Two-Stage Gate Drive Circuit for Surge Voltage and Turn-Off Loss
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Solution Overview
Problem
Power converters face challenges in managing surge voltages and turn-off losses in power switching devices like IGBTs and MOSFETs, which can lead to device destruction and converter malfunction due to the trade-off between surge voltage and turn-off loss.
Innovation Solution
A gate drive circuit with a first off-mode fast drive circuit and a second off-mode slow drive circuit, along with a delay circuit, is used to rapidly turn off the switching device initially to reduce turn-off loss and then transition to a slower drive to suppress surge voltage, with the delay time adjusted to balance both factors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the turning off speed of the power switching device is slowed to reduce surge voltage, then the surge voltage is reduced, but the turn-off loss increases
Solution Approach 1:
The gate drive circuit dynamically changes the gate discharge speed in two stages: initially discharging the gate capacitance quickly to reduce turn-off loss, then slowing down the discharge rate to suppress surge voltage. This dynamic adjustment of discharge speed resolves the contradiction between reducing surge voltage and minimizing turn-off loss.
Solution Approach 2:
The gate discharge process is divided into two distinct stages: a first off-mode fast drive circuit for initial rapid discharge, and a second off-mode slow drive circuit for subsequent slow discharge. This segmentation allows each circuit to optimize for its specific phase, achieving both low turn-off loss and surge voltage suppression.
2Loss of energy
If new materials such as SiC are used to increase switching speed, then the turn-off loss is reduced, but the ability to suppress surge voltage deteriorates due to inability to catch up with switching operation
Solution Approach 1:
The gate drive circuit adapts its discharge speed dynamically to match the switching characteristics of modern wide-bandgap devices like SiC. By initially discharging quickly and then slowing down, the circuit can effectively suppress surge voltage even in high-speed switching applications where conventional single-speed drive circuits fail.
Solution Approach 2:
The first off-mode fast drive circuit performs preliminary rapid discharge of the gate capacitance at the critical moment of switching, removing the majority of charge before the second slow drive circuit takes over. This preliminary action prevents excessive turn-off loss while setting up conditions for subsequent surge voltage suppression.
Data Source
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AI summary
A gate drive circuit according to an embodiment includes: a voltage detector that detects a voltage between a first terminal and a second terminal of a switching device; a delay circuit that outputs, with a delay for a predetermined time, a detected value of the voltage obtained from the voltage detector; and a first off-mode drive circuit and a second off-mode drive circuit that apply a control signal to a control terminal of the switching device for turning off the switching device, wherein the first off-mode drive circuit turns off the switching device faster than the second off-mode drive circuit, and stops its operation to turns off the switching device when the delayed voltage value output from the delay circuit exceeds a predetermined threshold value.