LLC Resonant Converter Current Balancing via Asymmetrical Control
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Solution Overview
Problem
Existing light source converters with LLC resonant circuits face asymmetrical load issues due to non-symmetrical secondary-side inductances, leading to uneven current distribution across diodes and potential single-path current flow, which can cause electrical and thermal imbalances.
Innovation Solution
A detection circuit is integrated to monitor current signals in both current paths and adjust the clocking of the half-bridge switches to balance current flows, ensuring symmetrical output currents through the use of a detection branch for each current path and a control circuit that adjusts the duty cycle and switch-on time based on detected signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a standard LLC resonant circuit with center-tapped transformer is used, then the circuit structure is simple and easy to manufacture, but asymmetrical load issues occur due to non-symmetrical secondary-side inductances leading to uneven current distribution
Solution Approach 1:
The patent intentionally introduces asymmetry into the originally symmetrical LLC resonant circuit by adding different detection inductors (L3a, L3b) and detection branches for each current path. This controlled asymmetry enables independent monitoring and balancing of currents through asymmetrical duty cycle adjustment, resolving the current distribution symmetry problem while maintaining manufacturing simplicity
Solution Approach 2:
The patent implements dynamic control by continuously monitoring currents through detection inductors and adjusting the duty cycles of switches S1 and S2 in real-time. The control circuit dynamically balances the asymmetrical currents by modifying switch timing based on detected current levels, transforming a static asymmetrical problem into a dynamically balanced system
2Reliability
If detection circuit and control mechanisms are added to balance current flows, then current distribution symmetry is improved, but device complexity increases
Solution Approach 1:
The patent applies local quality by adding detection components only where needed - specifically detection inductors L3a and L3b in each current path and corresponding detection branches. This localized approach provides necessary current monitoring and balancing functionality without unnecessarily complicating the entire circuit structure
Solution Approach 2:
The patent changes the control parameter from symmetrical duty cycle to asymmetrical duty cycle, allowing independent adjustment of switch S1 and S2 timing. This parameter change enables current balancing through differential duty cycle control, achieving reliability improvement with minimal additional complexity by reusing existing circuit components
3Ease of operation
If asymmetrical current flows are allowed to continue, then device operation is simple without additional control, but thermal and electrical stress on components increases leading to potential failure
Solution Approach 1:
The patent implements feedback control by using detection inductors L3a and L3b to continuously monitor currents in both paths, feeding this information to the control circuit, which then adjusts duty cycles to balance the currents. This closed-loop feedback prevents excessive current in either path, reducing thermal and electrical stress on diodes and other components while maintaining operational simplicity
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 solution ensures balanced current distribution across both current paths, preventing excessive load on individual diodes and improving the efficiency and reliability of the light source converter by maintaining symmetrical currents and reducing thermal and electrical stress on components.
Implementation Method 1
The primary winding L2a of transformer T1 is connected to the primary ground on its lower potential side, as is the lower potential side of the half-bridge switch S2. The current or voltage through the primary-side inductance L2a is transferred to the secondary side by transformer T1, thereby inducing the current I SP1 in the first current path SP1 and the current I SP2 in the second current path SP2.
Data Source
Figure 1~2
Figure 3a~3b
Figure 4a~4d
AI summary
The invention relates to a converter for light sources, comprising an LLC resonant circuit, from the secondary side of which light sources, e.g. an LED path, can be energized; the LLC resonant circuit includes a half-bridge circuit with two series-connected switches that are triggered by a control circuit, and further includes a resonant circuit that is energized from a central point between the two switches, as well as a transformer which is supplied with AC voltage from an output of the resonant circuit and on the secondary side of which two separate current paths for the two polarities of the AC voltage are provided; a detection circuit is provided which detects a signal representing currents in the two current paths and/or the ratio between the two currents, and the control circuit adjusts the timing of the two switches of the half-bridge circuit in accordance with the signal detected by the detection circuit.