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Author Topic: Drive 1W LEDs from batteries  (Read 2043 times)
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I'll show you PWM in action, it's a constant 5v, what you vary is the overall current the 555 will chop up the load giving the LED a break and you use less current, 555's not going to be that efficient.

I was testing this cheapy oscilloscope i bought off of ebay so i tried it with PWM (which can be done with a 555 or an Arduino)



That looks like a normal 5mm LED.  How will that circuit help me drive a 350mA LED?  Also, I don't need to dim the LED.

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I was watching a video at adafruit discussing a 4-AA battery pack for charging an iphone. Bottom line - you can only get 500mA from AA battery.

I suppose if I use the boost regulator off 2-AA's that won't be a problem as long as efficiency stays above 70%.   3V 500mA is 1.5 Watts.  But I'm okay with 2 batteries, so not a problem.
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I was watching a video at adafruit discussing a 4-AA battery pack for charging an iphone. Bottom line - you can only get 500mA from AA battery.

That would be an Alkaline battery.

Rechargeables can do a lot more than 500mA.
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I've spent a while with google, deal extreme, and aliexpress, but if you can point me in the right direction it would be helpful.

The prebuilt step-up LED drivers on Deal Extreme won't work? Have you tried FastTech or intl-outdoor? I know they have a few 1 or 2 AA 1W LED drivers which use the PAM2803 IC.

If you're in the US, I can give you a link a to US vendor that stocks them.
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The prebuilt step-up LED drivers on Deal Extreme won't work? Have you tried FastTech or intl-outdoor? I know they have a few 1 or 2 AA 1W LED drivers which use the PAM2803 IC.

If you're in the US, I can give you a link a to US vendor that stocks them.

Excellent question.  Deal Extreme has a bunch of items like http://dx.com/p/1-5v-350-400ma-constant-current-led-driver-board-for-diy-flashlights-128096 which may well be exactly what I want, but the description is so poor I can't tell.  "Voltage: 1.5V" do I just assume they mean input voltage and it outputs a higher voltage?  Even if so, what is the maximum output voltage, the maximum input current, will an Alkaline AA even be able to power it?  Does it have to be 1.5 volts, can I use 2 cells to lower the current needed?  It really is frustrating.  Maybe I should just order something that looks promising.

I took a look at the datasheet, PAM2803 based modules could be good.  Maybe that's what a lot of these modules use, they seem cheap enough.  I'm located in Canada.
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I took a look at the datasheet, PAM2803 based modules could be good.  Maybe that's what a lot of these modules use, they seem cheap enough.  I'm located in Canada.

I'd use two batteries (or more).

The bigger the difference between input/output voltages, the less efficient those boards are and the more amps you have to suck out of the battery to make it work.

eg. If you're only running at 50% efficiency then boosting a single battery to 5V with a 350mA output means you have to draw about 2.5 amps from the battery! Not good...

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Excellent question.  Deal Extreme has a bunch of items like http://dx.com/p/1-5v-350-400ma-constant-current-led-driver-board-for-diy-flashlights-128096 which may well be exactly what I want, but the description is so poor I can't tell.  "Voltage: 1.5V" do I just assume they mean input voltage and it outputs a higher voltage?  Even if so, what is the maximum output voltage, the maximum input current, will an Alkaline AA even be able to power it?  Does it have to be 1.5 volts, can I use 2 cells to lower the current needed?  It really is frustrating.  Maybe I should just order something that looks promising.

I took a look at the datasheet, PAM2803 based modules could be good.  Maybe that's what a lot of these modules use, they seem cheap enough.  I'm located in Canada.

Yeah, the one you linked ought to work. I have a similar one at home which I did some testing with.
http://i203.photobucket.com/albums/aa281/mg_steele/sk68_table_zps002aed83.jpg

This was all done on the bench using a bench power supply and a Cree XR-E. The current draw suggests that this driver wouldn't work too well with a single alkaline cell. Add to that the additional resistance from the switch and the battery contacts of the flashlight, and I would imagine it would still power the LED, but at much lower output current. I would recommend using a single NiMH or Lithium primary cell, or like fungus said, 2 AA alkalines.

In my experience as long as you keep the input voltage slightly lower than the Vf of the LED, you should be fine with just about any of these 1AA boost circuits.
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If you are thinking of using the module from DX, maybe this will better suit you.
http://dx.com/p/350-400ma-regulated-led-driver-circuit-board-for-diy-flashlight-1-2-1-5v-128084
You get 2 boards and they say 1.2v-1.5v input. Though the reviews say you get stable current at 1.5.
« Last Edit: August 26, 2013, 08:24:58 am by elac » Logged

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