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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
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?


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


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.

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.

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

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.

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