LCC LED Converter Shunt Switching for Low-Level Dimming
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Solution Overview
Problem
LCC-type resonant converters face challenges in achieving lower dimming levels without negative side effects such as secondary side current overshoot and ripple when shutting down the switching stage.
Innovation Solution
Incorporating a shunt switch operable to short-circuit the LCC resonant circuit via a shunt switching signal synchronized with the half-bridge switching frequency, allowing for dimming of the LED load through pulse width modulation, which avoids the negative side effects of shutting down the switching stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the switching stage is shut down to achieve lower dimming levels, then the dimming capability is improved, but secondary side current overshoot and ripple occur
Solution Approach 1:
The patent segments the dimming control into two independent mechanisms: frequency offset control for normal dimming range and shunt switch control for lower dimming levels. This segmentation allows each mechanism to operate in its optimal range, avoiding the harmful effects of shutting down the switching stage while achieving the desired dimming effect.
Solution Approach 2:
The shunt switch acts as an intermediary element that provides an alternative path for current during dimming operation. By introducing this intermediate component, the patent enables dimming control without completely shutting down the switching stage, thereby maintaining stable current characteristics while achieving the desired illumination reduction.
2Power
If the switching stage is shut down to achieve dimming, then the power conversion is improved, but the circuit complexity increases due to difficulty in shutting down resonant circuit
Solution Approach 1:
The patent separates the dimming function from the main switching stage operation by introducing a dedicated shunt switch circuit. This segmentation allows the main switching stage to continue operating normally while the shunt switch handles the dimming control, simplifying the overall control logic and reducing circuit complexity.
Solution Approach 2:
The shunt switch circuit is designed to automatically regulate current flow based on the dimming requirements, eliminating the need for complex control logic in the main switching stage. The resonant circuit continues to self-oscillate and regulate itself while the shunt switch provides the necessary current path adjustment for dimming operation.
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
This approach enables effective dimming of LED loads by temporary short-circuiting the resonant circuit, maintaining the current source behavior of LCC converters and preventing flicker and steps in the dimming curve, thus improving dimming capabilities without adverse effects.
Implementation Method 1
LCC-type resonant converters, there is a range of dimming levels which may be achieved via changing a frequency of their switching stage (typically a half bridge of serially connected switches), since the converted power changes depending on a frequency offset between an operating point and a resonance point of the converter
Implementation Method 2
a transformer, being operable to electrically isolate a primary side (also called input side) and a secondary side (also called output side) of the converter
Implementation Method 3
The secondary side comprises a rectifier circuit
Data Source
Figure 1~3
Figure 4~5
Figure 6~7
AI summary
Disclosed is an LCC converter (1) for driving an LED load. The converter (1) comprises a transformer (13), being operable to electrically isolate a primary side (11, 12) and a secondary side (14, 15) of the converter (1). The primary side (11, 12) comprises a half bridge (11) of serially connected switches (111, 112), being mutually exclusively operable in accordance with a half-bridge switching frequency, and an LCC resonant circuit (12). The secondary side (14, 15) comprises a rectifier circuit (14). The converter (1) further comprises a control circuit (16), being operable to generate a shunt switching signal (22); and a shunt switch (17), being arranged upstream of the rectifier circuit (14), and being operable to short-circuit the LCC resonant circuit (12) in accordance with the shunt switching signal (22) during ongoing operation of the half bridge (11). The short-circuiting of the LCC resonant circuit (12) avoids the negative side effects of shutting down the half bridge (11) of the resonant converter.