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Through a combination rectifier and inverter circuits achieve soft switching frequency transformer technology, the field of power electronics in today 's research is one of the most active , is widely used, mainly used in AC motor speed control and power supply and other fields. Power on any electronic devices have a very important position, however, a variety of electrical equipment needs are different forms of energy , therefore, variable frequency power supply research has important theoretical significance and practical value . This paper presents a microcontroller (PIC18F4431) inverter transformer power supply system , the voltage 220V Frequency 50Hz electrical power frequency , rectified, filtered into DC, then reverse into voltage 110V-220V Frequency 40Hz-70Hz adjustable AC power supplied to electronic equipment . The design uses a unipolar equal area sinusoidal pulse width modulation method and mixed up table method , calculated by the software to generate SPWM control signal , while the output voltage RMS for real-time sampling , form a closed loop control system , enabling the entire frequency transformer digital control . Control signal sent by the microcontroller , the bootstrap circuit floating amplified to the power FET gate drive provided by conduction and switching devices off the process of realization of the DC inverter . Meanwhile, to ensure safe and reliable operation , the system also has the output over- current, input under voltage, overheating and other self-protection. The design is simple , functional and meet the current high-frequency switching power supply , modular, digital, green trends, has a waveform , small size , high efficiency , high precision, reliability, wide input range , frequency wide range of features , has a good practical value. This article first variable frequency power supply on the structure and principles were introduced , and then the system were the main circuit modules, drivers and peripheral module, control module as the core , a detailed description of the various parts of the hardware and software design principles , and experimental results are given efficiency of the output waveform and analyzed. Experiments show that the design of practical , basic indicators meet the requirements.
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