Fixing cheap Chinese LED light

A place to hang out and chat with other like minded tinkerers

Moderators: phalanx, TS-Tim

Post Reply
Kaisha
Posts: 2
Joined: Sat Jul 14, 2018 3:05 pm

Fixing cheap Chinese LED light

Post by Kaisha » Sat Jul 14, 2018 3:18 pm

This isn't about sparkfun stuff, but you guys were helpful in the past about my arduino and other components I did order from sparkfun in the past, so I thought I'd put this here. If its the wrong forum, I apologize.

I bought a cheap Chinese LED light for my aquarium 2y ago and it failed. After pulling it apart it seems that each led (there's around 50 across two 'circuits' soldered to an aluminum pcb) has a diode in parallel with it. It looks like a small SMD glass zener diode with an orange and blue end. A few have burnt out and shorted which I'm guess is the reason for the lights failure. The leds are powered by a proper constant current AC to DC power supply, so I'm not sure why the diodes would be necessary.

Should I just desolder/remove the burnt/broken ones? Will this cause the others (or the LEDs or the drivers) to fail quicker? Should I try to replace them and if so, how do I find out which ones I would use? TBH I'm not entirely sure why they are even there so I have no clue which diodes I would order to replace them, or how necessary they even are. Given that the whole thing is powered by a constant current dc power supply it seems there would be little need for the diodes. Any ideas?

SabastianPerez
Posts: 3
Joined: Mon May 21, 2018 2:57 am

Re: Fixing cheap Chinese LED light

Post by SabastianPerez » Wed Jul 18, 2018 11:20 pm

You don't need to change diodes that are broken. Led light driver stabilizes diodes by current. Therefore less diodes don't influence work of led light.

n1ist
Support Volunteer
Posts: 1019
Joined: Wed Mar 22, 2006 11:02 am

Re: Fixing cheap Chinese LED light

Post by n1ist » Thu Jul 19, 2018 5:23 am

The zeners are there so that if one LED opens, they will close the circuit and keep the others lit. The zener voltage is slightly higher than the LED forward voltage so the zeners don't conduct during normal operation. If they are shorted, they will keep the parallel LED from lighting.

The current through the string will be constant, regardless of the number of LEDs in series, but the driver usually has a minimum voltage drop needed to stay in regulation. I would try to remove the shorted zeners and see if the parallel LED works. The zeners can probably be replaced with ones around 3.9 or 4.3v ones, with a current rating that is larger than the driver.
/mike

Kaisha
Posts: 2
Joined: Sat Jul 14, 2018 3:05 pm

Re: Fixing cheap Chinese LED light

Post by Kaisha » Thu Jul 19, 2018 5:49 pm

Thank-you for the replies.

Post Reply