Overcurrent Protection Circuit With Thermal Duty Switching
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Solution Overview
Problem
Conventional overcurrent protection circuits in semiconductor integrated circuit devices, particularly in-vehicle IPDs, face challenges in ensuring safety during load short-circuits, as they continue to operate in high temperature ranges due to repeated temperature abnormality detection and release, which can lead to reliability issues and safety concerns.
Innovation Solution
An overcurrent protection circuit that includes a current control part to limit output current and a duty control part to forcibly turn on/off the transistor at a predetermined duty ratio when a temperature protection circuit detects an abnormality, switching from current control mode to duty control mode to enhance safety and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the conventional current control mode is used to limit output current, then instantaneous current can be secured for capacitive loads, but the device continues to operate in high temperature ranges during load short-circuit due to repeated temperature abnormality detection and release
Solution Approach 1:
The patent applies periodic action by implementing a duty control mode that forcibly turns the transistor on and off at a predetermined duty ratio (e.g., 10% or 20%) when temperature abnormality is detected. This periodic switching prevents continuous operation in high temperature ranges, allowing the device to cool down periodically while still providing some current output, thereby resolving the contradiction between maintaining reliability and controlling operating temperature.
Solution Approach 2:
The patent implements dynamics by dynamically switching between two protection modes: current control mode (for normal overcurrent protection) and duty control mode (for high temperature protection). The system transitions from static current limiting to dynamic periodic switching when temperature exceeds thresholds, enabling adaptive response to different operational conditions and resolving the temperature reliability contradiction.
2Object-affected harmful factors
If the self-resetting type thermal shutdown is used, then the power transistor is forcibly turned off when junction temperature exceeds abnormality detection value, but the device repeats detection and release cycles in the 150-175°C range during load short-circuit
Solution Approach 1:
The patent applies preliminary action by implementing preventive duty control before the temperature reaches the critical shutdown threshold. When temperature abnormality is detected, the system immediately switches to duty control mode with a predetermined duty ratio, proactively preventing prolonged high temperature operation rather than waiting for the temperature to exceed the shutdown threshold and then resetting. This preliminary intervention reduces the duration of high temperature exposure.
Solution Approach 2:
The patent maintains continuity of useful action by keeping the transistor periodically active at a predetermined duty ratio during duty control mode, rather than completely shutting it down. This continuous periodic operation allows the device to remain partially functional while preventing dangerous temperature accumulation, thus maintaining useful action while controlling harmful thermal effects over extended periods.
Data Source
AI summary
An overcurrent protection circuit includes a current control part configured to control conductance of a transistor so as to limit an output current flowing when the transistor is turned on to a predetermined upper limit or less, and a duty control part configured to forcibly turning on/off the transistor at a predetermined duty ratio when a temperature protection circuit detects a temperature abnormality in a state where the current control part limits the output current.