| Power is an integral part of all kinds of electronic devices, whose performance has a direct impact on the specifications of these equipment such as reliability, etc. Typically, the communication systems and communication equipment have very high requirements of the composition and performances of power supplies. As a communication device, the power supplies can generally fall into two categories, according to their power types, that is DC power supplies and AC power supplies. Typically AC power supplies can find their use in fixed sites, while DC power supplies serve as a backup. DC power supplies are very popular where there are more mobility or AC power supplies are difficult to be implemented, for instance in emergency communication vehicles and vehicle communication. The main object in this paper is the switching power supply in the vehicle communication system.A set of batteries is generally employed to supply power in vehicle communication systems. Due to the recharging and discharging process in the batteries, the power supply of the vehicle communication has a wide voltage range from75%to125%of the rated value, approximately close to2octave. Meanwhile, a surge voltage will emerge when a car is started and stopped. Besides, there also exists interference between different electrical equipment in the same car. So as the power supply of a communication system, it should have a wide working voltage range and a strong anti-interference ability. In the same time, the interference generated by different devices in one car should be controlled within certain limits to guarantee that the power supply can work in a interface-friendly atmosphere. For example, the start-up current cannot be too large and the radiation and conduction energy by the input cables of the power supplies cannot exceed certain limits.DC-power switching power supplies not only have the basic characteristics of low weight, small size, low power consumption, wide operating voltage range, but also have the following characteristics:1) multiple outputs;2) small interference and a little stray voltage produced by output power, to prevent interference on voice communications, data communications, and etc;3) high efficiency, energy-effective, less heat. The DC-powered communication devices generally require high reliability, compact size and low weight. Reliability improvement, volume reduction and weight decreasing of the equipment both require high efficiency. Many circuit techniques (such as soft switching, back-energy absorption, etc.) are designated to improve efficiency.4) less pollution to input power and small harmonic currents;5) soft-start reduces inrush current.6) a wide working temperature range. As the communication equipment frequently moves with vehicles, so its working temperature is the plain temperature, typically-40℃to55℃.7) exhibit security, can be automatically protected. Once an abnormal phenomenon occurs, for example, input or output voltage and current is too large, or the temperature is too high, protection measures should be taken to cut off the power supply to avoid the expansion of the failure, and the system can automatically resume the normal operation when the failure is eliminated.For the characteristics and requirements mentioned above, together with the practical applications, a single-ended flyback small power DC/DC communication switching power supply based on TI’s chip LM3488is designed.Based on the in-depth study and analysis of the theory and key techniques concerning the switching power supply, the design of a single-ended flyback switching power supply system is completed, It covers specific modules, including EMI filtering circuits, high frequency transformer, the front-level protection circuits, passive clamp RCD circuits, a controlling loop, and the output filtering circuits; First reasonably choose, design and allocate the various circuit parameters of the switching power supply; then give the circuit schematic diagram; next PCB is drew according to the design specifications, and the power supply prototype is assembled; Finally, the verification of this design is carried out.The standard input voltage of the switching power supply is24V, and its input voltage range is from18V up to33V. Operating at the rated voltage, its output voltage accuracy is3.3V±0.05V,-3.3V±0.5V,16V±0.5V; Output load regulation is0.1V (3.3V),0.5V (3.3V),0.5V (16V); output voltage ripple is lOmV (3.3V),20mV (-3.3V),20mV (16V), respectively; On wide voltage input conditions, the output voltage is up to3.3V±0.1V,-3.3V±0.8V,16V±0.5V, showing high voltage stability. These performances meet the sample’s requirements:stability in output voltage, and good performance. |
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