Whatsup people, got some new LED's for a big SSD I'm building and I have a question regarding the current I'm supplying to my LED's.
The setup is a multiplexed SSD at a duty cycle of 30%. The LED's data sheet shows max forward current at 150mA but another place it sais 30mA. So that has already confused me.
I was running them at 38mA and I was wondering to myself "can I increase the current to 50mA seeing as though its only a 30% duty cycle" can I do this or will the LED's get damaged?
Sometimes the datasheet will specify max current at a particular duty cycle. Do you have a link to that datasheet? Strictly gut feel, but I'd think that 50mA at a 30% duty cycle would be ok.
Or are they saying that if u use a 10% duty cycle you can pump max 195mA through them provided your pulse width is 0.1ms?
The frequency I am driving my LED's is 200hz but I'm not sure if I have calculated that correctly. As a simple example of how I'm driving them let's say I have 3 led's, I'm switching between them every 5ms. And they stay on for 5ms. So my duty cycle is 5/15 = 30%. My frequency is 1/0.005 (1 second / switching every 5ms) = 200Hz? Is that right?
So that is 50 times longer than 0.1mS (100uS).
1/10 duty cycle at 0.1ms width means you go thru 10 cycles/mS. = 10,000Hz.
Otherwise, the LED will get too hot & fail.
calvingloster:
Or are they saying that if u use a 10% duty cycle you can pump max 195mA through them provided your pulse width is 0.1ms?
What Paul said. Unless you like the sound of "pfft".
calvingloster:
Or are they saying that if u use a 10% duty cycle you can pump max 195mA through them provided your pulse width is 0.1ms?
They are saying that for their test, their Peak current was 195mA, but it was only on for 10% of the time. This averages to 195/10=19.5mA < 30mA. The frequency is there to say you can't leave it on the 195mA peak for too long. You can hit the peak, but you're rapidly heating up the LED, so you need to turn off the current before it gets too hot, wait for it to cool down, then you can do it again.
So basically, you have to think about the average current, always stay below the peak current, and make sure the frequency is high enough so that the LED can cool down sufficiently before the next pulse. This min frequency is dependent on how close to the peak you are going (which determines how quickly you're heating the LED up) as well as the room temperature. Just stay well away from the maximums, and as long as your frequency is also decent you should be fine.
calvingloster:
Or are they saying that if u use a 10% duty cycle you can pump max 195mA through them provided your pulse width is 0.1ms?
What Paul said. Unless you like the sound of "pfft".
Word of warning to readers: I've got datasheets for LEDs that can take 180mA at 10% duty cycle, I've got datasheets for other LEDs that can only take 30mA at 10% duty cycle (ie. 20mA normal, 30mA peak).
If you don't have a proper datasheet, don't make any assumptions about what a LED can do.