| Along with the rapid development of Power Electronics, the power electronic equipments are closely associated with people’s life and work, while electronic equipments are connected to stable and reliable power supply. DC Regulated Power Supply falls into two categories which are Switching Mode Power Supply and Linear Power Supply. In terms of the cost, both costs grow as the output power increasing, but their growth rates are different. At certain output power point, the growth rate of Linear Power Supply exceeds that of Switching Mode Power Supply, which is called the cost of reversal points.At present, China is building a resource-saving and environmental protection demonstration society, therefore Switching Mode Power Supply has become an important research focus in this subject on account of its environmental protection, energy-efficiency and its short and thin size. Because the single forward switching power supply adopts new circuit structure and takes some measures to lower the output ripple which can protect itself when it outputs overcurrent, overpressure, overheating and its circuit works abnormally, it possesses certain advancement and innovation.This issue, belonging to some company’s project, will design a specific model industry product, aiming to grasp some theories about single forward switching power supply design, such as forward convertor topology, transformer, feedback loop and compensation network design, basic PWM switching convertor principles and designs. After learning the designing procedure, master the requirement and specification of product design, then develop the strict and cautious scientific thought and build the earnest and practical scientific attitude. The high practical utility and nice engineering application can provide some reference to developing and designing other switching power supply.In this paper, the designed single forward switching power supply’s wide DC input voltage ranges from 36V-75V, the standard input voltage is 48V, the output voltage is 18V, the output current is 1120mA, and the output watts is 20W. This power supply mainly uses integrated chips including controller chip UC3842, photoelectric coupler PC357 and adjustable precise shunt voltage regulator TL431 to all at once realize the function of input undervoltage protection, input overvoltage protection, input overcurrent protection and max duty ratio reduction. During the designing process, the following contrast experiments have been performed:contrast the transformer performance of different turn ratios, contrast the loss of different MOS types, and contrast the efficiency of different feedback compensation loops. Because of the above contrast experiments, we can get a best designing scheme. We have measured the sample’s black box, white box and the margin, the date and waveform show that the power supply has stable output voltage, the voltage accuracy is less than ±2%; the voltage regulation is less than ±0.5%; the load regulation is less than ±1%; the output ripple voltage is no more than 50mV/150mV (peak-peak), the ripple wave is tiny. Every voltage indicator reaches the design index, and has good performance.The main innovation points:1, by voltage feedback and current feedback dual closed loop cascade structure, so that the output voltage can be quite good stability; 2, Optocoupler H11A1 and three terminal adjustable voltage regulator tube TL431 with control greatly improves the transient response speed; 3, good design RCD suction back road and switch tube protection circuit, which can effectively eliminate the leakage inductance, the components can work stably and reliably. |
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