EEVblog #1253 - LED Flicker 2: Electric Boogaloo

[EEVblog]

Part 2 of the LED Flicker investigation.
Modding the driver for input and output capacitance and it's effect on power factor correction and thermal performance.

[johnlsenchak]

If you put   240 Volt Aussie  mains voltage    across a  50 volt rated  capacitor  then you would   have a  good  "Photonicinduction"  video  !

[boB]

Watched this video.  The real power is so small it dwarfs the reactive with those larger caps.

Just add several watts of resistor in front of it and watch the PF go up !

And watch the efficiency  go down too ! 

boB

[8bitcpu]

Hi all,
Quick question:
Why is there only one diode on the secondary side, is a full bridge rectifier that expensive? or is there a other reason?
Even the more expensive TI part shows only 1 diode in the datasheet.

Thanks for the video.

[Kleinstein]

The converter is flyback type and thus using only one halve-cycle for the output. The other half would act as a forward converter and have essentially no regulation and a possibly different voltage. So one diode at the output is normal.

The extra current regulator on the output side looks like it is a linear one. So there would be some extra loss in the output side current regulator.  As a kind of compensating factor the efficiency of the LED panel may be a little higher with low ripple. Usually the efficiency goes down a little with higher currents and thus with ripple.

[bitwelder]

To complete the comparison with the economical view, what's a reasonable Aussie price for both drivers (even better if you can tell the price for the 'flicker-free' one, but in a 24W version) ?

[BrianHG]

I'm willing to bet that if you were to place the 4.7uf cap on the primary mains side of the cheap LED power supply instead of the 33uf, it would still virtually eliminate the flicker and the power factor wouldn't have gone as low as it did with the 33uf.

[jazz]

Sooo is anyone else slightly disappointed that Dave didn't move the L and the I slightly closer together in the thumbnails, leaving just enough space between them for plausible deniability?

[sakujo7]

I'm willing to bet that if you were to place the 4.7uf cap on the primary mains side of the cheap LED power supply instead of the 33uf, it would still virtually eliminate the flicker and the power factor wouldn't have gone as low as it did with the 33uf.

Was thinking the same thing. 33uF is too much, 0.3 is obviously too low, so why not try a mid point? It's largely academic since I wouldn't install hand-modified drivers in my ceiling, but this is an educational channel, soooo...

Anyway, the fluorescent lighting those panels are meant to replace can be as low as 0.6 (inductive), so it would still be an improvement if you can "only" get the PF up to 0.8 (cap) or so with minimal flicker. If there's still some fluorescent lights on the circuit then it could even cancel out to near 1 at the meter (not that's it's metered).