Supply Rail Mirror Circuit for Class D Audio Amplifiers
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Solution Overview
Problem
The half-bridge class D amplifier topology in audio power conversion systems suffers from rail pumping, leading to excessive use of capacitors, higher costs, larger physical size, and unacceptable audio performance due to asymmetrical rail perturbation, which complicates the system and reduces product value.
Innovation Solution
The introduction of a Supply Rail Mirror (SRM) circuit that continuously redistributes pumping charge from the rail with higher voltage to the rail with lower voltage, using a high-frequency transformer and switching means to balance the supply rails, eliminating the need for additional control circuits and utilizing both rail capacitors efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If half-bridge class D amplifier topology is used, then component count and manufacturing cost are reduced, but rail pumping occurs causing excessive capacitor requirements and larger physical size
Solution Approach 1:
A supply rail mirror circuit is introduced as an intermediary component between the power supply rails and the amplifier. This circuit actively monitors and equalizes voltage differences between the positive and negative supply rails, preventing rail pumping effects. The mediator circuit transfers charge between rails through controlled switching, maintaining voltage balance without requiring excessive capacitor sizes.
Solution Approach 2:
The supply rail mirror circuit implements a feedback mechanism by continuously monitoring the voltage difference between the positive and negative supply rails. When an imbalance is detected, the circuit automatically activates switching elements to transfer charge and restore voltage equilibrium. This closed-loop control prevents rail voltage excursions that would otherwise require oversized capacitors to compensate for.
2Ease of operation
If dual rail supply is used with half-bridge topology, then amplifier operation is enabled, but asymmetrical rail perturbation degrades audio performance
Solution Approach 1:
The supply rail mirror circuit actively maintains equipotential conditions between the positive and negative supply rails by detecting voltage differences and transferring charge to equalize the potentials. This prevents asymmetrical rail perturbation that would otherwise be modulated onto the audio signal, thereby maintaining high audio performance while enabling dual rail supply operation.
Solution Approach 2:
The circuit converts the harmful rail pumping effect into a beneficial self-correcting mechanism. By monitoring voltage imbalances and automatically transferring charge from higher to lower voltage rails, the circuit transforms what would be a performance-degrading phenomenon into an active voltage balancing feature that improves overall system reliability and audio quality.
3Stability of the object's composition
If large rail capacitors are used to compensate for rail pumping, then rail voltage stability is improved, but system cost and physical size increase
Solution Approach 1:
Instead of using large capacitors as a passive compensation method, the invention introduces an active intermediary circuit (supply rail mirror) that dynamically manages voltage stability. This circuit uses controlled switching and charge transfer to maintain rail voltage stability with much smaller capacitor values, reducing both physical size and system complexity while achieving the same stability goal.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively cancels rail pumping, reduces system complexity and cost, improves audio performance, and enhances efficiency by maintaining soft-switching techniques, resulting in balanced rail voltages and reduced peak-to-average power ratio.
Implementation Method 1
a high-frequency transformer and switching means to balance the supply rails
Data Source
AI summary
An audio power conversion system includes a power supply having a positive supply rail and a negative supply rail for supplying power to a single ended class D amplifier. The system further includes a supply pump reduction circuit connected to the supply rails and adapted to redistribute a pumping charge from said power supply by forcing a current-flow from a rail with a higher voltage to a rail with a lower voltage. According to the at least one embodiment of the invention, the redistribution circuit is arranges to always distribute charge from the rail with the higher voltage. Thus, for practical circuits, the pump canceling occurs continuously and is not confined to every other cycle.