Connect with us

LM317 circuit

Discussion in 'General Electronics Discussion' started by PlagueHuntR, Dec 2, 2011.

Scroll to continue with content
  1. PlagueHuntR

    PlagueHuntR

    5
    0
    Aug 11, 2011
    Hey hey all! Plague here :D
    Since I last posted Ive done a few projects, and recently a friend suggested I try make a nice simple laser diode driver in the form of a LM317 regulator circuit. Having looked for a nice cheap laser diode over the internet I came across a nice looking $5, 300mw 808nw diode.
    Heres a link to datasheet: http://www.markettechinc.net/Libraries/MTI_PDFs/U-LD-80C046D.sflb.ashx
    It being so cheap I decided to get one and put together the circuit.
    Attached I have the circuit layout.
    I put it together the LM317 regulator circuit with easily, it being, thankfully, quite simple. I have added the details for the resistors, Vin, Vout and where I have connected the positive and negative to the circuit layout. The operating voltage for the Diode is 2.2v.

    Now with the help of my trusty multimeter I have determined that the circuit does appear to be working with an output of 2.36v. Now as a quick side question the LM317 should be outputing 2.198v so anyone have any idea why it is 2.36 instead? I am assuming (possibly my fatal noobish mistake) that this is just because of the age of my multimeter.

    I have attatched a pinout for my diode which agrees with the infomation on the datasheet at the beggining of the post. That is how I have connected my diode to the circuit.

    Now to my problem. The laser is not working. As in there is nothing happening at all. Its not getting hot, when I first connected it it didnt make a sound, and there isnt the slightest hint of light.
    I thought it might be a faulty diode at first so I got another diode from another seller, but it too is showing no signs of life.

    My theory is it might be fluctuations in the voltage when I turn the power on and off that are burning the diodes out?

    Another posibility is it is the frequency of the light, and I simple can't see it when it isnt focused? I believe 808nm is visible to the human eye but not very clearly. However at 300mw I would think I would at least be able to tell whether it is working or not. idk perhaps I am mistaken.

    Anyway I would be very grateful to anyone who could point out any problems and if none are clear I would love to hear any suggestions you guys can offer as to how I can identify the problem. :D

    Thanks all!
    Plague
     

    Attached Files:

  2. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Hi there. R1 sets the reference voltage, 220 ohms offers the best voltage stability, R2 sets the output voltage. I cant view your diagram until i fire up my pc later, my phone wont let me see your pic's. Any way the reference voltage is about 2.5 volts + - tolerance. Load the supply with a lamp close to the regulators max current, take a current reading on this test. ive not used laser diodes so cant advise on that part. perhaps another member with laser diode experience can have a look for you.
     
  3. davenn

    davenn Moderator

    13,382
    1,785
    Sep 5, 2009
    no you cant see it cuz its not visible to the eye !! lol
    808nm is well into the infra red... visible light ranges from red at 700nm to violet at 400nm

    now a voltage regulator circuit and appropriate series resistor is ok for a standard diode, but not for a laser diode which requires a very specific driver circuit.

    Dave
     
    Last edited: Dec 2, 2011
  4. duke37

    duke37

    5,268
    728
    Jan 9, 2011
    Surely the regulator should be connected as a current source, not a voltage source to drive a diode.
     
  5. davenn

    davenn Moderator

    13,382
    1,785
    Sep 5, 2009
    laser diodes are not standard diodes. They are a 3 pin beastie and as I said to the OP they require a specific driver circuit. :)

    Dave
     
  6. jackorocko

    jackorocko

    1,284
    1
    Apr 4, 2010
    Well since it is infrared spectrum, use your trustee video cam on the cell phone and have a look. But, davenn is probably correct in that his driver circuit is all wrong.
     
  7. TedA

    TedA

    156
    16
    Sep 26, 2011
    Plague,

    I don't think Dave D.'s reply makes much sense. Perhaps he was driving at the time?

    The data sheet shows that this part may have three pins, but only two are used.

    Do take heed to the suggestions about laser diodes requiring a current source, not a voltage source. A series resistor might work, but as long as you have the LM317, a current source is easy to construct.

    The IR diode's data sheet lists 2.0 V as the maximum operating voltage at the rated optical output at 25C. This voltage will drop as the junction temperature rises. Your regulator circuit was set for too high a voltage, anyway.

    Most digital cameras will respond to IR, even though they have filters to knock-down the sensitivity. Lacking a camera, you can detect the output using a photo diode or photo transistor. Check your detection device with the TV remote, etc.

