Filterless Switching Amplifier EMI Reduction via Duty Cycle Control
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Solution Overview
Problem
Conventional switching amplifiers face efficiency drops and increased costs due to the need for low-pass filters to mitigate electromagnetic interference (EMI) when connected to inductive loads, while filterless alternatives still struggle with EMI issues.
Innovation Solution
A filterless switching amplifier with an H-bridge circuit and control circuit that generates output signals with specific duty cycles and phase relationships, minimizing switching current and EMI without the need for low-pass filters, maintaining high efficiency and reducing EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a low-pass filter is introduced to filter out high-frequency current components, then EMI problems are reduced, but cost increases and efficiency drops
Solution Approach 1:
The patent extracts and eliminates the low-pass filter component from the conventional switching amplifier system. By using a specific switching control method where one transistor is kept off during certain periods, the harmful high-frequency current components are prevented from occurring in the first place, making the filter unnecessary and thereby maintaining efficiency while reducing EMI
Solution Approach 2:
The patent converts the potential harmful switching current into a beneficial control mechanism. By intentionally controlling one transistor to remain off during specific periods, the harmful EMI-generating current is prevented, and this control state is used to achieve both EMI reduction and efficiency maintenance simultaneously
2Object-affected harmful factors
If a low-pass filter is introduced to filter out high-frequency current components, then EMI problems are reduced, but device complexity and cost increase
Solution Approach 1:
The patent removes the low-pass filter from the system architecture by using a control method that prevents harmful current components from generating in the first place, thereby simplifying the device structure and reducing cost while maintaining EMI performance
3Loss of energy
If filterless switching is used to maintain high efficiency, then efficiency is maintained, but EMI problems persist
Solution Approach 1:
The patent converts the switching operation that would normally generate EMI into a controlled state where one transistor remains off during specific periods. This control strategy prevents harmful current components while maintaining the high efficiency benefits of filterless switching
Solution Approach 2:
The patent changes the switching parameters by controlling the duty cycle of transistors in a specific pattern where one transistor is kept off during certain periods. This parameter change prevents the generation of harmful high-frequency current components while maintaining efficiency
Data Source
AI summary
In a switching amplifier for generating a pair of output signals of square waves in response to an input signal, when the input signal is zero, the first output signal has a first duty cycle and the second output signal has a second duty cycle; when the input signal is greater than zero, the first output signal has a third duty cycle varying with the input signal and the second output signal still has the second duty cycle; and when the input signal is less than zero, the first output signal has the first duty cycle and the second output signal has a fourth duty cycle varying with the input signal. The first and second duty cycles are very small but equal to each other in size, and the phase difference between the first and second output signals could range from 0 to 180 degrees.