LLC Converter Control Circuit Reducing Light-Load Power Loss
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Solution Overview
Problem
Conventional LLC resonant converters experience significant switching loss and increased electromagnetic interference during light-load or no-load operations, with existing solutions either increasing volume, reducing efficiency, or complicating the control circuit with additional components.
Innovation Solution
A control circuit comprising a signal detection unit that senses the primary-side current from the transformer unit and converts it to a reference voltage signal, allowing the controller unit to regulate the duty cycle of the switch controlling signal, thereby reducing power loss and working temperature of the power switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If switching frequency is raised to enhance power density and shrink framework volume, then the SMPS can use small-size magnetic components and capacitors, but switching loss produced by power switches increases and electromagnetic interference becomes more severe
Solution Approach 1:
The patent implements dynamic switching frequency adjustment where the controller automatically raises switching frequency during light-load or no-load operations. This dynamic adaptation allows the system to operate at higher frequencies when load is low (reducing volume requirements) while maintaining lower frequencies during heavy-load operations (reducing switching loss), thus resolving the contradiction between volume reduction and energy loss.
Solution Approach 2:
The patent changes the switching frequency parameter dynamically based on load conditions. During light-load operations, the switching frequency is increased to enable smaller magnetic components and capacitors. During heavy-load operations, the frequency is reduced to minimize switching loss. This parameter change strategy resolves the contradiction by adapting the frequency parameter to different operating conditions.
2Object-affected harmful factors
If dummy load is added to attenuate parasitic stray capacitance during light-load operation, then capacitance effect is reduced, but framework volume is enlarged and power conversion efficiency is reduced
Solution Approach 1:
The patent extracts and eliminates the need for dummy load components by using control circuitry instead. The controller detects light-load or no-load conditions and adjusts switching frequency accordingly, removing the requirement for physical dummy load resistors or capacitors. This extraction approach reduces framework volume while avoiding the power loss associated with dummy loads.
Solution Approach 2:
The patent replaces the mechanical/component-based solution (dummy load) with an electronic control-based solution (frequency adjustment). Instead of adding physical components to attenuate parasitic capacitance, the system uses dynamic frequency control to manage the capacitance effects, thereby improving efficiency and reducing volume.
3Loss of energy
If burst mode controller is used to lower average switching frequency during light-load operation, then switching loss is reduced, but audio frequency noise is produced
Solution Approach 1:
The patent implements continuous dynamic frequency adjustment rather than discrete burst mode operation. The switching frequency is continuously modulated based on real-time load detection, avoiding the fixed-frequency-on/off pattern of burst mode that generates audible noise. This dynamic approach reduces switching loss while maintaining electromagnetic quietness.
Solution Approach 2:
The patent uses periodic frequency adjustment where the switching frequency is varied in a controlled periodic manner during light-load operations. This periodic modulation allows the system to achieve reduced average frequency (lowering switching loss) while avoiding the regular on/off bursts that create audible noise, by using smoother frequency transitions.
4Loss of energy
If variable-frequency or phase shifting process is applied to switch controlling signals, then power loss is reduced during light-load operation, but circuit complexity and manufacturing cost increase due to additional circuit chips
Solution Approach 1:
The patent integrates multiple functions into a single controller chip that performs load detection, frequency adjustment, and switching control. This multi-functional approach eliminates the need for separate circuit chips for each function, thereby reducing circuit complexity and manufacturing cost while achieving power loss reduction through frequency modulation.
Solution Approach 2:
The patent merges the signal detection unit and controller unit into an integrated control system. The controller chip combines the functions of detecting load conditions and generating adjusted switching signals, eliminating the need for additional discrete components and reducing overall circuit complexity while maintaining the power loss reduction benefits.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The control circuit effectively reduces power loss and working temperature of the power switches during light-load or no-load operations, while maintaining a simple circuit topology and low manufacturing costs.
Implementation Method 1
a signal detection unit, being electrically connected to a primary side of the transformer unit for sensing a current sampling signal, so as to convert the current sampling signal to a reference voltage signal
Data Source
AI summary
The present invention particularly discloses a control circuit comprising a signal detection unit and a controller unit for reducing power loss of a LLC resonant converter during light-load or no-load operation. In the present invention, the signal detection unit is adopted for sensing a primary-side current from a transformer unit of the LLC resonant converter, and then converting the primary-side current to a reference voltage signal. Thus, according to a level variation of the reference voltage signal, the controller unit is able to properly regulate duty cycle of a switch controlling signal based on a duty cycle reduction percentage. Eventually, by using the switch controlling signal to control the periodic ON-OFF switching of power switches, power loss of the LLC resonant converter operated under light load or no load can be obviously reduced; moreover, working temperature of the power switches is simultaneously lowered.