Boost Converter PFM Control Above Audible Buzz Threshold
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Solution Overview
Problem
Switching-mode power supplies (SMPS) generate audible buzz and degrade signal-to-noise ratio (SNR) due to pulse frequency modulation (PFM) frequencies lower than 20 KHz, which are not effectively addressed by existing closed-loop control methods that are complex, large, and slow.
Innovation Solution
A method and apparatus that modify the PFM frequency of a boost converter to operate above the audio-frequency threshold by selectively skipping switching pulses, using a control circuit to adjust the switching frequency and regulate output voltage with a dummy current, reducing audible noise and improving SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If PFM is used to reduce switching loss at light load, then efficiency is improved, but audible noise increases due to frequency dropping below 20 KHz
Solution Approach 1:
The patent applies periodic action by using pulse frequency modulation to vary the switching frequency of the power stage. At light load conditions, the PFM controller reduces the switching frequency to skip pulses and minimize switching losses. However, when the frequency approaches the audible range (20 KHz), the system periodically switches between PFM and PWM modes to maintain frequency above the audible threshold, thereby reducing audible noise while preserving efficiency benefits during light load operation.
2Object-generated harmful factors
If closed-loop control is used to regulate PFM frequency, then audible noise is reduced, but device complexity and chip area increase
Solution Approach 1:
The patent implements self-service by using a simple frequency detection circuit that automatically monitors the PFM frequency and triggers a mode switch when the frequency approaches the audible threshold. The system self-regulates by comparing the detected frequency with a reference threshold and automatically transitioning to PWM mode without requiring complex external control loops, thereby reducing audible noise while minimizing additional circuit complexity.
Solution Approach 2:
The patent employs feedback by incorporating a frequency detection circuit that continuously monitors the switching frequency and provides feedback to the control logic. When the detected frequency indicates that the PFM frequency is approaching the audible range, the feedback mechanism triggers a mode transition to PWM. This simple feedback loop effectively reduces audible noise without requiring complex control algorithms or large chip areas.
3Object-generated harmful factors
If closed-loop control is used to regulate PFM frequency, then audible noise is reduced, but control speed decreases
Solution Approach 1:
The patent applies preliminary action by pre-setting a frequency threshold reference value that represents the audible noise boundary. The frequency detection circuit continuously compares the actual PFM frequency against this pre-established threshold. When the detected frequency approaches the predetermined threshold, the system proactively switches to PWM mode before audible noise can significantly degrade performance. This preliminary action approach enables fast response without requiring complex real-time regulation loops.
Data Source
AI summary
An apparatus of the subject technology includes a circuit to switch a first current based on a switching frequency and generate an output voltage, and a first circuit coupled to the circuit to adjust the switching frequency through changing a frequency of the circuit to a value higher than a threshold.