LLC Power Controller with Soft Burst Mode for Light-Load Efficiency
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Solution Overview
Problem
LLC resonant power converters experience a significant deterioration in power conversion efficiency when the load is light or absent, due to increased switching frequency and switching loss of main power switches, leading to higher power consumption during standby conditions.
Innovation Solution
The implementation of a power controller that switches the LLC resonant power converter into a power-saving mode by alternating between burst times and pause times, using soft burst-in and burst-out operations to minimize power consumption and prevent audible noise, while maintaining a constant hiccup frequency to stabilize operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the LLC resonant power converter operates with increased switching frequency to handle light or no load conditions, then the power converter can maintain operation under varying load conditions, but the switching loss of the main power switches increases and power conversion efficiency deteriorates
Solution Approach 1:
The patent implements burst mode operation where the power converter operates in periodic cycles consisting of active burst periods followed by idle periods. During burst periods, the converter processes power in discrete packets, and during idle periods, switching is suspended entirely. This periodic operation allows the system to adapt to light load conditions while minimizing switching losses by avoiding continuous high-frequency switching, thereby resolving the contradiction between operational adaptability and energy efficiency.
2Loss of energy
If the power converter enters burst mode to reduce power consumption during light load, then power conversion efficiency improves, but audible noise may be generated due to sudden switching transitions
Solution Approach 1:
The patent employs soft burst-in and soft burst-out routines that gradually transition the power converter into and out of burst mode. During soft burst-in, the switching frequency or duty cycle is gradually increased rather than abruptly changed, and during soft burst-out, it is gradually decreased. These preliminary gradual transitions prevent sudden electromagnetic transients that cause audible noise, while still achieving the power consumption reduction benefits of burst mode operation.
3Object-affected harmful factors
If the power converter uses soft burst-in and burst-out routines to prevent audible noise, then audible noise is reduced, but the complexity of the control system increases
Solution Approach 1:
The patent implements soft burst-in and burst-out by dynamically adjusting switching parameters (frequency, duty cycle, or pulse width) during transition periods. The control system modifies these parameters in a controlled manner during burst mode entry and exit, rather than using abrupt changes. This approach reduces audible noise through parameter smoothing while maintaining relatively simple control logic that can be implemented with standard PWM controllers and minimal additional circuitry.
Data Source
AI summary
A control method is provided for operating a power converter with a power switch and an inductive device. A current-sense signal is provided to represent an inductor current through the inductive device. An ON time of the power switch is determined in response to a feedback signal and a saw-wave signal, to operate the power converter in a non-power-saving mode. The feedback signal is generated according to an output voltage of the power converter. The power converter can be operated in a power-saving mode, a burst mode. Operating in the burst mode, the ON time is determined in response to the current-sense signal and a current-limiting signal, which is increased during a soft burst-in time and is decreased during a soft burst-out time.