Is LED damaged by cap. discharge?
Is LED damaged by cap. discharge?
(OP)
Hello,
If i connect a 1 Amp LED straight to a 23u5F ceramic capacitor that's charged up to 26V, does the LED get damaged?
here is the LED datasheet
http://www.cree.com/products/pdf/XLamp7090XR-E.pdf
I can't see any I^2t data.
I need to know this since a customer may accidentally connect up a single LED to the output terminals of a certain LED driver which has the above capacitance at its output.
If i connect a 1 Amp LED straight to a 23u5F ceramic capacitor that's charged up to 26V, does the LED get damaged?
here is the LED datasheet
http://www.cree.com/products/pdf/XLamp7090XR-E.pdf
I can't see any I^2t data.
I need to know this since a customer may accidentally connect up a single LED to the output terminals of a certain LED driver which has the above capacitance at its output.





RE: Is LED damaged by cap. discharge?
TTFN
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RE: Is LED damaged by cap. discharge?
The 23u5F will soon discharge and i'm not sure just how damaged the LED will be, and just how much shorter it's lifespan will have been reduced to?
RE: Is LED damaged by cap. discharge?
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Is LED damaged by cap. discharge?
The current out of a capacitor is considered to be infinite.
The reason you don't get infinite current is because of the resistance of the wiring between the cap and the load.
If we offer up 100mOhm which is ball-park, we have 26V/0.010 = 260A. POP!
It is general knowledge that an intermittent wire on the drive side always blows the string of driven LEDs. The driver promptly runs up to maximum output voltage as it tries to maintain its set current. This charges the output capacitor to full voltage. Then reconnecting the string discharges that cap thru the LEDs with extreme prejudice.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Is LED damaged by cap. discharge?
If you know that it can happen, you need design a solution. Diode will not tolerate such abuse. Even if were to survive that indignity, it's life will probably be measured in the handfuls of hours, if at all.
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Is LED damaged by cap. discharge?
Therefore, i believe i now have absolutely no choice other than to use an "hysteretic" LED Driver such as AP8802.(?)
These do not require any capacitance on the output for the sake of feedback loop compensation.
Therefore, i need only use as much capacitance as i need to for EMC purposes.
http://www.diodes.com/datasheets/AP8802.pdf
The hysteretic IC has no oscillator and actually relys on the ripple in the current sense resistor to make it work.
RE: Is LED damaged by cap. discharge?
If this is often having the string connected while energized you can always consider a shunt or a parallel resistor to the LEDs that always provides some load. It would drop your efficiency some and I wouldn't do it for a normal setup where the strings are not hooked up live.
Keith Cress
kcress - http://www.flaminsystems.com