LLC Resonant Transformer Primary-Side Dimming Control
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Solution Overview
Problem
Conventional converters for light sources, particularly LEDs, face limitations in achieving dimming over a wide range without increasing circuit complexity or manufacturing costs, and struggle with brightness control in light sources that do not allow amplitude dimming.
Innovation Solution
An LLC resonant converter with a primary-side half-bridge and a control device that operates in two modes: amplitude dimming and pulse width modulation, allowing for flexible brightness control by adjusting switching frequency and pulse width, respectively, without the need for additional circuitry on the secondary side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If power switches are added on the secondary side for brightness control, then brightness control capability is improved, but device complexity and manufacturing costs increase
Solution Approach 1:
The patent merges the brightness control function into the primary side circuit by utilizing the existing half-bridge switches. Instead of adding separate control switches on the secondary side, the invention controls the primary side switches to generate pulse-width modulated signals that achieve brightness control. This integration eliminates additional circuit components and reduces overall system complexity while maintaining the desired adaptability for brightness control.
Solution Approach 2:
The primary side half-bridge switches are designed to serve multiple functions: both power conversion and brightness control. By configuring the control device to operate these switches in different modes (amplitude dimming and pulse width modulation), the existing components gain universal functionality. This multi-functionality approach eliminates the need for dedicated brightness control switches on the secondary side, thereby reducing device complexity while preserving brightness control capability.
2Device complexity
If conventional single-mode brightness control is used, then circuit simplicity is maintained, but dimming range is limited
Solution Approach 1:
The control device is designed to dynamically switch between two operating modes: amplitude dimming and pulse width modulation. This dynamic capability allows the system to adapt to different dimming requirements. By implementing multiple control modes within the same circuit framework, the patent achieves an extended dimming range without significantly increasing circuit complexity, as both modes utilize the existing half-bridge configuration.
Solution Approach 2:
The invention changes the control parameters of the half-bridge switches to achieve different brightness control modes. By varying the switching frequency and duty cycle parameters, the system can operate in amplitude dimming mode for certain brightness ranges and pulse width modulation mode for others. This parameter-based approach allows extensive dimming range coverage while maintaining circuit simplicity, as no additional hardware is required—only flexible parameter control.
3Adaptability or versatility
If amplitude dimming is used for light sources that do not allow amplitude dimming, then brightness control is attempted, but performance deteriorates
Solution Approach 1:
The control device dynamically adapts its operating mode based on the characteristics of the connected light source. For light sources that do not support amplitude dimming, the system automatically switches to pulse width modulation mode, which is effective for such sources. This dynamic mode selection ensures reliable brightness control across different light source types, maintaining both adaptability and control effectiveness by matching the control method to the light source capabilities.
Solution Approach 2:
The invention changes the control strategy parameters according to the light source type. When amplitude dimming is not suitable, the system transitions to pulse width modulation by altering the switching pattern of the half-bridge. This parameter change approach allows the converter to maintain high reliability and effectiveness for brightness control across various light source types, including those that cannot handle amplitude variations, thereby achieving universal compatibility without sacrificing performance.
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
Enables efficient energy transfer and wide-range dimming capabilities while reducing circuit complexity and costs, supporting both amplitude and pulse width modulation for various lighting applications, including those that do not allow amplitude dimming.
Implementation Method 1
A galvanic decoupled energy transfer can be achieved by using a transformer or other transmitter
Implementation Method 2
Resonant converters that include an LLC resonant circuit with two inductances and one capacitance can be controlled in a resonant or quasi-resonant manner on the primary side
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
An LLC resonant transformer (19) for a lamp (5) comprises a primary circuit (19) and a secondary side (30) galvanically isolated therefrom. A first switch (21) and a second switch (22) of a half-bridge to which an LLC resonant circuit (25-27) of the primary circuit (19) is connected are controlled during operation of the LLC resonant transformer (19). A control device (14) for controlling the first switch (21) and the second switch (22) of the half-bridge circuit is designed to adjust a switching frequency of the first switch (21) and the second switch (22) in order to adjust the brightness in a first operating mode while being designed to control the first switch (21) and the second switch (22) in order to generate a pulse width-modulated output signal at an output (35) on the secondary side (30) in a second operating mode.