Reliability of Piranha RGB leds

[cpedw]

Since 2010, I have built several Mood lights using up to 32 Piranha RGB leds. Intensity of R, G and B is regulated using PWM at 250Hz or 1kHz using either 3 08Ms or in later versions a 14M2. A power MOSFET drives each colour. Recently, two of these lights have developed an intermittent flicker (a few Hz) in one or two of the LEDs.

Confession time - I paralleled all the LEDs of the same colour and used 1 resistor in series for each colour. Is it likely that this short cut has caused some LEDs to fail intermittently?

Derek

 

[Technoman]

According to the website http://lednique.com/parallel-leds/, it's better to add a resistor in serie for each. Current through a led could be higher than the next one ; hard to say if it exceeds the maximum rating, you may try to measure the current. Were they old? Were they cooled enough?
Here, the flashing led failure at the bottom page : http://lednique.com/technology-basics/failure-modes-leds/

 

[inglewoodpete]

Confession time - I paralleled all the LEDs of the same colour and used 1 resistor in series for each colour. Is it likely that this short cut has caused some LEDs to fail intermittently?

You don't mention what current you have calculated for each LED. 50mA (Red) and 30mA(Green/Blue) are the absolute maximum. It's not wise to run them anywhere near this current, expecially if they are sharing a current limiting resistor. Thermal runnaway is a real problem when currents are high.

I never go over 80% of the absolute maximum rated current for LEDs.

 

[cpedw]

Were they old? Were they cooled enough?

They were new when they were installed. Now over 10 years old.
There's no active cooling but nothing nearby to heat them either.
I was aiming for 15-20mA in each LED. It's not practical to measure current in each LED but they all appear to be similar brightness when working correctly.

Derek