Part Number: UCC28780
Dear Expert
The attached files show the VSW and PWML waveforms measured under a 115Vac input condition. An abnormal waveform is observed: after VSW drops to 0V, it rises again. This phenomenon is particularly evident under the 10A output condition; no such issue has been observed in the 5A to 9A range; similar waveforms are also present below 5A, but VSW does not drop to 0V in these cases.
Similar abnormal waveforms also appear when the input is 270Vac high voltage
Transformer parameters: turns ratio 23:1:3, excitation inductance Lm=200uH, leakage inductance Lr=9uH, switching frequency 100kHz, with sandwich winding method.
I'd like to ask, from which directions can this abnormal waveform be investigated and improved?
I have attempted to modify the parameters of the RDM, RTZ, and BUR pins as well as the transformer's parameters and winding method, but there has been no improvement.
Schmetic
