Alan Shinn Wrote > >Date: Mon, 9 Jul 2001 20:13:51 +0300 > >From: "Peter L. Peres" > >Subject: Re: [EE]: Bulb Life > > > Peter L. Peres wrote: > >> > >> > LED traffic lights > >> > >> Of course everyone realises that in the event of a major surge or EMP > >> all the traffic lights will die. With or without switchers. (LEDs > >> don't like reverse biasing). > > > >> Interesting! Would you suggest a reverse diode across the LED array? > > Or better still a big zener or specialty surge diode, this would > > protect for both forward and backward surges, considering there should > > be a fair series resistance anyway? -Roman > -- > > If you put half of your LED bank in parallel but with reverse polarity > (anti-parallel?) to the other half you get full wave power use and no > reverse polarity problems. You could also feed a non-anti-parallel > system with a full wave bridge rectifier if you want to buy an extra > part. Now use a series cap for non-dissipative current limiting and you > might have a survivable system (with the bridge system the cap is on an > input leg). > At last. I have been watching this and waiting for someone to come up with the back-to-back solution. I will now throw in my groats worth. 1. Back each individual LED with another one. Do not parallel long chains of LED's. Why Not ? Hint : Consider the failure of a single LED. 2. Do not use a capacitor for current limiting. Why not ? Using Capacitive reactance is very attractive (and effective). However, what tends to be ignored is that interference travels through a series capacitive dropper like a hot knife travels through Butter. So with a capacitive current limiter your spike protection has to be considerably more robust than that for a resistive (or better still an inductive) current limiter....Discuss 3. The Groat is a redundant English Coin which even I do not remember as a lad, but I do remember the Farthing. Ah, happy days when there was 144 Pence to the Pound. Regards Chris Carr -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads