L4946A gives good PFC in discontinuous mode?

[amass.9]

Hi,

We wish to do a Boost PFC with L4986A and a  30uH inductor.

Power is 2200W and Mains is 85-265VAC.

When the mains is at 240VAC,  the inductor current would be discontinuous for some 80% of the mains half cycle.

Is this OK?

Will the L4986A be able to control it  to give a good power Factor with low THD?

[Peter BENSCH · Accepted solution]

If the question is still relevant:

the L4986A is designed for continuous‑conduction‑mode (CCM) boost PFC. At 240VAC and 2.2kW with only 30µH, operating 80% of the half‑cycle in discontinuous mode is not the intended use case.

In deep DCM the current waveform and loop gain change significantly; you can still get PFC action, but PF and THD will generally be worse and not in line with the datasheet performance figures.

For good PF/low THD you should:

• choose the boost inductor so that the design remains mostly in CCM at high line and full load (check L vs. ripple current from the application note), or
• if DCM/transition‑mode is desired, use a controller specifically intended for TM/DCM PFC

So with 30µH at 2.2kW I would not expect optimal PF/THD with L4986A.

Hope that helps?

Regards
/Peter