Buck-Boost Bootstrap Refresh Circuit for High-Side Voltage Stability
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Solution Overview
Problem
Conventional buck-boost DC-DC converters face inefficiencies and high silicon area occupation due to complex bootstrap voltage refresher circuitry, particularly when operating near input and output voltage equality, leading to driver circuits failing to maintain high-side switch voltage.
Innovation Solution
A buck-boost DC-DC converter with simplified bootstrap voltage refresher circuitry using PMOS transistors and charge transfer switches, controlled by voltage sensing and logic circuits to manage charge transfer between bootstrap capacitances, ensuring efficient operation across varying input and output voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bootstrap refresher circuitry is used in buck-boost DC-DC converters, then the high-side switch voltage can be maintained, but the circuit complexity increases and silicon area occupation increases
Solution Approach 1:
The patent merges the bootstrap refresher functionality into the existing half-bridge circuits by utilizing the body diodes of the high-side switches and the existing low-side switch capacitances. The refresher operation is achieved by controlling the high-side switches in a specific sequence during mode transitions, eliminating the need for separate refresher circuitry. This combining approach maintains the necessary voltage levels while reducing overall circuit complexity and silicon area occupation.
Solution Approach 2:
The bootstrap refresher function is achieved through self-service mechanisms within the converter itself. The body diodes of the high-side switches and the inherent capacitances in the circuit are utilized to automatically recharge the bootstrap capacitors during mode transitions. The control circuit triggers the high-side switches in a specific sequence that enables the circuit elements to refresh their own voltages without external intervention or dedicated refresher components.
2Reliability
If complex bootstrap refresher circuitry is implemented, then high-side switch voltage stability is improved, but manufacturing cost and silicon area increase
Solution Approach 1:
The patent combines the bootstrap refresher function with the existing power switching elements. The body diodes and capacitances that are already part of the half-bridge circuit are utilized for voltage refreshing, eliminating the need for additional manufactured components. This approach maintains voltage stability while simplifying the manufacturing process and reducing silicon area requirements.
Solution Approach 2:
The patent utilizes readily available, low-cost circuit elements such as body diodes and inherent capacitances that are already present in the converter design. These elements are used temporarily during mode transitions to achieve voltage refreshing, avoiding the need for expensive, dedicated refresher components. The solution leverages existing resources rather than adding new manufacturing complexity.
3Adaptability or versatility
If the converter operates in pure buck or boost mode with conventional bootstrap circuits, then the converter can function, but the inactive half-bridge bootstrap capacitance discharges and requires complex refresher circuitry
Solution Approach 1:
The patent implements dynamic control of the high-side switches based on the operating mode. During mode transitions, the control circuit activates specific high-side switches in a predetermined sequence that enables the body diodes to conduct and recharge the bootstrap capacitances of the inactive half-bridge. This dynamic switching strategy adapts to different operating modes (buck, boost, or buck-boost) and automatically refreshes voltages without requiring separate refresher circuitry for each mode.
Solution Approach 2:
The bootstrap refresher operation occurs periodically during mode transitions. The control circuit detects when transitions between buck and boost modes occur and triggers the appropriate high-side switch sequence at these periodic intervals. This periodic activation of the refresher mechanism, synchronized with mode changes, maintains voltage levels in the inactive half-bridge without requiring continuous operation of complex refresher circuits.
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 solution provides a more efficient and compact buck-boost converter design by minimizing silicon area and maintaining stable high-side switch voltage, enabling operation across a wide range of input and output voltages without discharge issues.
Implementation Method 1
two dedicated bootstrap circuits configured to supply, through external capacitances storing energy, the driver circuits that drive the high-side switches
Implementation Method 2
At least one charge transfer switch is directly connected between the first high-side supply voltage node and the second high-side supply voltage node
Data Source
AI summary
In accordance with an embodiment, a method of operating a buck-boost power supply includes operating the buck-boost power supply in a buck mode by providing a PWM signal to a first half-bridge circuit, and turning on a charge transfer switch coupled between a first boosted supply node of a second driver circuit coupled to the first half-bridge circuit and a second boosted supply node of a second driver circuit coupled to a second half-bridge circuit when a voltage between the second boosted supply node and an output of the second half-bridge circuit is below a first threshold; and operating the buck-boost power supply in a boost mode by providing a PWM signal to the second half-bridge circuit, and turning on the charge transfer switch when the voltage between the first boosted supply node and an output of the first half-bridge circuit is below a second threshold.