Switch Current Limiting for Short-Circuit Safety and Startup Stability
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Solution Overview
Problem
Conventional switch devices face challenges in reducing power consumption and ensuring functional safety, especially during output short circuits, while maintaining stable startup performance.
Innovation Solution
A switch device incorporating a switching element and an overcurrent protection circuit that adjusts the overcurrent limit value based on the power supply voltage, along with an intermittent control unit and output voltage monitoring to ensure safe and stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the overcurrent limit value is kept constant to ensure functional safety during output short circuit, then reliability is improved, but power consumption increases
Solution Approach 1:
The overcurrent limit value is made dynamically adjustable based on the output voltage status. During startup when output voltage is below a predetermined threshold, a first overcurrent limit value is applied. When output voltage reaches the threshold indicating stable operation, a second overcurrent limit value (different from the first) is applied. This dynamic adjustment resolves the contradiction by adapting the current limit to the operational phase, ensuring safety during startup while optimizing power consumption during stable operation.
Solution Approach 2:
The patent changes the overcurrent limit parameter based on the output voltage parameter. By monitoring output voltage and comparing it against a predetermined threshold, the system transitions between different overcurrent limit values. This parameter change strategy allows the system to maintain appropriate current protection levels while reducing unnecessary power consumption during stable operation phases.
2Use of energy by moving object
If the overcurrent limit value is reduced to decrease power consumption during output short circuit, then power consumption is improved, but reliability deteriorates
Solution Approach 1:
The system dynamically selects appropriate overcurrent limit values based on operational phase. During startup phase with low output voltage, a higher first overcurrent limit value ensures reliable protection. When output voltage reaches the predetermined threshold indicating stable operation, the system switches to a second overcurrent limit value that optimizes power consumption. This dynamic behavior prevents reliability deterioration by ensuring adequate current limits are maintained when needed.
Solution Approach 2:
The system performs preliminary current limiting during the startup phase before the output voltage reaches the predetermined threshold. This preliminary protection action ensures that functional safety requirements are met during the critical startup period when the load may be most vulnerable to overcurrent damage. After startup completion, the system adjusts the limit to reduce power consumption.
3Reliability
If intermittent control is activated immediately upon detecting abnormality, then reliability is improved, but startup stability deteriorates
Solution Approach 1:
The intermittent control function is dynamically enabled or disabled based on the output voltage status. When output voltage is below the predetermined threshold, intermittent control remains disabled to ensure stable startup. When output voltage reaches the threshold, intermittent control becomes enabled to provide protective functionality. This dynamic control strategy resolves the contradiction by activating reliability measures only when the system has reached stable operation.
Solution Approach 2:
The output voltage monitoring function serves as an intermediary that determines when to activate intermittent control. By using output voltage level as the triggering condition, the system indirectly controls the activation of protective measures. This intermediary mechanism ensures that startup stability is maintained while still enabling functional safety features when appropriate.
Data Source
AI summary
An example switch device includes a switching element to connect/disconnect a current path from a power supply terminal to a ground terminal via a load, and an overcurrent protection circuit to limit 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. The overcurrent protection circuit includes a reference current generation portion that includes: a differential amplifier portion, an upper side current generation portion arranged to generate a predetermined an upper side current, a lower side current generation portion arranged to generate a lower side current, and a difference current generation portion arranged to output a difference current based on the lower side current and the upper side current, as the reference current.