LM317 Vs. Driver

i'm lost now. all i am, and ever have been trying to do is tell the op about what he is doing. i never boldly said the lm317 isn't a current regulator. I only say, the way it is commonly used here is as a voltage regulator. and about the lm417 comment, that is exactly my point about you picking and choosing what to argue about. i typoed once and you chose to harp on it, knowing perfectly well i meant 317. just like in all my other posts.

and to make it clear, for a laser diode, and LM317 by itself is NOT a proper driver. it will properly on its own supply the correct voltage if too much voltage is applied. it will not on its own feed the correct amount of current because there is such a huge range of currnet that a diode can take.

michael.

chipdouglas said:

and to make it clear, for a laser diode, and LM317 by itself is NOT a proper driver. it will properly on its own supply the correct voltage if too much voltage is applied. it will not on its own feed the correct amount of current because there is such a huge range of currnet that a diode can take.

michael.

Click to expand...

It will supply 1.25 /R no matter what voltage you put in that is why the original poster said all you need is a lm317 and a resistor. So if you use a 1 ohm resistor it will supply 1.25 amps no matter what voltage is put in as long as it is approx 2+ the laser diode and below 40+2+the LD

midias said:

It will supply 1.25 /R no matter what voltage you put in that is why the original poster said all you need is a lm317 and a resistor. So if you use a 1 ohm resistor it will supply 1.25 amps no matter what voltage is put in as long as it is approx 2+ the laser diode and below 40+2+the LD

Click to expand...

ok, so what? by LPF standards that is still not a proper driver. And that is all that matters to me. I only cite what is relevant to the hobbyist here with info that is commonly used here. i also like to speak to people in the easiest way possible so they understand.



michael.

chipdouglas said:

ok, so what? by LPF standards that is still not a proper driver. And that is all that matters to me. I only cite what is relevant to the hobbyist here with info that is commonly used here. i also like to speak to people in the easiest way possible so they understand.



michael.

Click to expand...

What makes it not a proper driver it is a current regulator and can be soft started with caps?

chipdouglas said:

i'm lost now. all i am, and ever have been trying to do is tell the op about what he is doing. i never boldly said the lm317 isn't a current regulator. I only say, the way it is commonly used here is as a voltage regulator. and about the lm417 comment, that is exactly my point about you picking and choosing what to argue about. i typoed once and you chose to harp on it, knowing perfectly well i meant 317. just like in all my other posts.

and to make it clear, for a laser diode, and LM317 by itself is NOT a proper driver. it will properly on its own supply the correct voltage if too much voltage is applied. it will not on its own feed the correct amount of current because there is such a huge range of currnet that a diode can take.

michael.

Click to expand...

midias said:

What makes it not a proper driver it is a current regulator and can be soft started with caps?

Click to expand...

you just proved my point. an LM317 is not a proper driver on its own. A driver is a series of components. if you use just a resistor, you do not call it a driver. so why do would you call just a LM317 a driver. on its own it can not properly protect a laser diode. i am done arguing with you.

chipdouglas said:

you just proved my point. an LM317 is not a proper driver on its own. A driver is a series of components. if you use just a resistor, you do not call it a driver. so why do would you call just a LM317 a driver. on its own it can not properly protect a laser diode. i am done arguing with you.

Click to expand...

So what is a proper driver then?

chipdouglas said:

the way it is commonly used here is as a voltage regulator

Click to expand...

I'm not trying to get in the middle of anything but I'm going to have to disagree with you here. I have over 4 years worth of successful builds using the lm317 and as midias has stated it can be configured as either a voltage regulator or a current regulator. In contrary to your statement above it is commonly configured for our purposes is as a current regulator, NOT A VOLTAGE REGULATOR. This can be determined by viewing the data sheet for the lm317. I have read ALL of the posts that you have made in this thread and I'm not positive but I think that you may be mislead or confused about the way this works. It sounds to me like you may be under the assumption that the resistor in the circuit is what is regulating the current, however the resistors job is to set, or program if you will, the desired current to be regulated by the lm317. When configured in current regulation mode the the vf. of the diode is "floated" by the lm317, meaning that with the temperature change of the laser diode the forward voltage required also changes and the lm317 is able to account for the change while continuously delivering a prescribed amount of current. This, in my opinion deems the lm317 a PROPER driver for a laser diode as it does meet the requirements and has proven to be be safe and reliable over the years.

As a side note to the O.P. you may consider that the lm317 has a voltage drop of 3v meaning it takes 3v from the power source (ie. battery or power supply) to run. So your power source will need to be from 8.25v to 12.5v (depending on your diode type) to successfully drive your diode. I usually use 3 X 10440 in series (12.5v). You can expect battery life of about 1.5hrs between charges with a 12x br diode and your lm317 set at about 380ma.

+rep to midias

Holy drama!

LM317 will do the job cheaply but a micro driver will fit in a smaller space and usually lead to less headaches.


Side note: Just because it allows for batteries of varying voltages does not mean its acting as a voltage regulator... I think this may be part of what is causing the confusion.

The drawing states the ideal voltage because if it were higher, the lm317 would drop more voltage and therefore produce more heat and be less efficient, and if it were any lower, the lm317 would have trouble properly regulating the current.

And yes, as many other have said, for our purposes, the lm317 is used as a current regulator.

Sorry for the drama but this is the kind of thread people find while searching and I would hate for it to have wrong information and mess up people who search.