Adjustable Voltage regulator

Discussion in 'General Electronics Chat' started by gtr675, Mar 17, 2011.

  1. gtr675

    Thread Starter New Member

    Mar 17, 2011
    Hi all first post and very new to electronics and quite high aspirations. Please bear with me.

    I have a little understanding of the way electrons move i think, however i haven't built many circuits and i thought this forum might be the place to start.

    The first project i would like to accomplish is a laser trigger for high speed flash photography.

    I just need to build a circuit to power the laser which will provide 40-50mA @ 2.4-2.8 volts. This in turn with a photon resistor,arduino and an opto isolator triggering my flash-head should do the trick.
    I have a 3.3-12v power supply @ 2.54A, and a LM317T adj voltage regulator.

    I have searched and tried to work out the formula as best i could but without a better understanding of electronics i am at a loss.
    I can trigger my flash with my arduino safely but i need to work out the circuit for the laser without spending too much.

    Here is the link to the laser diode i intend to use.....

    If there is a thread which will help me please link it.

    Sorry for the essay but many,many thanks in advance.
  2. Jaguarjoe

    Active Member

    Apr 7, 2010
  3. SgtWookie


    Jul 17, 2007
    Connect the LM317 IN terminal to a 6v source.
    A 33 Ohm fixed resistor (I'll call it R1) connected from the LM317 OUT terminal to the ADJ terminal should give ~38mA current output from the ADJ terminal.

    The LM317 drops about 1.7v from the IN terminal to the OUT terminal, and another ~1.25v from OUT to ADJ, so just figure 3v "dropout" minimum for the LM317; your laser diode drops another 2.4v (nominal). 3v+2.4v = 5.4v. The "extra" 0.6v gives the regulator some "headroom" to provide current regulation.

    You are better off to supply slightly less current to the laser than too much. If excessive current is applied, the laser will be immediately destroyed.

    R1 ~= 1.25/DesiredCurrent; where 10mA <= DesiredCurrent <= 1.5A
    CurrentOut ~= 1.25/R1, where 0.8 Ohms <= R1 <= 120 Ohms
    Last edited: Mar 17, 2011
  4. someonesdad

    Senior Member

    Jul 7, 2009
    Since I was just looking up stuff yesterday, this info is fresh in mind... You can get an LM317 in a TO-92 metal can package, which might be handy over the TO-220 and TO-3 packages for size (or, if you have young eyes, you can get a small surface mount version). You might even find that running it at 40 mA doesn't require a heat sink.
  5. SgtWookie


    Jul 17, 2007
    The LM317L is the 100mA version; available in TO-92 plastic case as LM317LZ, 8-pin SOIC as LM317LM, and 6-bump micro-SMD as LM317LIxx.

    It's also available in a 500mA maximum version as an LM317M in a few SMD packages.
  6. gtr675

    Thread Starter New Member

    Mar 17, 2011
    Thanks guys worked perfectly with the 33 ohm resistor.
    The regulator i used was an LM317t/to-220.