Part Number: UCC28070
I am using UCC28070 interleaved PFC controller for 1.2kW battery charger design. I have few queries regarding this IC. These are mentioned below.
1. Does duty cycle in boost PFC varies according to input sine voltage?
2. What are the advantages and disadvantages if we keep duty cycle constant?
3. What are the advantages and disadvantages if we keep duty cycle variable?
4. Why loop bandwidth of PFC is always kept low such as at 20Hz?
In reply to John Griffin1:
In reply to Dhananjay Yadav:
John is travelling at present and his responses may be delayed.
In the meanwhile - I'd suggest you look at the material on PFC at http://www.ti.com/ww/en/power-training/login.shtml?DCMP=psdslibrary&HQS=tlead-power-psdslibrary-apec2015-pwrhouse-20150312-lp-en The article at https://www.ti.com/seclit/ml/slup203/slup203.pdf is a good introduction to PFC in general.
Overall, the slow loop response (typ 10 Hz or so) allows the controller to set an AVERAGE current level in the PFC inductor which is then modulated (or multiplied) by the instantaneous input voltage (a sinusoid). You can see the MULT block in the UCC28070 data sheet block diagram. This modulation is what modified the duty cycle as the line voltage goes through it's cycle. This way you get a sinusoidal input current whose AVERAGE level is correct for the load conditions at the output. there are some subtlties of course but that's the basic idea.
The minimum duty cycle is zero.
Hello John, Thanks for reply! Please let me know at maximum instantaneous input AC voltage duty cycle will be minimum or maximum?
And at zero instantaneous AC input voltage what will be duty cycle value? Regards, Dhananjay Yadav
Hello John, Thanks for reply! But I am not able to realize this concept. This is for the 1.2 KW battery charger PFC stage. Can you please tell me is duty cycle is in phase with input AC wave or it is out of phase? Please find below image for reference. Is it like the same as shown?
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