I want to know which factor causes switch node transient level high in buck converter

crutschow said:

Diode reverse recovery current would generate a very short spike, not the longer spike you are seeing.

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Then Dick Capples may be right. This buck runs at discontinuous mode and ripple generates from the third duration, which bjt and diode are not conducting. But the inductor still prevents the current go away quickly and keep voltage a while. Here is my graph for my statements.


You can see the when the indcutor current starts conducting, the diode current shows up. After then, the third period starts and diode and bjt are turned off at the same time until next inductor cycle. Then, it suppose not to generate any ripple.