EEVblog #1252 - LED Panel Lighting Flicker Investigated

Dave investigates why his new LED panel lights are flickering on camera.
Teardown and measurement time.

#LEDlighting #Flickering #Investigation

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[AnotherBrokenToaster]

Anybody else misread the thumbnail? :D

[JerryWalker]

'Flicker Free' from Chinease suppliers just means that they do not charge extra for the flickering.

[bostedtap]

New South Wales office employees increase in migraine headaches, government cannot see the problem.
Thanks for sharing.

[rocketmanprojects]

All of my cheap Chinese LED drivers have a big filter cap on the primary side and they don't have any visible flicker. I'm guessing they left out the filter caps on your driver to increase the power factor.

[Cltronix]

The PCB material is CEM-1. Inside is paper, but the binder is epoxy, not phenolic, and the outer layer on each side is glassfabric, usually 7628 type. CEM-1 can only be used for PCB without chemical through hole contacts, so it's mainly used for single side PCBs. It's still UL-V0 flame class (hence the red logo, UL-HB material has blue logos), same as FR4. "ZD" is the logo of Jinbao factory from Shandong. China also has a laminate type that uses a CEM-1 layer construction, but with phenolic binder. They call that 22F, it's not an ANSI type and has no UL classification. I guess it's not used in export products. Great video! Thanks!

[AgressiveHouse]

There is a good way to check flickering without any camera because camera would show you only certain frequency range. Even if there is no flickering on camera does not mean there is none.
You can connect a speaker to the small solar panel and actually "hear" the flickering up to maximum audible frequency. As it turns out, almost everything flickers (except for the bulbs)

[Stefan_Payne]

I'd really like to see an analysis of a decently high end ATX PSU with 80plus Gold certificate and the usual 25mV Ripple or less - and no big coil on the Output ;)

[reddcube]

First hand experience, Flickering light can give you headaches. Especially if the duty cycle is only 50%.

[Schwuuuuup]

Flicker free LEDs = Afterglow in the phosphors of the white LEDs?

[adrianknott]

Add 100uf on the primary side after the bridge rectifier and I'm betting the ripple will go away.

[AirCommandRockets]

I remember at our lab at work we spent some time trying to debug an intermittent 38Khz IR sensor problem that would occasionally pick up false triggers. Half a day later we found that it was a bad office flouro light occasionally flickering at exactly the same time as we picked up the false triggers. Replaced the tube and problem went away. I am not sure how that wouldn't have been filtered by the IR sensor, but perhaps as the light flickered it went through a range of frequencies and happen to get past the filter.

[markusepple]

At 5:37 you see the rectifier "D81". On its output, two solder dots without holes is the PCB follow. Drill them and place a 450 volt capacitor there. Before powering it up, use a resistive load and measure the current it delivers with and without the capacitor. Also check if the drive chip gets unexpected hot. Never touch the operating or connected circuit to avoid electrical hazard.

[todayonthebench]

Doing constant current on the output without secondary side sensing isn't "too hard", and there are off the shelf PWM based chips for it.
The main cheap out of this supply is the fact that it has bugger all in mains side bulk capacitance, two small film caps aren't going to do much.
Also, the two capacitors are rated 150 volts and are in parallel, thankfully these types of caps are usually derated by the manufacturer by a lot, but still.... And then they are placed facing each other, making the text harder to read, are they deliberately trying to hide this fact? Strange that they didn't apply glue to it, or would that offset the tiny savings on cheap caps....

[GadgetAddict]

Last year i.upgraded a bunch of "generic" brand LED bulbs with Philips branded bulbs. I was shocked to see the Philips bulbs caused major flickering on most of my cameras 🤦

[samchan]

Why can't you increase the output capacitance to reduce the ripple? Because larger cap tends to have hight serial inductance and resistance? or just too expensive.

[Stoneman]

Helpful info, Dave. Looking at replacing the single globe in my garage come lab with some LED lighting (of some sort) and stuff like this means I'm not going to make as many rookie mistakes during acquisition of parts. Building an LED driver looks like a reasonably approachable project, however. Not sure I'm keen to play with mains, but yeah, interesting stuff.

[adamkekow]

Hi!
I wonder, why this video is in 60fps. I know that eariel videos are in 50fps for a reason. It elminates 100hz flicker.

[steverobbins]

You would need a two-stage converter to maintain low output ripple current and high input power factor. If you only have one stage then it's a trade-off. For example, the cheap one is single-stage. For high power factor they must use a relatively low input filter cap, and the supply that runs the chip drops to zero every line cycle. You could eliminate the output ripple by increasing the input cap, so the converter runs continuously, but then you would have really low power factor. Increasing the output cap won't do any good because it is filtering the much higher switching freq, not the line freq.

[threeMetreJim]

Looks like a very small smoothing capacitor on the input. Do they do that to improve the power factor?

[Tupeutla]

37-44V with a 50V capacitor ? wow ! waranty is 3 months ?