Flashing LED circuit

It seems that your LEDs have built-in current-control. So wiring them in parallel should do.

HTH, Mark Van Borm

Thanks for your advice guys!

I was asking these questions because having constructed a few of these circuits in parallel arrangements for use at work, some of them have packed up completely. Presumably one LED blew and caused the others to blow.

Is there any way I can prevent this from happening again? Adding a resistor to each LED? If so what size would you recommend? Thanks in advance for your help!

Generally, each LED should have a resistor in series to limit the current through the LED. You will have to look at the spec. sheet for your particular LED, but most are looking for 2-3V and 20 mA operating current. The size of the resistor depends on supply voltage, and will have to be calculated accordingly. Paralleling LED's is not a good idea without a series restor on each LED.

Nels

Probably, the polarity was reversed when they blew, so adding a resistor won't help much.

Mark VB

This is probably not the mechanism. The LEDs in your original post DO NOT need a series dropping resistor. I'm guessing that you used ordinary LEDs in parallel, with only one dropping resistor. This will NOT work, because they have different forward voltage drops and one will hog all of the current until it blows, and then you get a cascade effect as the rest of the LEDs are overdriven by the lower-value resistor.

THESE LEDS:

do NOT need any resistor - in fact, you said yourself that the spec sheet specifically says not to use one.

Any other "standard" LED DOES need a series resistor, because when the forward voltage reaches 1.2V (or whatever the Vf), there is no mechanism to limit the LED's current other than the series resistor. This might be helpful:

Have Fun! Rich

those flashing leds detailed above are designed to operate off 9v DC. as long as they are connected correclty. Hook them up backwards and they'll die pretty quickly. if you're operating them off batteires I'd put a diode (eg 1N4001) in series with the group of flashing leds to protect against that.

not for those LEDS.

Bye. Jasen

Thanks for your helpful advice everyone!

Nick