Patent Description:
Vehicles, such as aircraft, typically include miles of wires and dozens of computers and other instruments and systems that control everything from the engines to passenger headsets. One or more power management and distribution (PMD) systems are typically provided to distribute power from a primary source to various vehicle systems. PMD systems often include so-called smart power management and distribution functionality enabled by SSPCs. A typical PMD system may include hundreds or thousands of SSPCs.

Aircraft computers and electrical systems, including PMD systems and their SSPCs, must be able to safely withstand overvoltage conditions and other transients that can result from a lightning strike. Traditionally, aircraft had an aluminum skin that attenuated the lightning current induced on the wires. Some aircraft now use composite materials instead of aluminum for weight and strength benefits. However, composite materials do not provide the same level of attenuation to lightning as aluminum. When lightning occurs, hundreds of volts may surge between a load in the vehicle system and the aircraft chassis. As such, the lightning requirements of PMD systems and their SSPCs have increased.

SSPCs generally use microprocessors to manage the operation of high-efficiency switching MOSFETs, which perform on/off control of the load and protect loads from short circuit and overload conditions. When these MOSFETs are subjected to lightning-induced power surges and other transients that are higher than the MOSFET voltage ratings and they are OFF, the MOSFETs break down and conduct, which typically results in the MOSFET being damaged or destroyed.

It is known to use TVS diodes to protect the MOSFET switches of an SSPC from lightning-induced power surges and other transients. TVS diodes provide protection to MOSFETs by shunting excess current when the lightning-induced voltage exceeds the diode avalanche breakdown potential. TVS diodes are, in effect, clamping devices that suppress all voltages above their breakdown voltages, and they automatically reset when the overvoltage goes away. A TVS diode may be either unidirectional or bidirectional. A unidirectional TVS diode operates as a rectifier in the forward direction like any other avalanche diode but is made and tested to handle very large peak currents.

Known TVS diode-based protection schemes for SSPC MOSFET switches require an individual TVS diode for every SSPC output channel. As the complexity of SSPCs for aircraft applications increases, a single SSPC card can include <NUM> or more output channels, which, following known transient protection schemes, would require <NUM> individual TVS diodes per SSPC card. Additionally, although TVS diodes have sufficient functionality to provide the necessary transient protection, known TVS designs exhibit dormant failures. Existing SSPCs that utilize TVS diode-based protection transient protection schemes do not have a way of testing the full functionality of its protection circuitry without removing the module containing the protection circuitry from the aircraft itself. As a result, the functionality of the protection circuitry is determined during maintenance and assumed to be maintained until the next maintenance. Verification is then performed at the next maintenance when the module is removed from the aircraft. Hidden or dormant TVS diode failures are not immediately evident to operations and maintenance personnel as soon as they occur, so the detection of such dormant failures require a specific action (e.g., a periodic application of BIT circuitry) in order for the dormant failure to be identified. Providing the necessary BIT circuitry to test <NUM> or more TVS diodes per SSPC card for dormant failures is complicated and typically cost prohibited. A TVS protection scheme is described in <CIT>.

It is therefore desirable to provide a TVS diode-based protection schemes that facilitates the simple, efficient and cost effective protection of SSPC power channels and components from exposure to overvoltage conditions caused by lightning-induced pulses and other transient events, while also facilitating the efficient and cost effective incorporation of BIT circuitry for identifying dormant TVS diode failures.

Embodiments are directed to an SSPC as defined in claim <NUM>.

Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein. For a better understanding of the disclosure with the advantages and the features, refer to the description and to the drawings.

The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification.

In the accompanying figures and following detailed description of the disclosed embodiments, the various elements illustrated in the figures are provided with three or four digit reference numbers. The leftmost digit(s) of each reference number corresponds to the figure in which its element is first illustrated.

Turning now to an overview of the present disclosure, PMD systems generally include modules that each includes multiple SSPC power channels. Each power channel has an input feed line, an output load and a power MOSFET that selectively couples the feed voltage to the output load when turned on. When the power MOSFET switch of a given channel is subjected to a voltage transient (e.g., a lightning induced transient) that is higher than the MOSFET voltage rating limit and it is OFF, the MOSFET will break down and conduct and usually be damaged or destroyed. Existing transient protection/suppression systems, examples of which are shown in <FIG> and <FIG>, provide transient protection. However, as the number of channels provided on an SSPC card continues to increase (e.g., up to about <NUM> SSPC channels per SSPC card), the complexity, cost and card area required to implement existing transient protection schemes continue to increase as well.

