Bootstrap Capacitor Charge Sharing for Low-Ripple Power Supplies

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Solution Overview

Problem

Existing power supplies experience large ripples in output voltage when switching modes due to restrictions on switching operations to charge bootstrap capacitors.

Innovation Solution

A power supply design incorporating inductors, power switches, bootstrap capacitors, and a charge sharing circuit with overlapping charge sharing paths to manage charge distribution across capacitors, allowing for reduced ripple during mode changes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If switching operations are restricted to charge the bootstrap capacitor, then the bootstrap capacitor can be properly charged, but large ripples occur in the output voltage when mode is changed

Engineering Contradiction:

Improvebootstrap capacitor charging reliabilityVSAvoidoutput voltage ripple

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A charge sharing circuit is introduced as an intermediary component between the first and second bootstrap capacitors. This circuit includes charge sharing paths with switching elements that enable controlled charge transfer between capacitors, allowing the system to maintain reliable capacitor charging while eliminating output voltage ripples during mode transitions.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The charge sharing circuit performs preliminary charge redistribution between the first and second bootstrap capacitors before mode changes occur. By anticipating the mode transition and pre-adjusting the charge distribution, the system avoids the harmful voltage ripples that would otherwise occur during the switching event.

Inventive Principle:

Principle #10Preliminary action

2Ease of operation

If separate charge sharing paths are used for first and second bootstrap capacitors, then each capacitor can be independently charged, but device complexity increases

Engineering Contradiction:

Improveindependent capacitor charging capabilityVSAvoidcharge sharing circuit structure

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The charge sharing circuit merges the charging functions for both bootstrap capacitors into a single integrated circuit structure. By combining the charge sharing paths and using shared switching elements, the system achieves independent charging capability for each capacitor while reducing overall circuit complexity compared to completely separate charging circuits.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The charge sharing circuit is designed with universal switching elements and paths that can serve multiple functions: charging the first bootstrap capacitor, charging the second bootstrap capacitor, and redistributing charge between them. This multi-functionality reduces the need for separate dedicated circuits for each capacitor.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 effectively reduces output voltage ripple by optimizing charge sharing across capacitors, enhancing stability and efficiency in power conversion modes.

Implementation Method 1

a first bootstrap capacitor including one end connected to the first switching node

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

a second bootstrap capacitor including one end connected to the second switching node

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 3

a charge sharing circuit configured to store a charge using a power supply voltage, to provide a first charge sharing path for the first bootstrap capacitor from the stored charge based on a first voltage charged in the first bootstrap capacitor, and to provide a second charge sharing path for the second bootstrap capacitor from the stored charge based on a second voltage charged in the second bootstrap capacitor

Methodology Applied

Scientific EffectCharge sharing: Electrical Accumulator

Implementation Method 4

an inductor connected between a first switching node and a second switching node

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS12556095B2Power supply including common sharing path and driving method thereof

Publication Date: 2026.02.17 SAMSUNG ELECTRONICS CO LTD

AI summary

A power supply includes a first and second switching node, a first power switch and a second power switch, and a first bootstrap capacitor, the first bootstrap capacitor including one end connected to the first switching node, a third and a fourth power switch, and a second bootstrap capacitor, the second bootstrap capacitor including one end connected to the second switching node, and a charge sharing circuit storing a charge using a power supply voltage, providing a first charge sharing path for the first bootstrap capacitor from the stored charge based on a first voltage charged in the first bootstrap capacitor, and to provide a second charge sharing path for the second bootstrap capacitor from the stored charge based on a second voltage charged in the second bootstrap capacitor. The first charge sharing path and the second charge sharing path include a common charge sharing path and overlap each other.