Adaptive Burst Generation for DC-Output Converter Noise Reduction
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Solution Overview
Problem
Flyback converters face efficiency drops at light loads due to increased reactive energy needs for zero voltage switching, leading to output ripples and audible noise, and require oversized capacitors when using burst mode control.
Innovation Solution
Adaptive burst generation that adjusts switching cycles based on load levels, using a non-audible threshold frequency and clamping pulse frequency to prevent audible noise, allowing for efficient operation across a wider load range without oversized capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If burst mode control is used to improve light load efficiency, then efficiency is improved, but output ripples increase and audible noise is introduced
Solution Approach 1:
The patent applies dynamics by making the burst frequency adaptive rather than fixed. The controller dynamically adjusts the burst frequency based on load conditions, transitioning from a fixed frequency approach that causes audible noise to a variable frequency approach that eliminates audible noise while maintaining light load efficiency improvements.
Solution Approach 2:
The patent changes the frequency parameter of the burst mode operation. By varying the burst frequency as a controllable parameter rather than keeping it constant, the system can optimize performance across different load conditions and avoid the audible noise problem associated with fixed frequencies in the audible range.
2Loss of energy
If burst mode control is used to improve light load efficiency, then efficiency is improved, but oversized output capacitors are required
Solution Approach 1:
The adaptive burst frequency control dynamically adjusts operating parameters to maintain output voltage stability across varying load conditions. This dynamic adjustment reduces the need for oversized capacitors that would be required with fixed frequency burst mode, as the system can better regulate output voltage without excessive ripple.
3Device complexity
If fixed burst frequency is used, then control is simplified, but audible noise is introduced
Solution Approach 1:
The patent implements dynamic frequency adjustment where the burst frequency varies based on operating conditions. This eliminates audible noise by keeping the frequency outside the audible range or varying it to prevent resonance, while the control complexity is managed through automated sensing and control circuitry that adapts the frequency without requiring complex external adjustment mechanisms.
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
Significantly reduces output ripples and audible noise, improves light load efficiency, and enables burst mode operation at heavier loads with reduced capacitor size requirements.
Implementation Method 1
The primary current and magnetic flux in the transformer increases, storing energy in the transformer
Implementation Method 2
The voltage induced in the secondary winding is negative
Implementation Method 3
An output capacitor then supplies energy to the output load
Data Source
AI summary
These teachings apply with respect to a direct current (DC)-output converter and provide for adjusting a number of switching pulses per burst cycle as a function, at least in part, of converter output loading. This adjustment can be made by controlling burst frequency with respect to at least one predetermined threshold frequency. The predetermined threshold frequency can comprise a non-audible frequency such that the number of switching pulses is adjusted to prevent the burst frequency from itself constituting an audible signal. The adjustment of the number of switching pulses per burst cycle may only occur when the output loading is less than a predetermined level of loading. These teachings may also provide for clamping the pulse frequency for the pulses in each burst package to a particular value when dynamically controlling the number of pulses in each burst package. The aforementioned particular value may constitute, for example, a highest available switching frequency.