Half-Bridge Bootstrap Voltage Regulation for GaN High-Side Supply
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Solution Overview
Problem
In half-bridge circuits with gallium nitride high-electron-mobility transistors, regulating the gate-to-source voltage of non-ground referenced power transistors is challenging due to voltage variations, which can lead to performance degradation or 'soft damage' if not maintained within a specific range, and existing solutions lack efficient control mechanisms for boot-strapped capacitors.
Innovation Solution
An adaptive CBOOT regulator that uses a switched-capacitor mechanism to sense and regulate the voltage across the boot-strapped capacitor, ensuring a consistent gate-to-source voltage of 6V±10% for the high-side transistor by separately charging the capacitor based on the voltage difference between its plates, eliminating the need for external components and providing a controlled charging path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a boot-strapped capacitor is used to provide floating voltage to the non-ground referenced power transistor, then the transistor can operate at high voltage levels, but the gate-to-source voltage becomes difficult to regulate and may drift outside the optimal range
Solution Approach 1:
The patent implements a feedback mechanism where the regulator continuously monitors the gate-to-source voltage of the high-side transistor and adjusts the charging current to the boot-strapped capacitor accordingly. This closed-loop control ensures the voltage remains within the optimal range (6V±10%) despite variations in operating conditions, resolving the contradiction between high voltage operation and voltage stability.
Solution Approach 2:
The regulator is integrated within the half-bridge circuit itself, allowing the circuit to self-regulate its own boot-strapped capacitor voltage without requiring external control components. The regulator automatically detects voltage deviations and compensates by charging or discharging the capacitor as needed, making the system self-correcting and maintaining reliable operation.
2Reliability
If external components are used to regulate the boot-strapped capacitor voltage, then voltage control can be achieved, but the device complexity and component count increase
Solution Approach 1:
The patent merges the regulator functionality directly into the half-bridge circuit integration, combining multiple functions (voltage regulation, capacitor charging control, and transistor driving) into a single unified device. This integration eliminates the need for separate external regulation components while maintaining effective gate-to-source voltage control, thus reducing overall device complexity.
Solution Approach 2:
The integrated regulator serves multiple functions simultaneously: it regulates the boot-strapped capacitor voltage, provides controlled charging paths, monitors gate-to-source voltage levels, and adjusts transistor driving signals. This multi-functionality consolidates what would traditionally require multiple separate components into a single universal control unit within the half-bridge.
3Adaptability or versatility
If the gate-to-source voltage is not maintained within the specific range, then the transistor can operate beyond rated conditions, but performance degradation and soft damage occur
Solution Approach 1:
The regulator proactively prevents gate-to-source voltage from deviating outside the safe operating range by continuously monitoring and adjusting the boot-strapped capacitor voltage before harmful conditions can develop. This preliminary protective action stops potential performance degradation and soft damage before they occur, maintaining transistor reliability while allowing broad operating conditions.
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 solution maintains optimal performance of the high-side transistor by regulating the gate-to-source voltage, preventing performance degradation and 'soft damage, while reducing power loss and eliminating the need for external components, thus enhancing the reliability and efficiency of the half-bridge circuit.
Implementation Method 1
An adaptive CBOOT regulator that uses a switched-capacitor mechanism to sense and regulate the voltage across the boot-strapped capacitor
Data Source
AI summary
An electrical circuit includes a ground-referenced transistor and a non-ground-referenced transistor configured in a half-bridge topology. The non-ground-referenced power transistor has a first conducting electrode coupled to a high voltage power supply, a control electrode coupled to a high-side pre-driver, and a second conducting electrode coupled to a switch node. The electrical circuit further includes a boot-strapped capacitor having a bottom plate coupled to the second conducting electrode and a top plate coupled to the high-side pre-driver, and an interface coupled to a first sense device for sensing a voltage at the top plate, a second sense device for sensing a voltage at the bottom plate, and a charging device for selectively increasing the voltage at the top plate. The interface controls the charging device based on the voltage at the top plate and the voltage at the bottom plate.