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Old 10-01-2020, 12:45 AM   #1
eccerr0r
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Default desk lamp stopped working... stars?

How many bcn readers does it take to screw in a light bulb into my LED desk lamp?

Answer: None. This is a nonreplacable-LED desklamp.

So this lamp has one of those aluminum stars and an LED on it. It appears to be some sort of BGA or something with pins underneath. Anyway the PSU is 500mA 3.6V-8V meaning this probably was either meant to massively overdrive 1W LEDs or slightly over drive 3W LEDs...

So it seems that typical 1W LEDs on stars are indeed 3.6V @ 300mA to get 1W which would be overdriven at 500mA, and 3W LEDs appear to be [email protected] which is a bit under spec, but would be less than 2W with the PSU I have.

The original star that I have is a 7.2V 2S configuration at 500mA which is 3.6W...

Question is where can I get a replacement... with heatsink, do I try to remove+replace the old LED from the heatsink, or do I bother replacing it and trashing the whole lamp? Appears the LED package has a die bond failure as I can press on the package and sometimes can get it to light again.
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Old 10-01-2020, 04:04 AM   #2
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Default Re: desk lamp stopped working... stars?

Post a picture of the item in question
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Old 10-01-2020, 04:58 AM   #3
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Default Re: desk lamp stopped working... stars?

not just a picture, show us the optics if any, and tell us the diameter.

you may be better off with a cob panel.
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Old 10-01-2020, 12:40 PM   #4
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Default Re: desk lamp stopped working... stars?

Hmm.. it's about 18mm in diameter, so yeah dunno... A lot can be told by a good closeup, not a BGA after all.

I have a few 1W SMT lensed devices I could solder on to the free pads but not sure how to attach the heatsink of the LED to the star.
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File Type: jpg bad3Wlamp.JPG (60.6 KB, 34 views)
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Old 10-01-2020, 02:53 PM   #5
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Default Re: desk lamp stopped working... stars?

It looks like typical 1W TV LED backlights.
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Old 10-01-2020, 08:11 PM   #6
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Default Re: desk lamp stopped working... stars?

Well this thing should be "4W" (wall power) and it should be around 7.2V or 2 LEDs in series.

Some more accurate measurements:

LED encapsulation is 5mm x 5mm so 5050(metric) SMD package?

Star is 20mm diameter.

Now where I could get these things without buying a boatload of them...
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Old 10-01-2020, 10:13 PM   #7
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Default Re: desk lamp stopped working... stars?

maybe fasttech
https://www.fasttech.com/
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Old 10-02-2020, 05:15 PM   #8
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Default Re: desk lamp stopped working... stars?

hmm...difficult to find 2S ... most are single diodes...
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Old 10-03-2020, 06:55 AM   #9
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Default Re: desk lamp stopped working... stars?

does the led get power?
it looks like the star may be shorted by the wrong screws
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Old 10-03-2020, 08:23 AM   #10
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Default Re: desk lamp stopped working... stars?

Yep it gets power all the time, just doesn't light.
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Old 10-04-2020, 02:11 AM   #11
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Default Re: desk lamp stopped working... stars?

so is the psu cased/marked ?
some are constant current - others are constant voltage.
be usefull for selecting a replacement.
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Old 10-04-2020, 10:34 AM   #12
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Default Re: desk lamp stopped working... stars?

PSU is CC @500mA.

If it comes down to swapping the PSU along with the LED, it really means throw out the whole lamp... Need LED only replacement if possible.
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Old 10-04-2020, 01:30 PM   #13
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Default Re: desk lamp stopped working... stars?

so any 500ma led then.
isnt that about 2w??
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Old 10-04-2020, 02:56 PM   #14
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Default Re: desk lamp stopped working... stars?

At 7.2V which is the 2S original diode, it would be just under 4W. It would be just under 2W if I had to go with a single diode.
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Old 10-04-2020, 04:33 PM   #15
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Default Re: desk lamp stopped working... stars?

So it is CC 500mA power supply , but what does it say as far as the Voltage is concern on the power supply?
CC 500mA power supply will force constant 500mA through the load, so if you connect one LED or two LEDs (in series), the current will be maintained at 500mA.

The Star board is 20mm Dia.
For example:
https://www.ebay.com/itm/1W-3W-5W-Wh.../324179513914?

Last edited by budm; 10-04-2020 at 04:42 PM..
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Old 10-05-2020, 12:28 PM   #16
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Default Re: desk lamp stopped working... stars?

Well, the PSU voltage range is 3.6V to 8V so it can drive a single (white) LED at 1.8W or two (white) LEDs in series at 3.6W, and can go up to 4W if the LEDs will go up to 8V.

Which means I could theoretically stick in three red LEDs in series and it'd still work though at 3.1W, unfortunately I don't need to stop...

(Which the original issue is ...where do I get an LED that won't fry when I put it in... I have a few 1W 3.6V LEDs but they'd be driven at 0.5A which will force the LED to dissipate near double its rated power. Perhaps I need to mod the PSU to run at 300mA?)

Last edited by eccerr0r; 10-05-2020 at 12:48 PM..
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Old 10-05-2020, 01:04 PM   #17
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Default Re: desk lamp stopped working... stars?

your looking for a round cob panel not an led.
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Old 10-05-2020, 03:42 PM   #18
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Default Re: desk lamp stopped working... stars?

I can desolder the LED from the plate too... well, with a back heater of course.
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Old 10-06-2020, 04:24 PM   #19
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Default Re: desk lamp stopped working... stars?

My current thinking is desolder the dead SMT LED and solder two 1W (1S, 300mA) LEDs in parallel though this is probably still going to end up with the same result as if I only put in one: one of the two LEDs will eat most of the 500mA and fry.

The other question is maybe the LEDs will take 500mA just fine if I can cool them... if I can cool them...
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Old 10-06-2020, 04:30 PM   #20
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Default Re: desk lamp stopped working... stars?

Show us the pictures of the CC power supply, may be all you have to do is to change the value of the current sensing resistor that is used for setting the CC.
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