I use UCC28950 to control a 400V to 24V phase shift converter. The full load is 150A
When the load current was increased 1A by 1A, the regulation is well until 20A is reached. Before 20A, the current and Vout are well regulated. But, once 20A is applied, the regulation is lost and Vout goes wild.
Yellow = Vct current
Blue = EAO (COMP)
Why EAO gets saturated by increase a little Iout?
Hi Teng,
No problem. I do have some more follow-up Q and information to add on.
Green = Vout
Purple = Vss
Yellow = Vct current
Blue = EAO (COMP)
0 to 15A load jump
At the beginning of the jump, there was no PWM. Vout (green) was drained out by 15A load. EAO started to rise from 0. Only when EAO reaches to 1V, PWM began.
Question:
What is the normal EAO voltage at zero load? Now it is zero.
Does EAO have 1V offset volta
ge at zero load?
Load jump from 15A to 20A.
Vct should increase according to EAO increase, but Vct increases only a little and then keeps constant. It looks like the controller got into cycle-by-cycle current limit mode under a small Vct (less than 0.4V), why?
The unit enters into constant current mode: Vout drops while Vct keeps constant no mater how larger the required load is.
