1、西安工程大学 本科 毕业设计（译文） 1 Low Voltage Flyback DC-DC Converter For Power Supply Applications Hangzhou Liu1, John Elmes2, Kejiu Zhang1, Thomas X. Wu1, Issa Batarseh1 Department of Electrical Engineering and Computer Science, University of Central Florida, Orlando, FL 32816, USA Advanced Power Electronics C
2、orporation, Orlando, FL 32826, USA Abstract In this paper, we design a low voltage DC-DC converter with a flyback transformer. The converter will be used as a biased power supply to drive IGBTs. The flyback transformer using planar EI-core is designed and simulated using ANSYS PExprt software. Besid
3、es, anLT3574 IC chip from Linear Technology has been chosen for converter control. Finally, the converter modeling and simulation are presented and PCB layout is designed. Keywords： Flyback, anLT3574IC, PCB I. INTRODUCTION The goal of this project is to develop and build a prototype of a high-effici
4、ency, high-temperature isolated DC-DC converter to be used as a biased power supply for driving a complementary IGBT pair. It is important that the converter can deliver the required power at an ambient temperature of up to 100 ； therefore it has to be efficient so that its components do not exceed
5、their maximum temperature ratings. The final converter will be completely sealed and potted in a metal case. The input voltage range for this converter is from 9V to 36V. The output sides have two terminals, one is 16V and the other one is 6V. In order to get the desired performance, anLT3574 IC chi
6、p from Linear Technology is used. The key to this design is the flyback transformer. The transformer using planar EI-core is designed and simulated using ANSYS PExprt software. Finally, the PCB layout of the converter will be presented. 西安工程大学 本科 毕业设计（译文） 2 II. KEY DESIGN OUTLINE For this flyback to
7、pology, the output voltage can be determined by both the transformer turns ratio and the flyback loop resistor pairs. Therefore, at the initial design stage, we can choose a convenient turns ratio for the transformer, and modify it later on if necessary to make sure the output performance is desirab
8、le and the transformer will not saturate 1. The relationship between transformers turns ratio and duty cycle can be found as Where n is the transformer turns ratio, D is the duty cycle, VO is the sum of the output voltage plus the rectifier drop voltage, VIN is the input voltage of the transformer.
9、The value of feedback resistor can be calculated as Where RREF is the reference resistor, whose value is typically 6.04k； is a constant of 0.986；VBG is the internal band gap reference voltage, 1.23V； and VTC is normally 0.55V 1. With a specific IC chosen, the converter circuit can be designed based
10、on a demo circuit and some parameters may need to be modified if necessary to optimize the performance. Furthermore, in LT Spice, a large number of simulations need to be done with different conditions such as load resistor values and input voltage levels. It is important to make sure that the outpu
11、t voltage can be regulated well with all these different conditions. The most critical part of the design is the flyback transformer. With high switching frequency, the AC resistance can only be estimated based on some traditional methods such as Dowells curve rule 2.In order to get more accurate values of AC resistance values； we propose to use finite element electromagnetic software ANSYS PExprt to do the design 3. At the initial design stage, key parameters such as the worst-case input voltage, frequency, material, inductance values will
