Speaker Drive Circuit Protection for Low-Level Abnormal Current

Solution Overview

Problem

Conventional overcurrent detection devices in audio apparatuses struggle to detect feeble abnormal currents during sound reproduction, leading to potential damage of speakers or power amplifiers due to continuous heat generation from resistive loss, as they are designed to detect abnormalities only when sound is not generated and are not effective in scenarios where sound is continuously played.

Innovation Solution

A protective device comprising a sound level detector, a current level detector, and a determination section that generates a protection command signal when the current level exceeds a threshold during periods of low sound levels, allowing for the detection of abnormal currents even when sound is regenerated, thereby preventing damage to speakers or power amplifiers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If threshold current is set high to avoid false detection during large volume periods, then false detection is reduced, but detection precision of feeble abnormal current deteriorates

Engineering Contradiction:

Improvefalse detection reductionVSAvoidabnormal current detection precision

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent applies dynamics by making the threshold current adaptive rather than fixed. The threshold current dynamically changes based on the sound level detection result, switching between a first threshold current (higher) during large volume periods and a second threshold current (lower) during small volume periods. This resolves the contradiction by allowing the system to maintain high reliability during large volume periods while achieving high detection precision during small volume periods.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent applies parameter changes by modifying the threshold current parameter according to the sound level condition. When the sound level drops below a predetermined level, the threshold current parameter is changed from the first value to the second value, enabling the system to detect feeble abnormal currents that would otherwise be missed during small volume periods while avoiding false detections during large volume periods.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If detection is performed only during mute periods, then false detection is avoided, but detection capability during sound reproduction is lost

Engineering Contradiction:

Improvedetection accuracyVSAvoiddetection coverage

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent applies dynamics by enabling the detection function to be active during both large volume periods and small volume periods, with the threshold automatically adjusting based on sound level. This resolves the contradiction by allowing continuous detection coverage (improving productivity) while maintaining high accuracy through dynamic threshold adjustment (maintaining reliability).

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent applies universality by making the overcurrent detection device functional during all operating conditions (both sound reproduction and mute periods) rather than being limited to mute periods only. The detection device universally monitors current across all states, with the threshold adaptation mechanism ensuring accurate detection regardless of the operating state.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Measurement precision

If threshold current is set low to detect feeble abnormal current, then detection precision improves, but false detection during large volume periods increases

Engineering Contradiction:

Improveabnormal current detection precisionVSAvoidfalse detection rate

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent applies dynamics by making the threshold current adaptive rather than fixed. The threshold current dynamically changes based on the sound level detection result, switching between a first threshold current (higher) during large volume periods and a second threshold current (lower) during small volume periods. This resolves the contradiction by allowing the system to maintain high reliability during large volume periods while achieving high detection precision during small volume periods.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentEP3379846B1Protective device

Publication Date: 2020.06.03 PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO LTD

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AI summary

A protective device that detects an abnormal current in a driving circuit for driving a speaker includes a sound level detector, a current level detector, and a determination section. The sound level detector detects a sound level of an audio signal output to the driving circuit. The current level detector detects a current level of a current flowing in the driving circuit from a power source. The determination section generates, based on a detection signal of the sound level and a detection signal of the current level, a protection command signal when the current level larger than a second threshold is detected when the sound level of the audio signal is smaller than a first threshold.