Switching Half-Bridge Gate Control for Parasitic Turn-On Prevention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
At high switching speeds, parasitic repowering of field-effect transistors occurs in switching half-bridges, leading to increased switch-off and switch-on losses due to capacitive displacement currents causing self-turn-on, which existing technologies fail to adequately mitigate.
Innovation Solution
A method and switching arrangement that temporarily increases the gate-source voltage of the field-effect transistor being switched off to a higher switch-off level, while simultaneously switching on the other transistor, thereby increasing the voltage gap and preventing parasitic switching back on, by adjusting control voltages and using supplementary circuits with inductors to manage gate-source voltage transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high switching speeds are used to increase power density, then switching frequency and power density are improved, but parasitic switching back on occurs leading to increased switching losses
Solution Approach 1:
The gate-source voltage is preliminarily reduced to a first switch-off level before the complementary transistor is switched on. This preliminary action ensures that the transistor being switched off remains firmly in the off state during the commutation process, preventing parasitic switching back on that would otherwise occur at high switching speeds.
Solution Approach 2:
The invention changes the gate-source voltage parameter through three distinct levels: a second switch-off level (more negative) during the commutation process, a first switch-off level (less negative) during normal operation, and a switch-on level (positive). This multi-level parameter change optimizes both high-speed switching capability and prevention of parasitic turn-on, resolving the contradiction between switching frequency and switching losses.
2Loss of energy
If gate-source voltage is reduced to prevent parasitic switching back on, then switching losses are reduced, but the voltage gap to threshold voltage decreases making the transistor more susceptible to self-turn-on
Solution Approach 1:
The gate-source voltage is made dynamic with three distinct levels rather than a fixed value. During commutation, it uses a second switch-off level (more negative) to ensure firm off state and prevent parasitic turn-on. During normal operation, it transitions to a first switch-off level (less negative) to reduce switching losses. This dynamic adjustment resolves the contradiction between energy loss and reliability.
Solution Approach 2:
The gate-source voltage undergoes periodic cycling through different levels: during each commutation event, it temporarily adopts the second switch-off level, then returns to the first switch-off level for normal operation. This periodic action pattern ensures reliable prevention of parasitic switching while minimizing energy losses during the majority of the operational cycle.
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 effectively reduces switching losses by preventing parasitic switching back on during rapid transistor switching, enhancing the efficiency of power converters with wide-bandgap field-effect transistors.
Implementation Method 1
Due to a capacitive displacement current, the gate-source voltage between gate and source of the field-effect transistor which is being switched off is here briefly raised above the threshold voltage of the field-effect transistor
Implementation Method 2
using supplementary circuits with inductors to manage gate-source voltage transitions
Data Source
AI summary
A switching half-bridge has two field-effect transistors and a supplementary circuit arranged upstream of a gate terminal of a first field-effect transistor and formed of a first circuit branch having a damping resistor and an inductor connected in series with the damping resistor and a second circuit branch being connected in parallel with the first circuit branch and having a series resistor and an auxiliary switch connected in series with the series resistor. The half-bridge can be switched from a first switching state to a second switching state, wherein while the auxiliary switch is open, a change in the control voltage causes the first circuit branch to temporarily change the gate-source voltage of the first field-effect transistor from the switch-on level to a second switch-off level greater than a first switch-off level, with the gate-source voltage thereafter returning to the first switch-off level.