USB Power?

[andd64]

Hey guys,

I need to power two lasers, each is 3.2 V, 25 mW, and somewhere between 40-60 mA - i was hoping to use the power from the USB port.  I know that a USB port outputs 5 V, about 500 mA max, so can someone please help me figure out how to properly power both the lasers?  I'm a novice at circuitry so help would be appreciated.  Thanks.

[SmAsH]

well, each laser runs at 3V2... the usb provides 5V... we have a Delmore...
you *could* runs two sets of series in parallel but then they would only get 2V5 each....
the best thing i can think of is getting a 3V regulator with a 500mA output and using that to step down the voltage.

[Razor Concepts]

well, each laser runs at 3V2... the usb provides 5V... we have a Delmore...
you *could* runs two sets of series in parallel but then they would only get 2V5 each....
the best thing i can think of is getting a 3V regulator with a 500mA output and using that to step down the voltage.

Two sets of series in parallel? That yes no not yes no make sense 

http://www.hebeiltd.com.cn/?p=zz.led.resistor.calculator
3.2 voltage drop at 60ma is a 30ohm resistor in series with the laser.

[SmAsH]

ahh crap lol, i thought he had four, no idea where i got that from

[andd64]

lol thanks.. so then should i get a 3V regulator?  How would the connection work? I just need one regulator for the two lasers?

[Soeren]

Hi,

You could get the 3.2V by means of a LDO (Low Drop-Out) regulator with an adjustable output or by placing an old school red LED in series with each LASER (even at 40..60mA the LED will probably last a good bit longer than the LASERs). Red LEDs drop around 1.8V.

But...

You should make sure that it's OK to run them this way, since the proper way to drive a semiconductor LASER is by regulating the current!
A LASER supply could, in your case, be a 50mA current limiter with a bit higher available voltage than what the LASER need - like the 5V you mention.

The most critical factor of a LASER supply is that it should never, even for 1 ms, be allowed to surge a higher current than it can safely handle, or it will convert into a weak LED with no ability to "LASE" at all (if it doesn't just die screaming).
1ms is ample time to kill a LASER several times over.
Surges are very likely to occur in a regulator/limiter at turn on. A slow turn on limiter is the best way to avoid surges.

[andd64]

Soren thanks for the information. The red led sounds like a better solution for me as i could use a red led in my setup.  How would i know if it's ok to run them this way?  All i know about the laser is that it's 3.2V, 25 mW, and between 40-60 mA (probably 40). 

So just to get this straight - in this case i would need two usb's since im using two lasers? Or can i just use one usb to drive both lasers? If so, how would that connection work?  Thanks for you help.

[Soeren]

Soren thanks for the information. The red led sounds like a better solution for me as i could use a red led in my setup.  How would i know if it's ok to run them this way?  All i know about the laser is that it's 3.2V, 25 mW, and between 40-60 mA (probably 40). 

So just to get this straight - in this case i would need two usb's since im using two lasers? Or can i just use one usb to drive both lasers? If so, how would that connection work?  Thanks for you help.

hI,

If they're good for running at 3.2V then adding a red LED will make them connectable to the +5V.

To run two, make up two with LEDs and connect the "assemblies" to the same points (+5V and 0V).