The Research Of Peak Current-mode Two-transistor Forwrad Switch Power Supply Modeling And Design

With the development of the modern power electronics technology, the power supply ismore and more power density, efficiency, light weight and size miniaturization. As a memberof switch power supply topologies, compared with other topologies the two-transistor forwardconverter has low voltage stress and the ability of anti-bridge arm straight, and so on. Allthese merits make it widely usefull in the computer power, the communication power, etc.First of all, the article describles the principle, advantages and disadvantages of thevarious types of control methods, then compares the character of the two-transistor and thesingle transistor forward converters; the working process of the two-transistor forwardconverter is given later. Through analyzing the BUCK working mode of CCM and DCM, itdraws the conclusion that the forward converter should choose the mode of CCM. Then, thisarticle will establish the model of the power part by the average switch modeling method; themodel shows that peak current control method simplifies the main transfer function. Based onthe transfer function of the current circle, we know that it be merged into the power part. Withthe simplified transfer function, the control circle will be established by the control chip ofUC3844Corporated TL431and the optocoupler, then the pose-zeros function of controlmodel will be given. Moreover, in order to verify the correctness of the system modeling andthe designing of the control circle, the paper will analysis the Bode diagram of the power partand the open-loop transfer function, then gives the dynamic response chart by the soft-wareSaber; all of these indicate that the model of the switch power converter is correct andaccurate. Then, the paper gives the improving drive circuit of the MOS tube. In the last, it alsodesigns the over-voltage, low-voltage, over-load and over-heat protection circuit.In order to verify the correctness of the analysis, a system is designed by the controlmethod of peak current two-transistor power converter with the input of single-phase AC380V. The output of the system is24V/10A, and the switching frequency is100kHz.Theexperiment shows that the dynamic response and the steady-state are very good, and theefficiency of the system over87.3%. All of these meet the requirements of the system.