SMPS On-Time Control for Audible Noise and Peak Current Limits
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional constant on-time (COT) control methods for switched-mode power supplies introduce audible noise due to lower switching frequencies at lighter loads and can lead to excessive peak currents, necessitating new control circuits and methods that avoid noise while maintaining efficiency and safety.
Innovation Solution
A control circuit and method that includes an on-time control unit adjusting the turn-off instant of a switch based on current and frequency signals to maintain a target frequency, switching to frequency-locked mode to avoid audible noise and limit peak currents, and adapting to loading conditions by adjusting the on-time duration to ensure efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional COT control is used to simplify the circuit structure, then the circuit complexity is reduced, but audible noise is introduced due to lower switching frequency at lighter loads
Solution Approach 1:
The patent implements dynamic switching frequency adjustment based on load conditions. The control circuit transitions between frequency modulation mode (at heavy loads) and frequency-locked mode (at light loads), dynamically adapting the switching frequency to maintain it above the audible range while simplifying the circuit structure. This resolves the contradiction by making the system flexible rather than static.
Solution Approach 2:
The patent changes the switching frequency parameter adaptively based on load conditions. At light loads, the frequency is locked to a value above the audible range (20kHz), while at heavy loads, frequency modulation is allowed. This parameter change eliminates audible noise while maintaining circuit simplicity.
2Ease of operation
If conventional COT control is used to achieve simple circuit operation, then the ease of operation is improved, but excessive peak currents occur at increased input voltage
Solution Approach 1:
The patent incorporates feedback mechanisms that monitor both switching frequency and current conditions. The control circuit uses frequency detection and current sensing to determine when to switch between operating modes, providing feedback-based protection against excessive peak currents while maintaining simple operation through automated mode transitions.
Solution Approach 2:
The patent implements preliminary protection by detecting current conditions before excessive peak currents can cause damage. The control circuit monitors current in real-time and takes preliminary action by switching to frequency-locked mode or adjusting the on-time to prevent excessive peak currents from occurring in the first place.
3Loss of energy
If switching frequency is reduced at lighter loads to improve efficiency, then energy loss is reduced, but audible noise is generated in the 200 Hz-20 kHz range
Solution Approach 1:
The patent changes the switching frequency parameter based on load conditions to resolve the contradiction between efficiency and audible noise. At light loads, the frequency is maintained above 20kHz to avoid noise, while at heavy loads where switching loss is more significant, frequency modulation is permitted, potentially allowing lower frequencies that reduce switching loss.
Solution Approach 2:
The patent implements dynamic frequency adjustment that adapts to load conditions. The system transitions between frequency-locked mode (preventing audible noise at light loads) and frequency modulation mode (allowing efficiency optimization at heavy loads), making the frequency characteristic flexible rather than fixed.
4Adaptability or versatility
If frequency modulation control is used to adapt to loading conditions, then adaptability is improved, but switching frequency may drop into the audio range causing noise
Solution Approach 1:
The patent segments the operating range into two distinct modes: frequency modulation mode for heavy loads and frequency-locked mode for light loads. This segmentation allows the system to adapt to loading conditions while preventing audible noise by locking the frequency above the audible range when the load is light.
Solution Approach 2:
The patent implements dynamic mode switching that adapts to loading conditions. The control circuit automatically transitions between frequency modulation and frequency-locked modes based on detected load levels, providing adaptability while maintaining frequency above the audible range at light loads to prevent noise.
Data Source
AI summary
A control circuit, system and method for switched-mode power supply are disclosed, the control circuit is for driving a first switch to convert an input voltage into an output voltage. The control circuit includes an on-time control unit, which receives a first signal characterizing switching frequency of first switch and a second signal characterizing current flowing through first switch and responsively generates a signal indicative of a turn-off instant for first switch. When a peak value of the current flowing through the first switch drops below a predefined value, the on-time control unit determines the turn-off instant for the first switch based on the first signal so that the switching frequency of the first switch is maintained at a target frequency. This design can effectively avoid the generation of audible noise, stabilize the output voltage against loading changes while maintaining desirable efficiency, and ensure operational safety of the switched-mode power supply.