an adhesive, and/or self-adhesive tape. The shell part or parts 171 may be properly positioned relative to the electronics assembly 105 using a jig or the like.

A liquid filler resin is injected or otherwise introduced through the larger of the fill holes 172c of the shell 172 into the shell cavity 172a. The smaller holes 172c may permit displaced air to escape. The liquid resin flows into the space or chamber defined by the outer surface of the film 180 and the inner surface of the shell 172. According to some embodiments, the liquid filler resin is introduced until this volume is substantially fully filled. According to some embodiments, the film 180 and tape pieces 182 are positioned such that the liquid filler resin flows about and engages portions of the pole plates 110, 112 on or adjacent the terminal portions 110b, 112b. Tape or the like may be temporarily placed adjacent the fill holes 172c to receive resin overflow for convenient removal.

The liquid filler resin is then cured in situ within the shell 172 to thereby form the inner housing 174. The resin may be cured by, for example, heat, UV radiation, microwave radiation, or air. According to some embodiments, the film 180 has a melting temperature greater than the peak temperature attained by the polyurethane resin during the curing process.

The inner housing 174 and the shell 172 cooperate to electrically isolate the terminal portions 110b, 112b from one another and to environmentally protect the electronics assembly 105 for an extended period in service. More particularly, the polyurethane resin of the inner housing 172 inhibits or prevents water and humidity from entering the electronic components (e.g., the varistor device 120, the coil 130, the thyristor 140, and the triggering circuit assembly 150). The polyurethane resin seals with the pole plates 110, 112 about or adjacent the terminal portions 110b, 112b and also seals the joint between the shell parts 171 to fully encapsulate the electronic components. According to some embodiments, the lengths L1, L2 (Figure 5) of the seals formed by the inner housing 174 about each plate 110, 112 extending from the gas chamber 184 are each at least about 8 mm and, according to some embodiments, between about 8 and 12 mm.

The polyurethane resin material has good anti-static electrical properties so that it does not tend to attract dust, which in the presence of humidity may otherwise create an electrically conductive film on an external surface of the module 100. Such an electrically conductive film could provide an unintended alternate path for current along the external surface between the terminal portions 110b, 112b that bypasses the electronic components. The polycarbonate shell 172 may serve as an ultraviolet (UV) shield to protect the integrity of the polyurethane resin inner housing 174.

The terminal portions 110b and 112b are located at opposite ends of the module 100, and may also be positioned in spaced apart, opposed top and bottom planes, respectively, as shown. In this way, the distance between the poles is increased to further prevent or inhibit short circuiting of the terminal portions 110b, 112b along an unintended external conductive path.

The gas chamber 184 may serve to accommodate expansion of the inner housing 174 and/or the shell 172 in service. Under some conditions, including where the module 100 generates or is exposed to extreme temperatures, the polyurethane inner housing 174 or polycarbonate shell 172 may thermally expand. The film 180 and the gas chamber 184, which is filled with a compressible gas such as air, accommodates such expansion by preventing or limiting contact or loading between the inner housing 174 and the electronic components 120, 130, 140, 150. Contact with some or portions of the electronic components may be permitted. For example, the inner surface of the inner housing 174 may be positioned directly adjacent (with the film 180 interposed therebetween) the capacitor 154 if the capacitor 154 is flexibly mounted or sufficiently robust or flexible enough to withstand or accommodate such stresses. For example, the flexible mounting of the PCB 152 via the spring metal terminal tabs 155, 156 may permit the inner housing to displace the capacitor 154 (and thereby the PCB 152) without damaging the capacitor 154 or the PCB 152. When the module 100 cools, the inner housing 174 will typically return to its original position, thereby restoring the gas chamber 184.

The gas chamber 184 may serve to reduce the weight of the module 100. The gas chamber 184 may also serve to reduce the amount of resin (e.g., polyurethane resin) required, thereby reducing the cost of manufacturing of the module 100.

The positive pole plate 110 and/or the negative pole plate 112 may serve as heat sinks during the operation of the module 100. In particular, the pole plate 110 and/or the pole plate 112 may have relatively high thermal capacities so that they may absorb and dissipate thermal energy or heat generated by the electronics assembly 105 in use. The pole plates 110, 112 may also provide structural integrity to the module 100.

The external shape or form factor of the housing 170 can be selected to reduce the amount of inner housing resin (e.g., polyurethane resin) and/or shell thermoplastic (e.g., polycarbonate) required, the weight of the module 100, and the space requirements for the module 100. For example, as best seen in Figures 2, 5 and 6, the lower side of the shell 172 is flat to match the flat shape of the positive pole plate 110 and the top side of the shell 172 is convex to generally approximate the contour of the top side of the electronics assembly 105.

