Gate Drive Device Precharge Circuit for SiC-MOSFET Surge Reduction
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Solution Overview
Problem
In electric power conversion devices, the negative gate surge voltage generated during switching in half-bridge circuits can exceed the rated voltage, leading to potential failure or deterioration of switching elements, particularly in SiC-MOSFETs, due to wiring impedance and feedback capacitance, especially when switching speed increases.
Innovation Solution
A gate drive device and method that precharge the gate voltage of the counter arm to a value higher than the negative gate power supply voltage but lower than the threshold voltage before turning off the drive arm, using a precharge control unit and mirror clamp circuits to reduce impedance and prevent excessive voltage fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If switching speed is increased to improve performance, then productivity is improved, but negative gate surge voltage increases causing reliability to deteriorate
Solution Approach 1:
The gate voltage is precharged to a voltage higher than the negative power supply voltage before the switching element is turned off. This preliminary action ensures that when the counter arm switching element turns off and feedback capacitance discharges, the gate voltage remains above the negative rated voltage, preventing malfunction even with high switching speeds
Solution Approach 2:
The precharge circuit applies a counteracting voltage in advance to offset the harmful negative gate surge voltage that will be generated by the feedback capacitance discharge. By precharging the gate voltage to a higher level, the discharge effect is counteracted and the gate voltage is prevented from dropping below the safe threshold
2Device complexity
If active mirror clamp circuit is used to reduce wiring impedance, then device complexity is improved, but negative gate surge voltage increases causing harmful factors to worsen
Solution Approach 1:
A precharge circuit is introduced as an intermediary component between the power supply and the gate terminal. This precharge circuit includes a precharge transistor and capacitor that work together to maintain the gate voltage at a safe level, mediating the harmful effect of the feedback capacitance discharge without requiring changes to the mirror clamp circuit
3Reliability
If gate voltage is charged to higher voltage to prevent negative surge, then reliability is improved, but energy consumption increases
Solution Approach 1:
The precharge transistor is activated periodically only when needed - specifically when the switching element is about to be turned off and the gate voltage needs to be maintained above the negative rated voltage. The control unit monitors switching signals and activates the precharge circuit only during critical periods, avoiding continuous energy consumption while ensuring reliability when required
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 the negative gate surge voltage, preventing excessive voltage from exceeding the rated voltage and enhancing the reliability of the switching elements by maintaining the gate voltage within a safe range, thereby reducing the risk of failure and deterioration.
Implementation Method 1
a voltage between one main terminal of the semiconductor device and a gate terminal of the semiconductor device is charged to a voltage value that is larger, in a positive direction, than a negative voltage of a negative gate power supply and smaller than a gate threshold voltage
Implementation Method 2
an active mirror clamp circuit is mounted inside the power semiconductor module to reduce wiring impedance between a gate terminal and a source terminal
Data Source
AI summary
The invention provides a gate drive device, a gate drive method, a power semiconductor module, and an electric power conversion device capable of reducing a negative gate surge voltage. The gate drive device drives a semiconductor device constituting an arm in an electric power conversion device. Before a turn-off start of a drive arm, in a counter arm, a voltage between one main terminal of the semiconductor device and a gate terminal of the semiconductor device is charged to a voltage value that is larger, in a positive direction, than a negative voltage of a negative gate power supply and smaller than a gate threshold voltage of the semiconductor device.