Class-AB Load Current Sensing for Real-Time Speaker Impedance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional class-AB amplifiers face challenges in accurately sensing small load currents due to the use of small sense resistors, leading to underutilization of audio speakers and potential damage from over-displacement and overheating, while also suffering from high quiescent current and crossover distortion.
Innovation Solution
A load current monitoring circuit that senses current without using sense resistors in series with the half-bridges of the output stage, allowing for real-time impedance estimation and protection of the audio speaker, using a current sensing circuit and analog-to-digital converter to convert sensed currents into digital form for real-time processing and optimization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If small sense resistors are used in conventional class-AB amplifiers, then the amplifier can operate with lower power consumption, but the ability to accurately sense small load currents deteriorates
Solution Approach 1:
The patent introduces an intermediary current sensing circuit that uses operational amplifiers and transistors to sense load current without requiring large sense resistors. The sensing circuit amplifies the small voltage drops across small resistors, enabling accurate measurement of small load currents while maintaining low power consumption in the main amplifier pathway.
2Object-affected harmful factors
If class-AB amplifiers use biasing circuits to reduce crossover distortion, then crossover distortion is reduced, but the quiescent current increases
Solution Approach 1:
The patent implements dynamic biasing control where the biasing circuit adjusts the operating point of the output stage based on the sensed load current. When load current is small, the biasing provides sufficient overlap to reduce crossover distortion. When load current increases, the biasing dynamically adjusts to reduce quiescent current consumption, achieving both low distortion and low power consumption under different operating conditions.
3Reliability
If conventional load current sensing is implemented, then load current can be monitored, but real-time impedance estimation and speaker protection capabilities are insufficient
Solution Approach 1:
The patent implements a feedback loop where the load current sensing circuit continuously monitors current, the microcontroller processes this data to estimate impedance in real-time, and the system adjusts operation accordingly. This closed-loop feedback enables accurate impedance estimation and provides active speaker protection by detecting abnormal conditions and responding appropriately, significantly improving reliability compared to conventional open-loop sensing.
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
In an embodiment, a class-AB amplifier includes: an output stage that includes a pair of half-bridges configured to be coupled to a load; and a current sensing circuit coupled to a first half-bridge of the pair of half-bridges. The current sensing circuit includes a resistive element and is configured to sense a load current flowing through the load by: mirroring a current flowing through a first transistor of the first half-bridge to generate a mirrored current, flowing the mirrored current through the resistive element, and sensing the load current based on a voltage of the resistive element.