Dear Sir,
we are developing 2900W telecom power and using UCC28070 for our PFC controller.
what's the condition caused fault of Cao active? behavior of fault Caob and Caoa.
during rectifier output transient 0W -->2900W at 276Vac, the PWM will be limited due to Cao drop to zero showed as figure.
what conditions will cause fault active?
Ch2: Cao
Ch4: PFC inductor
ear Sir
sorry, the attached file is not completely up load to web page.
re-update the figure.
Ch2: the comp of Cao
Ch4:PFC_inductor A
testing condition: 276Vac , NO LOAD -->2900W (Transient)
the current doesn't reach pk-limit point.
I don't know why the Cao drop to zero to limit the power delivery.
what the conditions cause the fault of Caoa active?
thank you
Hello chingyu Wang,
This section of the UCC28070 block schematic shows the conditions that will cause a fault condition on the CAO outputs
I think in your situation the shutdown is triggered by the Zero Power comparator tripping.
At high line an no load the EAO output is probably below the threshold of 0.75V nom (0.65V min)
This will cause the CAO to turn off and when you cycle from no load to full load the pwm turns off.
The voltage loop is designed to be slow and you probably have a large compensation cap on the output of the error amplifier.
My suggestions are:
Use the Excel calculator for this design .
You may not have enough capacitance on the pfc output.
Check for this issue at lower line voltages and with loads slightly greater than no load.
Regards
John
