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Classic case study of power principle analysis, waveform analysis, stress calculation, and loop layout

Table of Contents

1. Working Mode Analysis of the Flyback Converter;

2. Key Waveform Analysis of the Flyback Converter;

3. Design of RCD Absorption Circuit and Switching Device Stress;

4. Understanding Noise Circuits Through Wiring Points;

5. Practical Project-Based Flyback Power Supply Video Tutorial.

In the ON state, the switch is turned on, allowing the primary side of the transformer to charge. The diode is off, and the load is powered by the output filter capacitor.

During the OFF state, the switch turns off, the diode turns on, and the energy stored in the transformer is transferred to the load through the diode.

The basic input-output relationship of a Flyback converter can be expressed as a function of the duty cycle and the turns ratio of the transformer.

Ideal switching waveforms for a Flyback converter show distinct ON and OFF states with clear transitions between them.

Key Waveform Analysis of the Flyback Converter

Analysis of the MOSFET DS Voltage in DCM Operating Mode

Analysis of the MOSFET DS Voltage in CCM Operating Mode

Another view of the MOSFET DS voltage waveform under CCM mode

Waveform Analysis of Current Spike on the Switching Tube

Current spike waveform analysis (Part 1)

When the switch turns off, the secondary side of the transformer is clamped by the output voltage Vo. At this point, the parasitic capacitor Cp is charged to nVo. When the switch turns on again, the capacitor discharges through the winding, creating a resonant current due to the interaction between the parasitic inductance and the input voltage.

Current spike waveform analysis (Part 2)

Current spike waveform analysis (Part 3)

Design of the RCD Passive Absorption Circuit

Stress Analysis of Switching Devices

Main Switch S1 Voltage Stress:

Rectifier Diode D1 Voltage Stress:

Flyback Noise Loop and Layout Considerations

Common Flyback Converter Topology

Flyback Converters Generate Noise During Operation

Single Point Grounding to Avoid Loop Coupling

Reduce Loop Area Using High-Frequency Capacitors

Further Reduce High-Frequency Noise Through Proper Wiring

Further Reduce Ground Impedance Through Strategic Wiring

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