Other Parts Discussed in Thread: UCC28C43, UCC28C52
Hello Team
Attached is the simulation model of our SEPIC converter for wide input voltage. Facing issues with simulation. Kindly do the needful to proceed further.
Converter Specification:
SEPIC Converter
Input voltage range: 75V to 900V
Output Voltage range: 400V
Switching Frequency: 70kHz
Output Power: 120W.
Coupled inductor Lpri: 1.5mH Lsec : 1.5mH SEPIC Converter UCC28C56H Model..TSCSEPIC Converter UCC28C43 Model..TSC
Auxiliary winding to match required Vdd.
Problem Statement:
1. Ucc28c56H IC pulses are not coming properly. NO fixed frequency pulses are observed. Change in frequency and amplitude also observed at higher input voltage range. This observed when we fed voltage to Vdd pin through auxiliary as well as with external stable DC voltage supply.
Closed loop model is working from 150Vdc to 900Vdc input when the current sense limit is increased with UCC28c56H.
We also tried using UCC28c43 IC as well, but the pulses are not proper even with this model, but Closed loop model is working from 75Vdc to 900Vdc input when the current sense limit is increased with UCC28c43.
2. The currents measured at CS resistor is very high than beyond theory. CS resistor to be sized very small to measure higher currents then only the output is achieved or else if we size current sense resistor for calculated value it is not working.
In our case.,
Maximum primary peak current is 3A at 75Vdc. Adding some buffer, for 5A peak current if we select resistor for UCC28c56H 1V CS pin voltage, 200mOhm should be fine.
But were unable to get output. Primary current peaks are very high.
We used Nonlinear transformer part with separeted secondary coils to in place of coupled inductor to have auxiliary winding. As with coupled inductor we cannot model auxiliary winding.
Primary turns: 138T, Secondary 138T Auxiliary 37T.
3. Help in proper tuning of compensation if required.
Thanks
Vasu