Hi team,
If I use UCC28251 as primary side control , is it limted to 72Vdc as per your EVM? My design is to work on 100Vdc at the input side. Will it work if i feed forward input voltage to ramp pin of ucc28251?. And In primary side control, how will the circuit regulate the output voltage ?
Hello Subash,
Yes you can use the UCC28251 in a design with 100Vdc input.
Im not sure why the EVM has an input voltage range from 36V to 72V since the normal upper limit for a telecom application is 75V but
regardless you can use this part for a 100V application.
Primary side control is explained with the help of the drawing attached:
As the input voltage increases the ON time of the PWM ramp decreases.
This is exactly what you need in order to regulate Vout since Vout is directly proportional to Ton/Vin .
This gives excellent line regulation (control of Vout with changing Vin) but no load regulation (control of Vout as the load changes).
And it does this without feedback from the secondary side to the primary side.
Regards
John
