Solid-State Switch Integrity Testing for Fail-Open and Fail-Closed Faults
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Solution Overview
Problem
Existing fault detection methods for power control devices in aircraft applications are inadequate as they either require destructive elements like fuses or fail to detect abnormal open or closed states in power switches, leading to potential hazardous conditions.
Innovation Solution
A method and apparatus that use a controller to test the integrity of power switches by directing the switches to open and close sequences, sensing power presence, and indicating faults without requiring destructive elements, allowing for switch integrity testing before and during operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a second solid state power switch device is used to turn off the current when a primary solid state power switch fails, then the current can be interrupted, but the system cannot detect if one of the switches has failed closed
Solution Approach 1:
The patent implements preliminary testing of the power switch by applying a test voltage through a test current source before normal operation. The test detects whether the switch is properly open or closed by measuring voltage across the switch terminals, preventing undetected failed states from compromising system reliability.
Solution Approach 2:
The patent introduces a test current source and voltage sensing circuitry as intermediary elements to detect switch integrity. These intermediaries enable fault detection without requiring complex switching arrangements or additional power switches, resolving the contradiction between detection capability and circuit complexity.
2Reliability
If a mechanical fuse or circuit breaker is added in series with the solid state power switch device, then shorted load conditions can be detected, but the technique fails to detect a shorted solid state power switch where the power switch is shorted but the load is not
Solution Approach 1:
The patent performs preliminary integrity testing of the power switch itself before normal operation occurs. By applying a test voltage and measuring the resulting current or voltage across the switch, the system can detect whether the switch is shorted regardless of the load state, eliminating the need for series fuses or circuit breakers.
Solution Approach 2:
The power switch is tested using its own terminals and the existing circuit topology. The test current source applies a test voltage through the switch and measures the response, allowing the switch to be self-diagnosed without requiring external protective devices or complex series configurations.
3Reliability
If a thermal fuse is placed in close proximity to a power control device, then the circuit opens when the power switch overheats or exceeds temperature rating, but the technique requires the power control device to exceed the fuse's temperature or current rating
Solution Approach 1:
The patent performs preliminary testing of the power switch integrity before normal operation. By detecting open or closed failures in the switch through voltage measurements during a test phase, the system prevents hazardous conditions from developing, eliminating the need for thermal fuses that require dangerous temperature excursions.
Solution Approach 2:
The patent replaces the mechanical thermal fuse system with an electronic testing and detection system. Instead of relying on thermal expansion or melting to open a circuit, the system uses electronic voltage sensing and control logic to detect switch failures and prevent hazardous operation, avoiding excessive temperature exposure entirely.
4Reliability
If the output current is compared with the switch control voltage to detect faults, then thermal fuse can be heated to open the circuit, but the technique must be carefully adapted for different size loads and does not provide user-resettable capabilities
Solution Approach 1:
The patent implements preliminary testing of the power switch by applying a standardized test voltage through a test current source and measuring the voltage across the switch terminals. This preliminary test detects open or closed failures regardless of load size, providing universal applicability without requiring adaptation for different load configurations.
Solution Approach 2:
The patent changes the testing approach from comparing output current with control voltage to applying a standardized test voltage and measuring the resulting current or voltage across the switch. This parameter change enables universal testing across different load sizes and provides clear fault detection with user-resettable capabilities through electronic control.
Data Source
AI summary
A switching and fault detection circuit comprises two controllable switches capable of coupling a power source to a load. A controller can control the switches and test them for faults, and a voltage sensor can read the output voltage going to the load. Dual-redundant switches and fault detection circuitry can provide correct operation if one should fail. Control and feedback logic can determine if each of the solid-state switches is operating correctly during the power-on and power-off cycles and can also check for a fail-open condition during normal operations. If it is determined that a solid switch has failed open or closed, a fault can be generated.