120V led power supply. What do you recommend?

Hi everyone,



My cousin would like to have an LED hanging lamp above her table. I have put one together but I would like to have a safe reliable power supply.



The lamp uses 4 XRE emitters. I can wire them s p or any combination. I have tested the heat sinking and 600ma per seems to be about right.



Any help is appreciated.

Any updates on the build?

I havent used it but http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=945-1375-ND certainly looks interesting, Digikey had quite a few stocked constant current LED drivers with AC input, on their product index, its under power supplies, external, LED constant current.

jonathandowers said:

Any updates on the build?

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LOL I forgot all about this thread.

Yes I did build this lamp, I dont have any pics but it went quite well. I took an old stained glass hanging lamp and made a copper/aluminum heat sink and wired the emitters in series. I used a standard UL rated power supply that was about 15V 400 ma if I recall. Since the output voltage was higher than the combined vf of my leds I had to use a resistor to set the current, and I also fused the whole system. Its been handing in their kitchen for about a month or two now.

I have found that just about any UL rated power supply (like phone chargers and power cords from other electronics) can be used if you make sure to use a resistor to limit the current so it does not exceed the what the supply is rated for.

Hi! I'm looking in to something similar. How do you calculate and wire the resistance? Thanks.

us too! haha thanks

RCantor said:

Hi! I'm looking in to something similar. How do you calculate and wire the resistance? Thanks.

Click to expand...

RCantor said:

Hi! I'm looking in to something similar. How do you calculate and wire the resistance? Thanks.

Click to expand...

Two options:
Find the average forward voltage of your LEDs at the chosen drive level and figure things out:
*Vsupply - Vled - Vresistor = 0
Vled = Vforward @ I
Vresistor = I * R


OR

Make this circuit: Simple CC circuit

I used the CC circuit in my reading lamp. A cell phone charger supplies up to 350 mA at 5V, and the LM317 acts as a switching regulator giving either 1 or 100 mA. Note that you connect LED (+) to Vadj, not Vout. I suggest testing this before installing to ensure correct current. This does remove guesswork about your forward voltages, and adds a $2 part from The RatShack (Radio Shack).

The LM317 wants a bit of voltage headroom, so using a phone power supply would be just short of giving 600 mA to 4 LEDs, which produces about as much useful light as a 13W fluorescent. I have one XR-E in my reading lamp at 350 mA and it's plenty for reading.