Charge Pump Class D Audio Amplifier Battery Current Limiting
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Solution Overview
Problem
Class D audio amplifiers face challenges in effectively limiting battery current in portable systems, as existing methods either require significant board space for inductors or result in thermal power loss when increasing impedance, which are not ideal for prolonging battery operational time.
Innovation Solution
The implementation of a multiplexer-controlled audio amplifier circuit that selects between different input signals based on battery current levels, using a signal generator and driver circuit to manage the duty cycle of the pulse-width modulator, thereby controlling the battery current drawn by the amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If inductors are used for current limiting in class D audio amplifiers, then current limiting function is achieved, but board space is significantly increased
Solution Approach 1:
The patent extracts the current limiting function from the traditional inductor-based approach and implements it through a dedicated current limit circuit that senses battery current and controls the charge pump switching. This removes the need for large inductors while maintaining the current limiting function, directly resolving the contradiction between achieving current limiting and minimizing board space.
Solution Approach 2:
The patent replaces the passive inductor-based current limiting mechanism with an active electronic control system consisting of current sensing circuits, error amplifiers, and switch control logic. This substitution eliminates the need for bulky inductors while providing precise current limiting control, resolving the board space issue.
2Quantity of substance
If impedance is increased for current limiting, then current draw is reduced, but thermal power loss increases
Solution Approach 1:
The patent implements a feedback mechanism where the current limit circuit continuously monitors battery current through sensing resistors and adjusts the charge pump switching duty cycle accordingly. When current exceeds the limit, the feedback control reduces the switching duty cycle to limit current draw, achieving current limiting without increasing impedance and avoiding thermal power loss.
Solution Approach 2:
The patent makes the charge pump switching dynamic and adjustable through the current limit circuit. The switching duty cycle is dynamically controlled based on real-time battery current conditions, allowing the system to adapt current draw without fixed impedance changes, thereby avoiding thermal power loss while effectively limiting battery current.
Data Source
AI summary
Described embodiments include an audio amplifier circuit that includes a first amplifier having a differential first amplifier input adapted to be coupled to an audio input source, a multiplexer having first and second mux inputs, a control input and a mux output. The first mux input is coupled to the differential amplifier output. There is a signal generator having a generator input coupled to the mux output. There is also a driver circuit having a driver circuit input and a driver circuit output, the driver circuit input coupled to the generator output, and a second amplifier having a first error input coupled to a current sense terminal that is configured to provide a voltage proportional to a current supplied from a power supply terminal, and a second error input coupled to a current limit terminal configured to provide a reference voltage proportional to a current limit value.