Author Topic: EEVblog #1252 - LED Panel Lighting Flicker Investigated  (Read 736 times)

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Offline EEVblog

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EEVblog #1252 - LED Panel Lighting Flicker Investigated
« on: October 10, 2019, 09:40:32 pm »
Dave investigates why his new LED panel lights are flickering on camera.
Teardown and measurement time.

 
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Offline SparkyFX

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Re: EEVblog #1252 - LED Panel Lighting Flicker Investigated
« Reply #1 on: October 11, 2019, 12:57:50 am »
As much as i'd love to see this hacked, it'd probably push the transformer over its thermal limit. No good idea for a device like a lighting power supply, which should be able to operate 24/7.
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Re: EEVblog #1252 - LED Panel Lighting Flicker Investigated
« Reply #2 on: October 11, 2019, 01:45:54 am »

A bit   confused  you call it a  "feed back" winding,  I  always  understood  it as a   secondary  winding   that powers the P.W.M.  chip  after   start  up.     To me it's  real not sensing  much  as far as feedback on the output  and ends  up sending  low voltage to the VCC   pin  right  after the diode  half  wave rectification

 As you stated a opto-coupler  would be a  true   sense  of the output  voltage,  which  then would  adjust the pulse  width  accordingly. 

This would make a  good  video  topic  8)
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Offline EEVblog

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Re: EEVblog #1252 - LED Panel Lighting Flicker Investigated
« Reply #3 on: October 11, 2019, 01:58:02 am »
As much as i'd love to see this hacked, it'd probably push the transformer over its thermal limit. No good idea for a device like a lighting power supply, which should be able to operate 24/7.

Yeah, just not worth the hassle.
 

Offline EEVblog

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Re: EEVblog #1252 - LED Panel Lighting Flicker Investigated
« Reply #4 on: October 11, 2019, 02:01:26 am »
A bit   confused  you call it a  "feed back" winding,  I  always  understood  it as a   secondary  winding   that powers the P.W.M.  chip  after   start  up.     To me it's  real not sensing  much  as far as feedback on the output  and ends  up sending  low voltage to the VCC   pin  right  after the diode  half  wave rectification

Because it goes to the Feedback pin on the chip via a resistive divider.
 

Offline wilfred

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Re: EEVblog #1252 - LED Panel Lighting Flicker Investigated
« Reply #5 on: October 11, 2019, 02:46:47 am »
Is this the deal you got. https://energysaver.nsw.gov.au/business/discounts-and-incentives/lighting-for-small-business

It says "Other benefits include reduced maintenance because LEDs last longer than other lights. They will also lower your environmental impact."
I have always been skeptical of the longevity of LED lighting. Having watched Big Clive for quite a while LEDS don't seem all that reliable. When I go to Bunnings (big box hardware in Australia) I see lights flashing on the display.

Would the drivers you got be the standard driver everyone who takes advantage of the Gov subsidy get? 
 

Offline EEVblog

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Re: EEVblog #1252 - LED Panel Lighting Flicker Investigated
« Reply #6 on: October 11, 2019, 07:47:23 am »
Would the drivers you got be the standard driver everyone who takes advantage of the Gov subsidy get?

I don't think so. This is just one company among countless that offer the service, and this is their own brands panel and driver. I know that other companies use other panels, so likely the same for the drivers.
 

Offline alanambrose

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Re: EEVblog #1252 - LED Panel Lighting Flicker Investigated
« Reply #7 on: October 11, 2019, 10:10:33 am »
Hi Dave,

It would be interesting to look at the MEAN WELL LCM-40 LED Driver - it looks, on the surface, better engineered.

Alan
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Offline Kleinstein

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Re: EEVblog #1252 - LED Panel Lighting Flicker Investigated
« Reply #8 on: October 11, 2019, 11:46:40 am »
Low ripple current also has implications to the power factor.  A good power factor and low ripply at the same time needs energy storage.  The capacitors at the output side, directly at the LEDs are not very effective. The extra current regulator would cause extra losses.

In some regions the requirement on the power factor are quite strict for lightning products.

It might be interesting to see the power factor off the low ripple supply in comparison.
 

Offline Gerald

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Re: EEVblog #1252 - LED Panel Lighting Flicker Investigated
« Reply #9 on: October 11, 2019, 03:03:10 pm »
Isn't that input 4.7uF capacitor after the rectifier bridge causing the flicker ?
4.7uF which is barely enough to store the energy required for 10ms.
 

