Why LED replacement bulbs for incandescents (may) need isolation

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One other issue brought up by off line converters driving lighting is that it will defeat the voltage lowering technique employed by power companies to limit power consumption when the demand gets too high. Cutting the voltage from 120 VAC to say 105 VAC will not make an appreciable difference in power consumption. (In fact it's possible it could get higher!) I guess the question is how much of the total power demand is due to lighting. Tom M.

Well, I've seen a 12v DC house wiring system for lighting. I got called out to a high $ house with EMI/EMF issues. The high currents were causing major magnetic fields as twisted pair wiring was not used, or even Rolex. Single wire paths created huge fields, and with (200 Hz PWM) duty-cycle controlled lightning, it caused flickering and off-colors on very CRT and TV in the house. So, yes un-aware installers can majorly mess up a "simple" DC wiring installation, as a house is not a metal-based car with the body return path ground plane. But the main point I wanted to make, is that a practical DC house wiring system should be at 48v DC as it is the highest voltage considered to be "safe" and would reduce the (I) electrical current requirements to more practical levels. Also, this fits both solar panel(PV) and UPS systems well, for a full "systems approach" to a household DC system of wiring. Just remember to keep the conductors paired up this time !

10 times the current is 100 times the power wasted....it's that I squared R thing, which is why our transmission lines run at several hundred megavolts. If anything, maybe we should advocate a string of 1000 HBLEDs in series, which allows the use of perfect power factor boost regulation, and then letting Darwin take care of the careless and weakminded?

One has to wonder how much is actually being saved over the lifetime of all the new style of bulbs over the old incandescents. Lets see, incandescent bulb contents: glass, a little bit of various metals for the element and the base. New style bulbs: apparently on top of the previous listed items we have transfomers, heat sinks, power semiconductors, capacitors, resistors etc, etc.... All for each and EVERY bulb. All of which will be depleting many more individual resources over time than the old Edison's. Not to mention the energy cost of producing each and EVERY bulb. I don't know about the LED bulbs, but CFl's, at least the ones I own don't last any longer, have a larger environmental impact, and quite honestly have had ZERO impact on my electrical usage despite making the investment to replace every bulb in my house. So why in this country's infinite wisdom did we go off half cocked and BAN incadescents???

To prevent fatal electric shocks, corded drills are required to either have a three wire plug of be double insulated. I assume all electrical appliances, including toasters must meet a similar requirement. This makes them intrinsically safe from a single failure just in case the user in not standing on an insulated pad when using the appliance. Lamps are not quite the same as an appliance but they are similar. Florescent lamps sometimes have and exposed metal ring that attaches the insulator holding the power pins to the end of the glass tube. In general the florescent tubes are install in fixtures which prevent casual access to the exposed metal. Screw in lamps like those used in a child?s bedroom are a different story. Screw in lamps are not protected from casual contact and are therefore more likely to the subject of litigation when someone?s child comes in contact with an exposed metal heat sink and is killed. I suspect the best solution would be different classes of protection depending on operation environment. It wet or damp environments you want a grounded heat sink and/or completely self protected light assembly.

Could you meet safety codes by installing a GFI in the lamp cord? I think that would be cheaper than isolation. I've wondered why the standard Edison base lamp socket is allowed. It's not very safe... once you remove the bulb you can easily touch either of the conductors. But we've lived with it this long so I doubt anyone will ever do anything about since incandescent bulbs are on their way out anyway. And for that matter how safe is the standard 110 VAC plug? I bet someone with small fingers could touch the blades while they were hot. Tom M.

In further to my earlier post, This company (ledtronics) makes an LED bulb, 120 VAC that is fact sealed in glass and as safe as an incandesent bulb in terms of shock hazard. They have a very broad range of bulbs including ones for city traffic lights. This is of course an industry that will grow as the cost go down and lumens go up. They sure seem to make more sense than those CFL bulbs with their toxic metal issues.

If we are talking about replacement bulbs, I would like to know where the ground connection will be made. There is no ground on a standard "edison base" light socket. Despite the use of polarized outlets and plugs, it is possible to reverse the polarity of any table lamp. So, the use of of neutral for a ground is not a good option.

I agree Grasso, John. Designing LED based solutions around a 12V DC supply with be much less of a challenge for designers ! - It would also redcuce costs as there would be no filter / magnetics to worry about and greater efficiency / safer handling etc (providing the 12V DV supply to the house lighting was efficient with varying loads). I guess you would need to be aware of the wiring lengths from the power supply to each lamp socket. Using the latest LED driver BUCK converters from On-Semi, National Semiconductor can be designed to work with varying input voltage with great efficiency.

For safety reasons it will be necessary to install a 12V ac isolating transformer into each household with a separate wiring line specific for lighting. Bear in mind that users of these LED bulbs will be ordinary people and not professional engineers or trade electricians. Today a 240V/12V ac/dc converter exists in Europe for halogen bulbs and one of these converters is mandatory for each bulb. In my view this is the proper way to proceed.

In response to Hari's question. Isolation particularly in LED drivers is done using a transformer as part of the seperation from the rectified mains to the actual voltage / current that drives the LED's themselves. Of course the challenge for people designing very small mains powered LED lamps is that if isolation is used, that the transormer sizes can be an issue when fitting into the base of the actual LED lamp. It is important to note however that the secondary side of the transformer must not be connected physically in any way to the recified AC rail. True isolated designs will use an optocoupler on the output or additional secondary windings to provide feedback to the primary side controller to maintain the correct current / overvoltage protection. For non-isolated designs, note that one side of the LED itself is likely to be at rectified mains which is around 320V rms. So it is up to the designer to ensure the LED's are not user accessable. This is more the case with SMD power LED's as the traces are on the top side of the PCB, so EXPOSED. Using DIP LED's is much safer as traces can be on the lower side of the PCB and the actual LED mounted flush as not to expose the leads. Most semiconductor manufacturers like On-Semi, NXP, Power Integrations all provide isolated and non-isolation LED driver solutions. Pete