    I believe that these devices will function as IR LEDs below the threshold current. They emit IR, but the light is not coherent. Be careful not to exceed the 400mA and 40C values listed.

    Also, the device will require a heatsink for CW operation. There seem to be no specs for power dissipation or thermal resistance. One needs to tread carefully! To sidestep the heatsink problem, you might want to pulse the current to the diode, so it is on only briefly and is mostly off.

    Look at the LM317 application information, and you will find a single resistor circuit for making the current source you need. I think about 4 ohms would put the current close to what you need. You want a current somewhere between the Threshold current and the Max. Operating Current.

    If your meter will measure 100 - 400mA, connect it to the current source in place of the IR diode, to check the current.

    Although your LM317 circuit is not what you want for this application, your resistor calculations seem to be correct.

    So why do you measure a different voltage? Perhaps tolerances have stacked-up to move the measured output higher than the calculated value. Perhaps the LM317 is oscillating. You may need to add a capacitor across the 6V input to the LM317.

    Ted
     
  8. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    I came across an LM317 circuit yesterday for powering laser diodes, not sure if it will power this diode, ive not built a laser diode circuit yet, i do know some are out of the human visible spectrum range, my best info on them is the use of laser diodes in optical drives etc, i will post that LM317 circuit later from my pc, its a simple looking circuit, not sure if it helps the OP, but post it any way.
     
  9. jackorocko

    jackorocko

    1,284
    1
    Apr 4, 2010
    I really hope you haven't been staring into the LD with your naked eye all this time thinking the LD has not been working. Try not to blind yourself anymore then necessary.
     
  10. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
  11. PlagueHuntR

    PlagueHuntR

    5
    0
    Aug 11, 2011
    Hey all, soz it took me a while to respond, have been ill for a few days.
    Thanks for the numerous and swift replies :D much appreciated!

    I looked into this before selecting the specific diode I did. 390nm-750nm is more specifically the frequency band the human eye is sensitve too. 808nm is aparently visible if it is of high enough power and 300mw is enough for it to just be visible to the human eye when there arnt to many competing photons ;)
    This is atleast the case from what I have heard over the web (eg laser forums).

    My point in wondering whether it would be visible or not was more refering to the fact that the diode was not, whenever I was testing it, connected to a collimating lens. Thus the light emmited from the diode would be spread and thus greatly weakened, and with its already barely visibly frequency might be even more difficult, if even possible, to see.

    It is of course possible I am mistaken and it is a completely invisible frequency or my power is too low for it to be seen as much as I expected.

    However I have since thought even if this was the case I should still be able to feel at least trace amounts of heat from the diode shouldnt I?

    hahaha and dont worry Jockorocko I havnt been looking into the diode altho your concern is much appreciated!

    Ted I found your post to be incredibly helpful. I must have missed the part on the datasheet where they meantion 2.0 volts being the maximum operating voltage, and so I had gone with the sellers info of it being 2.2 volts.
    Now sorry for any noobish questions that appear hereafter but please be patient as this is my first time dealing with diodes and the many unique characteristics they seem to posses.
    So will any current between the max operating current and the threshold current work?
    If so will there be any efficiency differences?

    I like this idea of pusling the current to the diode, have never done this before however any idea if this will be just as effective as using a heatsink?

    I will now start looking into preparing a new circuit :D
    Thank you very much again everyone for your replies they have been most helpful!
    Hope u dont mind if I ask if I have any questions about assembing my new circuit :)

    Thanks,
    Plague
     
  12. TedA

    TedA

    156
    16
    Sep 26, 2011
    Plague,

    We all try to be of help. Just let us know how the project turns out.

    The diode should lase at currents between the threshold and the max operating current. If the current is far enough below the threshold, I believe the diode will still produce light, but the output will not be coherent or monochromatic. If the current is far enough above the maximum, the diode will be toast.

    I suggest that aiming for just a bit more than the threshold current would be a good plan at first. If you make the constant current source using the LM317, you can measure the current before connecting the diode.

    Be very careful about the temperature of the diode, I'm sure it will overheat without heatsinking, or a reduced duty factor - narrow pulses, with cooling time between.

    Again, this is a true semiconductor PN diode. The current to the diode must be limited externally. The voltage across the diode will vary with current and temperature, and from unit to unit, as well. The external circuit sets the current to the desired value, then the diode decides what the exact voltage will be, at the moment.

    I'm sure there are efficiency differences, as you vary the diode current, but the typical curves on the data sheet seem to imply that the efficiency differences are pretty minor, over changes in both current and temperature.

    Ted
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-