Hello,
I designed a flyback converter using the UCC28711. The DC input voltage ranges from 150V-1000V and the output voltage consists of 2 outputs of 17V each. Unfortunately, the circuit does not respond as expected. I observe different responses of the control law of the IC according to the input votlage. In particular, when the for input voltage is:
- up to 270V, the output is correct. (file name: 270V.pdf)
- From 270V-300V, the control law reduces the frequency and the duty cycle discharging the output up to 13.5V. Then it increases the frequency and the duty cycle again, until the output becomes 17V. After that, it repeats again the process. Thus, the output voltage, looks more like a sawtooth. (file name: 300V.pdf)
- For output voltage close to 320V, all of a sudden the output becomes 12.37V. (file name:330V.pdf)
In general, the level of input voltage at which the changes happen depends on the load, but overal the pattern is the same.
Have you seen anything similar in other applications?
In the following pdf you can find attached the waveforms of important parameters.
Blue:Vdd
Red:DRV
Green: voltage on the anode of the auxiliary winding diode
Yellow: Output270V.pdf
Thank you.
