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04-20-2011, 09:41 PM #1
 Junior Member Join Date: Apr 2011 Posts: 1 Rep Power: 0
THX1138
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Join Date: Apr 2011
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Caculating current from output power rating?

I have some 200mW red lasers (\$27.09 - High-Power 200mW Red Laser Pen (Burns Match + Visible Beam Daytime) - Red Lasers) that run from two CR2 (3V) batteries. I want to dismount one from the pointer and give it a constant-current driver supply. Given the input voltage of 6VDC, and the output rating of 200mW, and being ignorant of the various dissipations, how can I calculate the maximum current I should supply this thing? (Getting a milliammeter in there is a bit of a PITA, but I might fall back to that..)

The final product will be well heat-sunk.

Thanks!

04-21-2011, 09:12 AM #2
 Class 3R Laser Join Date: Mar 2011 Location: Smolyan, Bulgaria Posts: 1,076 Rep Power: 107
foulmist
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Join Date: Mar 2011
Location: Smolyan, Bulgaria
Posts: 1,076
Rep Power: 107
Re: Caculating current from output power rating?

read the reviews on that laser... as far as I can tell that diode is pushed to the maximum of it's limits and they soon burn out

SO i would not recommend using that laser... you could get an LPC-815 or LPC-826 and if you want a linear driver build the current should be ~450mA for the LPC-815 diode and ~520 for the
LPC-826 maximum

i suspect that the diode in this laser is Short Open Can pushed at maximum output or even more
short open cans have current limit at 350mA MAX so be careful if this is the short open can diode

you can calculate the current by this formula I = 1.25 / R
so if you want say ~460mA you have to put a 2.7 ohm resistor
for 500mA you set a 2.5ohm resistor
500 = 1.25/2.5
I = 1.25/R

that's for the linear drives where the Vref is 1.25V and you put the resistor between the OUT and ADJ pin of the voltage regulator to get a constant current source don't forget to put an output cap of at least 10uF to protect the diode

hope I helped you

Last edited by foulmist; 04-21-2011 at 09:20 AM.

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