Power Switch Current Limiting for Short-Circuit Safety
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Solution Overview
Problem
Conventional switch devices face challenges in reducing power consumption and ensuring functional safety, particularly during output short circuits, and in achieving stable startup and compatibility with safety standards like ISO26262 for in-vehicle ICs.
Innovation Solution
A switch device with a switching element, an overcurrent protection circuit that adjusts the overcurrent limit value based on power supply voltage, and an intermittent control unit that disables until the output voltage reaches a target value, ensuring safe and efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional switch device is used, then the device can operate as a basic on/off switch, but power consumption increases and functional safety cannot be ensured during output short circuits
Solution Approach 1:
The overcurrent limit value is made dynamic rather than fixed. The control circuit adjusts the overcurrent limit value based on detected abnormality information (such as output short circuit conditions), allowing the device to adapt its protection characteristics to different fault scenarios, thereby ensuring functional safety while optimizing power consumption during abnormal operations
Solution Approach 2:
The patent changes the parameter of overcurrent limit value based on power supply voltage and abnormality detection. By adjusting this parameter dynamically according to operating conditions and detected faults, the device achieves both functional safety compliance and reduced power consumption during short circuit events
2Use of energy by moving object
If the overcurrent limit value is decreased to reduce power consumption during short circuits, then power consumption is reduced, but the device may not provide sufficient protection at higher power supply voltages
Solution Approach 1:
The overcurrent limit value is dynamically adjusted based on the detected power supply voltage level. When the power supply voltage is higher, the control circuit sets a lower overcurrent limit value to reduce power consumption during short circuits. This dynamic adjustment ensures that protection effectiveness is maintained across different voltage conditions while optimizing power consumption
Solution Approach 2:
The control circuit implements feedback by detecting the power supply voltage level and using this information to adjust the overcurrent limit value accordingly. This closed-loop control ensures that the protection characteristics are optimized for the current operating voltage, maintaining both safety and power efficiency
3Reliability
If intermittent control is enabled immediately upon abnormality detection, then functional safety is improved, but stable startup is compromised due to premature disabling
Solution Approach 1:
The control circuit performs preliminary action by detecting whether the device is in a startup state before enabling intermittent control. This preliminary detection prevents premature disabling during normal startup sequences, ensuring stable startup while still enabling functional safety protection once the device is fully operational
Solution Approach 2:
The intermittent control function is dynamically enabled or disabled based on the detected operational state. The control circuit determines whether to apply intermittent control by analyzing startup conditions, allowing the device to maintain stable startup behavior while transitioning to safety-oriented intermittent control during normal operation
Data Source
AI summary
A switch device includes a switching element that connects/disconnects a current path from a power supply terminal to a ground terminal via a load, and an overcurrent protection circuit that limits output current flowing in the switching element to be an overcurrent limit value or less. When an output short circuit of the load is detected, the overcurrent protection circuit decreases the overcurrent limit value to be lower as a power supply voltage is higher. In addition, the switch device preferably includes a switching element that connects/disconnects a current path from a power supply terminal to a ground terminal via a load, an intermittent control unit that intermittently drives the switching element when an abnormality is detected, and an output voltage monitoring portion that disables the intermittent control unit until an output voltage applied to the load reaches its target value.