150W offline LED driver cannot possibly be 95% efficient?

[mtwieg]

90% peak efficiency for a two stage design is not extraordinary. The value of that efficiency is a more complicated matter...

 

[treez]

https://www.docs.lighting.philips.c....2-0.7A_SNLDAE_230V_S240_sXt_929000962206.pdf

....the above claims 93% efficiency from 230VAC input and at 150W.
Thats pretty amazing, do you believe this is possible from a Boost PFC followed by Downstream LED driver stage?
It also claims full mains isolation, making it even more amazing.

I woul d have thought to get full mains isolation, and 93% efficiency, a single stage flyback would not be able to do it.
But then what could have done it?
A boost PFC followed by LLC led driver surely couldnt have been 93% total efficiency?....a boost pfc is hard switching,, and couldnt by itself have exceeded 93% efficiency...surely?

 

[mtwieg]

A BCM boost PFC can easily get 95% efficiency with proper component selection. Especially with interleaved phases. Many device manufacturers give reference designs and app notes for validation.

 

[treez]

Thanks, i suspect they won't have used BCM Boost here...because this driver is fully dimmable, and as you know, the switching frequency of such BCM pfc's gets too high at light load...where PFC is still needed for lighting applications

 

[volker@muehlhaus]

To be honest, its a good point, ive never seen a LED datasheet which made clear that peak current can be twice the average, say

For COB, here's a documents from Cree that discusses pulse operation and how it affects luminous efficiency, color and lifetime:
https://www.cree.com/led-components/media/documents/XLampPulsedCurrent.pdf

On page 8:

Based on the 1-KHz pulse testing we have reviewed in this application note, Cree suggests the following guidelines for pulsed current operations:
1. For duty cycles between 51-100%, do not exceed 100% of the maximum rated current;
2. For duty cycles between 10-50%, do not exceed more than 200% of the maximum rated current;
3. For duty cycles less than 10%, do not exceed more than 300% of the maximum rated current

 

[mtwieg]

Thanks, i suspect they won't have used BCM Boost here...because this driver is fully dimmable, and as you know, the switching frequency of such BCM pfc's gets too high at light load...where PFC is still needed for lighting applications

What makes you think they use the same control scheme over the entire load/line range? It could easily switch to DCM at light load, or drop phases (if it uses interleaving).

 

[treez]

Thanks i didnt think of that, and if they are switching to say DCM, as load gets lighter, and still getting PFC, then that is a fairly exotic controller they are using....almost certainly not anything off the shelf.

 

[mtwieg]

Digital controllers allow for such arbitrary behavior, and are becoming increasingly common in offline power supplies. Especially those which require digital interfaces for configuration (DALI, etc).

edit: and phase dropping should be a common feature in off the shelf interleaved controllers.

 

[Easy peasy]

like most power electronics, LED chip performance is dominated by peak and average die temp, pulsed currents are fine as long as reasonable peak and ave temps are not exceeded, for pulsing above 1kHz the peak and average will be similar, thus an LED rated for 20mA average can easily have 60mA peaks as long as the on time is low enough that the peak and average are within ~20% of each other...

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I woul d have thought to get full mains isolation, and 93% efficiency, a single stage flyback would not be able to do it.

@ Treez, single stage flybacks (resonant, synch rect) have been meeting and exceeding this figure for a while, there is a company that does micro inverters - Enphase - whose whole product is based upon this topology, 24V in to 230Vac out 250W, have a guess at the efficiency? it's pretty high, also the complete behaviour is mapped and the duty cycle at any moment is based on where you are at the mains at that moment, output volt and current and temp - all feed forward - only a slow volt loop and fast current protect, gate drive is DSP generated ... comm's to other units (100's) fro power sharing ...