Supply Rail Mirror Circuit for Class D Rail Pumping
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Solution Overview
Problem
The half-bridge class D amplifier topology for audio power conversion suffers from rail pumping issues, leading to excessive use of capacitors, higher costs, larger physical size, and unacceptable audio performance due to asymmetrical rail perturbations, which diminish the benefits of using single-ended class D amplifiers.
Innovation Solution
A Supply Rail Mirror (SRM) circuit using a high-frequency transformer to continuously redistribute pumping charge from the rail with higher voltage to the rail with lower voltage, effectively canceling rail pumping and utilizing both rail capacitors efficiently, while implementing soft-switching techniques to reduce noise and complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If half-bridge class D amplifier topology is used, then cost and component count are reduced, but rail pumping causes excessive capacitor requirements and larger physical size
Solution Approach 1:
The patent introduces a full-bridge amplifier stage as an intermediary component between the power supply and the half-bridge class D amplifier. This full-bridge stage acts as a mediator that handles the rail pumping current, preventing it from affecting the half-bridge amplifier's power supply rails. By using this intermediary stage, the system maintains the cost advantages of the half-bridge topology while eliminating the physical size penalty from excessive capacitor requirements
Solution Approach 2:
The patent extracts the rail pumping problem from the half-bridge amplifier system by separating the functions: the half-bridge amplifier handles audio amplification while a dedicated full-bridge stage handles the power supply current balancing. This extraction allows the half-bridge amplifier to operate without the harmful rail pumping effects, reducing the required capacitor size and overall physical dimensions
2Device complexity
If half-bridge class D amplifier topology is used, then component count is reduced, but rail pumping leads to higher voltage-rated devices and increased cost
Solution Approach 1:
The full-bridge amplifier stage serves as an intermediary that absorbs the high-voltage stress from rail pumping currents. By placing this stage between the power supply and the half-bridge amplifier, the voltage-rated requirements for the half-bridge amplifier's capacitors and MOSFETs are reduced, allowing the use of lower-cost, lower-voltage-rated components while maintaining the simplified component count of the half-bridge topology
3Device complexity
If dual rail supply is used with single-ended class D amplifier, then topology simplicity is maintained, but asymmetrical rail perturbation degrades audio performance
Solution Approach 1:
The full-bridge amplifier stage acts as an intermediary buffer between the dual rail power supply and the half-bridge class D amplifier. It equalizes the current draw from both positive and negative rails, preventing asymmetrical rail perturbations from reaching the amplifier. This maintains the simplicity of the single-ended topology while ensuring clean, stable power delivery for high-fidelity audio performance
Solution Approach 2:
The patent implements a control system that monitors the current drawn from the power supply rails and uses feedback to adjust the full-bridge stage's operation. This feedback mechanism ensures that the current drawn from the positive and negative rails is equalized, eliminating asymmetrical perturbations that would otherwise degrade audio performance while maintaining topological simplicity
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
The solution significantly reduces rail pumping, improves audio performance, enhances system efficiency, and simplifies the circuit by autonomously correcting rail voltage variations, thereby maintaining better audio quality and reducing the peak-to-average power ratio.
Implementation Method 1
a high frequency transformer having a first and a second winding alternatingly connectable during a first and second cycle to said positive and negative supply rails, so as to cause a current to migrate from the rail with the highest voltage to the rail with the lowest voltage
Data Source
Figure 1~3
Figure 4~5
Figure 6~7
AI summary
An audio power conversion system (3) comprising a power supply (1) having a positive supply rail (100) and a negative supply rail (200) for supplying power to a single ended class D amplifier (2). The system further comprises a supply pump reduction circuit (6) connected to the supply rails (100, 200) 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 current invention, the redistribution circuit is arranges to always distribute charge from the rail with the higher voltage. This means that for practical circuits the pump canceling occurs continuously and is not confined to every other cycle as for the prior art.