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PFC with a CCM controller but low power

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AlienCircuits

AlienCircuits

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My questions are

1. A CCM operation implies constant current draw. So how can a CCM PFC work when there is no load? What about for very low loads where it forces the inductor to have discontinuous current in it?
2. How does this impact my PFC boost inductor selection? Should I need a larger or smaller inductor to stay in CCM? I think a larger inductor will force it towards CCM since V/L = di/dt.
3. Will my CCM chip (NPC1653) operate in a discontinuous current mode if the load is very light? If this is the case, won't my peak inductor currents be higher?
 

AlienCircuits said:
My questions are

1. A CCM operation implies constant current draw.
Click to expand...
No it doesn't?
So how can a CCM PFC work when there is no load? What about for very low loads where it forces the inductor to have discontinuous current in it?
Click to expand...
Then the controller will enter a discontinuous mode, if it has to.
2. How does this impact my PFC boost inductor selection? Should I need a larger or smaller inductor to stay in CCM? I think a larger inductor will force it towards CCM since V/L = di/dt.
Click to expand...
You shouldn't select your inductor based on light-load conditions. Staying in CCM at all times is not practical or necessary. Being in CCM improves efficiency, and can give lower distortion, but efficiency and distortion don't need to be great at very light loads.
3. Will my CCM chip (NPC1653) operate in a discontinuous current mode if the load is very light? If this is the case, won't my peak inductor currents be higher?
Click to expand...
It might operate in DCM at light loads near the zero crossings. No, it won't result in higher peak currents, certainly not higher than the peak currents you get during higher load conditions.
 

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