MOSFET Over-Power Protection With Dynamic Current Limiting
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Solution Overview
Problem
Conventional over-current protection circuits fail to adequately protect power MOSFETs from over-power conditions, leading to performance degradation and potential damage due to increased power consumption during over-current events, especially in high voltage applications.
Innovation Solution
An over-power protection circuit that continuously monitors the voltage across a power device and dynamically determines a maximum current limit based on a pre-defined power limit threshold, ensuring that the power consumption remains within safe limits by adjusting the current limit in response to varying voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pre-set current limit is used in over-current protection circuit, then the current through the device is limited to a safe value, but the power consumption of the power device can exceed the power limit especially in high voltage applications
Solution Approach 1:
The patent implements dynamic current limit adjustment based on real-time voltage monitoring. The current limit setting circuit continuously monitors the voltage across the power device and dynamically adjusts the current limit accordingly. When voltage increases, the current limit decreases proportionally to maintain power within safe limits, and vice versa. This dynamic adaptation resolves the contradiction by making the protection mechanism responsive to actual operating conditions rather than using a fixed current limit.
Solution Approach 2:
The patent employs a feedback mechanism where the voltage across the power device is continuously monitored and fed back to the current limit setting circuit. This feedback loop enables the system to automatically adjust the current limit based on the actual voltage level, ensuring that the product of current and voltage (power) remains within safe operating limits. The feedback mechanism resolves the contradiction by creating a closed-loop control system that adapts to changing conditions.
2Reliability
If the on-resistance of the power MOSFET is increased to limit current during over-current event, then the current is reduced, but the voltage across the power MOSFET increases leading to higher power consumption
Solution Approach 1:
The patent applies preliminary action by proactively adjusting the current limit before the power device operates in an unsafe condition. The current limit setting circuit continuously monitors voltage and preemptively reduces the current limit when voltage increases, preventing the power MOSFET from entering an over-power state. This proactive approach resolves the contradiction by addressing the power issue before it becomes a harmful over-power condition, rather than reacting after the fact.
3Ease of manufacture
If a constant current limit is used for all operating conditions, then the device is protected under normal voltages, but the device may still operate beyond specified conditions in high voltage scenarios
Solution Approach 1:
The patent implements parameter changes by making the current limit a variable parameter that changes with voltage conditions. Instead of using a constant current limit, the system dynamically adjusts the current limit parameter based on the monitored voltage across the power device. This resolves the contradiction by transforming the protection mechanism from a static design to an adaptive one that maintains effectiveness across varying operating conditions while remaining relatively simple in implementation.
Data Source
AI summary
An over-power protection circuit for a MOSFET includes an over-current protection circuit and a current limit setting circuit, and an over-power protection circuit configured to continuously monitor a voltage across the MOSFET being protected to prevent over-power conditions, and to dynamically determine a maximum current limit based on the monitored voltage and a pre-set maximum power limit.