According to some embodiments, overvoltage protection devices according to embodiments of the present invention (e.g., the overvoltage protection device 100) may include an overvoltage protection circuit 101a as schematically illustrated in Figure 8. Referring to Figure 8, the overvoltage protection circuit 101a includes the varistor device 120, the thyristor 140, a triggering circuit 150a (which may be embodied in whole or in part in the triggering circuit assembly 150), the inductive coil 130, and a protection network 500.

As discussed above, the positive main terminal 142 and the negative main terminal 144 of the thyristor 140 are respectively electrically connected to the positive and negative terminals 122e, 124e of the varistor device 120. The voltage between the main terminals 142, 144 of the thryistor 140 may be referred to herein as the voltage "across" the thyristor 140, V_thy.

Also, as discussed above, the inductive coil 130 is electrically connected between the positive terminal 142 of the thyristor 140 and the positive terminal 122e of the varistor device 120. The inductive coil 130 is configured to limit the current rate-of-change (di/dt) of the device 100, for example, to a value that is less than the maximum current rate-of-change rating of the thyristor 140.

The protection network 500 is electrically connected in parallel with the thyristor 140, and includes a diode 515, resistors 517 and 519, and a capacitor 525. The protection network 500 is configured to limit the voltage rate-of-change (dV/dt) of the device 100 to less than a predetermined value, for example, 250 V/µs.

Still referring to Figure 8, the triggering circuit 150a is electrically connected to the gate terminal 149 of the thyristor 140, as well as to the first and second main terminals 142, 144 of the thyristor 140. The triggering circuit 150a is configured to monitor the voltage V_thy between the main terminals 142, 144 of the thyristor 140 and selectively provide a triggering current to the gate terminal 149 based on the voltage V_thy across the thyristor 140. More specifically, the triggering circuit 150a is configured to provide the current to the gate terminal of the thrystor when the voltage V_thy across the thyristor 140 exceeds a desired value, referred to as the desired triggering voltage V_trig. As such, the triggering circuit 150a is designed to allow precise control over the operation of the thyristor 140. For example, the triggering circuit 150a may be configured to selectively provide the triggering current to the gate of the thyristor 140 when the voltage V_thy between the first and second terminals of the thyristor 140 is within about 0.1 V or less of the desired triggering voltage V_trig. Also, the operation of the triggering circuit 150a is designed to be independent of the operating temperature of the device 100. For example, the triggering voltage may be consistently provided over a range of about -40 °C to about 100 °C.

Figure 9 illustrates the overvoltage protection circuit 101a and the triggering circuit 150a of Figure 8 and related methods of operation in greater detail. As illustrated in Figure 9, the triggering circuit 150a includes a capacitor 630 electrically connected to the gate terminal 149 of the thyristor 140, and a bilateral voltage-triggered switch 635 electrically connected between the capacitor 630 and the gate terminal 149. The voltage triggered switch 635 may be any suitable bidirectional switching device that is configured to conduct current when its breakdown voltage has been exceeded, such as a diode for alternating current (DIAC) and/or a silicon diode for alternating current (SIDAC). As such, the voltage triggered switch 635 is configured to discharge the capacitor 630 to provide the triggering current the gate terminal 149 of the thyristor 140 when the voltage of the capacitor 630 is greater than or equal to the breakdown voltage of the voltage-triggered switch 635.

For example, as shown in Figure 9, the capacitor 630 may be charged through diode 685, resistor 680, and resistor 675 until the voltage reaches the breakdown voltage V_trip of the voltage-triggered switch 635 (for example, about 79V to about 90 V). Then, the capacitor 630 may be discharged to the gate terminal 149 of the thyristor 140 through the voltage-triggered switch 635 and a current limiting resistor 640, to trigger conduction of the thyristor 140. The capacitor 630 may provide an exponential triggering current, with a suitably high peak value and duration to assure a fast and reliable triggering of the thyristor 140. The diode 685 prevents reverse conduction of the triggering circuit 150a, while a Zener diode 670 electrically connected to the main terminals 142, 144 of the thyristor 140 limits the voltage to a "safe" value for the triggering circuit 150a.

Still referring to Figure 9, the triggering circuit 150a includes a voltage comparator 610 and a voltage divider network 625. The voltage divider network 625 is electrically connected to the positive and negative main terminals 142, 144 of the thyristor 140. As such, the voltage comparator 610 is configured to monitor the voltage V_thy between the main terminals 142, 144 of the thyristor 140 based on an output voltage of a voltage divider network 625, to thereby determine when the voltage V_thy across the thyristor 140 exceeds the desired triggering voltage V_trig. Accordingly, when an output of the voltage comparator 610 indicates that the voltage V_thy across the thyristor 140 is greater than the desired triggering voltage V_trig, the triggering circuit 150a may selectively charge the capacitor 630 to the breakdown voltage of the voltage-triggered switch 635, to thereby provide the triggering current to the gate terminal 149 of the thyristor 140.

