Patent Publication Number: US-2018048145-A1

Title: Transient voltage protection circuits

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to transient voltage protection circuits, and more particularly to transient voltage protection circuits for aircraft electrical systems. 
     2. Description of Related Art 
     Electrical systems, such as aircraft electrical systems, commonly include power generation systems, which generate power from turbine rotation, and wiring, which distributes the generated power to devices such as motors and onboard electronics. When an aircraft is struck by lightning at least a portion of the energy from the lightning strike can be transmitted through the electrical system wiring into electrical devices carried by the aircraft, e.g., motors and/or onboard electronics. The transmitted energy can potentially reducing the functionality of certain types of electronic devices, for example by tripping current flow control devices like breakers, or damaging electronic devices by applying excessive voltage stress to electronic devices. To the loss of functionality and/or damage to electronic devices from transients, some aircraft electrical systems employ lightening protection devices. The lightning protection devices typically prevent transient energy from reaching the onboard electronics, such as be dissipating the energy, thereby protecting onboard electronics from the lightning strike. 
     Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved lightening protection circuits, aircraft electrical systems employing such lightning protection circuits, and methods of dissipating energy from lightning strikes. The present disclosure provides a solution for this need. 
     SUMMARY OF THE INVENTION 
     A transient voltage protection circuit includes an inductor with a source-side terminal and a device-side terminal, a first stage with a protection element connected to the inductor source-side terminal, and a second stage with a protection element connected to the inductor device-side terminal. A ground terminal is connected to the inductor device-side terminal through the first stage and to the inductor source-side terminal through the first stage. The second stage defines a single conductive path between the inductor source-side terminal and the ground terminal. 
     In certain embodiments, the first stage can define a single conductive path between the inductor device-side terminal and the ground terminal. The first stage protection element can include a diode. The first stage can include a bus lead and a ground lead connected in series with one another through the diode. The diode can be a bidirectional transient voltage protection diode. 
     In accordance with certain embodiments, the second stage protection element can include a gas discharge tube. The second stage can include a bus lead and a ground lead connected in series with one another through the gas discharge tube. The gas discharge tube can have an inductor-side terminal and a ground-side terminal separated from one another by a spark gap. The spark gap can be a single spark gap. The inductor-side terminal of the gas discharge tube can connect directly to the inductor source-side terminal. The ground-side terminal of the gas discharge tube can connect directly to the ground terminal. 
     It is also contemplated that, in accordance with certain embodiments, a protected electrical device with a pin can be connected to the inductor device-side terminal. The first stage can be connected between the inductor device-side terminal and the pin of the protected electrical device. A power source lead can connect a power source to the inductor source-side terminal. The second stage of the transient voltage protection circuit can be connected between the inductor source-side terminal and the power source lead. 
     A lightening-protected electrical system includes a transient voltage protection circuit as described above. The first stage defines a single conductive path between the inductor device-side terminal and the ground terminal. The first stage protection element includes diode connected in series between a bus lead and a ground lead. The first stage bus lead connects to the inductor device-side terminal and the first stage ground lead connects to the ground terminal. The second stage protection element includes a gas discharge tube connected in series between a bus lead and a ground lead. The second stage bus lead connects to the inductor source-side terminal and the second stage ground lead connects to the ground terminal. 
     In certain embodiments, the system can include a protected electrical device with a pin. The pin can be connected to the inductor device-side terminal. The first stage bus lead can be connected between the inductor device-side terminal and the pin of the protected electrical device. A power source lead can connect a power source to the inductor source-side terminal. The second stage bus lead can be connected between the power source lead and the source-side terminal of the inductor. 
     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 protected electrical load connected to a transient voltage protection circuit; and 
         FIG. 2  is a schematic view of the electrical system of  FIG. 1 , showing an inductor of the transient voltage protection circuit connected to a ground terminal by parallel first and second stages of the transient voltage protection circuit. 
     
    
    
     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 protection circuit in accordance with the disclosure is shown in  FIG. 1  and is designated generally by reference character  100 . Other embodiments of transient voltage protection circuits and lightening protection systems employing such circuits in accordance with the disclosure, or aspects thereof, are provided in  FIG. 2 , as will be described. The systems and methods described herein can be used for protecting electronics on aircraft, though the present disclosure is not limited to aircraft electronics or to aircraft general. 
     Aircraft airframes have traditionally been partially constructed of aluminum, aluminum alloy, or other similar materials. This construction aids in lightning protection by distributing lightning energy through the body of the plane and by reducing magnetic field coupling to wires, thereby reducing the voltage level which would otherwise threaten the electronic devices onboard the plane. Recent innovations in airplane design however have led to increased use of composite materials owning to the strength and lightweight construction possible with composite materials. In part due to increased us of composite material construction, lightning strike requirements have changed to include require protection for higher transient voltages. 
     Referring to  FIG. 1 , an aircraft  10  is shown. Aircraft  10  includes a lightning-protected electrical system  12 . Electrical system  12  interconnects one or more protected electrical devices  14  with a power source  16 . Protection for the one or more electrical devices  14  is provided by transient voltage protection circuits  100  connected to respective electrical devices at low impedance interfaces of the one or more of the electrical devices  14 . 
     With reference to  FIG. 2 , electrical system  12  is shown. As will be appreciated by those of skill in the art in view of the present disclosure, electrical system  12  can be subject to electrical transients. Electrical transients can result from electromagnetic interference from devices like motors and generators. Electrical transients can also result from lightening, schematically indicated with reference numeral  22 . Since low impedance bus segment  18  will readily apply the transient voltage and transient current associated with lighting  22  to electrical device  14 , transient voltage protection circuit  100  is arranged at the interface of bus segment  18  and electrical device  14  to protect electrical device  14  form the energy associated with lightening  22 . In embodiments contemplated herein, it is contemplated that transient voltage protection circuit  100  provide protection to electrical device  14  for transients of, of about 3300 volts/3300 amps or greater. 
     Transient voltage protection circuit  100  includes a first stage  102  and a second stage  104 . First stage  102  and second stage  104  are connected electrically in parallel with one another between bus segment  18  of electrical system  12  and a ground terminal  20  of electrical system  12 . An inductor  106  is connected along bus segment  18  between first stage  102  and second stage  104  to bias, e.g., increase, voltage applied to second stage  104  in relation to voltage applied to first stage  102  upon application of a transient to bus segment  18 . 
     Inductor  106  includes a source-side terminal  128  and a device-side terminal  130 . A pin  24  connects electrical device  14  to device-side terminal  130 . First stage  102  is connected to between device-side terminal  130  and pin  24  of electrical device  14  at a terminal  114 . Between terminal  114  and ground terminal  20 , first stage  102  defines a single conductive path to ground terminal  20 , i.e., with no parallel electrical path(s) extending between first stage  102  and ground terminal  20 . 
     A source lead  26  connects a power source  16  to source-side terminal  128  of inductor  106 . Second stage  104  is connected to between source-side terminal  128  and a source lead  26  of power source  16 . Second stage  104  connects between source lead  26  and source-side terminal  128  at a terminal  124 . Between terminal  124  and ground terminal  20  second stage  104  defines a single conductive path to ground terminal  20 , i.e., with no parallel electrical path(s) extending from second stage  104  to ground terminal  20 . 
     First stage  102  includes a first stage protection element  108 . First stage protection element  108  is connected in series between a bus lead  110  and a ground lead  112  of first stage  102 . Bus lead  110  connects first stage protection element  108  to bus segment  18  at a terminal  114 . Ground lead  112  connects first stage protection element  108  with ground terminal  20 . First stage protection element  108  includes a diode  116 . 
     Diode  116  is a bidirectional transient voltage suppression (TVS) diode arranged to conduct current  30  between bus lead  110  and ground lead  112  upon application of a voltage potential above a breakdown voltage V D  of diode  116 . It is contemplated that diode  116  may be a transorb-type device. 
     Second stage  104  includes a second stage protection element  118 . Second stage protection element  118  is connected in series between a bus lead  120  and a ground lead  122 . Bus lead  120  connects second stage protection element  118  to bus segment  18  at a terminal  124 . Ground lead  122  connects second stage protection element  118  with ground terminal  20 . Second stage protection element  118  includes a gas discharge tube  126 . 
     Gas discharge tube  126  includes an inductor-side terminal  132  and a ground-side terminal  134 . Inductor-side terminal  132  is separated from ground-side terminal  134  by a spark gap  136 . In the illustrated exemplary embodiment spark gap  136  is a single spark gap, meaning that bus lead  120  defines an electrically continuous conductor extending between inductor-side terminal  132  and terminal  124  and ground lead  122  defines an electrically continuous conductor extending between ground-side terminal  134  and ground terminal  20 . In this respect inductor-side terminal  132  of gas discharge tube  126  connects directly a source-side terminal  128  of inductor  106 , and ground-side terminal  134  of gas discharge tube  126  connects directly to ground terminal  20 . Upon application of a voltage potential greater than a predetermined sparkover voltage across inductor-side terminal  132  and ground-side terminal  134 , gas discharge tube  126  conduct current  28  between bus lead  120  and ground lead  122   
     As will be appreciated by those of skill in the art in view of the present disclosure, diodes and gas discharge tubes generally begin conducting at different times upon application of a voltage above the breakdown voltage and spark over voltage of the respective element. In this respect the diode typically begins conducting prior to the gas discharge tube. This causes the diode to bear the full voltage stress of a voltage transient prior to the gas discharge tube sparking over and conducting. Below a certain transient threshold this typically is not of significant concern. However, high transients, e.g., at about 3300 volts/3300 amps or higher, the energy absorbed by the diode during the delay interval can potentially damage the diode. Accordingly, diodes of relatively large size can be required to accommodate such transients. 
     Upon application of a transient voltage, inductor  106  increases voltage applied to gas discharge tube  126  in relation to that applied to diode  116 . In this respect the voltage transient causes inductor  106  develop a magnetic field M which increase voltage applied at terminal  124  relative to that applied to  114 . The increased voltage applied at terminal  124  causes gas discharge tube  126  to sparkover more quickly, reducing the delay interval between diode  116  beginning to conduct and gas discharge tube  126  beginning to conduct. The reduced delay interval reduces the peak voltage stress exerted on diode  116  by the transient event, enabling reduction of the size of diode  116  for a given transient protection rating or increasing the transient voltage protection of transient voltage protection circuit  100 . Moreover, as gas discharge tube  126  is connected directly to ground terminal  20 , gas discharge tube  126  presents a relatively low impedance path to ground for the transient, thereby reducing the peak voltage (or current flow) associated with the transient. 
     The methods and systems of the present disclosure, as described above and shown in the drawings, provide for transient voltage protection circuits with superior properties including tolerance for electrical transients greater that those typically required for aircraft certification, e.g., about 3300 volts/3300 amps or greater. 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.