Transient voltage suppression protection circuit including built in testing

A lightning protection circuit includes a first lightning protection branch including at least one transient voltage suppression (TVS) protection element, and a testing element integral to the lightning protection circuit. The testing element is operable to test a functionality of the lightning protection circuit while he lightning protection circuit is installed in an electronic control system. A controller is connected to the testing element, such that the controller receives sensed signals from the testing element.

TECHNICAL FIELD

The present disclosure relates generally to lightning protection circuits for aircraft, and more specifically to a lightning protection circuit including a transient voltage suppression element and a built in testing functionality.

BACKGROUND OF THE INVENTION

Modern aircraft typically utilize multiple on-board electrical systems and controls during flight to ensure proper operation of the aircraft. One environmental risk aircraft are exposed to during flight is the potential of a lightning strike hitting the aircraft. When lightning strikes an aircraft, a surge of electricity passes through the aircraft and any unprotected electrical systems onboard the aircraft. The surge can overload unprotected electrical systems and damage or destroy the unprotected electrical system. This surge of electricity is referred to as a lightning transient surge. In order to protect against these lightning transient surges, aircraft include lightning protection circuits connected to one or more on board electrical systems. The lightning protection circuits shunt the lightning transient surge away from the protected electrical system, and to a neutral power line.

Some existing lightning protection circuits utilize a transient voltage suppression device as a clamping portion of the transient surge protection. Existing circuits utilizing this type of configuration do not have a way of testing the full functionality of a lightning protection circuit without removing the module containing the lightning protection circuit from the aircraft itself. As a result, the functionality of the lightning protection circuits is determined during maintenance and assumed to be maintained until the next maintenance. Verification of the functionality is then performed at the next maintenance when the module is removed from the aircraft.

SUMMARY OF THE INVENTION

Disclosed is a lightning protection circuit comprising: a first lightning protection branch including at least one transient voltage suppression (TVS) protection element, and a testing element integral to the lightning protection circuit, wherein the testing element is operable to test a functionality of the lightning protection circuit while the lightning protection circuit is installed in an electronic control system, and a controller connected to the testing element, such that the controller receives sensed signals from the testing element.

Also disclosed is a method for testing transient voltage suppression based lightning protection circuits without disconnecting the TVS circuit including the steps of: inverting a transient voltage suppression bias supply voltage and measuring an input to the lightning protection circuit and a transient voltage suppression wrap around voltage of the lightning protection circuit, analyzing the measured input to the lightning protection circuit and the measured transient voltage suppression wraparound voltage of the lightning protection circuit using a controller, and determining a functionality of a transient voltage suppression element in the lightning protection circuit and a functionality of a steering element in the lightning protection circuit.

Also disclosed is an aircraft power system including a power distribution system, at least one electrical system connected to, and receiving power from, the power distribution system, at least one lightning protection circuit connected to the power distribution in parallel with the electrical system, wherein the lightning protection circuit includes at least a first lightning protection branch including at least one transient voltage suppression (TVS) protection element and a testing element integral to the lightning protection circuit, wherein the testing element is operable to test a functionality of the first lightning protection branch while the lightning protection circuit is installed in the aircraft power system, and a controller connected to the testing element, such that the controller receives sensed signals from the testing element.

DETAILED DESCRIPTION OF AN EMBODIMENT

FIG. 1schematically illustrates an aircraft10including an on-board electronic control system20. The electronic control system20is representative of multiple different types of aircraft electronic control systems20that draw power from an aircraft power distribution system22. Connected at the signal input and output pins of the electronic control systems20is a lightning protection device30. The lightning protection device30shunts lightning transient voltage surges resulting from lightning strikes50to a neutral40, thereby protecting the electronic control system20.

The lightning protection device30includes a circuit having a transient voltage suppression (TVS) element32. The transient voltage suppression element32is an electronic component that operates by shunting excess current when the induced voltage of a transient surge (such as from the lightning transient surge) exceeds an avalanche breakdown potential of the transient voltage suppression element32. While illustrated in the example ofFIG. 1as a single element, it is understood that the transient voltage suppression element32can incorporate a single transient voltage suppression diode, multiple transient voltage suppression components in an array, or multiple transient voltage suppression components located in multiple protection circuit branches.

