Research On Active Clamp Forward Converter

Under the background of rapid development of information age,it is of great practical significance to vigorously develop brick power.The non-isolated converters such as Buck circuits and a series of derivative circuits cannot effectively adapt to the trend of low-voltage and high-current.In the future of brick power supply of 48 V input bus,Isolated converter will be the mainstream choice.In this paper,the active clamp forward converter is selected as the main research content,and its working principle,the establishment of mathematical model in peak current mode and the design of circuit parameters are studied.Aiming at the problem of excessive voltage stress of the switch of the traditional active clamp forward converter,this paper presents a new solution: the three-switch active clamp forward converter,and its working principle and circuit parameters are well studied.Firstly,four commonly used forward converter core reset methods are introduced in detail,focusing on the active clamp reset mode.The working state of the low-end active clamp forward converter in each time period and the soft switching of the switch tube are analyzed in detail.Then select and design the transformer,clamp capacitor,switch tube and filter inductor in the main circuit.The active clamp control chip UCC2897 A is introduced in detail,and its peripheral circuit parameters are designed.The system transfer function of the active clamp forward converter in peak current mode is derived,and the control loop is designed using a combination of optocoupler and reference regulator.Finally,Pspice simulation is established according to the main circuit parameters,and the corresponding experimental prototype is made.The rationality of the design is verified by simulation and experiment.The working principle of the three-switch active clamp forward converter and the soft switching of the switching tube are introduced in detail.The voltage stress of the switching tube of the two active clamp forward converters is analyzed and compared.Aiming at the high-end driving problem of the three-switch active clamp forward converter,a novel driving transformer scheme is given to solve the problem that the driving transformer amplitude is too low when the high duty cycle input is applied.Simulation and experiments show that the three-switch active clamp forward converter can realize the zero voltage turn-on of the switch tube,which effectively reduces the voltage stress of the switch tube.