1. Analysis of working mode of Flyback converter;
2. Flyback key waveform analysis;
3. RCD absorption circuit design and switch tube stress;
4. Look at the wiring points from the noise loop.
5. Based on the actual project, the original flyback switching power supply video tutorial exposure
Modal Analysis of Flyback Converter
ON: The switch tube is turned on, the primary side of the transformer is charged, the diode is turned off, and the load is powered by the output filter capacitor.
OFF: The switch tube is turned off, the diode is turned on, and the energy stored in the transformer is transmitted to the load side through the diode.
Basic input and output relationship:
Ideally the switching waveform
Key Waveform Analysis of Flyback Converter
Analysis of MOS DS Voltage Waveform in DCM Working Mode
Analysis of MOS DS Voltage Waveform in CCM Working Mode
Analysis of MOS DS Voltage Waveform in CCM Working Mode
Waveform Analysis of Current Spike on Switch Tube
Waveform Analysis of Current Spikes on Switching Tubes (1)
After the switch tube is turned off, the secondary side of the transformer is clamped for the output voltage Vo. At this time, the voltage across the parasitic capacitor Cp is nVo, and the direction is negative up and positive down. When the switch tube is turned on, the Cp capacitor discharges. The parasitic inductance and the input voltage form a resonant circuit, thereby forming the peak current (resonant current).
Waveform Analysis of Current Spike on Switching Tube (2)
Waveform Analysis of Current Spike on Switching Tube (3)
Design of RCD Passive Snubber Circuit
Stress Analysis of Switching Devices
Main switch tube S1 voltage stress:
Rectifier diode D1 voltage stress:
Flyback noise circuit and layout requirements
Common Flyback Converter Topologies
Flyback is noise in converter
Single-point grounding to avoid coupling between loops
Use high-frequency capacitors to reduce loop area
Further reduce high-frequency noise by wiring
Ground impedance is further reduced by wiring
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