Class D Amplifier Power Supply with Synchronous Rectifiers
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Solution Overview
Problem
Class D amplifiers face issues with off side charging and poor cross regulation of bipolar outputs, leading to inefficiencies and potential overvoltage or distortion in audio power amplifiers.
Innovation Solution
A power supply topology is designed with synchronous rectifiers and a modified power factor correction choke to minimize quiescent mode losses, reduce switching losses, and eliminate external resonant inductors, ensuring constant output voltage and improved cross regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional linear or quasi-linear amplifiers (Class A, B, G, H) are used, then high power audio output with low total harmonic distortion is achieved, but efficiency is poor (approximately 25% under normal operating conditions)
Solution Approach 1:
The patent transitions from linear operation to switching operation, fundamentally changing the operating parameters of the amplifier. Class D amplifiers use pulse-width modulation (PWM) to switch transistors between saturation and cutoff regions, achieving efficiencies exceeding 90% while maintaining audio quality through careful filtering and modulation techniques.
2Loss of energy
If Class D amplifiers are used to improve efficiency, then higher efficiency is achieved than traditional amplifiers, but problems of off side charging and poor cross regulation of bipolar outputs occur
Solution Approach 1:
The patent implements feedback control circuits that monitor the output voltages of both positive and negative bipolar supplies and adjust the switching duty cycles accordingly. This feedback mechanism corrects off-side charging effects and maintains precise voltage regulation, ensuring stable operation of the Class D amplifier.
3Stability of the object's composition
If power supply is designed to reduce off side charging and improve cross regulation, then output voltage stability is improved, but device complexity increases due to additional synchronous rectifiers and control circuits
Solution Approach 1:
The patent designs the power supply circuit where synchronous rectifiers serve multiple functions: they provide efficient voltage rectification, active regulation of output voltages, and compensation for off-side charging effects. This multi-functionality reduces the need for separate regulation circuits, thereby limiting the increase in overall device complexity while achieving superior voltage stability.
4Stability of the object's composition
If synchronous rectifiers are used to reduce off side charging, then output voltage stability is improved, but switching losses in power factor correction stage increase
Solution Approach 1:
The patent employs periodic resonant switching in the power factor correction stage, where switches are turned on and off at resonant frequencies to minimize switching losses. The synchronous rectifiers are also controlled with precise timing to switch at optimal moments, reducing overlap losses and maintaining high efficiency while achieving voltage regulation.
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 reduces quiescent power consumption from 12.1 W to 8.4 W, enhances efficiency, and prevents off side charging, thereby improving the power rating and sound quality of Class D amplifiers.
Implementation Method 1
a first transformer; a first set of transistors coupled to the primary side of the second transformer, where the first transformer is configured to drive the first set of transistors
Implementation Method 2
a first inductor coupled to the second set of transistors, and where the first inductor produces a magnetized inductance
Implementation Method 3
the first set of synchronous rectifiers are configured to reduce an off side charging of a supply voltage rail corresponding to the positive output from a first level to a second level lower than the first level
Data Source
AI summary
A power supply for use with Class D amplifiers in energy efficient applications is described herein. The power supply reduces the effects of off side charging and improves cross regulation. The topology of the power supply can be designed to minimize quiescent mode losses through resonant switching of some or all active switches. Additionally, the power supply can be implemented without external resonant inductors, the power supply can be implemented with smaller capacitors that have longer lifetime ratings, the switching losses present in a power factor correction stage of the power supply can be reduced, and/or a modified power factor correction choke can be utilized to reduce energy loss.