More particularly, the voltage divider network 625 is configured to provide an output voltage to the voltage comparator 610 based on the voltage across the thyristor 140 and a predetermined voltage division ratio. The voltage divider network 625 includes a plurality of resistors 625a, 625b, and 625c that are electrically connected to the main terminals 142, 144 of the thyristor 140. The values of the resistors 625a, 625b, and 625c may be chosen and/or adjusted to provide a desired voltage division ratio. For example, one or more of the resistors 625a, 625b, and 625c may be a potentiometer that is configured to provide an adjustable resistance, to thereby adjust the desired voltage division ratio. As such, an output voltage based on the voltage across the thyristor 140 and the voltage division ratio is provided to the voltage comparator 610. The output voltage may be any voltage that is less than the voltage V_thy across the thyristor 140. The voltage comparator 610 is configured to compare the output voltage of the voltage divider network 625 with a reference voltage in order to determine when the voltage V_thy between the positive and negative main terminals 142, 144 of the thyristor 140 is greater than the desired triggering voltage V_trig. For example, the reference voltage may be chosen based on the breakdown voltage of a zener diode 650 electrically connected to the voltage comparator 610, as discussed below.

As illustrated in Figure 9, the triggering circuit 150a further includes a N-channel field effect transistor (FET) 645. The transistor 645 includes a gate terminal 649 electrically connected to the voltage comparator 610 and a resistor 665, and at least one other terminal electrically connected to the capacitor 630. As such, the transistor 645 is configured to bypass the capacitor 630 when the voltage V_thy across the thyristor 140 is less than the desired triggering voltage V_trig, to thereby prevent charging of the capacitor 630. In addition, a zener diode 650 is electrically connected to the gate terminal 649 of the transistor 645 and the voltage comparator 610. The zener diode 650 is configured to deactivate the transistor 645 when the voltage V_thy between the main terminals 142, 144 of the thyristor 140 is greater than the desired triggering voltage V_trig, to thereby allow charging of the capacitor 630.

The operation of the transistor 645 and the zener diode 650 is controlled by the output of the voltage comparator 610, to selectively provide the triggering current to the gate terminal 149 of the thyristor 140. More particularly, when output of the voltage comparator 610 is less than the breakdown voltage of zener diode 650, the zener diode 650 does not conduct current. As such, a gate voltage is provided to the gate terminal 649 of the transistor 645 to switch the transistor 645 to a conducting (i.e., "on") state. Thus, current may flow through the diode 685, the resistors 680, 675, 660, and the transistor 645 to bypass the capacitor 630, preventing the capacitor 630 from being charged. In contrast, when output of the voltage comparator 610 is greater than or equal to the breakdown voltage of zener diode 650, the zener diode 650 conducts current, thereby short-circuiting the gate terminal 649 of the transistor 645 to switch the transistor 645 to a non-conducting (i.e., "off") state. Thus, current may flow through the diode 685 and the resistors 680 and 675 to charge the capacitor 630 to the breakdown voltage of the voltage-controlled switch 635, thereby triggering the thyristor 140.

The overvoltage protection circuit 101a and the triggering circuit 150a of Figure 9 will now be described with reference to the following example. In this example, it is assumed that the desired triggering voltage V_trig to activate the thyristor 140 is 120V, and the breakdown voltage of the zener diode 650 is 12V. Accordingly, the values of the resistors 625a, 625b, and 625c of the voltage divider network 625 may be selected and/or adjusted to divide down the voltage V_thy such that the output of the voltage comparator 610 exceeds 12V only when the voltage V_thy across the thyristor is greater than V_trig (i.e., greater than 120V). As such, if V_thy is less than 120V, the output of the voltage comparator 610 is less than 12V, and the zener diode 650 does not conduct. Thus, the output of the voltage comparator 610 (for example, 10V) is provided to the gate terminal 649 the transistor 645, and the transistor 645 is switched on, bypassing the capacitor 630. As such, charging of the capacitor 630 is prevented. On the other hand, if V_thy is greater than or equal to 120V, the output of the voltage comparator 610 is greater than or equal to 12V, and the zener diode 650 is reverse-biased, short-circuiting the gate terminal 649 of the transistor 645. Thus, the transistor 645 is switched off, allowing charging of the capacitor 630. When the capacitor 630 is charged to the breakdown voltage of the voltage-triggered switch 635, the voltage-triggered switch 635 conducts, discharging the capacitor 630 to the gate terminal of the thyristor 140. Accordingly, the thyristor 140 is activated to short the terminals 110 and 112 of the voltage source.

