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 Laser Pointer Forums - Discuss Laser Pointers actual CURRENT? after the dead LD and resistor dum

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01-29-2008, 07:26 AM #17
 Class 3B Laser Join Date: Jun 2007 Location: Dallas Tx Posts: 3,199 Rep Power: 180
Gazoo
Class 3B Laser

Join Date: Jun 2007
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Posts: 3,199
Rep Power: 180
Re: actual CURRENT? after the dead LD and resistor

Here is my &quot;canned&quot; response...lol

The LM317 is no mystery and very easy to work with. The following calculations always apply since it uses 1.25 volts for its reference voltage.

To calculate the resistor needed for a given current, take 1.25 and divide it by the current. So say you want to drive a SenKat diode with 250 ma's. 1.25 divided by .250 = a 5 ohm resistor.

Another way you could do this is to take 1.25 and divide it by the resistance. 1.25 divided by 5 = .250.

Next you will want to calculate the wattage of the resister needed. We know 1/2 watt resistors are common for use with the regulator. But to figure it out, simply take the 1.25 and multiply it times the current. 1.25 times .250 =.3125 watts.

The rule of thumb for the voltage going into the regulator is it should be 3 volts more than the voltage going to the diode. A SenKat diode running at 250ma's will have about 3 volts across it. Therefore a minimum if 6 volts is needed.
I recommend 6 nimh batteries or 2 RCR123's for use with Daedal's driver.

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01-29-2008, 07:35 AM #18
 Class 2 Laser Join Date: Oct 2007 Location: Pasay, Manila, Philippines Posts: 320 Rep Power: 11
Class 2 Laser

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Re: actual CURRENT? after the dead LD and resistor

its clear to me now : from your big help and concerns , im starting to build a nice and well DVD laser project, after i finished it i will post some images or video of the result. ;D

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