Switching Power Frequency Regulation for Light-Load Noise Control
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Solution Overview
Problem
Switching power supplies experience low system frequency and generate noise under light load conditions due to prolonged off times of the main and freewheeling transistors, leading to discontinuous operation.
Innovation Solution
A frequency regulation circuit and method that includes a switch signal circuit and a light load control circuit to control the on/off of transistors, actively turning on the freewheeling transistor after a preset time and adjusting its conduction duration based on output feedback signals to stabilize frequency and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the main power transistor and freewheeling transistor are turned off for a long time under light load conditions, then the switching power supply enters discontinuous operation mode to reduce power consumption, but the system frequency becomes very low and generates noise
Solution Approach 1:
The patent applies periodic action by forcing the freewheeling transistor to turn on at predetermined intervals during discontinuous operation mode. This periodic activation ensures the system frequency remains above a threshold level, preventing the low-frequency noise problem while maintaining the energy-saving discontinuous mode operation.
Solution Approach 2:
The patent uses preliminary action by detecting when both transistors are off and starting a timer in advance. When the timer reaches a preset threshold, the freewheeling transistor is proactively turned on before the frequency drops too low, preventing noise generation while maintaining efficient operation.
2Use of energy by moving object
If the main power transistor is turned off under light load conditions, then power consumption is reduced, but the system frequency drops and noise increases
Solution Approach 1:
The patent implements periodic action by scheduling periodic activation of the freewheeling transistor during light load discontinuous mode. This ensures the system frequency is periodically boosted to maintain it above the threshold, balancing energy efficiency with frequency requirements.
Solution Approach 2:
The patent employs feedback by monitoring the off-time duration of the transistors and using this information to trigger timely activation of the freewheeling transistor. This closed-loop control ensures frequency maintenance while preserving the energy benefits of discontinuous operation.
3Loss of energy
If the off time of transistors is extended under light load, then duty cycle is reduced and efficiency improves, but noise is generated due to low frequency
Solution Approach 1:
The patent applies preliminary action by detecting the transistor off-state and starting a timer in advance. When the timer reaches the threshold, the freewheeling transistor is activated before frequency degradation occurs, preventing noise while maintaining the efficiency benefits of extended off-times.
Solution Approach 2:
The patent uses feedback by monitoring the duration of transistor off-states and using this information to trigger timely freewheeling transistor activation. This ensures noise prevention through frequency maintenance while preserving the energy efficiency achieved by extended off-times.
Data Source
AI summary
The present application discloses a frequency regulation circuit and a regulation method for a switching power supply, and a switching power supply. By the regulation of a light load regulation circuit, in the discontinuous working mode, when the main power transistor and the freewheeling transistor are both turned off for a time exceeding a preset time, the freewheeling transistor is turned on to increase system frequency and system noise is reduced; moreover, the on time of the freewheeling transistor is regulated by the feedback of the output voltage, resulting in stable system frequency, stable output voltage, and low system loss.