Semiconductor Output Switch Protection for Capacitive Load Inrush
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Solution Overview
Problem
Existing semiconductor devices using mechanical fuses for protection in vehicles face issues with inaccurate reaction times and the need for complete system replacement when fuses blow, while electronic fuses increase cost due to larger switch sizes for capacitive loads, and pre-charge circuits add complexity.
Innovation Solution
A semiconductor device with integrated overcurrent and overheat protection circuits that switch between normal and capacitive load driving modes, allowing safe operation of capacitive loads without increasing switch size or adding external components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical fuses are used for protection, then overcurrent protection is provided, but reaction time is inaccurate and complete system replacement is needed when fuses blow
Solution Approach 1:
The patent replaces mechanical fuses with an electronic protection system consisting of a controller and protection circuits. The controller detects abnormal conditions (overcurrent, overheat) through sensing circuits and automatically controls the switch element to open the circuit when thresholds are exceeded, eliminating the need for mechanical fuse replacement and providing precise, programmable reaction times.
2Loss of time
If electronic fuses are used to replace mechanical fuses, then reaction time precision is improved, but cost increases due to larger switch sizes for capacitive loads
Solution Approach 1:
The patent implements dynamic switching between two protection threshold values based on the load type. The controller detects whether the load is capacitive or resistive and automatically selects appropriate threshold values: a first threshold for capacitive loads (allowing higher current during startup) and a second threshold for resistive loads. This dynamic adaptation prevents oversized switch elements while maintaining protection precision.
Solution Approach 2:
The patent changes the protection threshold parameter dynamically based on load characteristics. By storing multiple threshold values in memory and selecting the appropriate one based on load type detection, the system optimizes the protection parameters to match actual operating conditions, avoiding the need for oversized switches designed for worst-case capacitive load scenarios.
3Reliability
If pre-charge circuits are added to handle capacitive loads, then safe operation is achieved, but device complexity increases
Solution Approach 1:
The patent integrates multiple functions into the existing controller and protection circuit: normal overcurrent protection, overheat protection, capacitive load detection, and adaptive threshold selection all operate within a single integrated control unit. The controller automatically detects load type and switches between different protection modes without requiring separate pre-charge circuits or additional external components, maintaining simplicity while achieving safe operation.
Data Source
AI summary
A semiconductor device includes an output switch, an overcurrent protection circuit which detects an output current flowing through the output switch to perform overcurrent protection, an overheat protection circuit which detects a temperature to be monitored to perform overheat protection and a mode control circuit which switches between setting of each of the overcurrent protection circuit and the overheat protection circuit to a normal mode and setting of each of them to a capacitive load driving mode. In in the capacitive load driving mode, the overcurrent protection circuit restricts the output current to an overcurrent protection threshold value or less. Each time the temperature to be monitored rises to a second overheat protection threshold value lower than a first overheat protection threshold value set in the normal mode, the overheat protection circuit repeats forced turning off and restarting of the output switch.