Hi
I am designing a 120W PFC using a Texas instument UCC28051 controller. The converter works as it should when I look at the output voltage, which is about 396 V, but when I look at the current through the inductor it looks like the controller enters some kind of burst mode?!
You can see a plot of the inductor current (green) and gate signal (yellow) below, during a 50 Hz cycle, the converter was delivering 60 watt to a load when the plot was made:
![](http://i163.photobucket.com/albums/t315/jollekim/PFCburst.png)
Has anyone seen a PFC behave this way before and know why it behaves as it does?
Regards
I would check these:
- core saturation (linear voltage ramp on CS pin)
- spikes on CS pin
- device supply voltage Vcc
- ZCD pin
Does the output voltage fall or is regulated?
Fabio.
But isn't it supposed to behave something like that? A PFC is doing 2 things: maximize cos(phi) i.e. make voltage and current equal in phase, and secondly minimize current spiking due to capacitive load. The ideal would be a resistance-like V/I curve. The PFC cannot do anything to the instantaneous line voltage but by modulating it can distribute the current more evenly over the half-wave.
Just by looking at the picture i cannot say if that is what it is doing, or if it is some fault condition.
But isn't it supposed to behave something like that? A PFC is doing 2 things: maximize cos(phi) i.e. make voltage and
As far as I know to do so that current envelope should be like a sinusoid semiperiod,
the control loop then changes (acts on time scales slower than a semiperiod)
the current value to regulate the output voltage on the capacitor bank.
Fabio.
Well yes, but i am not familiar with that chip and its capabilities. In case it just does a rough approximation this could be the result. Or then it is just malfunctioning.
Kremmen hit the nail on the head with the comment about my IC being malfunctioning. I hadn't thought of that since the controller was regulating, but when I soldered on a new IC everything worked fine and my PF is now very close to 1
![Cheesy :D](https://www.eevblog.com/forum/Smileys/default/cheesy.gif)
So thanks to all of you who helped me with my relative simple problem.