On Sun, 24 Aug 2008 14:53:25 -0400, you wrote: >When running LEDs from the mains, I would be wary of the LED's >peak-reverse-voltage rating (typically only 5 or 10V). I *think* that >if you exceed that you simply cause avalanche breakdown (which, as >long as the resistor is there to limit current is probably OK) but >technically you are greatly exceeding the ratings of the LED. You >should use a silicon diode (like 1N4004) in series with the LED to >prevent it from seeing a couple hundred volts across it backwards. > >Also, I'd want to use more than one current limiting resistor in >series. That way, in the unlikely event that one fails shorted, at >least the others are there to limit the current. > Resistors don't fail short - even the standards for Intrinsically safe equipment for use in flammable atmospheres state that resistors can be assumed to be infallible as regards failure to lower values. however using multiples in series helps spread heat load. > > >On Sun, Aug 24, 2008 at 11:44 AM, Tony Smith wrote: >>> > Why have the 'bridges' between the parallel strings of LED's? >>> >>> Don't know. The LEDs won't be conducting half the time. It >>> would help with assembly a bit I guess, as you'd solder two >>> LEDs in anti- parallel and then join them to the next pair. Maybe ? >> >> >> Has any ever made a bridge out of LEDs? It rectifies and lights up! >> >> I've seen LEDs run off mains simply by using a resistor. The last one I saw >> was in one of those cheap main filter things. Not the best for a lamp, but >> it seemed to work ok as an indicator, if the layer of dust was any guide to >> its age. >> >> Usually it's a physically large resistor, either because dropping 240v >> produces a few watts or to give a large gap for isolation in case something >> goes wrong (sure!), but sometimes 2 or 3 small wattage ones in series. The >> series method is for the really cheap stuff. >> >> Tony >> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist