5v to 12v Circuit

You need a boost circuit.

You can buy DC-DC converters for this kind of application, but they may violate your 'low cost' requirement. You can probably get them surplus. I know I've seen them at halted specialties in san jose for a few bucks.

Here is a web page that describes the basics, if you want to try to build your own:

You can also use switched capacitor circuits to do this, but it's hard to get 120mA from one of these.

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Does it have to be a 12V LED lamp?

I would probably be cheaper and easier to use ordinary LEDs and run them from 5V.

As Colin said, you need a different LED. Most of them are intrinsically around 3 volts or so, so a 12V LED is just an LED in a package with an appropriate resistor. Building a power supply to overcome the resistance is a lot more complex than changing the resistor (or getting the same LED with a resistor sized for 5V supply).

just use a different dropping resistor...

a "12v" led and a "6v" led are really the same...

it's just a matter of the dropping resistor (which is in series)

"LED Man" schreef in bericht news:1gsf4l8.1ltpue2sphra8N% snipped-for-privacy@3v.invalid...

It helps if you tell us what kind and type of 12V LED you're talking about. I never saw 12V LEDs so your 12V type is an appliance of some kind. May be electronic, may be some LEDs in series or only a LED with a simple series resistor. An optimum solution depends on this information.

petrus bitbyter

"LED Man" schreef in bericht news:1gsf4l8.1ltpue2sphra8N% snipped-for-privacy@3v.invalid...

It helps if you tell us what kind and type of 12V LED you're talking about. I never saw 12V LEDs so your 12V type is an appliance of some kind. May be electronic, may be some LEDs in series or only a LED with a simple series resistor. An optimum solution depends on this information.

petrus bitbyter

It's not a single led, it's a 30 led package MR16, which is a good area light, in a nice neat package.

Works well, 10 hours off 10xnimh AA, just looking to run off 4 AA

HTH! :-) Rich

Struck me too that AFIK most LEDs operate from 1.5 to 3.0 volts? So the 12 volt package must either have a) A dropping resistor which wastes some 8 or 9 volts, or b) LEDs in series (unlikely?). Simplest would be, if possible, to modify the package so as to waste only two or three volts of the 6 volts that four AAs will provide?

I seem to recall hearing of 12 volt LEDs designed as drop-in replacements for automotive/truck lamps in tail-lights, etc.

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12V visible light LEDs can't exist. They would be in the hard ultra violet.

What you are describing are circuits of multiple LEDs and ballast resistors and such.

Duane

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In message , Terry writes

Or a switch mode constant current power supply ?

Why unlikely ?? Works for us !

J/.

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I believe it was already mentioned that the item this thread started about was a 10 or 12 LED in one package lighting unit, which is probably a few series strings in parallel, depending on the LED operating voltage.

LEDs in series makes all kinds of sense. If you change from wasting power on a dropping resistor to running as many as you can (depends on voltage available) from a constant current supply (easily made from an LM317 voltage regulator [for less than a dollar], among other methods) you get more light out for the same power in. And you can more precisely control the current (which is what LEDs care about and die from too much of) so that you can run them at maximum rated current (for maximum light out) without paying too much attention to the supply voltage. With a dropping resistor, the resistor value must not permit more than rated current at maximum voltage in, and in most applications is taking more power than the LED is.

Nothing is free, in that the regulator is eating some power (it basically acts like a smart resistor) but for a 12V supply, with a typical LED operating voltage of 2 or 3 volts, the same power that would be running one LED and a dropping resistor can run 3-5 LEDs. One can approximate this with a smaller dropping resistor, but the constant current supply does a better job.

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I suspect that your LED lamp might be designed to replace a normal halogen lamp. Remember that normal 12V halogen downlights operate from 12V _AC_ not

12V DC.

+5V to +12V at 600ma Bill Kaszeta Photovoltaic Resources Int'l Tempe Arizona USA snipped-for-privacy@pvri-removethis.biz