.50 W High-frequency Switching Power Efficient Design

Switching mode power supply(SMPS) is a significant part of the power electronics, which effects the performance and volume of the electronic equipment. Recently, because of the miniaturization of the instruments, higher requirement is advanced for SMPS. The main development of the power electronics is smaller volume, lighter weigh and higher efficiency. SMPS is required for high working frequency. In order to fasten the switching frequency, the switching loss should be minimized. High performance magnetic materials and fast switch components are also required. Therefore, the technology innovation focuses on optimization design methods, higher efficiency and smaller volume.The principle of high frequency transformers in SMPS was investigated, the factor of effecting the high frequency power transformer was analyzed. A great deal of performance of the high frequency magnetic core was tested and the best one was chosen to make the power transformer. The results depicted that P core had low leakage inductance, and the magnetic core's highest working frequency was 500KHz. The primary side inductance was 1929.1μH, and the leakage inductance was 82.3μH. Comparing lots of experimental results, the Sandwich method whose leakage inductance was minimal minimized skin effect and proximity effect. Consequently, copper loss was reduced. At the same time, the transformer and the output circuit were simulated and the circuit parameters were optimized. The optimized parameters: output filter inductance was 250μH, output filter capacitor was 147μF.The EMC principal and the methods of reducing the EMI were analyzed and the input EMI filter was designed. Then, the EMI filter was simulated by computer. Though the simulation, the parameters was optimized. The optimized parameters: Common-mode inductance was 3.5mH, Differential-mode capacitor was 170nF, Common-mode capacitor was 33nF.Based on the research results given above, a prototype with control circuit, feedback circuit and rectification circuit was made and its working performance is stable through plenty of experimental. The input voltage was 220V(±20%)and then 309V through the EMI filter and input rectifier;the converting frequency was 500KHz; the maxism output power was 50W; the output voltage was 12.1V, the output ripple voltage was under 50mV.