In one or more embodiments of the present disclosure, instead of providing individual TVS diodes for each power channel, a shared transient voltage suppressor is provided in communication with a shared protection line coupled to each individual power channel. Transient energy above a threshold (e.g., above the MOSFET voltage rating limit) on any one of the multiple SSPC power channels is dissipated through the shared transient voltage suppressor. In one or more embodiments, the shared transient voltage suppressor includes a single TVS diode. In one or more embodiments, the shared transient voltage suppressor includes a plurality of simple diodes and a single TVS diode. In one or more embodiments, the shared transient voltage suppressor includes a TVS diode circuit having multiple TVS diodes, wherein the number of TVS diodes is less than the number of power channels. In any of the disclosed shared transient voltage suppressors, the reliance on TVS diodes, which provide the necessary voltage suppression functionality but exhibit dormant failures, is reduced by sharing either one or a few (i.e., less than the number of power channels) TVS diodes among a plurality of power channels.

Because the present disclosure significantly reduces the number of TVS diodes that are required to provide protection from lightning-induced and other transients, the present disclosure makes it efficient and cost effective to provide a BIT circuit to test the disclosed shared transient voltage suppressor for dormant failures. The BIT circuit applies a pulsed BIT signal to the shared transient voltage suppressor and measures the resulting voltage across the shared transient voltage suppressor. The BIT signal applied to the shared transient voltage suppressor is a voltage (positive or negative) to verify that the shared transient voltage suppressor is clamping at a proper value. Because of the significant reduction in the number of TVS diodes that are required to provide protection from lightning-induced and other transients, the added cost/area of providing a BIT circuit is relatively small. Additionally, for embodiments wherein the shared transient voltage suppressor is augmented by or supplemented with simple diodes (e.g., one simple diode per channel), the simple diodes prevent BIT circuit test pulses applied to the shared protection line from affecting the normal operating outputs of the channels.

Lightning-induced transients may occur as a positive or negative pulse on the feed line side of a channel or as a positive or negative pulse on the load side of a channel. Accordingly, a BIT circuit of the present disclosure may be provided on the feed line side of a channel or on the load side of a channel, or on both the feed side and load side of a channel. When provided on the load line side of a channel, the BIT circuit tests with a negative voltage on the load line side shared protection line. When provided on the feed line side of a channel, the BIT circuit tests with a positive voltage at the cathode of the shared transient voltage suppressor. Additionally, because the actual transients on the feed line or the load line can vary, the disclosed transient suppression schemes may or may not include the same voltage threshold for the TVS diodes on the feed side and the load side.

Turning now to a more detailed description of the drawings, <FIG> depicts a known TVS diode-based protection scheme, and <FIG> depicts a known non-TVS diode-based protection scheme. In either <FIG> or <FIG>, the protection scheme includes multiple power channels, only two of which are shown for ease of illustration. Each power channel is coupled to a FEED BUS LINE and a Load Line and includes a MOSFET switch, a MOSFET body diode, a LOAD, a ON/OFF MOSFET control line coupled at one end through a resistor to the MOSFET gate and coupled at its other end to a gate drive (not shown). Each channel further includes an output line (i.e., the Load Line) having thereon either a TVS diode (<FIG>) or a simple diode (<FIG>).

As shown in <FIG>, in the normal operation of the MOSFET switches, the FEED BUS LINE feeds power into Channel-A through the MOSFET switch and the Load Line into LOAD-A. A lightning-induced pulse or other transient on either the FEED BUS LINE or through the Load Line of Channel-A forces a positive or negative voltage on the FEED BUS LINE or a positive or negative voltage on the Load Line. In either case, large currents attempt to flow through the MOSFET switch. If for example a positive transient is on the Load Line of Channel-A in <FIG>, the transient will conduct through the MOSFET body diode until the TVS diode reaches its breakdown voltage at which point it conducts the excess to Chassis Ground (Chassisgnd), which in effect shunts the high levels of transient current away from the MOSFET. The TVS diode shunts transient current by providing a low resistance path for current to pass through the TVS diode. This also limits the voltage increase at the FEED BUS LINE for cases wherein the FEED BUS LINE has high source impedance.

