Switching Amplifier With Linear Totem Pole Zero-Crossing Control
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Solution Overview
Problem
Conventional switching amplifiers face challenges in minimizing total harmonic distortion (THD) and electromagnetic interference (EMI) while maintaining low switching losses, often requiring costly filter components and introducing power consumption issues and 'pop' noises.
Innovation Solution
A switching amplifier with a linear transition totem pole topology, incorporating a PWM control loop and a linear amplifier, which reduces THD by transitioning the low-frequency output slowly around zero crossing and eliminates the need for an inductor in the filter circuitry, thereby simplifying the filter design and reducing switching losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If totem pole LSR modulation is used to minimize EMI pulses, then EMI is reduced, but power consumption increases due to frequent switching activity
Solution Approach 1:
The patent implements dynamic control of the low-side switch by transitioning it slowly around zero-crossing points rather than using fixed-frequency switching. This dynamic approach reduces EMI by minimizing abrupt transitions while simultaneously reducing power consumption by avoiding unnecessary switching activity during low signal levels.
Solution Approach 2:
The patent changes the switching parameter from fixed-frequency to variable-frequency modulation, where the switching frequency and duty cycle are dynamically adjusted based on the input signal amplitude and zero-crossing detection. This allows the system to minimize EMI pulses while reducing overall switching activity to lower power consumption.
2Loss of energy
If toggling time is extended to reduce switching losses, then switching losses decrease, but EMI pulses increase
Solution Approach 1:
The patent employs periodic zero-crossing detection and synchronization, where the low-side switch transitions are timed to occur at regular zero-crossing intervals of the input signal. This periodic action allows for optimized transition timing that minimizes both switching losses and EMI pulses by aligning transitions with natural signal cycles.
3Use of energy by moving object
If duty cycle is reduced to minimize power consumption, then power consumption decreases, but THD increases due to insufficient on-time
Solution Approach 1:
The patent implements preliminary zero-crossing detection and prediction mechanisms that prepare the low-side switch for upcoming transitions. By anticipating zero-crossing points in advance, the system can optimize the timing and duration of switch on-states to maintain adequate on-time for low duty cycle operation while preserving signal fidelity and minimizing THD.
4Object-affected harmful factors
If LC filter is added to remove switching components, then EMI is reduced, but device complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates the need for complex LC filter circuitry by fundamentally changing the switching modulation approach. The low-side recycle modulation technique with zero-crossing detection inherently minimizes EMI pulses at the source, allowing the system to achieve EMI reduction without adding bulky and costly filter components to the output stage.
Data Source
AI summary
A switching amplifier includes a first portion of a power stage; a second portion of a power stage; a pulse-width modulation (PWM) control loop coupled to control inputs of the first portion of the power stage; and a linear amplifier coupled to control inputs of the second portion of the power stage. The PWM control loop controls a first switch and a second switch of the first portion of the power stage. Between current terminals of the first switch and the second switch is a first signal output of the switching amplifier. The linear amplifier controls a third switch and a fourth switch of the second portion of the power stage. Between current terminals of the third switch and the fourth switch is a second signal output of the switching amplifier.