Problem: in the buck mode, the static current will increase synchronously with the increase of the input voltage. The phenomenon is that the MOSFET U4 will be very hot. See the attachment for the schematic diagram. The waveforms of the four MOS base stages are as follows:
Note: the ringing part of the MOS end is caused by the radiation interference of the oscilloscope probe. Take off the probe, and one measurement will be much smaller。