Bootstrap Refresh Control Circuit for Voltage Converter Stability

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Solution Overview

Problem

Voltage converters face issues with timely refreshing of the bootstrap voltage, leading to improper operation and potential damage due to voltage spikes, especially in light load or no load conditions where the bootstrap capacitor is not charged or recharged in time.

Innovation Solution

A bootstrap refresh control circuit is introduced, comprising a comparing module and a voltage difference module that compares the bootstrap voltage with a refresh threshold and adjusts the output voltage to charge the bootstrap capacitor by controlling the high side and low side switches, ensuring timely refreshment of the bootstrap voltage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If the voltage converter operates in light load or no load conditions, then energy consumption is reduced, but the bootstrap capacitor cannot be charged or recharged in time leading to improper operation

Engineering Contradiction:

Improveenergy consumptionVSAvoidbootstrap voltage refresh reliability

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The control circuit proactively monitors the bootstrap capacitor voltage and initiates charging action before the voltage drops to a critical level. By detecting the voltage state in advance and triggering the low-side switch to charge the capacitor during the off-period of the high-side switch, the system ensures the bootstrap voltage is refreshed timely even under light load conditions, preventing operation failure while maintaining energy efficiency.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If the high side switch is driven with insufficient bootstrap voltage, then the circuit operates safely, but the switch cannot be fully turned on reducing conversion efficiency

Engineering Contradiction:

Improveswitch operation safetyVSAvoidconversion efficiency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The control circuit continuously monitors the bootstrap capacitor voltage and uses this feedback to determine when charging is needed. By comparing the monitored voltage against a threshold and dynamically controlling the low-side switch based on this feedback, the system ensures the bootstrap capacitor is charged to the appropriate voltage level, enabling the high-side switch to fully turn on and achieve high conversion efficiency while maintaining safe operation.

Inventive Principle:

Principle #23Feedback

3Device complexity

If the bootstrap capacitor is not charged timely, then the circuit structure remains simple, but voltage spikes occur causing potential damage

Engineering Contradiction:

Improvecircuit structure complexityVSAvoidvoltage spikes

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The control circuit uses the existing off-period of the high-side switch to automatically charge the bootstrap capacitor through the low-side switch, without requiring external intervention or additional dedicated charging circuitry. This self-service mechanism leverages the natural switching cycles to refresh the bootstrap voltage, preventing harmful voltage spikes while adding minimal complexity to the overall circuit structure.

Inventive Principle:

Principle #25Self-service

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 ensures the bootstrap voltage is refreshed promptly, preventing voltage converter malfunctions and reducing the risk of damage by maintaining stable operation even in light load conditions.

Implementation Method 1

a bootstrap capacitor for providing a bootstrap voltage signal to supply a high side driver of the high side switch

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

a first comparing module having a first input terminal, a second input terminal and an output terminal, and wherein the first input terminal of the first comparing module is configured to receive the bootstrap voltage signal, the second input terminal of the first comparing module is configured to receive a bootstrap refresh threshold, and the first comparing module is configured to compare the bootstrap voltage signal with the bootstrap refresh threshold

Methodology Applied

Scientific EffectVoltage comparison:

Implementation Method 3

the voltage converter is configured to receive an input voltage at an input terminal and to provide an output voltage at an output terminal based on driving the high side switch and the low side switch to switch on and off

Methodology Applied

Scientific EffectElectrical energy transformation:

Data Source

PatentUS9590608B2Bootstrap refresh control circuit, voltage converter and associated method

Publication Date: 2017.03.07 MONOLITHIC POWER SYSTEMS INC

AI summary

A voltage converter having a bootstrap refresh control circuit and a method for controlling the voltage converter. The bootstrap refresh control circuit monitors a bootstrap voltage across a bootstrap capacitor and provides a high side driving signal to a high side switch of the voltage converter. The bootstrap refresh control circuit also controls the charging of the bootstrap capacitor through decreasing the output voltage of the voltage converter once the bootstrap voltage is dropped to be smaller than a bootstrap refresh threshold. When the output voltage of the voltage converter is decreased enough, the bootstrap refresh control circuit switches the high side switch and the low side switch on and off to refresh the bootstrap voltage.