Bootstrap Gate Drive Circuit for GaN FET Breakdown Prevention
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Solution Overview
Problem
The existing semiconductor devices using GaN FETs face a problem where a voltage exceeding the withstand voltage is applied between the gate and source of the high-voltage side transistor, leading to breakdown, due to both high-voltage and low-voltage side transistors being in the ON state, which is not a concern in CMOS circuits.
Innovation Solution
Incorporating a load transistor or resistance element between the source and drain of the high-voltage side transistor and the low-voltage side transistor to reduce the applied voltage between the gate and source, and using a controller to manage the electrical potentials of the transistors, ensuring the voltage remains within the withstand voltage range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If both high-voltage and low-voltage side transistors are in the ON state to enable efficient operation, then the operational efficiency is improved, but the voltage between gate and source of the high-voltage side transistor exceeds the withstand voltage causing breakdown
Solution Approach 1:
A bootstrap capacitor is introduced as an intermediary element between the gate and source of the high-voltage side transistor. This capacitor couples the gate voltage to the source voltage, automatically adjusting the gate voltage to maintain a safe voltage difference below the withstand voltage while allowing both transistors to remain in the ON state for efficient operation.
2Reliability
If a bootstrap capacitor is added to prevent voltage breakdown, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The bootstrap capacitor is configured to automatically charge and discharge based on the operating state of the transistors. When the low-voltage side transistor switches, the capacitor naturally charges; when the high-voltage side transistor needs to switch, the capacitor discharges to provide the necessary gate voltage. This self-regulating mechanism prevents transistor breakdown without requiring external control circuits or additional active components.
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
Prevents breakdown of the high-voltage side transistor by maintaining the voltage between the gate and source below the withstand voltage, while allowing efficient operation of the bootstrap circuit, with the choice of load element affecting charge time and manufacturing cost.
Implementation Method 1
a capacitor element having one end connected to the control terminal of the first field effect transistor, the capacitor element being charged by the control of the controller
Data Source
AI summary
A semiconductor device, includes: a first field effect transistor having one terminal to which a first electrical potential is given; a second field effect transistor having one terminal to which a second electrical potential smaller than the first electrical potential is given; a controller that controls each electrical potential of each control terminal of the first field effect transistor and the second field effect transistor; a capacitor element having one end connected to the control terminal of the first field effect transistor, the capacitor element being charged by the control of the controller; and a load element connected between another terminal of the first field effect transistor and another terminal of the second field effect transistor.