Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Power factor corrected LED driver couldnt be this highly efficient?

Status
Not open for further replies.
T

treez

Guest
Hello,

We dispute Efficiency claims of 89% in the datasheet of this 40W Phillips Xitanium outdoor offline LED driver…..

Xi LP 75W 0.2-0.7A SN 230V S240 sXt


Topology:
However, when we opened it up, we found it was a L6562 controlled Boost PFC stage, followed by an L6562 controlled isolated Flyback stage. There is also a Viper controlled little Buck converter to provide bias power. The Boost PFC output capacitor is a 22uF , 450V electrolytic.

This surely could not be 89% efficient?
If it was that efficient, then that would mean the Boost PFC would be about 96% efficient, and the Flyback would be about 93% efficient. That surely could not be possible? In my experience, I find 90% tops is about the efficiency of low power offline flybacks, even with BCM operation

The L6562 controller operates in Boundary Conduction Mode, so turn on switching losses are about zero, but turn-off switching losses are high.

We won’t yet have time to test it for ourselves as we are way too busy at present.

Electrolytic capacitor
Also, why does the datasheet claim that its has “ultimate robustness” and ” long lifetime” when it has a big internal electrolytic capacitor.?

High switching frequency at lighter loading
Also, its necessary for offline LED drivers to maintain high power factor right down to 25W. Now, if operating in BCM, then that means that as the load gets lighter, the switching frequency of a BCM controller will increase…..As such, switching losses will increase. If the switching frequency needs to go above 150kHz to maintain BCM operation, then that has severe repurcussions in terms of conducted EMC.
The L6562 datasheet makes no mention of a maximum frequency limitation, or a minimum off time.
Maybe they are operating the L6562 as a constant off time controller? ..which is possible with addition of a few extra components….however, the L6562 doesn’t possess the necessary internal circuits to allow it to maintain high enough power factor when operated in constant off time.


Datasheet:
Xi LP 75W 0.2-0.7A SN 230V S240 sXt
Datasheet available here…..
https://www.lighting.philips.co.uk/oem-emea/support/technical-downloads

L6562 Datasheet:
https://www.st.com/en/power-management/l6562.html

Do you agree this LED driver couldn’t be that efficient?
 

Why not measure efficiency yourself. It's surely possible, but guesses without detailed circuit analysis and accurate measurements are pointless IMHO.
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
at 40W load it should only dissipate ~ 4W in losses - does it look to dissipate around this level or more....?
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
thanks,, there are no internal heatsinks on the FETs or diodes.
Boost FET = DPAK
Boost diode = SMB
Flyback FET = "Black tab TO220"
Flyback diode = "Black tab TO220"

..no heatsinks on any of them.
Sorry we have broken it and cant power it up.
 

We dispute Efficiency claims of 89% in the datasheet of this 40W Phillips Xitanium outdoor offline LED driver…..

The high efficiency is at a specified input and specified output load; It is usually possible to have high conversion efficiency at a single point.
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
Talking about this efficiency curve. I guess it's real.

eff.jpg
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
thanks, yes, but as we know, that isnt 96% efficiency.

Also, As can be seen in the following app note for a flyback PFC for example……you never see >91% efficiency for offline flyback converters. Ive never seen a 93% offline flyback on the bench nor in any app note. I admit that the L6562 based flyback is in BCM, which has low turn-on switching losses, however, BCM has high switch-off switching losses.
www.onsemi.com/pub/Collateral/DN05016-D.PDF

I am not knocking ST.com or philips here.......they are top of the range.....just that i debate a 93% offline flyback and a 96% pfc booster.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top