I am considering to use Buck-Boost topology for Power Factor Correction but I'm having trouble finding much literature on it. My appliance is an LED fixture so it will always have a (fairly) constant load (150mA @ 30V). Since the input voltage range is going to be between 100-240 VAC and the output is 30VDC, using a Boost Converter with PFC is a bit unfeasible. I would prefer if the solution is single-stage due to space and cost. I want to avoid using a Flyback topology because at 240VAC input it will place a huge peak voltage stress on the power switch.
From looking at the waveform (page 10 and 11) of a Boost topology working in Critical Conduction Mode, the peak current is:
$$
I_{pk}=\frac{2\sqrt2 P_{in}}{V_{rms-min}}
$$
My question is, does this result hold for Buck-Boost as well? I feel that it should because it is based on the waveforms and not on the topology. Another way to look at this would be that during \$t_{on}\$, the Buck-Boost and the Boost topology's inductor both have \$V_{in}\$ applied across them.
I am actually not considering the above linked part. I am considering Richtek RT7302. Unfortunately, for this IC, most of the literature is for Flyback topology and not for Buck-Boost – including their Excel Design Tool.
Best Answer
There is a simple way to transfer the Flyback design method to Buck-Boost. Just assume the secondary winding in the Flyback method having the same number of turns as the primary, then the calculations become equivalent.