Transistor Gate Drive with Intermediate Turn-Off to Limit Voltage Spikes
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Solution Overview
Problem
Transistor devices, such as MOSFETs, experience voltage spikes due to parasitic inductances when switching from an on-state to an off-state, leading to potential irreversible performance degradation and increased on-resistance, which can be mitigated by reducing the drive voltage from a maximum level to an intermediate level higher than the threshold voltage and maintaining it for a predefined time before switching off.
Innovation Solution
A method involving a drive circuit that reduces the drive voltage of a transistor device from a maximum voltage level to an intermediate voltage level higher than the threshold voltage, maintains this intermediate level for a predefined time, and then decreases it below the threshold voltage to switch the transistor device to an off-state, thereby reducing voltage spikes and energy stored in parasitic inductances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the transistor device switches quickly from on-state to off-state, then the switching speed is improved, but voltage spikes occur due to parasitic inductances causing performance degradation
Solution Approach 1:
The drive voltage is reduced to an intermediate level before the transistor fully turns off, preparing the device for a smoother transition. This preliminary voltage reduction prevents abrupt current changes that would otherwise cause voltage spikes across parasitic inductances, thereby maintaining both switching speed and performance stability
Solution Approach 2:
By maintaining an intermediate drive voltage level for a predefined time period, the patent creates a cushioning effect that dampens the impact of parasitic inductances. This intermediate state acts as a buffer, reducing the severity of voltage overshoots and protecting the transistor from performance degradation during the switching transition
2Reliability
If the drive voltage is reduced to an intermediate level before switching off, then voltage spikes are reduced, but the switching time increases
Solution Approach 1:
The patent applies partial action by reducing the drive voltage only to an intermediate level (not completely to zero) for a predefined time period. This partial reduction is sufficient to dampen voltage spikes caused by parasitic inductances while minimizing the extension of switching time. The predefined time period is optimized to provide just enough cushioning without excessive delay
Solution Approach 2:
The patent changes the drive voltage parameter from a binary state (full on/off) to a three-level state (maximum, intermediate, and below threshold). By introducing the intermediate voltage level as a temporary state, the system achieves smoother current transitions that reduce voltage spikes, while the predefined duration of this intermediate state ensures the total switching time remains acceptable
Data Source
AI summary
Disclosed is a method for driving a transistor device and an electronic circuit. The method includes: in an on-state of the transistor device (1), reducing a drive voltage (VGS) of the transistor device (1) from a maximum voltage level (VMAX) to an intermediate voltage level (VINT) that is higher than a threshold voltage level (VTH) of the transistor device (1); maintaining the intermediate voltage level (VINT) for a predefined time period (TINT); and reducing the drive voltage (VGS) to below the threshold voltage level (VTH) after the predefined time period (TINT) to switch the transistor device to an off-state.