UCC28070: No load，The DS waveform of the PFC FET

Hello Neil,

At true no load there is no switching of the FET and the drain voltage is charged up to the peak of the AC input.
However because there are always some power losses, there will be some very narrow gate drive pulses in order to maintain the set output voltage.

The drain voltage will switch from its instantaneous value to ground for this short time. When the FET turns off, the drain voltage is clamped at the level of the output voltage. This continues as long as the inductor is conducting current to the output. There follows a ringing set by the inductance and the drain source capacitance of the FET. Afterwards the drain voltage tracks the voltage on the DC side of the bridge rectifier.

Regards,

John