Class D Amplifier Compensation Circuit for Reverse Current Control
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Solution Overview
Problem
Class D amplifiers experience power supply voltage fluctuations due to reverse current, leading to loss of output voltage regulation, as existing solutions are either inefficient, require additional space, or are not universally applicable across different amplifier topologies.
Innovation Solution
A compensation circuit that models and matches the reverse current characteristics with a compensation current controlled by the output voltage, providing a gradually-sloped stepping compensation current to minimize power loss and maintain positive current flow from the power supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a battery is used to power the class D amplifier, then reverse current can charge the battery, but the design is not suitable for systems requiring well-controlled voltage sources
Solution Approach 1:
The patent introduces an intermediary energy storage element (capacitor) between the class D amplifier and the power supply. This capacitor absorbs the reverse current during switching transitions and releases it when needed, mediating between the amplifier's bidirectional current flow and the power supply's unidirectional current capability, thus enabling use with regulated voltage sources
Solution Approach 2:
The patent creates a simplified model of the complex reverse current waveform by capturing its essential characteristics (amplitude and duration). This modeled representation is then used to design the compensation circuit, replacing the need for complex real-time analysis of the actual reverse current behavior
2Reliability
If a large capacitor is used to recover reverse current energy, then power supply stability is improved, but significant real estate is required in the system floor plan
Solution Approach 1:
The patent changes the operating parameters of a smaller capacitor by dynamically adjusting its voltage swing range and timing of charge/discharge cycles. By optimizing these parameters, the capacitor achieves effective reverse current compensation with significantly reduced capacitance value and physical size compared to traditional approaches
Solution Approach 2:
The patent employs dynamic control of the compensation circuit, adjusting the capacitor's charge and discharge timing based on the actual reverse current waveform characteristics. This dynamic operation allows a smaller capacitor to achieve the same energy recovery effect that would require a much larger static capacitor
3Reliability
If a resistor is added between the power supply output and ground to sink reverse current, then LDO stability is maintained, but system power is continuously wasted
Solution Approach 1:
The patent replaces continuous current sinking with periodic action - the compensation capacitor charges during reverse current intervals and discharges during normal operation. This periodic charge-discharge cycle maintains LDO stability only when needed, eliminating continuous power dissipation while preserving regulation stability
Solution Approach 2:
The patent recovers the reverse current energy that would otherwise be wasted by the resistor. The capacitor captures this energy during reverse current flow and returns it to the power supply system during appropriate intervals, converting a purely dissipative approach into a regenerative approach
4Reliability
If differential loading is used to ensure forward current exceeds reverse current, then LDO operation is maintained, but the solution is not available for single-ended loads
Solution Approach 1:
The patent creates a universal compensation circuit that works with any load topology (single-ended, differential, balanced, unbalanced). The circuit monitors the power supply current and provides compensation regardless of the load configuration, making it applicable to headphones, speakers, and other various load types without requiring topology-specific design
Data Source
AI summary
The present invention discloses a bus pumping compensation for a pulse modulation circuit such as class D modulators. The compensation according to the present invention provides a compensation current controlled by the output voltage, with the compensation characteristics matching the reverse current for improving circuit efficiency. Embodiments of the present invention also disclose a designable compensation circuit, comprising a linear compensation current, offering a good trade-off between circuit efficiency and ease of design. The present invention compensation circuit is preferably employed in a class D amplifier with substantial reverse current, and most preferably added into a LDO power supply in a class D amplifier circuit to prevent reverse current problem. The disclosed class D amplifier circuit is preferably used in an audio media player.