Switching Power Supply Noise Reduction via Dynamic Turn-On Control
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Solution Overview
Problem
Conventional methods for reducing vibration noise in switching power supplies, particularly in light load operations, are ineffective due to increased switching losses, transformer size issues, and difficulty in applying soft-start circuits at low energy conditions, leading to audible noise and inefficiency.
Innovation Solution
A DC power supply device with an IS terminal voltage correction circuit that adjusts the turn-ON time of the FET and switching frequency to match or avoid the transformer's resonant frequency, using a series LC circuit to oscillate the IS terminal voltage and control the FET's operation, thereby reducing vibration noise and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the turn-ON time of the switching element is lengthened to reduce switching losses, then power efficiency is improved, but the switching frequency decreases causing audible vibration noise from the transformer
Solution Approach 1:
The patent applies dynamics by making the turn-ON time variable rather than fixed. The control unit dynamically adjusts the turn-ON time based on the relationship between switching frequency and the transformer's resonant frequency. When the switching frequency approaches the resonant frequency, the turn-ON time is shortened to avoid excessive vibration; when away from resonance, the turn-ON time is extended to reduce switching losses. This dynamic adjustment resolves the contradiction between power efficiency and vibration noise.
2Productivity
If the switching frequency is reduced to decrease the number of switching operations, then power efficiency is improved, but the vibration noise becomes audible to human ears
Solution Approach 1:
The patent applies parameter changes by modifying the turn-ON time parameter in response to switching frequency conditions. The control unit monitors the switching frequency and adjusts the turn-ON time parameter accordingly. When switching frequency approaches the transformer's resonant frequency, the turn-ON time is reduced to minimize magnetic field variation and vibration noise. This parameter adjustment allows the system to maintain lower switching frequencies for efficiency while avoiding the audible noise problem.
3Object-generated harmful factors
If a core material with large cross-sectional area is used for the transformer, then vibration noise is reduced, but the transformer size increases making it difficult to downsize the power supply device
Solution Approach 1:
The patent applies parameter changes by controlling the turn-ON time parameter to manage the magnetic field variation in the existing transformer core. Instead of changing the physical parameter of the core material (cross-sectional area), the patent changes the operational parameter (turn-ON time) to achieve the same noise reduction effect. The control unit shortens the turn-ON time when switching frequency approaches resonant frequency, thereby reducing magnetic field variation and vibration noise without requiring a larger core, thus maintaining compact transformer size.
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 vibration noise and power consumption by shortening the turn-ON time of the FET and shifting the switching frequency, ensuring stable voltage output and minimizing harsh noise at the transformer's resonant frequency.
Implementation Method 1
when a switching frequency for driving the switching unit falls within a predetermined frequency range including a resonant frequency of the transformer, the control unit controls the switching unit so as to shorten a turn-ON time of the switching unit in accordance with an output from the detection unit
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
The power supply device includes a transformer, a switching unit for driving a primary side of the transformer, a detection unit for detecting an output corresponding to a current flowing on the primary side, a transmission unit for transmitting an output voltage from a secondary side to the primary side, and a control unit for controlling an operation of the switching unit in accordance with an output from the transmission unit, in which, when a switching frequency for driving the switching unit falls within a predetermined frequency range including a resonant frequency of the transformer, the control unit controls the switching unit so as to shorten a turn-ON time of the switching unit in accordance with an output from the detection unit.