Gate Drive Circuit Reduces Surge Voltage in SiC Devices
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Solution Overview
Problem
Silicon Carbide (SiC) and Gallium Nitride (GaN) power devices are prone to erroneous turning-on due to their low threshold voltage and small capacitance ratios, leading to surge voltage issues and misoperation when driven at high voltage or high speed.
Innovation Solution
A gate drive circuit is designed with a gate resistance connected to the switching device and a gated diode in parallel, where the threshold voltage of the diode is lower than that of the switching device, to reduce surge voltage and prevent erroneous turning-on.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If gate resistance is reduced to prevent erroneous turning-on, then switching speed is improved, but surge voltage increases
Solution Approach 1:
A gated diode is introduced as an intermediary component between the gate driver and the switching device gate. The diode conducts during voltage transitions to provide a low-impedance path, preventing surge voltage while maintaining fast switching speed. The diode's forward voltage drop naturally limits the gate voltage to stay below the switching device threshold.
Solution Approach 2:
The gate drive circuit parameters are dynamically changed by using a diode with specific forward voltage characteristics. The diode's voltage-current relationship transforms the gate drive waveform, ensuring that even with low series resistance, the gate voltage remains controlled and does not cause erroneous turning-on.
2Object-affected harmful factors
If gate resistance is increased to reduce surge voltage, then surge voltage is reduced, but switching speed decreases and erroneous turning-on increases
Solution Approach 1:
The gated diode acts as a mediator that decouples the conflict between surge voltage reduction and erroneous turning-on prevention. It provides controlled voltage delivery to the gate, ensuring the voltage stays within safe limits while maintaining sufficient drive strength for reliable switching operation.
Solution Approach 2:
The diode provides beforehand cushioning by limiting the maximum gate voltage through its forward voltage drop. This prevents voltage spikes from causing erroneous turning-on before they can occur, acting as a protective barrier during voltage transitions.
3Speed
If dVds/dt is increased for high-speed operation, then switching speed is improved, but voltage Vgs rises causing erroneous turning-on
Solution Approach 1:
The gated diode serves as an intermediary that blocks the transmission of high dVds/dt effects to the gate. By providing a low-impedance path during transitions, it prevents the capacitive coupling through Cgd from causing excessive Vgs rise, even during high-speed switching operations.
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
The solution achieves high-speed switching performance with reduced misoperation and surge voltage, effectively addressing the issues of erroneous turning-on in SiC and GaN power devices.
Implementation Method 1
a gated diode connected in parallel to the gate resistance, wherein a relationship of Vth(Di)＜Vth(Tr) is satisfied, where Vth(Di) is a forward threshold voltage value of the gated diode, and Vth(Tr) is a threshold voltage value of the switching device
Data Source
AI summary
The gate drive circuit includes: a gate resistance RG1 connected to a gate G1 of a switching device Q1; and a gated diode DG1 connected in parallel to the gate resistance RG1, wherein a relationship of Vth(Di)<Vth(Tr) is satisfied, where Vth(Di) is a forward threshold voltage of the gated diode DG1, and Vth(Tr) is a threshold voltage of the switching device Q1. There is provided: a gate drive circuit having high speed switching performance in which a misoperation is suppressed and surge voltage is reduced; and a power supply mounted with such a gate drive circuit.