Connecting LED's to direct 120VAC?

No

Yes

Sounds like a neon lamp.

For the neon ? About 100kohm in the US and other 120V countries, 220kohm in Europe and other 230V countries.

Graham

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No. You\'ll need, as a minimum, another diode.

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No, it _is_ a diode.  

That\'s why it\'s called a "light emitting diode."


>forward current
>is when the LED is emitting. and backward current 4etf..
>beside the fact that it may leak a bit on reverser current.
>  i don\'t see a problem there.

well, the LED is a diode in a sence, forward current is when the LED is emitting. and backward current 4etf.. beside the fact that it may leak a bit on reverser current. i don't see a problem there. R := (E-LED_Voltage"1.7")/LED_Current"0.050ma" = 2366 ohms W = I*V = ~6 Watts.

not sure if the reverse side of the diooe would cause some problems. you could always throw a diode across the LED to force current flow in the diode on the reverser side of the voltage for the LED>

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Real Programmers Do things like this.
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One thing I forgot to mention was that if you use a high-efficiency
LED like an HLMP4700, which only needs 2mA to work, then the
resistor can go up to 62K and the dissipation will drop to 0.224
watts.  That means you can use a single 62k 5% 1/2 watt resistor for
the job.  Much better, huh? :-)

Hi, Phillip. Graham and Mr. Fields have given good advice. Whether you're using an LED or neon bulb, though, remember neither is rated to isolate line voltage. Make sure to use a cover of some kind (like the diffusing cap you have over the neon bulb in the power strip) to ensure that no one can touch the surface of the element when it's at line voltage potential.

Good luck, and play safe Chris

Good Lord !

You don't understand how to use peak and RMS either ?

John is correct.

Graham

I got to say, its a good thing the readers here have you around to set them straight.!

Yeah ok, you got me there, i forgot that,. i was thinking RMS etc..

And you haven't seen LED's at these ratings?

Now wait a minute, since you have picked out a mistake i made i will also pick out one that i think your making.!. first of all you did say 170 V which is peek, now your using 120 volts here and the above math looks like it assumes DC voltage ? you are using 20 ma Leds for your case. last time i remember P = I*V*cos(angle). in cases where we are dealing with Sine wave energy.

gee. thanks, coming from you i take that as a complement! :=)

btw, i have seen many simple LED light systems from the

120 service using nothing more than a single resistor which worked fine.. we have some LED upgrades for incandescent lamp holders for control panels which you can clearly see that they are a LED and Resistor combo for a 120 vac fixture.(no back diodes).

oh well, happier days are coming.

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Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

If you haven't learned how to power an LED in thirty years its time to quit. :(

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Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

you make me laugh. you leave out the most relevant part of the quote just to re'engineer another one and there by, miss lead others into your little poke. John is a popular guy but, he isn't perfect nor is he always correct! but i must say that at least he tries to keep it professional.

btw, because i decided to use a 50 ma Led and 1.7 variety does that mean something ?, it was only an example! and yes i did over look over the Peak voltage which i did admit doing but i guess you just didn't want to include that because that would have spoiled your fun?

and please do not reply to this, it most likely will be crap i have heard in the profession since i started 30+ years ago.

have a good time..

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Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

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Not the readers, the writers, sometimes.

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Nope, there are no magic LEDs.  Might seem like magic to you,
though, if you don\'t know how they work.

{lots of crap removed}

i don't know what to tell you, we must be using magic LED's then. last night i set up a test on the bench using a zip cord and a network of resistors operating a Jumbo, a small RED led and a green one that i had in my junk box. , no back diodes on any of them. as i sit and type this i can look over to the bench and they are operating just fine. we have been slowly updating our panel lights that are in a range of 6,12, 24 and 120 volt ac types with LED's with nothing but a Resistor in series. as far as i know they are all still working accept for maybe one of them that needed replacing due to a electrician putting a 6 volt set up in a 24 volt fixture. i'll leave it as this point, maybe we are using special LED's that i am not aware of. who knows. all i can say is they work..

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Real Programmers Do things like this.
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You just can't get the staff these days, John !

Graham

I saw it analysed once, the led conducts some current in the reverse direction (but always less than in the forwards direction) and as long as the current isn't enough to overheat the LED little damage is done. given that the reverse breakdown voltage may be much higher than the forwards voltage there can be much more heating during reverse conduction.

In a thread in another newsgroup I ran a LED directly off a 5V supply for an hour (but it didn't last much longer than that). Going outside manufacturers specifications can give unpredictable results.

I'd still reccomend putting a diode in there to stop the led conducting backwards. If nothing else it'll make the led last longer or allow you to run it brighter.

Bye. Jasen