FIG. 2illustrates an example lightning protection circuit100in greater detail. The lightning protection circuit100includes two branches, a positive branch110for shunting positive transients, and a negative branch120for shunting negative transients. Each branch110,120is connected to an input of the protected component (the electronic control system20, illustrated inFIG. 1) at node150via an input line130. Also connected to the input line130is an external sensor140that detects a voltage, relative to neutral, at a connection point150. In some example embodiments, the external sensor140is a resistor divider sensor. Alternately, the external sensor140can be any type of sensor that detects the voltage, relative to neutral, of the input line130.

Each branch110,120of the lightning protection circuit100is connected to the input line130via a steering diode112,122. The steering diode112,122ensures that the branch110,120only admits the corresponding transient type. In addition, the steering diodes112,122and bias resistors119,129effectively minimize any effects from TVS leakage currents and TVS capacitance. By way of example, the steering diode112of the positive branch110is connected to the input line130via the anode of the steering diode112. Conversely, the steering diode122of the negative branch120is connected to the input line130via the cathode of the steering diode122. As a result of the inverted connections of the steering diodes112,122, positive transient surges from a lightning strike are blocked from entering the negative branch120, and negative transient surges from lightning strikes are blocked from entering the positive branch110.

Each steering diode112,122is connected to a transient voltage suppression diode114,124that provides a voltage clamping affect, allowing the lightning transient voltage surge to be shunted to a neutral. Also connected at the node connecting the steering diode112,122to the transient voltage suppression diode114,124is a switchable bias voltage source118,128. A positive switchable bias voltage source118ordinarily provides a positive bias voltage to the transient voltage suppression diode114through a bias resistor119in the positive branch110. Similarly, a negative switchable bias voltage source128ordinarily provides a negative bias voltage to the transient voltage suppression diode124, through a bias resistor129, in the negative branch120. Each of the switchable bias voltage sources118,128provides the necessary bias voltage to the corresponding transient voltage suppression diode114,124to place the corresponding transient voltage suppression diode114,124in an avalanche mode.

The switchable bias voltage sources118,128include control connections117,127that allow a controller160to alter the bias voltage generated by the switchable bias voltage sources118,128during a test of the functionality of the lightning protection circuit100. In one example, the output voltage of the switchable bias voltage sources118,128are inverted. In alternate systems, the output voltage of the switchable bias voltage sources118,128are shifted to a voltage level that ensures that the steering diodes112,122conduct and pulls the signal on the input line130out of range.

Thus, during a lightning protection circuit100functionality test, the switchable bias voltage source118of the first example is switched from providing a positive bias voltage to a negative bias voltage for the duration of the test. Similarly, in the first example, the negative bias voltage source128switches from a negative bias voltage to a positive bias voltage for the duration of the test. The controller160can be any external controller, such as a controller for the protected electronic control system20, or a dedicated lightning protection controller160.

Also connected to the node connecting each of the transient voltage suppression diodes114,124to the corresponding steering diode112,122is a voltage sensor116,126. The voltage sensor116,126senses the voltage at the input of the transient voltage suppression diode114,124and provides the sensed voltage to the controller160. The sensed voltage is referred to herein as a “transient voltage suppression wraparound voltage.” The controller160uses the transient voltage suppression wraparound voltage and the voltage sensed by the external sensor140to determine the functionality of both the steering diodes112,122and the transient voltage suppression diodes114,124using the process described below with regards toFIG. 4.

In some example aircraft10, multiple lightning protection circuits30are utilized to protect multiple different electronic control system20, with each lightning protection circuit30requiring the same bias voltage.FIG. 3schematically illustrates one such arrangement including three lightning transient protection circuits200. Each of the lightning transient protection circuits200includes a positive branch210and a negative branch220, as in the example circuit ofFIG. 2.

Each of the positive branches210is connected to a single positive switchable bias voltage source218. Similarly, each of the negative branches220is connected to a single negative switchable bias voltage source224. In such a configuration, all of the lightning protection circuits200sharing bias voltage sources218,224undergo functionality testing at the same time. It is further understood that additional lightning protection circuits200beyond three can similarly be connected to the bias voltage sources218,224and retain functionality.

With reference toFIG. 2, the transient voltage suppression diodes114,124are ordinarily biased on and the controller160can test the functionality of the transient voltage suppression diodes114,124as well as testing the connection between the bias resistor119,129and the bias voltage source118,128using conventional means without removing the lightning protection circuit100. The conventional testing means do not, however, include a way of verifying the functionality of the steering diode112,122.

