Abstract:
A transient voltage suppressor device includes a transient voltage suppression circuit, a first voltage monitor lead connected to the transient voltage suppression circuit, and a second voltage monitor lead connected to the transient voltage suppression circuit. A voltage injection circuit having a plurality of output voltage levels is also connected to the transient voltage suppression circuit to provide indication via the first and second voltage monitors if the transient voltage suppression circuit is shorted or open.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to transient voltage protection devices, and more particularly to in-circuit testing of transient voltage protection devices. 
     2. Description of Related Art 
     Electrical systems commonly include transient voltage suppression (TVS) devices to protect electronic circuits from damage due to externally induced voltage transients. TVS devices are generally selected such that the do not conduct under normal operating conditions, and conduct when the voltage on the TVS device exceeds a turn-on voltage for the TVS device. The turn-on voltage of the TVS device is typically selected such that it is below the voltage rating of the electronic circuit protected by the TVS device. Some TVS devices may become unreliable during service by developing an open circuit or short circuit condition. This potentially reduces the protection ordinarily afforded by such TVS devices, and can leave the electronic circuit unprotected from voltage transients. While short circuits can sometimes be identified through observation of the protected electronic circuit, open circuit conditions can be more challenging to identify and correct. In some circumstances an open circuit condition in a TVS device may remain latent until the electronic circuit exhibits aberrant performance as a result of experiencing a voltage transient. 
     Such conventional methods and systems for protecting sensitive components within circuitry have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved transient overvoltage protection systems that allow for improved protection device reliability. The present disclosure provides a solution for this need. 
     SUMMARY OF THE INVENTION 
     A transient voltage suppressor device includes a transient voltage suppression circuit, a first voltage monitor lead connected to the transient voltage suppression circuit, and a second voltage monitor lead connected to the transient voltage suppression circuit. A voltage injection circuit having a plurality of output voltage levels is also connected to the transient voltage suppression circuit to provide indication via the first and second voltage monitors if the transient voltage suppression circuit is shorted or open. 
     In certain embodiments, the transient voltage suppressor circuit can include a first diode and a second diode connected between source and return leads. The first diode can be connected in series with the second diode. The first diode can be connected to the second diode such that each diode opposes current flow in the same direction. For example, the first and second diodes can each be arranged such that no current flows from the source lead to the return lead when voltage is below a predetermined value. The first and second diodes can be Zener diodes, and the predetermined value can be the sum of the avalanche voltages of the diodes. A source disconnect switch can be connected between the voltage source lead and the transient voltage suppression circuit. 
     In accordance with certain embodiments, the voltage inject circuit can include a voltage source. The voltage source can include positive and negative voltage inject rails. The positive and negative voltage inject rails can be of unequal magnitudes relative to a ground reference. A voltage inject switch with three switch positions can be connected in series with the voltage source. In a switch first position, the voltage inject switch can connect a voltage inject circuit resistor with the positive voltage inject rail. In the switch second position, the voltage inject switch can connect the voltage inject resistor to the negative voltage inject rail. In the switch third position, the voltage inject circuit is disconnected from the voltage inject circuit resistor. It is contemplated that the voltage inject resistor can be connected to a voltage node interposed between the first and second diodes. 
     It is also contemplated that, in accordance with certain embodiments, the transient voltage suppression circuit can include a first resistor leg. The first resistor leg can be connected in parallel with the transient voltage suppression circuit and can include source and return resistors connected in series with one another. Each of the source and return resistors can have resistances, and the resistances can be equivalent to one another. A first resistance leg voltage node can be interposed between the source resistor and the return resistor, and the second voltage monitor lead can be connected to the first resistance leg voltage node. It is further contemplated that a second resistance leg can be connected in parallel with the first resistor leg between the source and return legs. The second resistance leg can have a resistor with a resistance that is less than the resistance of the resistors of the first resistance leg. 
