Research Of The PFM Controlled LLC Half-bridge Resonant Converter

In recent years,which has the function of electric energy conversion switch power supply has been widely used in aerospace,electronic communications,new energy and other fields.As an indispensable part of high-frequency switching power supply,DC/DC converters are of great variety and have significant research significance.In the soft switch technology,DC/DC converter in the work will be accompanied by a variety of switching loss and magnetic loss,cause its use shorter time,limit the development of the high frequency of their own.A half-bridge LLC resonant converter is because of its high switching frequency,strong anti-interference performance and popular,become the research hot spot.A half-bridge LLC resonant converter is often adopted the technique of pulse width modulation and pulse frequency modulation technology to achieve the goal of the output voltage stability.The PWM control means that when the input voltage range is wide,the loss of control signal is easily lost,and the efficiency of the converter decreases.So this article will use excellent control effect of PFM control way,adopting the control method of resonant converter has some advantages such as simple circuit structure,the system response speed,high efficiency,etc.In this paper,the main work content is as follows:(1)This paper analyzes the working principle of five DC/DC converters combined with soft switch technology,and compares their advantages and disadvantages with the design of the half-bridge LLC resonant converter.This paper analyzes the working principle of the transducer,builds the converter equivalent circuit,deduces the relation between the output voltage and the working frequency,and determines its working frequency domain.(2)The design indexes of the resonant transducer of the half-bridge are given,and the main circuit parts are designed,including the transformer,the resonant network,the main switch and so on.When designing the resonant network,the value of K and the quality factor Q are selected,and the parameters of the resonant elementsare obtained according to the relevant formula.(3)This paper analyzes several common modes of control,selects the control method of PFM with good control effect,and then introduces the characteristics and function of the control chip UC3863.After the analysis of the peripheral circuit of the chip,the capacitance resistance parameter is calculated.Finally,the power drive circuit and the optical coupling feedback circuit are designed.(4)With the Saber software to the simulation analysis of the designed converter,respectively for switch tube,the resonant network and vice and diode and the whole circuit system has carried on the simulation analysis.The result of simulation shows that the transducer of this design realizes the function of the soft switch,and its output voltage ripple is small,which verifies the correctness of the theoretical analysis.