FIG. 4illustrates a flow chart demonstrating a method by which the lightning protection circuit100ofFIG. 2verifies the functionality of the transient voltage protection diodes114,124, the steering diode112,122, and the bias resistors119,129, thereby testing the full functionality of the lightning protection circuit100without removing the lightning protection circuit100from the aircraft10.

Initially, the controller160verifies the functionality of the transient voltage suppression diodes114,124and the bias resistors119,129using conventional functionality testing means in a “Verify TVS Element Functionality” step310and a “Verify Bias Resistor Functionality” step320. Once the controller160has verified the functionality of the transient voltage suppression diodes114,124and the bias resistors119,129, the controller160switches the switchable bias voltage supplies in a “Switch Bias Voltage” step330. The bias voltage switching is accomplished in one example by sending an active command from the controller160to the switchable bias voltage supply118,128, thereby inverting the bias voltage provided by the switchable bias voltage supply118,128. In an alternate example, each branch110,120of the lightning protection circuit100is physically connected to a different bias voltage supply, providing the inverted bias voltage, in response to the active command.

Once switched, the controller160monitors the input voltage of the lightning protection circuit100using the external sensor140and the wraparound voltage using the internal voltage sensor116,126in a “Monitor Input Voltage and Wraparound Voltage During Test” step340. In a fully functioning lightning protection circuit100, as long as the input voltage remains at a voltage such that the steering diodes112,122will conduct, the steering diode112,122conducts and the transient voltage suppression wraparound voltage measured by the voltage sensors116,126will be low. By way of example, if the transient voltage suppression element32has a clamp value of −6.4V (negative 6.4 volts), then the transient voltage suppression wraparound voltage will be −6.4V (negative 6.4 volts) during the test as long as the steering diode112,122is functional.

Once the testing of the functionality of the steering diode112,122is completed, the controller160evaluates the monitored voltages and verifies the functionality of the steering diodes112,122in a “Evaluate Monitored Voltages and Verify Steering Diode Functionality” step350, and ends the test in an “End Test” step360. If the controller160detects that any of the transient voltage suppression diodes114,124, the steering diodes112,122, or the bias resistors119,129are not functioning during the test, the controller160can diagnose the cause of the failure based on multiple potential outputs determined during design of the particular lightning protection circuit100.

When the controller160detects a failure during the functionality test illustrated inFIG. 4, and described above, there are multiple possible causes for the failure. By analyzing the sensor readings of the external sensor140and the wraparound voltage sensor116,126over the course of the test, the controller160can narrow the particular failure to a limited number of failure modes.

By way of example, if the input voltage, measured by the external sensor140, and the negative branch120of the lightning protection circuit100stay always positive during the “Verify TVS Element Functionality” step310and the “Verify Bias Resistor Functionality” step320, then the negative bias voltage128source has failed in a low voltage position. Similarly, if the TVS element of the negative branch120does not go positive during the “Monitor Input Voltage and Wraparound Voltage During Test” step340, then the negative bias voltage source128has either failed open, includes a short circuit, or failed in a high voltage position.

If the wraparound voltage of a given branch110,120is always the same as the output of the corresponding bias voltage source118,128, then the corresponding bias resistor119,129is short circuited. If the input voltage and the wraparound voltage measurements do not go positive in the positive branch110then the bias resistor119has failed open. Similarly, if the input voltage and the wraparound voltage measurements do not go negative in the negative branch120then the bias resistor129has failed open.

The preceding are non-limiting examples of various determinations that can be made by the controller160based on the measurements of the external sensor140and the wraparound voltage sensor116,126for the specific example lightning protection circuit100illustrated inFIG. 2, it is understood that similar detection capabilities exist for similar lightning protection circuits100. The particular conditions for a given failure mode are determined in a lab environment and programmed into a look up table contained within a memory on the controller160. In this way the controller160can determine a particular failure mode, based on the specific sensor140,116,126readings, or narrow the possible failure modes, and provide the determined information to a maintenance personnel when a failure is detected.

In one example, the preceding method is performed during initialization of the aircraft10(illustrated inFIG. 1), and takes minimal time. As such, a lightning protection circuit100according to the instant description can be tested and validated prior to each flight without requiring the lightning protection module to be removed from the aircraft.

While the above disclosure is described with regards to inverting the output voltage of the switchable bias voltage sources118,128, a similar process can be utilized by shifting the output voltage of the switchable bias voltage sources118,128to any voltage level that ensures that the steering diodes112,122conduct and pulls the signal on the input line130out of range when read by the external sensor140, and a true inversion of the output voltage of the bias voltage source118,128is not necessary.