| With the continuous improvement of the performance of the central processing unit(CPU)used in various kinds of high reliability system equipment.The point-of-load converters often require high volume and power density,and needs good transient response to meet the load up to 10A/μs or even faster step speed.This work will take this kind of high current DC-DC converter as the research target.In order to improve the transient response of the valley current-mode constant ontime control,the principle of transient response process and optimal transient response is analyzed by introducing the state trajectory.A near single-cycle response control method based on time-optimal-control is proposed.It is easy to implement with analog circuit and insensitive to transient detection threshold,which simplifies the difficulty of system design.The describing function method is used to model the valley current-mode constant on-time control,by comparing with the simulation value,it is verified that it has high accuracy in the range of 10-200KHz.Taking the active clamp forward converter as the research object,an integrated scheme of transformer and inductor is proposed to reduce the volume of magnetic components and improve the power density.Its effect on reducing the ripple of inductor current was analyzed.The equivalent circuit model is established by introducing the nonlinear characteristics of magnetic core through the analogical modeling method of permeability and capacitance.The model and conclusion are verified by simulation.Based on the above analysis,a quarter-brick active clamp forward converter is designed.With Vin=36～60V,Vout=1.1V,the operating temperature range of the prototype is wide to-40℃～85℃,its maximum load current of prototype is 40A,the output accuracy error is less than 3%,the output ripple voltage is less than 10mV,and the maximum output voltage undershoot is less than 20mV. |
