Parallel Resonant Converter And Its Application In LED Driver

LED lighting is rapidly growing and popularizing in worldwide now replacing mainstream fluorescent lighting. Unlike fluorescent lamp driven by AC current, LED lighting is DC-driven.LED driver topology is commonly PWM converter(Pulse Width Modulation), the structure and operation principle of PWM converter is simple, but power inefficient, poor performance, bulky and low power density so it is generally more suitable for low-power and the lower-end LED applications. With the development and maturation of LED lighting market, high-power and high-performance LED applications are rapid developing that PWM converter based LED driver have been unable to meet demand.Resonant converter is made to solve the limitations of PWM converter as another converter topology. Resonant converter is high efficiency, small size, and high frequency, so very suitable for high power and miniaturization of the higher-end LED lighting applications. There are many types of resonant converter, this paper chooses the parallel resonant converter as the subject of this study and applies it to the LED driver design.Parallel resonant converter, while having superior performance than PWM converter, but it is less used in LED driver applications, and the operation principle and analysis are complex, currently it is lack of existing theoretical analysis and design guidelines for this kind of resonant converter, in order to solve this problem, this paper uses a method of first harmonic approximation(FHA) for parallel resonant converter theoretical analysis. This method extracts the fundamental component of the parallel resonant converter input square wave voltage as the input voltage source to make the AC analysis of the circuit to derive circuit voltage, current and transfer function in theory for analysis. Although the method adopted approximation method, but the result of it is also relatively accurate, and it is simple, intuitive, and easy to design so it is easier to apply in actual product development and has great practical significance.LED driver introduces LED output current close-loop feedback circuit, its purpose is to provide a constant LED current, but the introduction of a feedback circuit brings the problem of system stability. In order to solve and optimize the system stability, this paper presents the method of frequency response analyzer by measuring the amplitude-frequency and phase-frequency characteristic curve. With the analysis of measurement results, it is targeted to design a compensator to increase phase margin to improve system stability.Finally, this article provides an LED driver example. The LED driver product requirement is the development of a high efficiency thin linear 75 W wide output voltage and current window LED driver. The actual design is parallel resonant converter based on control chip UBA1313 from NXP Semiconductor. According to the analysis work of first harmonic approximation in this paper, the circuit parameters can be calculated then and the calculated results of the parallel resonant converter can be compared to the results of circuit computer simulation and actual product test results, three results agree well.