Adaptive In-Rush Current Control for MOSFET Peak Temperature
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Solution Overview
Problem
Conventional hot swap systems fail to optimally control in-rush currents through power MOSFETs during voltage step conditions, leading to potential overheating and extended charging times, as the current limit is not adapted for start-up or voltage step conditions.
Innovation Solution
The system adaptively controls the in-rush current through the MOSFET to be twice the capacitor charging current, ensuring the MOSFET operates within a specified peak temperature by using a feedback circuit with a ramp capacitor to track the charging current and set the optimal pass current through the MOSFET.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the in-rush current is limited to a predetermined value above worst case acceptable load condition, then the system is protected from over-currents, but the charging time becomes unduly long and the MOSFET overheats due to extended power dissipation time
Solution Approach 1:
The patent applies dynamics by transitioning from a static current limit to a dynamic adaptive current limit that changes over time. The controller adjusts the current limit based on real-time monitoring of MOSFET temperature and capacitor charging state, allowing the system to optimize between protection and charging speed at different stages of the in-rush current event.
Solution Approach 2:
The patent implements feedback by continuously monitoring MOSFET temperature through a temperature sensor and using this information to adjust the current limit. The controller receives temperature feedback and dynamically modifies the current limiting behavior to prevent overheating while minimizing charging time, creating a closed-loop control system.
2Temperature
If the in-rush current is made too low to prevent MOSFET overheating, then the MOSFET temperature is controlled, but the load takes a long time to be fully powered up
Solution Approach 1:
The patent uses dynamics to adjust the current limit in real-time based on MOSFET temperature conditions. Rather than using a fixed low current limit, the system dynamically increases or decreases the current limit according to the actual thermal state of the MOSFET, enabling faster charging when temperatures permit while preventing overheating when they don't.
Solution Approach 2:
The patent applies parameter changes by modifying the current limit parameter based on temperature conditions. The controller changes the current limit parameter dynamically according to temperature feedback, allowing the system to optimize between temperature control and start-up speed by adjusting this key parameter in real-time.
3Reliability
If a conventional current limit circuit is used during normal operation, then over-current protection is provided, but the in-rush current is not optimized for start-up or voltage step conditions
Solution Approach 1:
The patent implements dynamics by creating a time-varying and condition-varying current limit that adapts to different operational phases. The controller dynamically switches between different current limit behaviors depending on whether the system is in start-up, voltage step, or normal operation mode, providing both protection and optimization for specific conditions.
Solution Approach 2:
The patent applies parameter changes by modifying the current limit parameter based on operational conditions. The controller changes the current limit parameter according to the system state (start-up vs. normal operation), enabling the system to adapt its protection characteristics to match the specific requirements of each operational phase.
4Reliability
If a capacitor is used in the hot swap controller to ramp up the gate voltage of the pass MOSFET, then the in-rush current is controlled, but there is no adaptive optimizing of the in-rush current for the particular load
Solution Approach 1:
The patent implements feedback by monitoring MOSFET temperature and using this information to dynamically adjust the current limit. This closed-loop feedback mechanism enables adaptive optimization for particular loads and conditions, as the system responds to actual thermal conditions rather than using a fixed predetermined current limit.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the current limit parameter based on temperature feedback and load conditions. This enables adaptive optimization for particular loads, as the controller modifies the current parameter in real-time according to the specific thermal and electrical conditions encountered.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach minimizes the peak temperature of the MOSFET during in-rush current phases, reducing the risk of overheating and optimizing start-up time while allowing for the use of less expensive MOSFETs.
Implementation Method 1
the MOSFET will overheat due to the extended power dissipation time
Data Source
AI summary
In one embodiment, a pass MOSFET is coupled in series between an input voltage and a load, and a bypass capacitor is connected in parallel with the load. In response to a voltage step across the MOSFET, the MOSFET is adaptively controlled to conduct an in-rush current of 2ICL=2IL during the bypass capacitor 12 charging time, where ICL is the capacitive current and IL is the load current. This optimizes the in-rush current to achieve a minimum peak temperature of the MOSFET. In one embodiment, a ramp capacitor connected to the drain of the MOSFET is part of a feedback path that tracks the MOSFET drain voltage to control the gate voltage.