(Off Season) Blinking LED Problems

[Al Skierkiewicz]

Originally Posted by Alex698

I am having a problem with some LED's that I am using for a backlight (they draw less power for my project). The LED's are powered by a 5V regulator then into a 10 ohm resistor then paralleled together with a common ground. The LED's work fine for about seven hours then they begin to blink (fail). Any ideas or solutions?

Alex,
A little more info please...Is the 5 volt regulator getting hot to the touch? Can it survive the 5 second rule? (can you hold your finger on it for five seconds?) Typical 7805 type regulators have thermal and over current protection which cause them to shutdown or scale back on current under certain conditions. How many LEDs are you trying to power? Also, as Don has pointed out above, the resistor may be sized wrong. I like to use the rule of thumb of 2 volts drop across a standard LED and a 20 ma forward current for calculating the series resistor for one LED. Under these conditions, a 150 ohm resistor is the calculation. Standard values of 120 or 180 should work fine. If you are paralleling all the LEDs than you need to modify the resistor for the parallel current. If you are using a super brite white or blue LED these may have up to 4 volts forward drop and the calculation needs to be modified for those particular devices. Know the beast you are dealing with.