The anode of the TVS diode shown in <FIG> is tied to Chassisgnd, and the cathode of the TVS diode is tied to the Load Line. Accordingly, the Load Line has to reach the breakdown voltage of the TVS diode in order for the TVS diode to conduct. Thus, from the Load Line side of the TVS diode, the voltage rating of the TVS diode for a typical aircraft application would be approximately 48V. For negative load transients, the TVS diode in <FIG> functions as a simple diode and the voltage drop across the TVS diode would be approximately <NUM> V.

A drawback to the approach in <FIG> is that because the negative transient is clamped to a small value such as 1V, inductive loads take much longer to de-energize when the SSPC MOSFET turns off. For relay or contactor coil loads, this longer time allows more contact arcing, which adversely impacts the relay or contactor reliability. For this reason the unidirectional TVS device configuration shown in <FIG> is not preferred. Accordingly, some applications chose to use bidirectional TVS devices sized at a voltage rating with margin below the rating of the MOSFET devices.

In <FIG>, the TVS diode is replaced with a Simple Diode. The Simple Diode blocks the transient current in one direction but does not provide that breakdown voltage protection that is provided by the TVS diode shown in <FIG>. Accordingly, the Simple Diode typically has a relatively large voltage rating. For example, in a typical aircraft application, the Simple Diode of <FIG> would be approximately 600V. Although simple, the drawback to the approach in <FIG> is that because the negative transient is clamped to a small value such as 1V, inductive loads take much longer to de-energize when the SSPC MOSFET turns off. For relay or contactor coil loads, this longer time allows more contact arcing, which adversely impacts the relay or contactor reliability. Accordingly, simple diodes on SSPC outputs as shown in <FIG> are not preferred.

Turning now to a more detailed description of the present disclosure, <FIG> depicts selected portions of a SSPC module <NUM> having a shared protection line <NUM>, a shared transient voltage suppressor <NUM> and a BIT circuit <NUM> according to one or more embodiments. In terms of its overall functionality, module <NUM> may be part of a PMD system utilized to control power management and distribution on a vehicle, such as an aircraft (not shown). Under some conditions, such as a lightning strike, a transient current may surge through the vehicle. The transient current may be, for example, an induced current, other known type of transient current, or a transient current from another source besides lightning. In the disclosed example, shared protection line <NUM>, shared transient voltage suppressor <NUM> and BIT circuit <NUM> of SSPC <NUM> provide lightning protection to reduce the risk that module <NUM>, and particularly the channel MOSFETS, becomes damaged from the transient current. As will be appreciated from the illustration and the following description, in accordance with one or more disclosed embodiments, shared protection line <NUM>, shared transient voltage suppressor <NUM> and BIT circuit <NUM> of module <NUM> facilitate the simple, efficient and cost effective protection of SSPC power channels and components thereof (e.g., the channel MOSFETs) from exposure to overvoltage conditions caused by lightning-induced pulses and other transient events that exceed a threshold (e.g., the voltage rating limit of the channel MOSFET), while also facilitating the efficient and cost effective incorporation of BIT circuit <NUM> for identifying dormant TVS diode failure points.

Module <NUM> couples multiple power channels to multiple loads. For ease of illustration, only two power channels, Channel-A and Channel-B, and two loads, Load-A and Load-B, are shown. In the present disclosure, a description of the operation of one channel applies equally to all channels. Channel-A transmits power down Feed Bus Line-A, through the channel-A MOSFET to Load-A. Lightning strikes can result in transients through Channel-A that exceed the operating range of the channel-A MOSFET.

Lightning-induced and other transients may occur as a positive or negative pulse on the feed line side of Channel-A, or as a positive or negative pulse on the load side of Channel-A. For the embodiment shown in <FIG>, shared protection line <NUM>, shared transient voltage suppressor <NUM> and BIT circuit <NUM> are provided on the load side of Channel-A. Additionally, a TVS diode <NUM>, a simple diode <NUM> and a BIT circuit <NUM> are also provided between the FEED BUS LINE and Chassisgnd. BIT circuit <NUM> tests with a negative voltage across shared transient voltage suppressor <NUM>. BIT circuit <NUM> tests with a positive voltage on TVS diode <NUM>.

