Bidirectional Load Switch Ground Fault Isolation
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Solution Overview
Problem
In automotive systems, ground faults in dual main ground paths can cause undesirable current flow through electronic control units (ECUs), potentially leading to damage and fire hazards due to design and manufacturing constraints on wire harnesses and ECUs, which have limited current ratings.
Innovation Solution
The implementation of bidirectional load switch circuits and current sensing circuitry in ECUs to disconnect the internal ground from faulty ground paths, preventing undesirable current flow and providing reverse battery protection, thereby isolating the ECU from batteries and external loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dual main ground paths are used to provide redundancy, then reliability is improved, but the risk of ground faults causing undesirable current flow increases
Solution Approach 1:
The ground path is segmented into multiple independent paths (first main ground path and second main ground path) that can be individually disconnected. Each path has its own load switch (first bidirectional load switch and second bidirectional load switch) that can isolate faulty segments while maintaining connectivity through healthy segments, thus providing redundancy while managing ground fault risks.
Solution Approach 2:
Bidirectional load switches are introduced as intermediary devices between the ECU and the ground paths. These switches act as controllable intermediaries that can detect ground faults and automatically disconnect the faulty path, preventing harmful current flow while maintaining the redundant ground path configuration.
2Ease of manufacture
If wire harnesses and ECUs are designed with standard current ratings, then ease of manufacture is improved, but they become vulnerable to damage from ground fault currents
Solution Approach 1:
The system performs preliminary detection of ground faults through current sensing circuitry before damaging currents can flow through the ECU. The bidirectional load switches are pre-configured to automatically disconnect upon detecting ground fault conditions, preventing damage to the wire harnesses and ECU while allowing them to be manufactured with standard current ratings.
Solution Approach 2:
The bidirectional load switches and current sensing circuitry provide beforehand protection by detecting and isolating ground faults before they can cause damage. This cushioning effect protects the standard-rated wire harnesses and ECUs from exceeding their current ratings, maintaining ease of manufacture while improving reliability.
3Reliability
If bidirectional load switch circuits and current sensing circuitry are added, then protection against ground faults is improved, but device complexity increases
Solution Approach 1:
The bidirectional load switches serve multiple functions: they enable normal ground current flow, detect ground faults through integrated sensing, and automatically disconnect faulty paths. This multi-functionality reduces the need for separate protection circuits, thereby limiting the increase in device complexity while providing comprehensive ground fault protection.
Solution Approach 2:
The current sensing circuitry is merged with the bidirectional load switch circuits, combining ground fault detection and isolation functions into integrated units. This merging approach provides robust ground fault protection while minimizing the increase in overall device complexity by consolidating multiple functions into unified circuit blocks.
Data Source
AI summary
In some examples, an ECU includes a microcontroller, a first load switch, a first amplifier, a first control circuit, and an internal ground connected to an external ground. The first load switch is operable to connect and disconnect the ECU from a first ground path to the external ground. The first amplifier is operable to sense a current flow relative to the first ground path. The first control circuit is operable to receive an output from the first amplifier and to control the first load switch. When the ECU is non-operational and the microcontroller is in an OFF state, the first amplifier is operable to sense current indicative of a ground fault occurring relative to the first ground path. In response, the first amplifier outputs a signal which causes the first load switch to disconnect the internal ground from the first ground path.