Offline Kleinstein

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Re: EEVblog #1252 - LED Panel Lighting Flicker Investigated
« Reply #10 on: October 11, 2019, 03:22:15 pm »
The filter cap has to be relatively  small to get a good power factor without active PFC. Different from a normal power-supply it is normal to get quiet a lot of ripple just after the filter cap. Kind of making the best use of the capacitance. It is kind of a balance: with  large cap the current is highest when the voltage rises. With a small cap the current is highest when the voltage is low, but still high enough to get the full current out. Both extremes give a poor power factor. A compromise may be acceptable, though still more current before the voltage peak and less after the peak.

For the current sensing with the clamp on probe, one has to check the probe if it likes the DC part. Daves probe seem to be a good one.
 

Online nctnico

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Re: EEVblog #1252 - LED Panel Lighting Flicker Investigated
« Reply #11 on: October 11, 2019, 05:31:54 pm »
It says "Other benefits include reduced maintenance because LEDs last longer than other lights. They will also lower your environmental impact."
I have always been skeptical of the longevity of LED lighting. Having watched Big Clive for quite a while LEDS don't seem all that reliable. When I go to Bunnings (big box hardware in Australia) I see lights flashing on the display.
A lot depends on the kind of lamp fitting you use. If a lamp can get rids of it's heat well then it will last long. In the EU a LED lamp should last for 60k hours (to 80% of the original brightness).
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline SparkyFX

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Re: EEVblog #1252 - LED Panel Lighting Flicker Investigated
« Reply #12 on: October 11, 2019, 05:50:03 pm »
Could it be the result of a defect or other design issue (other than dimensioning of the secondary side)? What does the voltage on the Vdd pin look like?
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Online james_s

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Re: EEVblog #1252 - LED Panel Lighting Flicker Investigated
« Reply #13 on: October 11, 2019, 06:29:06 pm »
I have always been skeptical of the longevity of LED lighting. Having watched Big Clive for quite a while LEDS don't seem all that reliable. When I go to Bunnings (big box hardware in Australia) I see lights flashing on the display.

Quality varies widely. I migrated all of the general illumination in my house over to LED over 2011-2013 so at this point I feel that I have some worthwhile data. I have a number of outdoor light fixtures that are on timers or photocells and run dusk till dawn 7 days a week. I installed a mix of Philips and Ecosmart LED bulbs in those in late 2011 and as of today I have had zero failures, they look as good as the day I installed them. Indoors I have had I think 3 LED bulbs fail, all of those were installed in fully enclosed fixtures despite the bulbs warning not to do that, so I don't really feel like I can blame the bulbs.

Clive tends to play with all the really cheap bulbs direct from China and from discount stores, it's hardly surprising that a lot of that dodgey dirt cheap stuff is less than spectacular. Look for decent quality LED bulbs from reputable brands like Philips and Cree and you should find them to be fairly reliable. To some degree you get what you pay for.
 
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Online T3sl4co1l

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Re: EEVblog #1252 - LED Panel Lighting Flicker Investigated
« Reply #14 on: October 18, 2019, 06:37:48 am »
Latest video on EEVblog2 -- I can't quite figure out the PFC on that new LED driver.  May be worth a video investigating.

Also interesting that it's 700mA on the nameplate but ~420mA measured.  You got bamboozled!

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Offline NANDBlog

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Re: EEVblog #1252 - LED Panel Lighting Flicker Investigated
« Reply #15 on: October 18, 2019, 11:56:23 am »
Honestly, flickering lights should be illegal to import, not subsidised by the government.  :palm:
 

Offline corecode

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Re: EEVblog #1252 - LED Panel Lighting Flicker Investigated
« Reply #16 on: October 18, 2019, 02:31:27 pm »
Latest video on EEVblog2 -- I can't quite figure out the PFC on that new LED driver.  May be worth a video investigating.

I'm stuck trying to figure out how the converter works at all.  Superficially it does not look like a simple flyback converter, and there is a lot of magnetics going on on the primary side...
 

Online T3sl4co1l

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Re: EEVblog #1252 - LED Panel Lighting Flicker Investigated
« Reply #17 on: October 18, 2019, 02:47:51 pm »
It's a half bridge BJT resonant circuit, the smaller transformer is drive.  The control IC apparently starts and stops operation, to kickstart it and presumably to control frequency and thus power.

The split-bobbin construction provides leakage inductance, making an LLC resonant converter.  This is why the output is FWCT rectified, with no filter choke.

I can't tell why they put extra diodes in there, or what the one resonant cap back to the AC side of the FWB is doing.  I think that must be where the PFC is coming from.  The 12uF filter cap is much too large to give low PFC by itself.

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