     A transient voltage suppression system includes the transient voltage suppression circuit, first voltage monitor lead, second voltage monitor lead, and voltage inject circuit as described above. The system also includes a control module having a processor and memory that is operatively associated with the source disconnect switch, voltage inject circuit, and first and second voltage monitors that are coupled to the first and second voltage monitor leads. The memory has instructions recorded thereon that, when read by the processor, cause the processor to (a) determine if the first diode is shorted, (b) determine if the first diode is open, (c) determine if the second diode is shorted, and (d) determine if the second diode is open. 
     These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, embodiments thereof will be described in detail herein below with reference to certain figures, wherein: 
         FIG. 1  is a schematic view of an exemplary embodiment of an electrical system constructed in accordance with the present disclosure, showing a transient voltage suppression and built-in test circuit connected between a voltage source and a load; 
         FIG. 2  is a circuit diagram of a transient voltage suppression circuit including a built-in test circuit according to an embodiment, showing a high-side source disconnect switch; 
         FIG. 3  is a circuit diagram another embodiment of a voltage suppression circuit including a built-in test circuit, showing a low-side source disconnect switch; and 
         FIG. 4  is schematic view of an exemplary embodiment of a method of testing a transient voltage suppression device for open circuits and short circuits across diodes arranged in series within a transient voltage suppression circuit of the device. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a transient voltage suppression (TVS) device in accordance with the disclosure is shown in  FIG. 1  and is designated generally by reference character  100 . Other embodiments of TVS devices in accordance with the disclosure, or aspects thereof, are provided in  FIGS. 2-4 , as will be described. The systems and methods described herein can be used in power distribution systems and electronics devices, such as for marine, terrestrial and/or air vehicle electrical systems. 
     With reference to  FIG. 1 , an exemplary embodiment of an electrical system  10  is shown. Electrical system  10  includes a voltage source  12 , a transient voltage suppression device  100 , and an electrical load  14 . A voltage source lead  16  interconnects a positive terminal of voltage source  12  with load  14 , and a voltage return lead  18  interconnects a negative terminal of voltage source  12  with load  14 . Transient voltage suppression device  100  is connected between voltage source lead  16  and voltage return lead  18 , and includes a transient voltage circuit  110 , a built-in test circuit  120 , and a ground terminal  102 . 
     Built-in test circuit  120  is connected to transient voltage circuit  110  for determining whether a fault exists within transient voltage suppression device  100 , such as an open circuit or a short-circuit that could reduce the reliability of electrical system  10  of prevent dissipation of a transient voltage event. Non-limiting examples of transient voltage events include lightning strikes and arcing with certain types of loads, like motors. 
     With reference to  FIG. 2 , transient voltage suppression device  100  is shown. Transient voltage suppression device  100  includes a first diode  104  connected to voltage source lead  16  and a second diode  106  connected to voltage return lead  18 . First diode  104  and second diode  106  are connected in series with one another between voltage source lead  16  and voltage return lead  18 . A voltage node  108  is interposed between first diode  104  and second diode  106 , first diode  104  connecting to voltage node  108  on an end opposite voltage source lead  16  and second diode  106  connecting to voltage node  108  on an end opposite voltage return lead  18 . Using a pair of diodes arranged in series instead of a single diode in the voltage protection circuit enables testing the diodes for both short and open conditions. While two diodes are illustrated in the illustrated exemplary transient voltage protection circuit, it is to be understood that voltage protection circuits with more than two diodes are also contemplated. 
     First diode  104  and second diode  106  are connected to one another in series between voltage source lead  16  and voltage return lead  18  such that both diodes oppose current flow from voltage source lead  16  and voltage return lead  18 , i.e. with cathode ends of the diode facing voltage source lead  16 . In embodiments, both first diode  104  and second diode  106  have avalanche (breakdown) voltages that are substantially equivalent to one another. For example, in an illustrative exemplary embodiment, voltage source  12  (shown in  FIG. 1 ) includes a 28-volt source and first diode  104  and second diode  106  have avalanche voltages of about 40-volts. This renders TVS circuit suitable for use in aircraft power systems for purposes of dissipating transient voltages to ground, such as in lightning protection applications. In certain embodiments, first diode  104  and second diode  106  are Zener diodes. 