According to some embodiments, the device 100 may include an alternative overvoltage protection circuit 101b. Figure 10 illustrates an alternate overvoltage protection circuit 101b including an alternate triggering circuit 150b and related methods of operation according to further embodiments of the present invention. The triggering circuit 150b may include many of the same components of the triggering circuit 150a of Figure 9, and as such, like components may be illustrated by like numbers. Referring now to Figure 10, the triggering circuit 150b further includes a constant current source 705 electrically connected to the capacitor 630, in place of the resistor 675 of Figure 9. The constant current source 705 may be selectively activated to provide the current to charge the capacitor 630 based on the voltage V_thy between the positive and negative main terminals 142, 144 of the thyristor 140. More specifically, the constant current source 705 may be activated to charge the capacitor 630 when the voltage between the main terminals 142, 144 of the thyristor 140 is greater than the desired triggering voltage V_trig, and may be deactivated to prevent charging of the capacitor 630 when the voltage V_thy across the thyristor 140 is less than the desired triggering voltage V_trig.

In particular, as shown in Figure 10, the constant current source 705 includes a P-channel FET 702, a resistor 701 connected to the source of the FET 702, and a PNP transistor 703. Additional resistors 710, 715, and 720 are also provided to couple the constant current source 705 to the transistor 645. The current provided by the current source 705 may be determined by the base-emitter voltage (V_BE) of the transistor 703 (for example, about 0.7V) divided by the value of the resistor 701. A PNP transistor 708, driven by the transistor 645, activates or deactivates the current source 705 depending on whether the output of the voltage comparator 610 is greater than or less than the breakdown voltage of the zener diode 650, as discussed above with reference to Figure 9.

As such, the constant current source 705 provides a current to charge the capacitor 630 (and thus, to trigger the thyristor 140) only if the voltage V_thy across the thyristor 140 is equal or greater to V_trig. In comparison, in Figure 9, when the thyristor 140 is not conducting (i.e., when V_thy is lower than V_trig), there may be substantial current flow through the series combination of resistors 660, 675, and 680. Accordingly, by employing the constant current source 705 of Figure 10 to selectively turn-on the current to charge the capacitor 630, the current flow through the resistors 660, 675, and 680 can be reduced to a negligible value.

Accordingly, the overvoltage protection device 100 including the triggering circuit 150a or 150b of Figures 8-10 offers various advantages over overvoltage protection devices of the prior art. In particular, the design of the voltage comparator 610 and the voltage divider network 625 of the triggering circuit 150a or 150b allows for more precise triggering of the thyristor 140. According to some embodiments, the triggering circuit enables control of triggering of the thyristor 140 to within about 0.1 V or less of a desired triggering voltage V_trig.

The voltage comparator 610 and the voltage divider network 625 of the triggering circuits 150a and 150b may also be designed to operate independently of the operating temperature of the voltage-limiting device 100. According to some embodiments, the resistors 625a, 625b, and 625c of the voltage divider network 625 may be metal film resistors formed of the same material, or may be otherwise designed to provide a temperature-insensitive voltage division ratio. An exemplary variation of the desired triggering voltage V_trig as a function of temperature as may be provided by overvoltage protection circuits in accordance with embodiments of the present invention is illustrated in Figure 11. As shown in Figure 11, since the desired triggering voltage V_trig is determined by the reference voltage of the voltage comparator 610 and the temperature-insensitive voltage division ratio of the voltage divider network 625, the voltage V_trig remains relatively constant over a range of about -40 °C to about 100 °C.

The module 100 as described above may be well-suited for use in a direct current (DC) powered network. According to some embodiments, the modules according to embodiments of the present invention may be adapted for use in alternating current (AC) powered networks. According to some embodiments, an overvoltage protection module for use in an AC network corresponds to the module 100 except that there are provided two thyristors and two triggering circuit assemblies (and hence, two triggering circuits). Each triggering circuit assembly is associated with a respective one of the thyristors to control operation of the respective thyristor as described above. The thyristor/triggering circuit pairs are electrically connected in parallel with one another such that each thyristor conducts current in a direction opposite to the other when an appropriate trigger signal is applied to the respective gate terminals of the thyristors. The thyristor/triggering circuit pairs are otherwise connected to the remainder of the electrical circuit in the same manner as described above. According to some embodiments, the thyristors are mounted side-by-side across the width of the pole plate. According to some embodiments, the two triggering circuits are mounted on a single PCB.

Many alterations and modifications may be made by those having ordinary skill in the art, given the benefit of present disclosure, without departing from the spirit and scope of the invention. Therefore, it must be understood that the illustrated embodiments have been set forth only for the purposes of example, and that it should not be taken as limiting the invention as defined by the following claims. The following claims, therefore, are to be read to include not only the combination of elements which are literally set forth but all equivalent elements for performing substantially the same function in substantially the same way to obtain substantially the same result. The claims are thus to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, and also what incorporates the essential idea of the invention.