| In recent years,with the rapid development of internet technology,the scale of basic telecommunications equipment and mobile equipment has been greatly increased,which poses severe challenges to the use of energy and the architecture of the power supply system.Distributed power system has been widely used in basic telecommunication equipment due to its high reliability,strong expandability,and good flexibility.In order to improve energy utilization and adapt to the modular development of distributed power systems,the efficiency and volume of the converter are facing new challenges.In addition,today’s mobile devices are becoming thinner and lighter,which also places new requirements on charging devices.The above-mentioned development has promoted small and medium power converters to move towards high efficiency and high power density.This paper takes the pursuit of high-efficiency and high-power-density converters by basic telecommunication equipment and charging equipment as the starting point,and the application of active clamp circuits and GaN HEMT in flyback circuits and forward circuits as the research objects.Optimization and the influence of device parasitic parameters have been studied and discussed in depth.Aiming at the circuit topology optimization:Firstly,the characteristics of active clamp flyback and active clamp forward circuits under different clamping methods are analyzed.Secondly,the principle analysis of the active clamp flyback circuit with three different resonance modes is carried out and the key waveforms are derived and explained.Finally,the traditional active clamp forward circuit is discussed,and the conditions for its realization of zero voltage turn-on are analyzed.On this basis,this paper proposes a new type of secondary resonant active clamp forward circuit.Aiming at the influence of device parasitic parameters:Firstly,the influence of the junction capacitance of the primary side switch is analyzed,which shows the advantages of GaN devices in high-frequency applications.Secondly,the influence of the junction capacitance of the secondary side switch on the circuit is analyzed:the current drop phenomenon of the active clamp flyback circuit is analyzed in detail,and the corresponding circuit equivalent model is established.The reason for the voltage oscillation of the synchronous rectifier of the novel secondary-resonant active clamp forward circuit is explained,and the corresponding equivalent circuit model is also established and mathematically analyzed.Aiming at the realization of high efficiency and high power density:This paper designs the secondary-resonant active clamp flyback and the novel secondary-resonant active clamp forward converter,and conducts simulation verification in PSIM.On this basis,two 65W prototypes were built to verify the consistency of theory and experiment.The peak efficiency of the prototype using the secondary resonant active clamp flyback scheme is 93.7%and the power density is 25W/in~3;the prototype using the new secondary resonant active clamp forward scheme has a peak efficiency of 93.2%and a power density of 28W/in~3.Compared with traditional flyback and forward converters,the efficiency and power density are greatly improved. |
