Why'd my LEDs pop? - Page 3

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Re: Why'd my LEDs pop?


Michael,
         There is a possible explanation for what you've experienced.

All LED's do not have an equal operational voltage, even those of the
same type. It varies with manufacture tolerances, some higher and some
lower, hence the datasheet gives a range of operation.

Those with a higher operational voltage will at any current of
operation, dissipate more power, turning it into heat and light. Thus
some LEDs get hotter than others.

If your circuit was not running off pure DC then it's possible that when
your meter shows less than 10v the RMS voltage value was much higher,
thus overdriving your LED chain and cooking the one with the highest Vf
or lowest tolerance for overdriving first.

To solve your problems, make sure you have pure DC, as much as possible,
then measure current of your chain running it through various resistors,
start with a value about 1K and reduce the resistor value until you get
to about 20mA through the chain. The use this value to run the LEDs
permanently.

As the current will now be roughly constant in the chain, all the LEDs
will live happily ever after.

Best Regards,
             Brenden Ede

Michael C wrote:
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Re: Why'd my LEDs pop?


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That makes sense. I suspected the power supply was giving a dirty DC signal
when testing a voltage reg with it. I tried the reg with a 9V battery and it
gave a certain voltage out, with 4 AAs it gave the same voltage but with the
DC power pack the voltage was different. The peaks wouldn't have shown in
the LEDs as they actually put out less light after a certain voltage.

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I've changed the design a bit now so that each LED will have it's own
resistor and they will all be in parallel, that way if one dies the others
will keep working.

Michael



Re: Why'd my LEDs pop?


You are looking for an explanation...
Another potential explanation is the effect of capacitance.
Rather than thinking about the static DC operation.... consider what happens
when the thing is first turned on....
A mass of electrons fly through the circuit, to build up the operating bias
point for each LED, this can be modelled as a capacitance for each LED, but
if one has less capacitance than the others, then it will reach this point
sonner, and hence become the soul resistive load in a chain of 'shorts' . Of
course, this all happens in a microsecond or so.

To the people in this group who are unfortunately exposed to the pointless
abuse from others...I suspect they are simply socially inept, oblivious to
their human defects seen by others, and continually thought of as sad,
angry, friendless people.

They get a cruel sense of fun when abusing / flaming  others, so dont bother
arguing with them




Re: Why'd my LEDs pop?



"Simone Merrett"
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**  What utterly  * bizarre *  crapology  !~!

   This one deserves an honorary  PhD in Crapology.





.......  Phil





Re: Why'd my LEDs pop?


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Must be close to the truth to get such a strong denial. :-)

Michael



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