Design Of Power Supply Control System Based On USB

Most people may be annoyed by messy cables, incompatible interfaces, and non-unified adapters. These problems can be solved by using a unified USB interface. Now, general intelligent mobile phones and small electronic equipment, such as tablet PC, digital camera and e-book reader, can be charged by a USB cable connected to a computer. Power supply configuration using USB as unified interfaces can be found at hotel rooms, airport waiting halls, coach stations and railway station waiting halls. So, it is necessary to offer unified USB power supply control at places such as home, office, hotels and apartments.As the Power Supply Control System, a part of the project "Application Research of Innovative USB Transmission Technology in Home Network", this design is proposed to design a power supply control system based on USB with high efficiency, low power-consumption, environmental protection and energy saving, to achieve charging devices simply by a USB cable.This design mainly includes two parts, hardware design and software development. The environment for hardware design is software Altium Designer, and the simulator for it is Proteus. The hardware design includes three parts, the design of switched-mode voltage-stabilized power supply, the development of FPGA Minimum system and the design of DAC switching circuit. The environment of software design is Quartus II, and the simulator for the design is Quartus II its own simulator. Software design module includes five parts, the top-level module, frequency division module, key capture and process module, LED display module and DAC conversion module.At the input circuit of the switched-mode voltage-stabilized power supply system, an EMI filter is designed to barrage the high-frequency jamming between Alternating Current network and the high-frequency switched-mode power supply system. A full-bridge rectifier is designed, for it can provide voltage with small ripple wave and stable DC for the switching circuit. The DC-DC power converter is designed separately, driving symmetrically and of half-bridge topology. In this circuit, there are two switching tubes be connected alternatively to make chopped wave, and then these chopped wave will be converted to direct current to output over the full-bridge rectifier. TL494 chip with two error amplifiers is selected to control the switching tube. One amplifier is designed as a voltage regulator, voltage control signal which is feedback from the output circuit is connected to the reverse end of the error amplifier, and the positive end is connected to the reference. When the control signal is higher than the reference, the pulse will be modulated to be narrowed by the inner circuit automatically, and then the output voltage will remain the same as the set value. The other amplifier is designed for overcurrent protection, when the output current is higher than the set value, the pulse will be modulated to be narrowed by the inner circuit automatically, and then the output current will be decreased. The driving circuit is designed to be complemental, that can make the rising and down edges characteristic of the switching tube in the power supply circuit to be better, and reduce the power loss on the switching tube.Bottom-up design is used for the FPGA developing. The frequency module divides the system clock and outputs two low frequency clocks, one is used for key capture, and the other is used for LED dynamic display. When the key capture module and processing module detects some key is being pressed, after some computing, it will output a set voltage value to the LED display module and DAC converting module, and then the LED display module will display the set voltage on the LED, while the DAC converting module will convert the set voltage value to a 8-bit binary, and pass it to the data entry of the DAC chip.The last but also important are the simulation and testing for the USB-based power supply control system, including the test of the output of DAC0832 circuit, the feature of TL494 chip, and the output voltage scope of the switched-mode power supply system. The result of the test indicates that, the output of the practice test and the theoretical research finally reach consensus. This system design will provide a reference for the research of program "Application Research of Innovative USB Transmission Technology in Home Network".