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# Flyback Converter This course introduces the operating principles of and the uses for Flyback converters. It describes the similarities between the...

Question: 3.2

Sketch the circuit diagram of the " Flyback" converter switch-mode dc power supply and shortly describe the operation thereof.

Question: 3.3

The average (or dc) output voltage of the flyback circuit in question: 3.2 is Vo = 30V at a resistive load of R = 0.9 Ohm.

The duty-cycle ratio is k = 40% and the switching frequency is f = 900Hz.

The ON-state voltage drops of transistors and diodes are Vt = 0.7V, respectively.

The turns ratio of the transformer is a= Ns/Np = 0.25.

Neglect the losses in the transformer, and the ripple current of the load and determine.

(a) the average input current;

(b) the efficiency;

(c) the average transistor current;

(d) the peak transistor current;

(e) the rms transistor current;

(f) the open-circuit transistor voltage;

(g) the primary magnetizing inductor.
Flyback Converter This course introduces the operating principles of and the uses for Flyback converters. It describes the similarities between the Flyback converter and the Buck-Boost converter and introduces the basic equations use in Flyback converter design. Potential design issues are discussed and a design example is provided. Course Map/Table of Contents 1. Course Navigation 1.1 Course Navigation 1. 1.2 Course Objectives 2. 2. Flyback Converter Topology 2.1 Fundamental DC-DC Converter Topologies 1. 2.2 Isolated Topologies 2. 2.3 Forward / Flyback Comparison 3. 2.4 Flyback Converter Characteristics 4. 2.5 Flyback Merits and Applications 5. 3. Flyback Converter Operating Principles 3.1 Key Waveforms 1. 3.2 Study State Analysis 2. 3.3 Study State Analysis Continued 3. 4. Flyback Converter Design Issues 4.1 Key Design Issues 1. 4.2 Flyback Transformer 2. 4.3 Example - Design Specifications 3. 4.4 Primary Turns Ratio, Core Selection 4. 4.5 Bobbin Area Use 5. 4.6 Secondary Winding 6. 4.7 Copper Losses 7. 4.8 Gapping the Core 8. 4.9 Core Gapping Formula 9. 4.10 Inductance Flow Factor 10. 4.11 Flux and Ripple Calculations 11. 4.12 Auxiliary Winding 12. 4.13 Other Components 13. 4.14 Filter Capacitors 14. 5. Controller Selection 5.1 Controller Choices 1. 5.2 Current Mode vs. Voltage Mode 2. 5.3 LM5020 Controller 3. 5.4 Load Compensation 4. 5.5 Right Half Plan (RHP) Zero 5. 5.6 Slope Compensation 6. 5.7 LM5020 Slope Compensation 7. 5.8 Loop Compensation 8. 5.9 Error Amplifier Design 9. 5.10 Loop Gain Results 10. 6. Flyback Circuit Examples 6.1 Isolated Flyback Design 1. 6.2 Non-isolated Flyback Design 2. 6.3 Sync Rectifier Modification 3. 6.4 LM5020 Demo Board 4. 6.5 Demo Board Efficiency 5. 6.6 Primary Switch Drain Voltage 6. 6.7 Ripple Voltage 7. 7. Conclusions 7.1 Conclusions 1. 1. Course Navigation
1.1 Course Navigation 1.2 Course Objectives 1.1 Course Navigation This course is organized like a book with multiple chapters. Each chapter may have one or more pages. The previous and next arrows move you forward and back through the course page by page. The left navigation bar takes you to any chapter. It also contains the bookmarking buttons, 'save' and 'go to.' To save your place in a course, press the 'save' button. The next time you open the course, clicking on 'go to' will take you to the page you saved or bookmarked. The 'Go to Final Test' button on the left navigation bar takes you back to the Analog University course listing, where you started. Take the course final test by clicking on 'Test Yourself.' The top services bar contains additional information such as glossary of terms, who to go to for help with this subject and an FAQ. Clicking home on this bar will take you back to the course beginning. Don't miss the hints, references, exercises and quizzes which appear at the bottom of some pages. 1.2 Course Objectives Upon successful completion of this course the student will be able to: Determine when a Flyback Regulator would be the best design choice. Given a specific design requirment explain the benefits of using a Flyback Regulator instead of another type of regulating circuit. Provide solutions to common problems associated with Flyback Regulator designs. 2. Flyback Converter Topology This chapter introduces Flyback Regulator topology and discusses some suitable applications. 2.1 Fundamental DC-DC Converter Topologies 2.2 Isolated Topologies 2.3 Forward / Flyback Comparison 2.4 Flyback Converter Characteristics 2.5 Flyback Merits and Applications 2.1 Fundamental DC-DC Converter Topologies These graphics show the three fundamental DC-DC power converter topologies. Based on these other popular topologies are derived; including the flyback, forward, push-pull, half-bridge, and full bridge converter topologies. In these three fundamental topologies, the two switching elements, namely the switch and rectifier diode, are under different voltage stresses. In a Buck, the voltage stress is Vin, while
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