Boost Circuit Open-Loop Frequency Hold for Audible Buzz Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Switching-mode power supplies (SMPS) generate audible buzz noise due to pulse frequency modulation (PFM) frequencies dropping into the audible band at light loads, degrading signal-to-noise ratio (SNR) and causing noise issues, and existing closed-loop control methods are complex and limited in speed.
Innovation Solution
Implementing an open-loop scheme with a digital-to-analog converter (DAC) to generate a dummy current that maintains the boost circuit's switching frequency above the audible threshold, suppressing audible noise and improving SNR by using an open-loop control system without feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If pulse frequency modulation (PFM) is used to achieve higher efficiency at light load, then switching loss is reduced, but the PFM frequency drops below 20 KHz and enters the audible band causing audible buzz
Solution Approach 1:
The patent applies preliminary action by proactively injecting a dummy load current before the PFM frequency drops into the audible band. The controller monitors the load current and preemptively adds compensation current through a DAC when light load conditions are detected, preventing the frequency from entering the audible range rather than reacting after the buzz occurs.
Solution Approach 2:
The patent changes the parameter of switching frequency by dynamically adjusting it through dummy load injection. When the actual load current falls below a threshold, the controller activates a DAC to inject compensation current, which effectively increases the total load current and maintains the PFM frequency above the audible threshold of 20 KHz.
2Object-generated harmful factors
If a closed control loop is used to sense and regulate PFM frequency, then audible buzz can be suppressed, but the circuit complexity and chip area increase
Solution Approach 1:
The patent extracts the feedback function from the control loop and replaces it with an open-loop detection and compensation mechanism. Instead of using a complex closed-loop frequency sensing circuit, the invention extracts only the essential function of detecting light load conditions and applies a predetermined dummy load current through a simple DAC, eliminating the need for complex frequency sensing and regulation circuits.
Solution Approach 2:
The patent uses a simple DAC-based dummy load injection mechanism instead of a complex closed-loop control system. The DAC generates compensation current based on load current thresholds, providing an inexpensive and simple solution that achieves audible buzz suppression without requiring expensive or complex frequency sensing and regulation circuits.
3Object-generated harmful factors
If a closed control loop is used to regulate PFM frequency, then audible buzz can be suppressed, but the control speed is limited
Solution Approach 1:
The patent introduces a DAC as an intermediary component that directly converts digital compensation current values into analog dummy load current. This intermediary mechanism allows for rapid current injection in response to load changes, achieving fast control speed without the bandwidth limitations of traditional closed-loop frequency sensing and regulation circuits.
Data Source
AI summary
A circuit includes a boost circuit, a first circuit coupled to the boost circuit and a second circuit coupled to the boost circuit. The boost circuit, the first circuit, and the second circuit form an open loop. The first circuit and the second circuit maintain a switching frequency of the boost circuit above a threshold frequency.