Other Parts Discussed in Thread: , PMP10726, PMP22322
Dear Engineer,
Hello, I am a beginner in power electronics. I encountered some problems while trying to design a flyback power supply using UCC28782 and hope to get your help:
1.How is the switching frequency of the chip determined? I saw the description of fBUR burst frequency in the datasheet, but I couldn't find relevant information about the individual switching cycles within the data packet. Could you please explain how the switching frequency in AAM (Auto Adjustment Mode) and the individual switching frequency within the data packet are determined? I noticed that the document mentions its switching frequency is a variable frequency with a maximum of 1.5 MHz. However, there seems to be no pin or other component for frequency setting. Could you please tell me how to set the switching frequency? Or I dont need to consider about it ,the chip will adapt by itself?
2.In the reference design, I noticed that the FB pin seems to use feedback through the internal DAC of the fast-charging chip. Does it set different output voltages of the PD chip through different bias voltages output by the DAC? What is the conventional scheme for setting different voltages? Is choosing 4 voltage divider resistor networks for switching a good idea?
3.I have some questions about the function of the boost converter composed of BIN, BSW, and BGND from the auxiliary winding. My understanding is that it is used to supply power to VDD, with an overall maximum power of 18.5V and 0.33A. Is a separate boost converter used because the power is relatively large and the voltage is special?
I hope to receive your help. Thank you very much!
