Switching Regulator Off-Time Control for Light Load Efficiency
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Solution Overview
Problem
Existing switching power supplies face efficiency issues at light loads due to fixed switching frequencies, leading to decreased efficiency and audible noise when trying to regulate output voltage, as they either maintain constant switching frequency or constant peak current.
Innovation Solution
Implementing an off-time control method in switching regulators, where the off-time of the switch is adjusted based on load conditions, allowing for variable current thresholds at light loads to maintain output voltage stability without generating audible noise, and using a control circuit to manage the on and off times of the switch based on current and voltage feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixed switching frequency control is used, then output voltage regulation is achieved, but efficiency decreases at light load
Solution Approach 1:
The patent implements dynamic switching frequency adjustment by controlling the off-time of the switch based on load conditions. At light load, the off-time is extended to reduce switching frequency, thereby reducing switching losses and improving efficiency while maintaining output voltage regulation through feedback control.
Solution Approach 2:
The patent changes the switching frequency parameter dynamically by adjusting the off-time duration. This allows the system to operate at lower frequencies during light load conditions to reduce energy loss, while maintaining adequate frequency at heavy load for proper voltage regulation, thus resolving the efficiency-regulation trade-off.
2Loss of energy
If switching frequency is reduced at light load, then efficiency improves, but audible noise is generated
Solution Approach 1:
The patent implements a minimum off-time constraint that prevents the switching frequency from dropping below a certain threshold. This ensures that even at light load conditions where efficiency improvement would benefit from lower frequency, the switching frequency remains high enough to avoid audible noise generation, thus resolving the efficiency-noise trade-off.
3Device complexity
If peak current is regulated with fixed switching frequency, then control simplicity is maintained, but efficiency decreases at light load
Solution Approach 1:
The patent adds dynamic off-time control to the existing peak current control scheme. The control circuit adjusts the off-time duration based on the relationship between output voltage and reference voltage, enabling efficiency improvement at light load while maintaining the relatively simple peak current control architecture, thus resolving the complexity-efficiency trade-off.
Data Source
AI summary
The present invention provides an off time control method and switching regulator using it. The current flowing through a switch is compared with a current threshold, and the switch is turned off if the current flowing through the switch is larger than the current threshold. The off time of the switch is determined by the load. The current threshold is variable at light load to prevent generating the audible noise and improve the whole efficiency.