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A 24V 150W power supply's power ratings is marked on its surface as follows:

enter image description here

In this case as you can read the cos phi is 0.45.

I know that the utility which provides power to the systems wants to supply low current so by compensation the current going into the system is lowered. And if I'm not wrong they use capacitors to reduce the power factor for inductive loads in industry.

But back to this power supply's case. If we think this power supply as our system and if we want to bring the power factor from 0.45 to around 0.9 or close to unity, is there a way to do that?

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    \$\begingroup\$ Buy one with PFC instead? \$\endgroup\$
    – winny
    Sep 25, 2019 at 10:19
  • \$\begingroup\$ I was wondering how it is technically achieved for this case? Adding caps across the line and neutral? Question is out of curiosity. \$\endgroup\$
    – GNZ
    Sep 25, 2019 at 10:21
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    \$\begingroup\$ No, because the current isn't a sinewave. PFC is the way. \$\endgroup\$ Sep 25, 2019 at 10:27
  • \$\begingroup\$ Adding caps across the line and neutral? No that's just filtering. Use Google to find "PFC circuit" and search for images and you'll see some examples. \$\endgroup\$ Sep 25, 2019 at 10:30
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    \$\begingroup\$ And if I'm not wrong they use capacitors to reduce the power factor for inductive loads in industry. Yes but that only works for loads that are mostly inductive. A power supply isn't and it behaves quite differently. \$\endgroup\$ Sep 25, 2019 at 10:32

1 Answer 1

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The load this power supply imposes on the mains is not sinusoidal, so placing any value of cap across it's mains will not properly correct power factor.

The only way is with a "Power Factor Correction" front-end. Essentially this is a special boost switcher which is optimized to pull sinusoidal-like power from the mains, thus increasing the power factor. Output is DC.

If your supply has a DC input, you could implement a PFC stage and just supply it with DC to achieve higher power-factor.

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