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Gadget Freak Case #239: Bridge Rectifier Eliminates LED Light Flicker

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szyhxc
User Rank
Iron
Re: Product improvement
szyhxc   5/2/2013 4:15:08 PM
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Thanks Liz!

armorris
User Rank
Platinum
Re: Product improvement
armorris   5/17/2013 12:54:18 PM
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Bernard,

My circuit in Gadget Freak case #230 solves the problem of flicker and stress on the LEDs through the use of an electrolytic capacitor and an energy efficient dimming method. I have built 4 such lamps, which I use every day. The circuit is cheap and simple, but not as much so as your bridge rectifier idea. My circuit also employs a bridge rectifier. My circuit is a lot less stressful to the LEDs and the eyes than a triac or PWM type of dimmer. One of my LED lamps is an LED spotlight from Lowe's, during Christmas season, that I converted to an indoor LED spotlight by replacing the wasteful Chinese electronics with my circuit. The flicker in the Chinese circuit, using a 2.2uF filter capacitor was very bad, where mine uses a 100uF capacitor to smooth out the ripple (and therefore the flicker).

My circuit could be built as an add-on device, like yours.

 

George Kaye
User Rank
Silver
Re: One warning
George Kaye   6/7/2013 3:19:50 PM
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Or add a 10-25mfd lytic to the output of the bridge rect. Not so big as to toast the leds but big enough to extend the duty cycle a bit to reduce flicker. Or go with a choke input L-C filter to give you fairly nice DC=RMS output. Better than a switcher and won't fry radio reception nearby. Yes, I still like AM radio.

 

Jarhead
User Rank
Iron
Re: Product improvement
Jarhead   6/7/2013 4:19:18 PM
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I've bought quite a number of Philips LED Christmas strings over the past 6 years, and they are all wired using LEDs as rectifiers, and they are wired so half of them light up, on each half cycle of the AC.  They have been a massively huge pain, from the LED failure stand point.  

I buy the brand for it's color qualities, even though it takes days (*yes* days) each Christmas to get all the strings working every year.  I like their white, and I like the wavelength they use for blue.

 

Unfortunately Philips changes the LED socket construction in some way each year, so I can't buy a new string and use the LEDs from that one.

Being here in Oregon it rains all the time in December, and on top of it all the leads on the LEDs rust/corrode/etch away.  So, DigiKey gets an order for LEDs every year, on top of the ones that get blown because Phillips was too cheap to use a real rectifier.  You know what, the DigiKey LEDs ended up being higher quality, they don't use the super cheap leads that are iron which then has a conductive plating over it (common in uber cheap bargin basement low-end China/Hong-Kong LEDs), which is part of why the Philips LED leads were actually rusting.  The "de-plating" of the conductive coating on the Philips LED iron leads is another mess, it occurs due to water getting in the socket, add electricity, and you end up with a Middle School Earth Science level mess to say the least.

Philips must make a major killing with their huge profit margin- and maybe drive sales due to failures.  Yes, these were in fact actually outdoor strings.  Warranty support has been impossible to actually get, they want the original box and the original receipts.

 

However, last year I cleaned each socket, put many new LEDs in, and then filled each with dielectric grease before putting the LEDs back in.  Guess what, all the failures I have to fix after the displays nearly quit, besides the LEDs getting blown by spikes on the AC power... 

Guess I should build an inline filter now.

szyhxc
User Rank
Iron
Re: Product improvement
szyhxc   6/7/2013 5:12:55 PM
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Armo,

 

Thanks for the insight.  I'll look at your 230 this fall.

 

Bernie

szyhxc
User Rank
Iron
Re: Product improvement
szyhxc   6/7/2013 5:25:43 PM
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Jarhead,

I too have several led strings that I use all year.  All are on (or share) one my FWBRs. I have three strings of white that surround 3 walls of my sunroom and I have two custom made strings of Red White and Blue that sit behind two columns of glass blocks between my garage doors.  I have had no problems with the white but I do tend to replace a couple blue leds each Christmas when I replace the strings with Christmas colors and use the down time to clean and repair the RW&Bs.  (These are the oldest leds I have at about 6 year.  I have no complaints.)

I only use Phillips where I replaced my old C7s.  The Phillips strings are the only ones I have found that have the same 12" spacing and the hang on the 240 legacy staples in my house.      I had heard about the rusting and coated them with grease when I first bought them on sale after the hoildays.  I got through one season with them with no burnout. (I did buy a spare string but of far it is intact.)

Thanks for the feed back.,,, Bernie

 

RobLewis
User Rank
Gold
What am I missing?
RobLewis   6/7/2013 6:04:33 PM
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Do these light strings (unmodified) only operate on one half-cycle of AC? Is there a series diode to protect from the negative swing, or do they just rely on the reverse voltage blocking of the LEDs in series? 

Another thing I've never understood: why don't people use a series capacitor to limit current in AC-powered LEDs? It would eliminate power dissipation of a resistor. Vulnerability to transients, maybe? 

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