     Built-in test (BIT) circuit  120  includes a source disconnect switch  122 , a first voltage monitor lead  124 , a second voltage monitor lead  126 , and a voltage inject circuit  128 . Source disconnect switch  122  is connected to voltage source lead  16  between voltage source  12  (shown in  FIG. 1 ) TVS circuit  110 . Source disconnect switch  122  may include a solid-state switch, such as a field effect transistor (MOSFET) or insulated gate bipolar transistor (IGBT). As illustrated in  FIG. 2 , source disconnect switch  122  may be arranged as a high-side source disconnect switch. 
     With reference to  FIG. 3 , another embodiment of transient voltage suppression device  200  is shown. Transient voltage suppression device  200  includes a TVS circuit  210  and BIT circuit  220 . TVS circuit  210  is similar to TVS circuit  110  (shown in  FIG. 2 ) and additionally includes a return disconnect switch  222  coupled to voltage return lead  18  and on a side of load  14  opposite source lead  16 . BIT circuit  220  is similar to BIT circuit  120  (shown in  FIG. 2 ). 
     With continuing reference to  FIG. 2 , first voltage monitor lead  124  is connected to voltage source lead  16  on a first end between source disconnect switch  122  and BIT circuit  120 , and to a first voltage monitor  130  on an opposite second end. Second voltage monitor lead  126  is connected to voltage node  108  on a first end (i.e. between first diode  104  and second diode  106 ), and to a second voltage monitor  132  on an opposite second end. First voltage monitor  130  is used to measure voltage applied to load  14  (shown in  FIG. 1 ). Second voltage monitor  132  is used to measure voltage applied to voltage node  108 . 
     Voltage inject circuit  128  is used to apply a voltage potential to voltage node  108  and includes a voltage source  134 , a voltage inject circuit switch  136 , and voltage inject circuit resistor  138 . Voltage source  134  includes positive and negative voltage inject rails, with respect to ground terminal  102 , for injecting voltage for testing diodes of the transient voltage protection circuit, e.g. first diode  104  and second diode  106 . Voltage inject circuit switch  136  is connected in series with voltage source  134  and voltage inject circuit resistor  138  is connected in series between voltage inject circuit switch  136  and voltage node  108 . It is contemplated that the voltage positive and negative inject rails have magnitudes that are both high enough to forward bias either diode of the TVS circuit and which are below the avalanche voltage of the diode. In embodiments, magnitude of the positive and negative voltage inject rails is greater than about two (2) times forward voltage drop of the voltage protection circuit diodes and is less than the breakdown (avalanche) voltages of the voltage protection circuit diodes. This provides diagnostic capability for each of the diodes. In certain embodiments, the magnitude positive and negative voltage inject is about 10-volts for a 28-volt bus protected by two 40-volt diodes as illustrated in the exemplary circuit of  FIG. 2 . 
     Voltage inject circuit switch  136  and has three switch positions. In the switch first position, voltage inject circuit switch  136  connects voltage inject circuit resistor  138  with the positive voltage inject rail of voltage source  134 . In the switch second position, voltage inject circuit switch  136  connects voltage inject circuit resistor  138  with the negative voltage inject rail of voltage source  134 . In the switch third position, voltage inject circuit switch  136  is open and voltage source  134  of voltage inject circuit  128  is disconnected from voltage node  108 . 
     BIT circuit  120  also includes a first resistor leg  140  and a second resistor leg  150 . First resistor leg  140  is connected between voltage source lead  16  and voltage return lead  18 , and is in parallel with second resistor leg  150 . First resistor leg  140  includes a source-side resistor  142  connected in series with a return-side resistor  144  with a first leg voltage node  146  interposed between source-side resistor  142  and return-side resistor  144 . Source-side resistor  142  and return-side resistor  144  have equivalent resistances, and second voltage monitor lead  126  is connected to first leg voltage node  146 . 
