Gate Driver Miller Clamp Using Harvested Start-Up Current
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Solution Overview
Problem
Low threshold voltage power semiconductor devices, such as gallium nitride (GaN) devices, are susceptible to spurious activations due to the Miller effect during start-up cycles, where insufficient supply voltage prevents activation of the Miller clamp circuit, leading to shoot-through in half-bridge configurations.
Innovation Solution
A gate driver system incorporating a clamp transistor, energy harvesting circuit, and bootstrap capacitor to generate a supply voltage, which converts AC Miller current to DC for activating the clamp transistor, providing a low impedance path to shunt Miller current during start-up, thereby preventing spurious activations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the supply voltage is insufficient during start-up cycles, then the gate driver cannot properly activate the power semiconductor device, but the Miller clamp circuit cannot be activated to prevent spurious activations
Solution Approach 1:
The energy harvesting circuit proactively captures Miller current during the start-up phase before the bootstrap capacitor is fully charged. By performing this energy capture in advance, the circuit ensures that sufficient voltage is available on the clamp signal input terminal to activate the clamp transistor when needed, preventing the timing conflict between bootstrap charging and clamp circuit activation.
Solution Approach 2:
The Miller current, which normally represents a harmful effect causing spurious activations, is converted into a beneficial resource. The energy harvesting circuit captures this Miller current and transforms it into useful voltage energy that powers the clamp transistor, turning the harmful Miller effect into a protective mechanism that prevents shoot-through conditions.
2Reliability
If the clamp transistor is activated using harvested energy from Miller current, then spurious activations are prevented, but the circuit complexity increases
Solution Approach 1:
The energy harvesting circuit merges multiple functions into a single integrated structure. It combines the Miller current capture, energy conversion, and clamp transistor activation control into one cohesive circuit block. This merging approach prevents spurious activations while minimizing the increase in overall circuit complexity by consolidating protective functions rather than adding separate independent circuits.
3Productivity
If the bootstrap capacitor is charged during start-up, then the gate driver can operate, but the Miller clamp circuit remains inactive due to insufficient voltage
Solution Approach 1:
The energy harvesting circuit acts as an intermediary between the Miller current and the clamp transistor gate. It mediates the voltage requirement by capturing and converting Miller current into sufficient voltage levels, enabling the clamp transistor to activate independently of the bootstrap capacitor charge status. This intermediary function resolves the conflict between bootstrap charging and clamp circuit activation.
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 system effectively suppresses spurious activations and shoot-through in low threshold voltage power transistors by harnessing energy from the Miller current to activate the clamp transistor, ensuring stable operation during start-up cycles.
Implementation Method 1
Low threshold voltage power semiconductor devices, such as gallium nitride (GaN) devices, are susceptible to spurious activations due to the Miller effect during start-up cycles
Implementation Method 2
a bootstrap capacitor connected to the bootstrap terminal
Implementation Method 3
activating a clamp transistor connected between a clamp signal input terminal and a reference voltage terminal using the harvested energy to provide a low impedance path from the clamp signal input terminal to the reference voltage terminal
Data Source
AI summary
A gate driver has a supply voltage terminal, a bootstrap terminal connected to the supply voltage terminal, a driver having a power input terminal connected to the bootstrap terminal and an output connected to a gate control signal output terminal and configured to generate a gate drive signal at the gate control signal output terminal based on a voltage on the power input terminal, a clamp driver connected to the bootstrap terminal, a clamp transistor connected between a clamp signal input terminal and a reference voltage terminal and having a gate connected to the clamp driver, and an energy harvesting circuit connected between the clamp signal input terminal and the gate of the clamp transistor.