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Help with simple power circuit Answered

Really quick, I have a REALLY SIMPLE circuit I'm building for halloween decorations that looks like this: http://imgur.com/dkU3LbT
B
asically there are 6-7 Lasers that draw 3V at 250-300mA.
The most practical power supply I could think of is a 5V 2.1A iPad power adapter, with a usb cable with the leads exposed.
I forgot the basics of electronics... What positioning of what rated resistors are to be used?
Did I make a mistake in the basic setup?

THANKS SO MUCH FOR YOUR HELP

**EDIT: I suppose I should clarify. These 'lasers' are actually fully built with the drivers inside. Specifically they are those cheapie 5mw green pens.

Discussions

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mpilchfamily

Best Answer 5 years ago

Don't use resistors. Lasers are different from LEDs. They don't need current limiting resistors but they do need a good regulated supply. You will need to get a voltage regulator if you want to use the 5V wall wart. Or find a good 9V power source (not a 9V battery). Wire 3 in series, then wire the 2 sets of 3 together in parallel.

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steveastroukmpilchfamily

Answer 5 years ago

Actually Laser diodes are similar enough to LEDs for the same precautions to work: They really need constant current drives, but the main difference is that even slight over voltaging will kill them dead.

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madman11steveastrouk

Answer 5 years ago

Can I underdrive? (2.5v per laser?) and can I use a power supply over the needed amperage?

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steveastroukmadman11

Answer 5 years ago

They probably won't glow properly if you underun them that far. So long as a the MINIMUM current that the supply will provide is more than the MAXIMUM of your load, you'll be fine. You can buy 3V regulators for peanuts.

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steveastrouk

5 years ago

Always safer for lasers to use a regulated suppl, but you can try 8 Ohm, 1/2W resistors