Switched Reference Gate Drive Assist Circuit for Bootstrap Charging
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Solution Overview
Problem
Non-isolated buck power conversion topologies without a common connection node between the high-side and low-side MOSFETs face challenges in charging the bootstrap capacitor, rendering conventional methods ineffective for enhancing high-side MOSFET performance.
Innovation Solution
A switched reference gate drive assist circuit actively controls the bootstrap capacitor's reference terminal as a function of the ON-states of both high-side and low-side MOSFETs, providing an independent voltage source for the high-side MOSFET, allowing it to operate above the input voltage without varying with operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional bootstrap capacitor-based method is used to enhance the high-side MOSFET, then the high-side MOSFET can be turned ON properly, but this method is not applicable to topologies without a common connection node between high-side and low-side MOSFETs
Solution Approach 1:
The patent introduces an intermediary circuit (the switched reference gate drive assist circuit) that mediates between the available voltage sources and the bootstrap capacitor reference terminal. This intermediary actively controls the reference terminal voltage based on the switching states of both MOSFETs, enabling the bootstrap capacitor to be properly charged even without a direct common connection node between high-side and low-side MOSFETs.
2Reliability
If a voltage source that dynamically varies with operating conditions is added to charge the high-side bootstrap capacitor, then proper converter operation is enabled, but the circuit complexity increases
Solution Approach 1:
The patent implements a dynamic control mechanism where the reference terminal voltage of the bootstrap capacitor is actively adjusted based on the real-time switching states of the high-side and low-side MOSFETs. This dynamic approach ensures that the voltage source adapts to operating conditions while maintaining reliable MOSFET operation, rather than using a static or overly complex variable voltage source.
3Adaptability or versatility
If the source of the high-side MOSFET is not directly connected to the drain of the low-side MOSFET, then switched-capacitor topology is achieved, but the conventional bootstrap capacitor charging method becomes impossible
Solution Approach 1:
The patent employs a feedback mechanism where the control circuit monitors the switching states of both MOSFETs and uses this information to actively control the reference terminal voltage of the bootstrap capacitor. This feedback-based control enables the bootstrap capacitor to be charged appropriately even in the switched-capacitor topology where the direct common connection node is eliminated, thus maintaining ease of operation despite the topological modification.
Data Source
AI summary
A power converter includes at least a first phase including a high-side MOSFET transistor (HSA) and a low-side (LS) MOSFET transistor (LSA) driving a first output inductor. The first phase further includes an active gate drive assist circuit including first MOSFET switch (first switch) and second MOSFET switch (second switch) positioned in series between a source of HSA and a drain of LSA. A capacitor (CS) is between the source of HSA and drain of LSA. A bootstrap capacitor (CA) having a reference terminal is connected to a node between the first switch and the second switch.