Design Of Digital Switched-Mode Power Supply And Factor Corrector Based On DSP

Switching power supply has been widely used for its high efficiency and low cost in various fields. Low power factor of the traditional switching power supply results in the distortion of the input current and high harmonic components, which causes the harmonic pollution of the power grid and reduces the utilization rate of electric energy. Therefore, improvement of the power factor is the solution to decrease harmonic pollution of power electronic equipment, improve the reliability of power system and power quality. With the development of digital control technology more and more control strategy can be implemented in power electronics by digital sinal processor (DSP). The implementation of power factor correction (PFC) using digital signal processors has become the research hotspot at present.Digital switching power supply based on DSP was studied and designed in this disseratation to realize high efficiency, high precision and high integration switching power supply, in which PFC and PWM soft switching were adopted to improve the performance of switching power supply and power factor. The main works of this disseration were as the follows:(1) Design and implementation of DC/DC converter soft switch. The operating process of the phase-shifted full-bridge soft switching PWM DC/DC converter was introduced. High frequency transformer was designed with dsPIC33FJ16GS504 by PWM peripherals into the dead time, and resonace was formed with the leakage inductance of the transformer and MOS pipe junction capacitance. The design realized the inverter main power tube operating at soft switching state, which reduced the device switch stress and loss, improved the efficiency of power supply.(2) Design and implementation of synchronous rectifier. In this part the traditional diode was replaced by MOSFET and the synchronization of driving signal and full bridge conversion in the MOS was achieved, which helped to get the stable output voltage+12V. Double current technology was used to optimize the transformer and the filter circuit design. Constant voltage and current limiting circuit was completed by the feedback of voltage and current feedback, which could maintain stable the output voltage and limit the output current.(3) Design and implementation of the auxiliary power supply network and the corresponding protection circuit according to the specific needs, including TV,13 V, 17V DC regulated power supply, over-temperature, over-current, over-voltage, under-voltage protection circuit.(4) Design and implementation of digital PFC. The power check power correction topology and circuit analysis were done. Digital power factor corrector was designed based on the booster (Boost) circuit topology structure. The voltage and current signal was acquired with digital signal processor dsPIC33FJ16GS504. The PWM wave duty cycle was calculated by voltage and current control loop. A fixed switching frequency (125KHz) power factor correction was achieved with constant output voltage control MOSFET tube turn-on and turn-off.(5) Experimental test including power PFC and switch power source. According to the experiments, the waveform of input current were similiar with the waveform of the input voltage, the power factor is close to 1, which achieved the basic requirements of PFC design. When the input voltage was 260V and the input frequency is 45-65Hz, three measured power output voltages were respectively 11.8V,3.1V and 4.9V.