PFM Buck Regulator Clocking to Suppress Audible Noise
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Solution Overview
Problem
PFM buck regulators produce audible noise due to operating within the audible frequency range, causing mechanical vibrations and harmonics that contribute to overall noise.
Innovation Solution
Pseudo-randomly varying the PFM period to attenuate and equalize frequency peaks and harmonics, transforming them into white noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the PFM buck regulator operates at a fixed frequency within the audible range, then the regulator can efficiently manage power conversion, but it produces audible noise and mechanical vibrations
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed PFM frequency to a dynamically varying frequency. A pseudo-random binary sequence (PRBS) modulates the PFM clock signal, causing the switching frequency to fluctuate within a defined range. This dynamic frequency variation prevents the regulator from operating continuously at a single audible frequency, thereby reducing mechanical vibrations and audible noise while maintaining power conversion efficiency
Solution Approach 2:
The patent implements parameter changes by modifying the frequency parameter of the PFM regulator through PRBS modulation. The modulation index and frequency deviation are adjusted to spread the spectral energy of the switching noise across a broader frequency range, transforming concentrated audible frequency peaks into distributed white noise characteristics that are less perceptible to the human ear
2Object-generated harmful factors
If the PFM frequency is varied to reduce audible noise, then noise emissions are minimized, but the frequency stability and predictability of the regulator decreases
Solution Approach 1:
The patent incorporates feedback mechanisms to maintain frequency stability despite PRBS modulation. The control circuit monitors the actual switching frequency and adjusts the modulation depth or clock timing to ensure the average frequency remains at the desired operating point. This feedback control prevents excessive frequency drift while preserving the noise-reduction benefits of frequency variation
Solution Approach 2:
The patent uses periodic action through the structured PRBS modulation pattern. The pseudo-random sequence follows a deterministic periodic structure with a known period, ensuring that while the instantaneous frequency varies, the overall frequency distribution repeats predictably. This periodic modulation approach maintains statistical frequency stability while achieving noise spreading
Data Source
AI summary
The present disclosure provides an approach that determines a pulse frequency modulation (PFM) period of a buck regulator. The PFM period comprises a first charging stage and a first discharging stage, and wherein the buck regulator switches from the first discharging stage to the first charging stage based on comparing a feedback voltage to a low threshold voltage. The approach generates a pseudo random pulse at a pseudo random period, wherein the pseudo random period is independent from the low threshold voltage. Then, the approach initiates a transition from a second discharging stage to a second charging stage based on the pseudo random pulse.