Channel-A couples power on the FEED BUS LINE through a channel-A MOSFET having an intrinsic body diode <NUM> and an ON/OFF MOSFET control line coupled at one end through a resistor <NUM> to the channel-A MOSFET and coupled at its other end to a functional gate driver (not shown). From the channel-A MOSFET, power is coupled through the Load Line to LOAD-A. A simple diode <NUM> is coupled between the Load Line and shared protection line <NUM>, which is coupled to and shared by all channels of module <NUM>. Shared TVS diode <NUM> is coupled between shared protection line <NUM> and Chassisgnd. Shared TVS diode <NUM> increases the clamping voltage and addresses the reliability concern with simple diode clamping (provided by simple diode <NUM>) when interfacing to inductive loads such as relays and contactors. Through its coupling to shared protection line <NUM>, shared TVS diode <NUM> is coupled to and shared by all channels of module <NUM>.

As shown in <FIG>, shared protection line <NUM> sits between simple diode <NUM> and shared TVS diode <NUM>. Shared protection line 358A is a "protected line" in that it can never go more than the value of the voltage across shared TVS diode <NUM> below Chassisgnd. Because simple diode <NUM> is connected between shared protection line 358A and LOAD-A, when a negative transient is present on the Load Line and the channel-A MOSFET is off, simple diode <NUM> conducts and applies the negative transient voltage to shared protection line <NUM>. When shared protection line <NUM> reaches the breakdown voltage of shared TVS diode <NUM>, TVS diode <NUM> starts to conduct and carries current through shared TVS diode <NUM> over shared protection line <NUM> through simple diode <NUM> and out to LOAD-A, thereby clamping the negative overvoltage. Accordingly, for a negative lightning-induced transient pulse, the channel-A MOSFET stays off and all of the transient energy is dissipated by shared protection line <NUM>, simple diode <NUM> and shared TVS diode <NUM>.

When a positive transient is present on the Load Line and the channel-A MOSFET is off, the positive transient current goes through body diode <NUM> of the channel-A MOSFET and goes out through the FEED BUS LINE. Body diode <NUM> of the channel-A MOSFET is the intrinsic body diode of the channel-A MOSFET based on the structure of the channel-A MOSFET.

BIT circuit <NUM> is coupled through shared protection line <NUM> to shared TVS diode <NUM>. To ensure that shared TVS diode <NUM> does not have a dormant "stuck at" fault, BIT circuit <NUM> stimulates shared TVS diode <NUM> to a known value momentarily, and then monitors shared TVS diode <NUM> for the correct response to the stimulus.

<FIG> also depicts feed-side TVS diode <NUM> in series with simple diode <NUM> between the FEED BUS LINE and Chassisgnd. Positive transients on the FEED BUS LINE are shunted through simple diode <NUM> and TVS diode <NUM>. When a negative transient is present on the FEED BUS LINE, the negative transient current goes through the channel-A MOSFET body diode <NUM> and out through the Load Line.

BIT circuit <NUM> is coupled between simple diode <NUM> and TVS diode <NUM>. To ensure that TVS diode <NUM> does not have a dormant "stuck at" fault, BIT circuit <NUM> stimulates TVS diode <NUM> to a known value momentarily, and then monitors TVS diode <NUM> for the correct response to the stimulus.

While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the scope of the invention as defined by the claims.

Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments. Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claim 1:
A DC solid state power controller, SSPC, comprising a plurality of power channels, each power channel comprising a MOSFET and a MOSFET body diode (<NUM>), the SSPC having a transient protection circuit, the transient protection circuit comprising:
a shared transient voltage suppressor (<NUM>) communicatively coupled to ground; and
a shared protection line (<NUM>) communicatively coupled to the shared transient voltage suppressor; characterized in that:
the shared protection line is configured to be communicatively coupled to and shared by the plurality of power channels;
wherein the plurality of power channels are configured to be communicatively coupled to a shared feed line (FEED BUS LINE);
wherein each of the plurality of power channels is configured to be communicatively coupled to a non-shared load line;
wherein, when the shared protection line is communicatively coupled to and shared by the plurality of power channels, positive pulses above a threshold originated from the non-shared load line of any one of the plurality of power channels are dissipated through the any one of the plurality of power channels to the shared feed line;
wherein, when the shared protection line is communicatively coupled to and shared by the plurality of power channels, negative pulses above a threshold originated from the non-shared load line of any one of the plurality of power channels are dissipated through the shared protection line and the shared transient voltage suppressor.