You asked about the high peak-to-peak value. I don't know if you are asking about the back pressure of the output rectifier or the ripple of the output voltage, but according to my judgment, you should be asking about the ripple of the output voltage. Below I give several ways to reduce ripple.

First of all, the ripple commonly known in the industry is fingerprint wave+noise.

Methods to reduce the ripple of forward power supply;

1, increase the electrolytic capacitor capacity of the output filter.

2. Increase the inductance of the energy storage inductor, because the lower the inductance, the greater the average value of the switching current, the more natural the current, the greater the ripple, and more capacitors are needed for filtering.

3. The output terminal can be connected in parallel with nonpolar capacitors, such as CBB capacitor and Melaleuca cake capacitor. ESR (Equivalent Series Resistance) and ESL (Equivalent Series Inductance) of electrolytic capacitors are large, so the filtering of high-frequency current is not ideal, while the capacitance parameters of nonpolar film are low, which can better filter high-frequency ripple.

Ways to reduce noise:

1. Change the parameters of RC absorption circuit for output rectification (appropriately increase the capacitance and decrease the resistance value), and increase the absorption of voltage spikes generated by transformer leakage inductance.

2. Add * * mode inductance at the output end.

3. If the above two points are not solved, it is necessary to change the winding method of the transformer to reduce the leakage inductance.