Buck-Boost Circuit Bootstrap Control for Dual-Mode High-Side Driving

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Solution Overview

Problem

Existing buck-boost circuits face high circuit costs due to complex designs with independent driving power supplies or bootstrap circuits, and conventional bootstrap circuits cannot drive high-side switching transistors effectively in both Buck and Boost modes.

Innovation Solution

A method for controlling a buck-boost circuit using first and second bootstrap circuits to drive high-side switching transistors, with a control strategy that includes stages of transistor conduction to charge bootstrap capacitors and implement topological control and waveform generation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an independent driving power supply is used to drive switching transistors in the buck-boost circuit, then the switching transistors can be driven reliably, but the circuit complexity and overall cost increase significantly

Engineering Contradiction:

Improveswitching transistor driving reliabilityVSAvoidcircuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent combines the driving functions for both high-side switching transistors into a single bootstrap circuit architecture, merging what would traditionally require separate independent power supplies into one integrated solution. This reduces component count and circuit complexity while maintaining reliable driving capability through the bootstrap charging mechanism.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The bootstrap circuit is designed to serve multiple functions: it charges the bootstrap capacitor during the low-side transistor conduction phase and then uses this stored charge to drive both high-side switching transistors in subsequent phases. This multi-functional approach eliminates the need for dedicated independent power supplies for each high-side transistor.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Device complexity

If a conventional bootstrap circuit is used to drive high-side switching transistors, then circuit costs are reduced, but the high-side switching transistors cannot be driven effectively in both Buck and Boost modes

Engineering Contradiction:

Improvecircuit costVSAvoidmode adaptability

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent implements dynamic control of the switching transistors with differentiated conduction timing between Buck and Boost modes. In Buck mode, specific transistors conduct during specific phases to charge the bootstrap capacitor, while in Boost mode, the conduction sequence is adjusted. This dynamic adaptation allows the same bootstrap circuit to effectively drive high-side transistors in both operating modes.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The control method changes the conduction parameters (timing and duration) of switching transistors based on the operating mode. By adjusting which transistors conduct and for how long, the bootstrap capacitor is charged appropriately in both Buck and Boost modes, enabling the bootstrap circuit to adapt to different voltage conversion directions without requiring separate driving circuits.

Inventive Principle:

Principle #35Parameter changes

3Stability of the object's composition

If high-side switching transistors are kept in normally-on state and low-side switching transistors in normally-off state, then the circuit operates in conventional mode, but the bootstrap capacitor cannot be charged in buck-boost mode

Engineering Contradiction:

Improveswitching transistor state stabilityVSAvoidbootstrap capacitor charging capability

Core Design Contradiction:

Stability of the object's compositionVSAdaptability or versatility

Solution Approach 1:

The patent employs preliminary action by charging the bootstrap capacitor during specific phases before the high-side switching transistors need to be driven. In the first stage, low-side transistors are controlled to conduct, which automatically charges the bootstrap capacitor through the bootstrap diode and resistor. This preliminary charging ensures that when high-side transistors need to switch in subsequent stages, the bootstrap capacitor is already charged and ready to provide the necessary gate drive voltage.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS20260025073A1Method for controlling buck-boost circuit, power conversion device, energy storage device, and storage medium

Publication Date: 2026.01.22 ECOFLOW INC

AI summary

A method for controlling a buck-boost circuit includes: obtaining an input voltage and an output voltage; controlling the buck-boost circuit to enter a buck-boost mode when an absolute value of a voltage difference between the input voltage and the output voltage is less than a preset voltage threshold; and executing within each control cycle: in a first stage, controlling both first and second low-side switching transistors to be conductive and controlling both first and second high-side switching transistors to be non-conductive; in a second stage, controlling both the first and second high-side switching transistors to be conductive and controlling both first and second low-side switching transistors to be non-conductive; and in a third stage, controlling both the first and second high-side switching transistors to be conductive and controlling both the first and second low-side switching transistors to be non-conductive.