     Second resistor leg  150  is connected between voltage source lead  16  and voltage return lead  18  such that it is parallel with first resistor leg  140 . Second resistor leg  150  includes a second leg resistor  152  with a resistance that may be equal to the resistance of voltage inject circuit resistor  138  and smaller than respective resistances of source-side resistor  142  and return-side resistor  144 . Second leg resistor  152  is also connected in parallel with load  14  such that, in circuit having high resistance loads (or open loads), the functionality of the voltage protection circuit can still be tested due to the path to ground provided through second leg resistor  152 . 
     In an exemplary embodiment, both voltage inject circuit resistor  138  and second leg resistor  152  have resistances of about 5 kilo ohms and source-side resistor  142  and return-side resistor  144  have resistances of about 100 kilo ohms. The positive rail of voltage source  134  has a voltage of about positive 10 volts and the negative rail of voltage source  134  has a voltage of about negative 10 volts. This enables BIT circuit  120  suitable for verifying the operability of TVS circuit with an 80-volt rating that is suitable for a 28-volt direct current power system. As will be appreciated, elements with other voltages and resistances may be used in other embodiments of devices described herein. 
     During normal operation, voltage inject circuit  128  is disconnected. When source disconnect switch  122  is closed, first voltage monitor  130  indicates the voltage applied to voltage source lead  16  by voltage source  12  (shown in  FIG. 1 ). When source disconnect switch  122  is open, first voltage monitor  130  indicates zero (0) volts. During a transient voltage event, first diode  104  and second diode  106  limits voltage across source disconnect switch  122  and the controller module operatively associated therewith. 
     With reference to  FIG. 4 , a method  300  of testing TVS circuit  110  using BIT circuit  120  is shown. Method  300  generally includes determining whether a first diode, e.g. first diode  104 , is shorted, as shown with box  310 . Method  300  also includes determining whether the first diode is open, as shown with box  320 . Method  300  further includes determining whether a second diode, e.g. second diode  106 , is shorted, as shown with box  330 . Method  300  additionally includes determining whether the second diode is open, as shown with box  340 . Each of these determinations are made by comparing voltage indications provided by first voltage monitor  130  and second voltage monitor  132  with switches of BIT circuit  120  in different switch positions. 
     For example, with reference to TVS circuit  110  and BIT circuit  120  shown in  FIG. 2 , when source disconnect switch  122  is closed and voltage inject circuit switch  136  is in the switch third position (i.e. the open position), voltage from a voltage source connected to source disconnect switch  122  is applied to first voltage monitor  130  and TVS circuit  110 . Accordingly, first voltage monitor  130  should indicate the same voltage as voltage source  12 , and second voltage monitor  132  should indicate about one-half of the voltage indicated by first voltage monitor  130 . If so, this verifies that first diode  104  and second diode  106  are not shorted. Resistors  140  and  144  may be equal to each other, thereby forming a 2:1 voltage divider if neither of the first and second diodes are shorted. 
     With source disconnect switch  122  open and voltage inject circuit switch  136  in the switch third position, no voltage is applied to TVS circuit  110  and BIT circuit  120 . Both first voltage monitor  130  and second voltage monitor  132  should read zero volts. This (a) verifies that first voltage monitor  130  and second voltage monitor  132  can accurately read a zero voltage, and (b) verifies that source disconnect switch  122  and voltage inject circuit switch  136  are functional. 
     With source disconnect switch  122  open and voltage inject circuit switch  136  in the switch first position, a positive voltage is applied to voltage node  108 . First voltage monitor  130  and second voltage monitor  132  indicate respective voltages that are influenced by voltage inject circuit resistor  138 , second leg resistor  152 , load  14 , and a voltage drop associated with first diode  104 . If first diode  104  is not open, second voltage monitor  132  will indicate a voltage level that is more positive than a voltage indicated by first voltage monitor  130  by an amount that is equivalent to the forward voltage drop of first diode  104  (i.e. about one volt in the illustrated exemplary circuit). If first diode  104  is open, second voltage monitor  132  will indicate a voltage that is much greater than that indicated by first voltage monitor  130 , e.g. about  10  volts in the illustrated exemplary circuit. When first voltage monitor  130  and second voltage monitor  132  indicate the equivalent voltages, first diode  104  is shorted. 
