(Dry goods exchange) Power principle analysis, waveform analysis, voltage calculation, circuit diagram

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1. Analysis of operating mode of flyback converter;

2. Reverse key waveform analysis;

3. RCD snubber circuit design and switch tube voltage;

4. Look at key wiring points in terms of noise loops.

5. Based on an actual design, the original instructional video on switching power supply with feedback

1. Modal flyback converter analysis

ON: The switching tube is on, primary side of transformer is charged, diode is off, and load is powered by output filter capacitor.

OFF: The switching tube is off, diode is on, and energy stored in transformer is transferred to load side through diode.

Basic input and output relationships:

Perfect signal switching

2. Analyzing main signals of a flyback converter

Analyzing MOS DC voltage waveform in DCM mode

Analysis of MOS DC voltage waveform in CCM mode

Analysis of MOS DC voltage waveform in CCM mode

Analysis of shape of current pulse on switch tube

Analysis of shape of current pulse on switching tube (1)

After switch tube is turned off, secondary side of transformer is clamped with Vo output voltage. At this time, voltage across parasitic capacitor Cp is nVo, and direction is negative up and positive down. When switch tube is turned on, capacitor CP is discharged, and at this time, CP forms a resonant circuit with parasitic line inductance and input voltage, thereby generating a peak current (resonant current).

Analysis of shape of current pulse on switching tube (2)

Analysis of shape of current pulse on switching tube (3)

3. RCD passive absorption circuit calculation

4. Load analysis of switching devices

Main switch S1 voltage:

D1 rectifier voltage:

5. Feedback scheme and layout requirements

Overall flyback converter topology

Flyback is noise in converter

Single point grounding to avoid coupling between loops

Using high frequency capacitors to reduce circuit area

Further reduction of high frequency noise through wiring

Wiring further reduce ground resistance