OT: Connecting a 12v LED to 73v AC ....?

[Gil]

Hi,

I thought some of you might be able to help. I'd like to connect a 12v LED to a powersupply of 73v AC.
Can anyone tell me how do I do that ? Should I used a resistor and a diode for converting AC to DC ?
What values ?

Thanks !!

[Papa_lazerous]

The voltage isnt too significant its the current limiting resistor that counts. find out the forward voltage of the LED and also the max current and then use ohms law to work out the resistor value,  with regards to it being AC I guess if it is was a high enough frequency then the LED would just work and maybe flicker a little.  you could always drop in a suitable diode and give it DC voltage though then its sure to work

[Sir H C]

An LED is a diode.  Not sure the reverse breakdown on the one you have is, so a series diode would be good to use, but it should work with a diode and a proper resistor.  Even at 60Hz, you shouldn't see the flicker.

[Paul Perry (Frostwave)]

What do you mean by a "12V led"?

[Gil]

Thanks,

Well, the LED marked "12v" on it, dunno exactly about the amperage... what values of resistors can I try there ?
should the rectifier diode get connected in paralel with the LED ?

[CGDARK]

Thanks,

Well, the LED marked "12v" on it, dunno exactly about the amperage... what values of resistors can I try there ?
should the rectifier diode get connected in paralel with the LED ?

Not in parallel, but in series. Connect the rectifier to the 73VAC signal then you must filter the DC output with a high value electrolytic then put a resistor in series with the rectifier diode then connect the LED. Remember when you rectify a  73VAC signal you will get more than 100Vdc so be careful choosing components. You can try a 100uF 160V electrolytic and for the resistor begin with 100k to have a good margin of protection to the LED and from there adjust to your taste. Be careful with the AC signals.

CG

[slacker]

What do you mean by a "12V led"?

You can buy things called 12 volt LEDs, really they're just normal LEDs with a current limiting resistor built in so you can run them straight off 12 volts.

There's an article that explains how to hook an LED up to an AC supply at AMZ.
http://www.muzique.com/news/index.php/?p=18#more-18.
I think this should work equally well for higher voltages only you'd probably need to replace the 1N4001 with a diode that could handle a the higher reverse voltage/current.

[Gil]

Thanks,

this one is nice...

http://www.muzique.com/schem/led.htm

I put the following values:

Voltage Supply 73v

LED forward voltage 12v

LED current 5ma (default)

Got:

Resistor value (R1) is 11Kohm.


Does that make sense ?

Also, I do see that the rectifier diode is placed in paralel to the LED in that circuit refering to that calculator ?.... 

[Gil]

anyone ?

[Paul Perry (Frostwave)]

I believe that leds in general have a 'low' reverse breakdown voltage. So that's why the protection diode is there.
No reason why the protection diode shouldn't be another led, of course!

[Gil]

How about the resistor value ? does my calculation results makes any sense ?

[slacker]

Yeah the resistor value looks OK, I make it 12k but 11k would be fine. You will need to use at least a half watt resistor though because 61 volts * 0.005 amps = 0.3watts.