LED's and AC Power

LED\'s and AC Power

Has anyone tell me if the Nichia NSPW500BS can be used with AC power with only a current limiting resistor...javascript: x()
Confused

If they can or can not... I would like to know how to if anyone can explain hope I might construct a light blub that using regular household AC power (115 - 120 volts).

I'm puzzeled and get somemany different answers.javascript: x()
Confused

Thanks!javascript: x()
Big Grin

[email protected]

Re: LED\'s and AC Power

This is First Topic... Not to use to UBB Code yet.... javascript: x()Roll Eyes

Re: LED\'s and AC Power

We just finished off part of our house and I put the CCrane 3 LED light behind the handle in the shower and ran it from a 3vdc wal wart. It ran all 3 LED's about 50mA and makes the bar glow quite nicely, so you could go that route. Otherwise a place like Jade mountain sells then already made with 12LED that run on either 120vac or 12vdc in a standard medium base lamp.

Re: LED\'s and AC Power

I was thinking more about trying to make them myself. But there seems to be a lack of information on the AC power thing and leds...

It may be to complex and I might have to revert to Jade Mountain for pre-made lights...

Re: LED\'s and AC Power

Let's approach the issue from a practical standpoint, using Ohm's Law. First, determine what resistor will provide 20mA of current through the LED.

Assume 120 volts, and an LED drop of 4 volts. The voltage across the resistor is therefore 116 volts, so the correct resistance is 116/0.02 = 5.8K.

Next, we need to examine the reverse characteristics, since AC is reverse voltage half the time. A typical Nichia leaks 50uA, according to http://www.nichia.co.jp/lamp-e.htm, and is rated 5 volts reverse max.

If the backward LED leaks 50uA and can tolerate 5 volts, what is its effective resistance at breakdown? R = E/I = 5/50E-6 = 100K.

Put a 5.8K and a 100K in series across a 120-volt source, and you get 113 volts across the 100K LED---way too much.

What's the solution? Put a regular diode in series with the LED, one rated to handle at least 170 peak inverse volts and less than 50uA of leakage current.

A common 1N4003 will do nicely. It typically only allows 0.05uA in the reverse direction, 10uA max. Even at 10uA, the LED only sees 1 volt, which is well below the 5 volt max.

Re: LED\'s and AC Power

I might add a quick comment since I went through all this already. Those calculations seem correct, but because of the voltage drop across the resistor and the amperage of 20 ma, the power capacity of the resistor has to be 2.3 watts or higher. A fair amount of heat is generated in the process and may start a fire or blow something. Someone had posted an elegant solution using a capacitor which allowed just enough alternating current to pass to power the LED. I don't know if this worked for sure as I did not try it. However I did try the resistor and diode and it got plenty hot...

Re: LED\'s and AC Power

Thanks for the information! I bet that the resistor and diode sure do get rather hot...
I would guess that I would have to use one of those large 5 watt resistors...
Hopefully someone will post the total solution to the this... AC power thing... Looked at the JadeMountain site and saw there AC type light blub and it looked to have a rather large cap on it.... That sure sounds like the soultion...
Again Thanks for the information....

Re: LED\'s and AC Power

I've found this ...
maybe someone can figure it out.schematic 230V
and a formula to calculate the capacitor,formula
My German is far worse than my English, but maybe sombody can make sense of it...
the complete PDF-file can be found here:PDF Led
Hope you can do anything with it

Re: LED\'s and AC Power

Would any of you explain to me how the
ForeverBright Christmas lights work?

I have several strings, they just
plug in to 110vac, small fused plug,
100 lights on a string.
Nothing gets hot, there is no place
for large parts (caps), they seem to
be in series-parallel, maybe 1/3.

I guess it's a 'dumb' question...
but I can't figure these out!

Re: LED\'s and AC Power

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by zyrtecx:
Thanks for the information! I bet that the resistor and diode sure do get rather hot...
I would guess that I would have to use one of those large 5 watt resistors... <HR></BLOCKQUOTE>

Or you could use a combination of smaller resistors. For example, five inexpensive 1/2-watt resistors can dissipate 2.5 watts.

You would either need five 30K's wired in parallel, or five 1.2K's in series.

Re: LED\'s and AC Power

Somebody else contributed the following circuit and desciption, but I unfortuneately don't know who it was. I will summarize below. The circuit worked for me.

AC in (line) ------ CAP ---|Rect.|---- LED(s) ---+
AC in (neutral) --- RES ---|____|--------------+

(Sorry I couldn't get the circuit diagram to work. The idea is that on the input side of the rectifier you have the CAP on the line voltage end, the RES on the neutral side. On the output side of the rectifier you connect your LEDs.)

Rect. = A full wave rectifier rated for 250V or more.
CAP = a self healing capacitor (I got mine at Digikey).
LED(s) = 1 or more LEDs in series (I used about 10 in my project)
RES = 120 ohm 1/2W resistor.

