Audio-Skipping Constant On-Time Power Converter

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Solution Overview

Problem

Constant on-time power converters experience efficiency degradation and audio noise due to switching frequency decreasing to audible ranges at light loading, leading to increased output voltage and negative inductor currents.

Innovation Solution

The power converter is switched to a quasi-constant off-time mode by triggering the off-time of the high-side switch when the output voltage reaches the peak point, using a timer and voltage-controlled voltage source to maintain a constant off-time and prevent switching frequency from entering audible ranges, thereby eliminating negative inductor currents.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If pulse-skipping mode is employed to reduce switching loss at light loading, then conversion efficiency is improved, but switching frequency decreases to audible range causing audio noise

Engineering Contradiction:

Improveswitching lossVSAvoidaudio noise

Core Design Contradiction:

Loss of energyVSObject-affected harmful factors

Solution Approach 1:

The patent changes the control parameter from constant on-time to variable on-time by introducing a modulation signal that adjusts the on-time duration. This allows the switching frequency to be maintained above the audible range while still operating in pulse-skipping mode at light loading, thereby eliminating audio noise while preserving efficiency improvements

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces a dynamic modulation signal that varies the on-time parameter based on operating conditions. The modulation signal is generated by comparing a triangle wave with a reference voltage, creating a dynamic control mechanism that adapts the switching characteristics to prevent audio noise while maintaining efficiency

Inventive Principle:

Principle #15Dynamics

2Object-affected harmful factors

If switching frequency is limited to 25 kHz to eliminate audio noise, then audio noise is eliminated, but output voltage increases and conversion efficiency deteriorates

Engineering Contradiction:

Improveaudio noiseVSAvoidconversion efficiency

Core Design Contradiction:

Object-affected harmful factorsVSLoss of energy

Solution Approach 1:

Instead of a fixed frequency limit, the patent implements a dynamic modulation approach where the effective switching frequency is varied through on-time modulation. This dynamic control allows the system to operate efficiently across different loading conditions while maintaining switching frequencies above the audible range, avoiding both audio noise and efficiency degradation

Inventive Principle:

Principle #15Dynamics

3Reliability

If constant on-time is used for high-side switch to regulate output voltage, then output voltage regulation is achieved, but at light loading the switching cycle increases causing switching frequency to enter audible range

Engineering Contradiction:

Improveoutput voltage regulationVSAvoidaudio noise

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent transforms the constant on-time control into a variable on-time control by applying modulation. The on-time duration becomes dynamic, adjusted by the modulation signal generated from the triangle wave comparison, allowing the system to maintain output voltage regulation while adapting the switching characteristics to prevent audio noise at light loading

Inventive Principle:

Principle #15Dynamics

4Object-affected harmful factors

If low-side switch is turned on early to prevent audible frequency, then switching frequency is maintained above audible range, but negative inductor current occurs degrading conversion efficiency

Engineering Contradiction:

Improveaudio noiseVSAvoidconversion efficiency

Core Design Contradiction:

Object-affected harmful factorsVSLoss of energy

Solution Approach 1:

Instead of controlling when to turn on the low-side switch to prevent audio noise, the patent inverts the approach by controlling the on-time of the high-side switch through modulation. This indirect control method prevents negative inductor current while still maintaining switching frequency above the audible range, avoiding efficiency degradation

Inventive Principle:

Principle #13The other way round (Inversion)

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 approach enhances conversion efficiency by preventing negative inductor currents and reducing audio noise, maintaining output voltage balance without the need for complex analog circuits, and is simpler to implement by adding digital logic to existing converters.

Implementation Method 1

activates a voltage-controlled voltage source to provide a bias voltage to shift a reference voltage or a feedback signal for determining a peak point of an output voltage

Methodology Applied

Scientific EffectVoltage control:

Data Source

PatentUS8664929B2Audio-skipping of a constant on-time power converter

Publication Date: 2014.03.04 RICHTEK TECH

AI summary

When the switching frequency of a constant on-time power converter decreases to a threshold, the power converter is switched from the original operation of triggering a constant on-time of a high-side switch responsive to the output voltage of the power converter reaching a valley point to the operation of triggering a constant off-time of the high-side switch responsive to the output voltage reaching a peak point, to thereby prevent the power converter from operating in an audio frequency range.