Switching Power Supply Frequency Modulation for Noise Reduction
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Solution Overview
Problem
Conventional switching power supply apparatuses face challenges in reducing terminal noise and sound generation due to fixed switching frequencies, leading to increased costs and complexity, especially in light load states where noise tends to concentrate in audible frequency regions.
Innovation Solution
A switching power supply apparatus with a control circuit that modulates the switching frequency of a switching element based on load state feedback, using a PFM control circuit to vary the switching frequency and cyclically modulate the peak current, thereby dispersing spectral components and reducing noise and sound generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a fixed switching frequency is used in PFM control, then power efficiency is improved by reducing switching losses, but terminal noise and sound generation increase due to concentration of spectral components
Solution Approach 1:
The patent applies dynamics by making the switching frequency variable rather than fixed. The frequency modulation unit dynamically adjusts the switching frequency around a base frequency determined by PFM control, creating a frequency sweep effect that disperses spectral components and reduces terminal noise while maintaining the power efficiency benefits of PFM control.
Solution Approach 2:
The patent implements periodic action through frequency modulation where the switching frequency periodically varies around the base frequency. This periodic variation causes the spectral components to spread over time and frequency, preventing concentration at a single frequency and thereby reducing terminal noise and sound generation.
2Device complexity
If a fixed switching frequency is used, then control circuit complexity is reduced, but additional noise-reducing measures are required increasing device complexity
Solution Approach 1:
The patent merges the noise reduction function with the existing PFM control circuitry. The frequency modulation unit is integrated into the control circuit, combining the base frequency determination from PFM control with frequency modulation in a unified structure, thereby reducing overall device complexity compared to adding separate noise reduction measures.
3Loss of energy
If switching frequency is decreased in light load state, then power efficiency is improved, but spectral components concentrate in audible frequency region causing sound generation
Solution Approach 1:
The patent applies dynamics by implementing frequency modulation that causes the switching frequency to dynamically vary around the PFM-determined base frequency. This dynamic frequency variation prevents spectral components from concentrating in the audible frequency region, thereby eliminating sound generation while preserving the power efficiency improvements achieved through frequency reduction in light load states.
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
The solution effectively reduces terminal noise and sound generation in the switching power supply apparatus, allowing for a wide operating frequency range without the need for additional noise-reducing measures, while maintaining power efficiency.
Implementation Method 1
a transformer (1) including a primary coil (1a) and a secondary coil (1b)
Data Source
AI summary
A switching power supply apparatus includes a PFM control circuit that outputs a clock signal Set such that a switching frequency of a switching element varies in accordance with a load state. The clock signal Set determines a turn-on timing of the switching element. A reference value of a current flowing through the switching element determines a turn-off timing of the switching element. A modulation signal is applied to the turn-off timing of the switching element to modulate one of a peak value of a drain current flowing through the switching element and an on-time of the switching element. Input control is performed separately on the clock signal Set and the modulation signal. Accordingly, even when the clock signal Set and the modulation signal contribute to each other to offset each other, modulation effects are not cancelled.