How can an offline LED driver last 20 years?

[treez]

Regarding long life offline SMPS's , page 3 (bottom) of the below says that lightning surge withstand can be increased by making the post PFC bus capacitor bank 330uF instead of 100uF.

I have never heard of people increasing the lifetime of an smps by massively increasing the Post PFC bus capacitance by that much......is this right?

700W PFC module datasheet
**broken link removed**

 

[dick_freebird]

I wouldn't conflate 1-pulse (or N-pulse) abnormal event
withstand, with basic long term reliability. Not unless
you declare and accept a particular model for such
things as a part of the application envelope that the
reliability rating is predicated upon / proven against.

If the dominant failure mode is second-stage overvoltage
then soaking up some of the lightning crest between PFC
and regulator could pay off. But how this relates to a
normal-ish reliability figure, I don't see.

 

[Easy peasy]

I have never heard of people increasing the lifetime of an smps by massively increasing the Post PFC bus capacitance by that much......is this right?

Bigger caps with lower ESR soak up a lot of transient energy P-N before the volts get too high on them, this is an old trick by power electronics engineers to meet P-N transient standards...

 

[Audioguru]

What good is an LED driver that lasts for 20 years when the LEDs it drives get dimmer and dimmer until they are thrown away in a few years? NASA does not allow opto-couplers in spacecraft because the LED gets dimmer then fails to do its job. I have a clock radio with a display so dim that it cannot be seen in daylight. It has been on continuously for (OMG) 36 years!

 

[FvM]

The specification of the Dyson LED light discussed is this thread is 180,000h L70 (light intensity falls to 70 percent of initial value).

 

[dick_freebird]

Optoisilators' LED (and in-fill darkening, and receiver BJT
gain degradation) has more to do with the radiation
environment than simple aging. NASA concerns don't
translate entirely to the living room.

Not to say the LEDs won't age.

 

[treez]

the led light of the first post uses heat pipes to give the leds long life.....and better quality (brightness) for longer due to cool operation. 180000 hrs is 20 years,,,so the power supply must last the 20 years too or else it wouldnt be worth having the heet pipes.

 

[Audioguru]

Some of the LED street lights in my city have failed within 1 year so I guess my electric utility company bought cheap Chinese ones from ebay, instead of expensive British ones from Dyson.

 

[D.A.(Tony)Stewart]

The problem is that so many LED companies lack real quality/test discipline and experience. I drove north of Chicago and counted 5% off all freeway LED standards dead. Every day that I spent at least 30 minutes driving in Toronto, (which is very easy to do) I see at least 1 different new car, again every day, with a dead LED headlamp or perimeter string. This is for all brands including Audi, the pioneers of LEDs in cars.

Why? I can tell you in a nutshell. Lack of Test Engineering / Quality Management experience. Yet the auto industry has is second best in this regard, compared to Aerospace.

When I was in the HDD TEst Engineering business, I quickly realized these were the most complex instruments on earth, but not as harsh environments as Nuclear reactors or Space environment. Yet they have thousands of critical tolerances; contamination avoidance, thermo-magnetic dependancies, vibe&shock reduction methods for tracking, many anti-resonant controlled servo loops, critical HDA aerodynamics with heads flying at 100kph on an xx nanometer air bearing surface with lateral seek times of milliseconds to a position with x micron position error, adjacent track interference, susceptible to right angle rotational impacts, nanoparticle media contamination, high humidity head stiction, etc etc etc.

It takes an extreme set of skills and experiences to perform these tasks. All it takes is one critical review of the DVT and some boss to say we can't afford to do ORT or someone to overlook supplier quality tests and all of a sudden, a simple cost reduction or material change results in process "escapes" .

I can give you the benefit of my experience doing Design Validation Testing (DVT) and ORT for 5 years in a row and off and on for 30 years. Very few companies have this experience or perform this level of diligence necessary to prevent escapes.

Most LED suppliers allow Tj of the junction to rise to 125'C in the maximum ambient. The ambient is not the normal temeprature range of -40'C to +40'C, but the ambient of the heatsink under the sun with 1200 W/ sq.m. of solar power and no wind at max humidity.

Dysan has done a proper Engineering design from my quick review, to improve the area for passive cooling with good materials (sintered copper). Bravo, but only 85 Lumens per watt?. same as my much cheaper better Philips true daylight tri-phosphor 5000k tubes

This Dysan design may result in their heatsink temp rise being 15-20 deg lower than the standard adopted by many companies for Tj rise. From Arhennius Law we know a 10'C drop in Tj rise above ambient will reduce MTBF by x2. Thus I estimate Dysan's design of Tj rise is 15'C cooler than the worst case designs which spec 50kh and they would have to validate that number using large qty of units and measure Lumen deg. rates projected to LM70.

But what we dont know is how they do ORT and how do they know how much margin exists in shearing the Anode connection with the ultrasonically cold-welded micron size gold wire. THIS IS THE MOST COMMON failure mode in LEDs. It can occur for many reasons. Some designs use dual wire bond. But all must survive the extreme thermal stress from different coefficients of material expansion not get "wounded" from shock, vibration, ESD, thermal shock, transient overpower etc etc.

I do know I could buy 4x tri-phosphor 4' FL 32 or 28W tubes for at least half the price and twice the Lumen output, with the same efficacy in the mid 80LPW but slight better CRI by 2-5% as LEDs do not have triPhosphor bands, only 1 blue & 1 phosphor gets CRI=80-82 depending on CCT. These will last 50kh if left on 24x7 but only 30kh if cycled 3 times a day.

all for now, must fix son-inlaw's 92Camry with stuck thermostat from excess leakstop that I added to rad. Then hopefully he can get a job.