Optimization And Design Of Circuit Parameters Of Peak Current Control Active Clamp Forward Converter

Electrolytic capacitors and ceramic capacitors are two commonly used capacitors.It is beneficial to reduce voltage ripple and optimize the transient response of converter by replacing electrolytic capacitor with ceramic capacitor.In recent years,more and more applications require reduction of volume and weight,thus module power supply needs to remove electrolytic capacitors.Forward converter is a common topology in the power supply for small and medium power.Therefore,it is of great significance to study forward converter with ceramic capacitor output.In this paper,the working principle of an active clamped forward converter controlled by peak current control is analyzed in detail.The design steps of the main circuit parameters are given.By comparing the simulation of voltage mode control and current control mode,it's found that the former can work in the range of duty ratio when the ceramic capacitor is used.But the instability of low frequency oscillation will occur in the latter when the parameters of the clamping network are not at the time.In order to analyze the effect of clamp circuit on the stability of the converter,small signal model of peak current control active clamp forward converter is established.It can be qualitative analysised that the insertion of a clamped network produces a phase mutation at the characteristic frequency of the clamping network.When the characteristic frequency of the output network is close to it,the system's phase margin is insufficient and the system is unstable.Meanwhile,the influence trend of duty cycle and clamp network on the frequency domain characteristics of converter is analyzed.Finally,the loop design steps are given according to the frequency domain characteristics shown by the model.However,it can not be used to quantitatively deduce the stable boundary according to the model.Time domain analysis is thus adopted.Consider the effect of resonance between clamp circuit on the reset of the transformer core,its process is analyzed and deduced in detail.The stable boundary is obtained according to the condition of the core reduction.As magnetization inductor is not easy to change,thus clamp capacitor is redesigned.The clamping voltage ripple can be reduced as much as possible under the condition of stable work.Finally,simulation and experimental results are given to verify the correctness of theoretical analysis all above.The various modes of work are introduced.