Vin is 230Vac/50Hz, Vout is set to 408V/850W, Vout has jitter: 380V to 430V,Pin6(Vsense):4.46V to 5.4V. When Pin6(Vsense) rises to 5.0V, the duty cycle slowly decreases, and the Gate will close when Pin6(Vsense) rises to 5.4V. When Pin6(Vsense) drops to 5V, Gate starts to drive, duty cycle slowly increases, Pin6(Vsense) slowly drops to about 4.4V, and Vout also drops. (The above is the 230Vac/50Hz on-load (850W) startup or directly with 850W after startup)
When the input Vin is reduced to 180, this phenomenon does not appear, or when the 230Vac input frequency is changed from 50Hz to 60Hz, this phenomenon does not appear. Or Vout with half load 400W and then cut full load, this phenomenon will not appear.
Abnormal Vcomp waveform for 230V/50Hz input:
Normal Vcomp waveform for 230V/60Hz input:
This is Sch.