The theory of operation is that at line frequency (50-60Hz) a line rated self healing capacitor is chosen with a value that has an impedance that will supply a desired amount of current. The load should have nearly constant current draw (as an LED would).

The capacitors impedance = 1/(2*pi*C*F)

where
C = cap value in FARADs (not micro Farads)
pi = 3.14159
F = line frequency (60)

To create an LED light from a 120VAC line a 0.47uF polyester 250 volt (or higher) rated cap would function like a 5.6K ohm resistor. This supplies 120/5.6K or about 21mA - just right for an LED. The resistor is 120ohms (1/2 watt) and is there mostly for safety.

This circuit runs cool.

Disclaimer - If you don't know what you are doing then don't play with AC power! Don't blame me if you start a fire.

Re: LED\'s and AC Power

try dat2zip's homepage http://home.attbi.com/~theledguy
here you can find your circuit.

Re: LED\'s and AC Power

Here's my schematic:
http://members.aol.com/xaxo/index.html

(scroll down)

You will note there is an extra capacitor
and 10 ohm resistor. These were added to
snub out any possible line surges or
turn on surges that may occur at random
intervals, not to filter the ac current.

Take care,
Al

Re: LED\'s and AC Power

Mr Al,

Your web site has such great schematic drawings. What tool are you using for publishing on the web?

My scribble doesn't compare.

Re: LED\'s and AC Power

Hi there again dat2zip,

I just use MS Paint that came with Windows98
to draw the pics, then convert to gif.
I use the program that comes with aol
to actually upload the pics and create the
web pages. I think it's called
"Easy Designer". If you want to find out
more about it, i think you can click on the
link at the bottom of the page. i guess you
have to use aol in order to use that web
program. There isnt a whole lot to it with
that program. The drawback seems to be that
the page length is limited, unlike many
other sites ive seen. Perhaps more recent
versions of aol improve upon this.

Good luck with it,
Al

Re: LED\'s and AC Power

We have converted a 12v AC Halogen desk lamp to White leds sucesssfully, on a trial and error basis, this is what i learned.

Ac voltages are not what they seem, they are RMS, which mean root means square, or some doodely anyways that means the AVERAGE of the ac sine wave is the listed voltage, not the possibilities for volatages which can toast an led.

the lamps have 12v tranformers in them for the 12v halogen light Approx 14.4v no load.
so one lamp with 4 lights per bank max possible for the leds would be 16v right ?
well not if the sine wave of the ac is going over that, so the adding of a cap could blend out some of the sine , i donno.

anyways ONE of the desk lamps has always gone through halogen bulbs by burning them out after a month of use, but the other burned the halogen lamp normally.
so the one that didnt burn up the 12v halogen lamp has been working with banks of 4leds per row now for MONTHS, uses 1/10 the power of the halogen, is obnoxiously blue and flickers just a bit, it very directional and only puts out about 1/2 the actual light of the halogen it replaced.

the other one that always ran the halogen lamp hotter, toasts its 4 bank of leds in about 2 months of use, and might have worked with 5 per bank, but 5 per bank was low voltage and it looked quite dim, this one has been scrapped as a good idea , and was returned back to halogen.

the other thing about ac is it is only on 1/2 the time for Diodes (leds) so it flickers lots with only one bank, by parellelling 2 banks with reversed polarity this flicker was reduced to acceptable levels.

so for every other set of 4 leds the next set added was reversed.

the total led count in the working forever AC lamp conversion is 28white leds power consumption at the plug is approx 2watts
small power surges hit this lamp OFTEN and it has not been a problem YET

so there is one ac that worked


IF i was to attempt this with full 115-120ac i would start with 80 leds in two banks 40 then 40 reversed in polarity, the problem with this is the 120$ cost and the resultant flicker would not work better than a nice compact florescent bulb at 9$

Re: LED\'s and AC Power

Al,

I find on R4 of your schematic here:

http://members.aol.com/xaxo/page2.html

If you put a capacitor of proper value across it, you can greatly speed up the turn on and turn off time of the Luxeon.

I added a few additional parts on mine to reduce the turn-on and turn off time, to under 10nS, and to get it within regulation in under 20nS, with the slow LM358.

Re: LED\'s and AC Power

I thought it went

Ac-> Rectifier -> Capacitor -> Lm317T Vin , resistor V Adj to Vout then from Vout side of resistor to LED.

That how I have been running my setup and it works great even with unlcear and uneven AC power.

I don't understand how to hook up a cap to AC since a cap has a + and - side!

You will need some type of resistor to initial drop the voltage also.

Re: LED\'s and AC Power

Is there any reason why someone could take something like a 6v 500ma wall wart, run it through a "downboy" dc/dc buck circuit and then power a luxeon or string of 5mm's?

Jon

Re: LED\'s and AC Power

Hello,

This thread should really be in Electronics, as i didnt
remember to check this area until just now

Wouldnt it be a good idea to put the circuits in
that forum...

Take care,
Al