Digital Audio Amplifier Overcurrent Protection with Dynamic Threshold

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Solution Overview

Problem

Conventional digital audio amplifiers often inadvertently shut down due to dynamic impedance from modern loudspeakers, leading to undesirable audio interruptions and increased manufacturing costs from overdesign for overload protection.

Innovation Solution

Implementing a digital audio amplifier with cycle-by-cycle overload protection that monitors output current relative to a dynamically changing overcurrent threshold, resetting only at the next pulse-width-modulation cycle or frame, and adjusting the overcurrent threshold based on the frequency of overload cycles to prevent audible clicks and pops.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional overcurrent protection systems are designed with high current margins to accommodate dynamic impedance of modern loudspeakers, then false shutdowns are avoided, but manufacturing cost increases due to overdesign

Engineering Contradiction:

Improveavoidance of false shutdownsVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The overcurrent threshold is made dynamic rather than fixed. The system adjusts the threshold based on operating conditions, specifically raising it during transient periods when dynamic impedance causes temporary current spikes. This allows the protection system to tolerate normal dynamic variations while still protecting against genuine faults, eliminating the need for conservative overdesign margins.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system performs preliminary detection and evaluation of overcurrent conditions before triggering a shutdown. It monitors the duration and characteristics of current excursions, distinguishing between transient spikes caused by dynamic impedance and sustained overcurrent conditions indicating actual faults. This preliminary action prevents false shutdowns while maintaining protection.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If conventional digital audio amplifiers implement overcurrent protection that shuts down on detecting overload conditions, then output protection is provided, but audible interruptions occur requiring user reset

Engineering Contradiction:

Improveoutput protectionVSAvoiduser convenience

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The protection system dynamically evaluates overcurrent conditions based on their duration and characteristics. For transient overcurrent conditions caused by dynamic impedance, the system maintains output continuity without shutdown. For sustained genuine overcurrent faults, protection shutdown is triggered. This dynamic response eliminates unnecessary interruptions while maintaining genuine protection.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system performs preliminary assessment of overcurrent conditions before initiating shutdown. It evaluates whether the overcurrent is transient (normal dynamic operation) or sustained (genuine fault). This preliminary discrimination prevents unnecessary shutdowns for normal dynamic variations while maintaining protection for actual faults, improving user convenience without sacrificing reliability.

Inventive Principle:

Principle #10Preliminary action

3Ease of operation

If auto-recovery function is implemented to automatically reset after overload trips, then audio content continues playing, but audible clicks and pops occur in the output

Engineering Contradiction:

Improvecontinuous audio playbackVSAvoidaudible clicks and pops

Core Design Contradiction:

Ease of operationVSObject-affected harmful factors

Solution Approach 1:

The system performs preliminary detection and evaluation of overcurrent conditions before they can cause audible artifacts. By detecting and responding to transient overcurrent conditions caused by dynamic impedance before they result in shutdown and recovery cycles, the system prevents the generation of clicks and pops entirely. The protection action is taken preliminarily to avoid the need for recovery that would cause audible disturbances.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system converts the potentially harmful effect of dynamic impedance-induced current spikes into beneficial information. By monitoring and recognizing these transient spikes as normal operating conditions rather than faults, the system uses them to inform its protection decisions, adjusting its response to prevent unnecessary shutdowns and subsequent audible recovery artifacts.

Inventive Principle:

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

Data Source

PatentUS7773358B2Output current control and overload protection in digital audio amplifiers

Publication Date: 2010.08.10 TEXAS INSTRUMENTS INC

AI summary

Overcurrent and overload protection for the power output of a pulse-width-modulated digital audio system is disclosed. The overcurrent protection circuitry includes a latch that is set in responsive to output current from the power output stage that exceeds an overcurrent threshold; the output of the latch gates the pulse-width-modulated control signal to block power output for the remainder of the current pulse-width-modulated cycle; upon the end of the cycle, or the beginning of the next, the latch is cleared to enable power output in that next cycle. Overload protection is provided by circuitry including counters for counting the relative number of overcurrent cycles to normal, non-overcurrent cycles, and generating an overload signal to block power output in the event of too frequent overcurrent cycles.