MOSFET Switch Current Limiting for Fast Overcurrent Protection
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Solution Overview
Problem
Existing switch systems in voltage converters for rotary electric machines are slow to react to overcurrents, which can exceed safety thresholds and damage electronic components due to latency in Hall effect sensor responses, leading to prolonged exposure to unsafe current levels.
Innovation Solution
A switch system with a current-limiting device that reduces the control current entering the control terminal when the main current exceeds a threshold, allowing the main switch to transition to a semi-closed state quickly, thereby limiting the current without relying on the control circuit, and utilizing matched transistors and resistors to regulate the resistance and control current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Hall effect sensor is used to detect overcurrent and control the main switch to open state, then the components are protected from excessive current, but the response time is too slow (approximately a dozen μs) to prevent current from reaching dangerous levels (several hundred amperes in less than 3 μs)
Solution Approach 1:
The current-limiting device is configured to act before the control circuit reacts by directly reducing the control current to the main switch when overcurrent is detected. This preliminary action bypasses the slow Hall effect sensor and control circuit, achieving rapid current limitation within microseconds by transitioning the MOSFET to semi-closed state before dangerous current levels are reached
Solution Approach 2:
The invention introduces a current-limiting device as an intermediary between the power line and the control circuit. This intermediary device includes a shunt transistor that diverts control current away from the main switch when overcurrent conditions occur, enabling faster response than the original control system alone could achieve
2Reliability
If the main switch is opened quickly to limit current, then component damage is prevented, but the control circuit latency prevents effective current limitation
Solution Approach 1:
The current-limiting device performs preliminary current limitation by directly affecting the control current before the control circuit's latency can cause dangerous current levels. The shunt transistor activates immediately when overcurrent is detected, reducing control current and transitioning the main switch to semi-closed state within microseconds
Solution Approach 2:
The invention implements a feedback mechanism where the current-limiting device continuously monitors the control current and automatically adjusts it based on the main line current conditions. When overcurrent is detected, the feedback loop activates the shunt transistor to reduce control current, creating a self-regulating system that responds faster than the original control circuit alone
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
The solution enables rapid limitation of main current, reducing the risk of component damage by quickly transitioning the switch to a semi-closed state, thus protecting fragile components from excessive currents and maintaining the 'Safe Operating Area' of MOSFETs.
Implementation Method 1
the main switch in its semi-closed state being equivalent to a variable resistor controlled by the control terminal and connected between the first and the second main terminal
Implementation Method 2
the current circulating in the main power line is measured by a Hall effect sensor
Data Source
AI summary
The invention relates to a switch system (1) comprising a power line (2) for supplying a charge from a voltage source (+Vbat), said power line having a main switch (Q1) comprising a first main terminal (D) and a second main terminal (S), between which a main current (Ip) is intended to pass, and a control terminal (G) for selectively placing the main switch (Q1) in a closed, open or semi-closed state, the main switch (Q1) in its semi-closed state being equivalent to a variable resistor controlled by the control terminal and connected between the first and the second main terminal, characterized in that the switch system (1) further comprises a current-limiting device (3) designed to, when the main current (Ip) exceeds a maximum current threshold, decrease a control current (Ig) entering the control terminal (G), so as to cause the main switch (Q1) to transition from the closed state to the semi-closed state, so as to limit the main current.