DC-DC Converter Audio Noise Suppression via Dummy Pulses

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing DC-DC switching converters face inefficiencies at light loads due to dominant switching losses and high quiescent current when using PWM control, and they allow audio noise due to uncontrolled switching frequencies during hysteretic control.

Innovation Solution

A circuit and method that utilize a first-order gm amplifier and hysteretic Burst control logic to generate dummy pulses, ensuring a minimum switching frequency above 20 kHz, thereby regulating output voltage and suppressing audio noise by dissipating excess energy through the gm amplifier.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If PWM control is used at light loads, then constant switching frequency is maintained, but switching losses dominate and quiescent current increases reducing efficiency

Engineering Contradiction:

Improveswitching lossesVSAvoidefficiency at light loads

Core Design Contradiction:

Loss of energyVSProductivity

Solution Approach 1:

The patent implements dynamic switching between PWM and hysteretic control modes based on load conditions. At light loads, the system transitions to hysteretic control which dynamically adjusts switching frequency to minimize switching losses, while at heavier loads it uses PWM for constant frequency operation. This dynamic adaptation resolves the contradiction by optimizing the control mode according to operating conditions.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the control parameter (switching frequency) dynamically based on load conditions. During light load operations, hysteretic control allows the switching frequency to vary naturally, reducing switching losses. The patent also introduces dummy pulses to modify the effective switching frequency parameter to maintain it above audio noise thresholds when operating in hysteretic mode.

Inventive Principle:

Principle #35Parameter changes

2Loss of energy

If hysteretic control is used at light loads, then switching frequency is reduced improving efficiency, but uncontrolled switching frequency allows audio noise

Engineering Contradiction:

Improveswitching lossesVSAvoidaudio noise

Core Design Contradiction:

Loss of energyVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary anti-action by introducing dummy pulses before the natural hysteretic switching occurs. These dummy pulses are specifically designed to prevent the switching frequency from falling into the audio noise range (below 20 kHz). By proactively adding these compensating pulses, the system counteracts the potential harmful effect of low-frequency switching before it can occur.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The dummy pulses act as an intermediary mechanism between the hysteretic control and the output. They mediate the switching frequency to ensure it remains above the audio noise threshold while still allowing the system to operate in efficient hysteretic mode at light loads. The gm amplifier also serves as an intermediary to dissipate the excess energy introduced by these dummy pulses.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Object-affected harmful factors

If dummy pulses are added to enforce minimum switching frequency, then audio noise is suppressed, but excess energy is introduced reducing efficiency

Engineering Contradiction:

Improveaudio noiseVSAvoidexcess energy from dummy pulses

Core Design Contradiction:

Object-affected harmful factorsVSLoss of energy

Solution Approach 1:

The patent converts the harmful effect of excess energy from dummy pulses into a beneficial dissipation mechanism. The gm amplifier is specifically designed to sink and dissipate this excess energy efficiently. By redirecting the harmful excess energy through a controlled dissipation path, the system transforms what would be a waste into a managed parameter that maintains overall efficiency while achieving audio noise suppression.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

4Use of energy by moving object

If switching frequency is reduced to improve efficiency, then quiescent current decreases, but switching activity falls into audio noise range

Engineering Contradiction:

Improvequiescent currentVSAvoidaudio noise

Core Design Contradiction:

Use of energy by moving objectVSObject-affected harmful factors

Solution Approach 1:

The system dynamically adjusts the switching frequency based on operational requirements. During light load conditions, it operates in hysteretic mode with naturally lower switching frequency to reduce quiescent current and switching losses. When the frequency approaches the audio noise threshold, the system dynamically introduces dummy pulses to elevate the effective switching frequency above 20 kHz, thus maintaining low power consumption while avoiding audio noise.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS10615694B2Circuit and method for suppressing audio noise in DC-DC converters

Publication Date: 2020.04.07 DIALOG SEMICONDUCTOR (UK) LTD

AI summary

A solution is provided for suppressing audio noise in a DC-DC switching converter. A means for limiting the minimum switching frequency of a pulse-frequency modulation (PFM) control is described. A first order gm amplifier dissipates the excess energy added to the inductor, when magnetizing at faster rate than the native PFM. A higher resistance, low-side scaled switch helps reduce wasted energy losses. The low-side scaled switch reduces the rise in the inductor current during magnetization, and hence keeps efficiency up at low loads, when the PFM minimum switching frequency is active.