Hello everyone,
I need help reviewing the design of the flyback power supply with UCC28700. My design specification is according to the following:
- Vin = 60 V - 410 V ( input DC voltage range)
- Vo = 12 V / 4 A ( output DC voltage)
I used WEBENCH to come up with the design and I used the same circuit presented in the datasheet:
The components that I used:
RS1 = 105 kΩ
RS2 = 27.7 kΩ
Rcs = 100 mΩ
RLC = 2.2 kΩ
Cdd = 472 uF
Np: 10
Ns: 1
Cout: 1000 uF
Rpl: 2k2
I also put a 100 pF capacitor in parallel to the CS pin.
CBC pin I left open, but also tried to put a 10 kΩ resistor.
UCC28700 is supposed to start switching when VDD reaches 21 V, but it is not working. The voltage is quite above 21 V, reaching about 25 V but the converter doesn't start switching. It seems the operation enters in fault condition and I don't know why.
I would be grateful with any clue on how to solve this problem.
Thanks in advance.
