LLC LED Converter With Integrated PFC and Low THD
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Solution Overview
Problem
Existing converters for LED-based loads face challenges in achieving high efficiency and reliability while maintaining low Total Harmonic Distortion (THD) and high power factor, particularly in a cost-effective manner.
Innovation Solution
A converter design incorporating an LLC circuit with a coupled inductor and integrated power factor correction (PFC) functionality, utilizing a half-bridge and a coupled inductor configuration to generate current pulses that track the input voltage, eliminating the need for additional PFC switches and limiting bus voltage at light loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional converters are used for LED-based loads, then basic power conversion is achieved, but THD is high and power factor is low
Solution Approach 1:
The patent combines the PFC inductor and coupled inductor into a single integrated magnetic component structure. The PFC inductor is magnetically coupled with the coupled inductor through shared magnetic cores, merging two separate inductors into one unified device that performs both power factor correction and voltage transformation functions simultaneously, thereby reducing component count while achieving low THD and high power factor
Solution Approach 2:
The integrated inductor structure serves multiple functions: it acts as both the PFC inductor for power factor correction and the coupled inductor for voltage transformation and isolation. This multi-functional design eliminates the need for separate PFC and transformer components, reducing device complexity while maintaining excellent THD and power factor performance
2Object-generated harmful factors
If additional PFC switches are added to improve power factor, then power factor increases, but device complexity and cost increase
Solution Approach 1:
The patent utilizes the existing half-bridge switches (S1, S2) to perform both LLC resonance switching and PFC current regulation functions. The control unit manages the switching of these existing components to achieve power factor correction without requiring any additional PFC switches, thereby maintaining high power factor while avoiding increased device complexity and cost
3Device complexity
If bus voltage is allowed to rise at light loads, then voltage regulation is simplified, but excessive voltage occurs causing reliability issues
Solution Approach 1:
The control unit continuously monitors the bus voltage and adjusts the switching duty cycle of the half-bridge switches accordingly. When bus voltage approaches the reflected secondary voltage level at light loads, the control unit reduces the duty cycle to prevent excessive voltage rise, providing active feedback control that maintains voltage stability and prevents reliability issues without adding complex external voltage regulation circuits
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 solution achieves a THD of 2% or less, efficiency of 87% or higher, and a power factor of 0.994 or greater, ensuring reliable and efficient LED lighting with reduced harmonic distortion and cost-effective operation.
Implementation Method 1
the coupled inductor is magnetically coupled with two inductors, one in each supply path of the AC voltage to the rectifier
Implementation Method 2
the coupled inductors which are in the supply path of the AC voltage, alternately charge and discharge. This charging and discharging process generates current pulses from the input, with peaks proportional to the input voltage
Data Source
Figure 1
AI summary
A converter (10) for supplying an LED-based load (21) is provided. Said converter (10) comprises a rectifier (12) being supplied with an AC voltage (11) and supplying an LLC circuit (13) comprising a half-bridge (14a) and a coupled inductor (15a), said coupled inductor (15a) being connected between a midpoint of two switches (16a, 16b) of the half-bridge (14a) and a midpoint between two capacitors (17a, 17b) arranged in parallel on the supply side of the half-bridge (14a), and being magnetically coupled with two inductors (15b, 15c), one in each supply path of the AC voltage (11) to the rectifier (12).