As you might know, LED lamps over 25W require a minimum 0.9 power factor in Europe.

I have designed a PSU for a specific LED lamp which is rated about 50W. There is a PFC-stage (crm) in order to achieve a high PF. However, if I reduce the load to 25W (input) by dimming the light, the pf will be below this value (0.85 - 0.87) for 230VAC. For 264VAC, there is not even a chance to come close (below 0.8).

Now the question is, has the power factor requirement of the lamp to be fulfilled for the nominal rating or also for different loads (dim level)?

I have checked some datasheets of 50W LED drivers which would not achieve 0.9 pf at 25W load although they have a build-in active pfc function. At nominal load, there is no issue. I have also checked a UCC28051 TI Eval Board with same issue (0.87 at about 25W):- datasheet, See Table 5 in Chapter 6.1.1.

If the requirement has to be fulfilled for different dim levels as well, how is it possible to achieve this with a standard pfc? What about 265VAC?

  • \$\begingroup\$ Has the rules changed? PF was not a factor other than indirectly and it was only the harmonics in relation to the 50 Hz component which mattered and measured at full power and nominal voltage. \$\endgroup\$
    – winny
    Feb 8, 2019 at 14:57

1 Answer 1


Given that power factor requirements come from government regulators, you want to look at your country's rules. Here is example for US Energy Star:


It specifically says:

Minimum efficacy, light output, CCT, CRI, and power factor of dimmable lamps will be confirmed with the lamp operated at full power.

Unfortunately, I don't know if there are other power factor requiring standards -- so I guess check your jurisdiction?

  • \$\begingroup\$ Thank you for this information. Do you have any info about Europe for example Germany or UK? Is the requirement at full load as well? \$\endgroup\$
    – Justme
    Feb 11, 2019 at 9:04

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