     With source disconnect switch  122  open and voltage inject circuit switch  136  in the switch second position, voltage from the negative voltage inject rail of voltage source  134  is applied to voltage node  108 . First voltage monitor  130  should indicate zero volts. Second voltage monitor  132  should indicate a voltage that is equivalent to the forward voltage drop of second diode  106  (i.e. about negative one volt in the illustrated exemplary circuit). This verifies that second diode  106  is not open. In the event that second diode  106  is open, then second voltage monitor  132  will read a negative voltage with a magnitude that is larger than the forward voltage drop across second diode  106  (i.e. about negative ten volts in the illustrated exemplary circuit). 
     With reference to TVS circuit  210  and BIT circuit  220  shown in  FIG. 3 , when return disconnect switch  222  is open and voltage inject circuit switch  236  is in the switch third position, voltage from load  14  (and resistor  252  connected across the load) is applied to first voltage monitor  230  and TVS circuit  210 . This causes first voltage monitor  230  to indicate a voltage that is the same as that voltage to voltage source lead  16 . This also causes second voltage monitor  232  to indicate about one-half the voltage indicated by first voltage monitor  230  if neither first diode  204  nor second diode  206  are shorted. As will be appreciated, since first resistor  242  and second resistor  244  have equivalent resistance, the resistors form a 2:1 voltage divider when neither of the diodes of the TVS circuit are shorted. 
     When return disconnect switch  222  is closed and voltage inject circuit switch  236  is in the third switch position (open), no voltage is applied to voltage node  208 , TVS circuit  210  and BIT circuit  220 . Both first voltage monitor  230  and second voltage monitor  232  should indicate zero volts. If zero voltage is indicated on each, this verifies that (a) first voltage monitor  230  and second voltage monitor  232  can accurately read a zero voltage, and (b) return disconnect switch  222  and voltage inject circuit switch  236  are functional. 
     When return disconnect switch  222  is closed and voltage inject circuit switch  236  is in the switch first position, a positive voltage is applied to voltage node  208 . This causes first voltage monitor  230  and second voltage monitor  232  to indicate voltages that are influenced by voltage inject circuit resistor  238  and a voltage drop associated with first diode  204 . If first diode  204  is not open, second voltage monitor  232  will indicate a voltage level that is greater than the forward voltage drop of first diode  204  (i.e. about one volt in the illustrated exemplary circuit) relative to a voltage indicated by first voltage monitor  230 . If first diode  204  is open, second voltage monitor  232  will indicate a voltage that is much greater than that indicated by first voltage monitor  230 , e.g. about 10-volts in the illustrated exemplary circuit. When first voltage monitor  230  and second voltage monitor  232  indicate the same voltages first diode  204  is shorted. 
     When return disconnect switch  222  is closed and voltage inject circuit switch  236  is the switch second position, voltage from the negative voltage inject rail of voltage source  234  is applied to voltage node  208 . If second diode  206  is not open, first voltage monitor  230  will indicate zero volts and second voltage monitor  232  will indicate a voltage that is equivalent to the forward voltage drop of second diode  206  (i.e. about negative one volt is the illustrated exemplary circuit). In the event that second diode  206  is open, second voltage monitor  232  will read a negative voltage with a magnitude that is of larger magnitude, e.g. about negative ten volts in the illustrated exemplary embodiment. 
     The methods and systems of the present disclosure, as described above and shown in the drawings, provide for transient voltage suppression devices with superior properties including improved reliability. In embodiments, currents associated with transient voltages only traverse the TVS circuit. In certain embodiments, detection of failed TVS circuit components can be detected while the TVS circuit protection devices are arranged in-circuit. It is also not necessary to include switches between the protected circuit and the transient protection devices (i.e. diodes) for purposes of isolating the devices for testing purposes. Since some types of switches can degrade in response to voltage stress from transient voltage events, this can improve the reliability of the TVS circuit by avoiding application of stresses on such interposed switches. 
     While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the scope of the subject disclosure. For example, groups of circuit elements from either or both of the BIT circuit and TVS circuit can be formed as discrete circuit elements, one or more integrated circuits, and/or a combination of software and firmware.