Asymmetric Common Source Inductance for MOSFET Turn-Off Overvoltage
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Solution Overview
Problem
Parasitic inductances in metal-oxide semiconductor field-effect transistors (MOSFETs) cause overshoot and ringing, leading to excessive drain-to-source voltage that can damage the transistor and reduce power conversion efficiency.
Innovation Solution
Implement an asymmetric common source inductance (Lcs) scheme by using inductors with different values in the gate-source loop during turn-on and turn-off states, incorporating a switch to alternate between these inductances and a current-limiting element to manage gate loop currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a small common source inductance is used, then turn-on switching speed is improved, but turn-off overvoltage increases causing transistor damage
Solution Approach 1:
The patent applies dynamics by making the common source inductance value changeable based on the switching state. A first inductor with small inductance is used during turn-on to achieve fast switching, while a second inductor with large inductance is used during turn-off to suppress overvoltage. This dynamic adjustment of inductance value resolves the contradiction between turn-on speed and turn-off overvoltage suppression.
Solution Approach 2:
The patent changes the inductance parameter based on the operating condition. By switching between two different inductance values (small for turn-on, large for turn-off), the system optimizes performance for each state. The switch controlled by gate voltage automatically selects the appropriate inductance value, transforming a static parameter into a dynamic one to resolve the technical contradiction.
2Object-affected harmful factors
If a large common source inductance is used, then turn-off overvoltage is reduced, but turn-on switching speed decreases and switching power loss increases
Solution Approach 1:
The patent uses a dynamic inductance selection mechanism where the common source inductance value is adjusted based on the switching phase. During turn-on, the small inductance of the first inductor minimizes switching power loss and maintains fast switching speed. During turn-off, the large inductance of the second inductor suppresses overvoltage. This dynamic adaptation resolves the contradiction between overvoltage suppression and switching efficiency.
Solution Approach 2:
The inductance parameter is changed based on the switching state to optimize both overvoltage suppression and switching power loss. The switch controlled by gate voltage selects between two inductance values, allowing the system to have small inductance during turn-on (reducing switching loss) and large inductance during turn-off (suppressing overvoltage), thereby resolving the technical contradiction.
3Productivity
If asymmetric inductors are introduced, then switching performance is optimized, but device complexity increases
Solution Approach 1:
The patent merges the functions of two different inductors (first inductor with small inductance and second inductor with large inductance) into a single common source inductance structure. The switch controlled by gate voltage enables one inductor to serve dual purposes: the first inductor handles both turn-on current and turn-off current when the switch is on, while the second inductor handles turn-off current when the switch is off. This merging approach optimizes switching performance while managing device complexity.
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
Reduces turn-off overvoltage and switching power loss in MOSFETs without penalizing performance, thereby enhancing reliability and efficiency.
Implementation Method 1
a first inductor, a second inductor... The first inductor has a small inductance value that is less than a larger inductance value of the second inductor
Data Source
AI summary
A circuit includes a metal-oxide semiconductor field-effect transistor (MOSFET) having a gate, a source, and a drain. The circuit further includes a first inductor and a second inductor. The first inductor has a small inductance value that is less than a larger inductance value of the second inductor. The circuit further includes a switch configured to include the first inductor in a current path shared by a gate loop and a source loop of the MOSFET when the MOSFET is turning on, and to include the second inductor in the current path shared by the gate loop and the source loop when the MOSFET is turning off.