Research On Communication Power Supply Based On UC3875 Phase-shift Control Technology

With the wide applications of new technologies in communication systems,the requirement for communication power are constantly increasing.And communication power is also towards to small size,light weight,high efficiency,and high reliability.The phase-shifted full-bridge DC/DC converter has many advantages,such as high efficiency,high density,simple structure,easy implementation of soft switching,and low voltage and current stress on the switch tube.This thesis designs a phase-shifted full-bridge converter using UC3875 with output power of 480 W and output voltage of 48 V for communication power.In this thesis,we compare the passive power factor correction circuit with the active power factor correction circuit in order to reduce the influence of harmonics on the communication power,and finally selects the Boost active power factor circuit as the pre-stage circuit.TI's UCC28019 is taken as a circuit control chip.Then the phase-shifted full-bridge topology and working process are analyzed,and the parameters of each device are calculated.The simulations are performed with PSIM software to verify the rationality and accuracy of the parameter calculation.UC3875 of UNITRODE is taken as the phase-shift control chip.The peripheral circuit of this chip is also designed.In order to analyze the stability of the system,the small signal model of phase-shifted full-bridge DC/DC converter,which is built on the basis of the BUCK circuit,is analyzed using MATLAB software.In order to stabilize the output voltage and improve the over voltage and over current protection performance of the system,the closed-loop feedback network and its protection system have also been developed.In the communication system,the output of each module is not uniform due to some failures.This thesis also discussed a digital control algorithm based on DSP implemented in the communication power supply current sharing module.Finally,a communication power prototype was built,and its waveform was tested and analyzed to verify the rationality of theoretical analysis and design ideas.