LM317 Vs. Driver

Hi, I am finishing a build on a 150mw 405nm laser and all I need to get is a driver. I know what current to set it to and everything, but it is much cheaper to just buy a LM317 and a resistor instead of a driver. What are the advantages to a driver vs an LM317, since they both basically just regulate current? Won't both work just fine?

The LM317 IS a proper driver, albeit a linear one.
That means it cannot deliver more voltage on it's output then it gets from the input.
In fact, it even drops ~2V of voltage, so to drive a BluRay you would need at least
7~8 volt on the input side.

Advantages lm317:
- cheap
- DIY is fun
- you can "pimp" it any way you'd like (diodes and caps for extra protection)
...

Disadvantages lm317:
- bulky (might not fit easily in a small host)
- needs alot of voltage to drive
....

A lm317 doesn't actually regulate current. It is a voltage regulator. So when you use that and a resistor you have a crude driver. Look up the ddl driver it is lm317 based

Alright, thanks for the feedback guys, I'll take it into consideration

chipdouglas said:

A lm317 doesn't actually regulate current. It is a voltage regulator.

Click to expand...

No, it can be wired as either. For our purposes, it is wired with current regulation.

For the LM317 I like to add a few caps and a diode for protection

Cyparagon said:

No, it can be wired as either. For our purposes, it is wired with current regulation.

Click to expand...

thats why i loosely said "actually". he wants a driver. so i was giving him correct advice for his route.

michael.

You said "A lm317 doesn't actually regulate current" but it does. Was it really demoted to crude? Or is this some Dr. Lava fanboy propaganda (no disrespect )? The LM317 makes an excellent current regulator.

Cyparagon said:

You said "A lm317 doesn't actually regulate current" but it does. Was it really demoted to crude? Or is this some Dr. Lava fanboy propaganda (no disrespect )? The LM317 makes an excellent current regulator.

Click to expand...

The lm317 is a fine regulator sure it does not boost voltagebut it does the job. Yes it is intended to be a voltage regulator but the current use is in its datasheet as a suggested application. Just add some caps and a reverse protect diode

i get what you are saying cyp, but in the scope of his question he wants to make his own driver. and i am telling him the the lm317 around here is used as a voltage regulator. If you notice his first post he says isn't an LM317 and a resistor cheaper. so i highly doubt he wants to use the LM317 as a current regulator when he is also mentioning a resistor.

chipdouglas said:

i get what you are saying cyp, but in the scope of his question he wants to make his own driver. and i am telling him the the lm317 around here is used as a voltage regulator. If you notice his first post he says isn't an LM317 and a resistor cheaper. so i highly doubt he wants to use the LM317 as a current regulator when he is also mentioning a resistor.

Click to expand...

This is very confusing I have yet to hear about anyone using a Lm317 as a voltage regulator in this forum vs a current regulator. Also why would using a resistor make him not want to use the LM317 as a current regulator? The Current regulator version uses 1 resistor while the voltage regulator version uses 2.

midas, the most common diy driver is the daedal or more commonly called the ddL driver. it is LM417 based. while he did not invent it, he is the former member that popularized it here. The ddl uses a pot and resistors as for regulation of the current. the l317 is what lets you use a range of battery combinations.

please read this midas, it explains it well. http://laserpointerforums.com/f42/diy-homemade-laser-diode-driver-26339.html



michael.

chipdouglas said:

midas, the most common diy driver is the daedal or more commonly called the ddL driver. it is LM417 based. while he did not invent it, he is the former member that popularized it here. The ddl uses a pot and resistors as for regulation of the current. the l317 is what lets you use a range of battery combinations.

please read this midas, it explains it well. http://laserpointerforums.com/f42/diy-homemade-laser-diode-driver-26339.html

michael.

Click to expand...

As far as I can tell there is no such thing as a LM 417. I am surprised you are not aware of what is going on in this circuit with your high post count. The LM317 is the current regulator. It has a built in comparator and a 1.25V reference inside and the resistors and pot allow the current drop across the output to match the reference thus making it a current regulator. The internal comparator outputs a voltage to make the correct current a reality with the load in parallel to the ref and thus you get a current regulator. Even the picture you posted has nothing to do with a LM417. Also that entire post talks about the use of the LM317 as a current regulator. You only need a single resistor as the original poster mentioned and even without the pot and caps it is still a current regulator.

So the LM317 is both a current regulator and a voltage regulator and yes it is a proper driver all day long.

midias said:

As far as I can tell there is no such thing as a LM 417. I am surprised you are not aware of what is going on in this circuit with your high post count. The LM317 is the current regulator. It has a built in comparator and a 1.25V reference inside and the resistors and pot allow the current drop across the output to match the reference thus making it a current regulator. The internal comparator outputs a voltage to make the correct current a reality with the load in parallel to the ref and thus you get a current regulator. Even the picture you posted has nothing to do with a LM417. Also that entire post talks about the use of the LM317 as a current regulator. You only need a single resistor as the original poster mentioned and even without the pot and caps it is still a current regulator.


So the LM317 is both a current regulator and a voltage regulator and yes it is a proper driver all day long.

Click to expand...

what does anything in your post have to do with what i'm talking about? My first post only adresses what the OP wants info on. Have you even taken a look at any of my posts or do you just pick and choose specific words to argue against?



midas i am sure you are wrong in this. the lm317 is the voltage regulator in this schematic. it enables you to use varying voltage above your minimum rated all the way up the the maximum voltage that the lm317 can handle. i think the max is like 14 or 18vdc. look in the pic... where it says "ideal voltage 7.2", now why do you think it says that? it is because you can go higer because of the LM317. and why do you keep saying "LM417"? is this a typo? the lm317 by itself is not a "proper driver"

and my post count has nothing to do with my electronics knowledge.... religion and physics are major topics here but i am no scholar in those fields LoL. i know about the ddl driver because i have made only one back in 2008 when i first joined here. from information i learned here. i had no previous electronics knowledge.
michael.

chipdouglas said:

midas i am sure you are wrong in this. the lm317 is the voltage regulator in this schematic. it enables you to use varying voltage above your minimum rated all the way up the the maximum voltage that the lm317 can handle. i think the max is like 14 or 18vdc.

michael.

Click to expand...

Lets take a look at the LM317 data sheet. Now as a part I have often used in my job I know it well. It is one of the most common adjustable voltage regulators.

http://www.national.com/ds/LM/LM117.pdf

Lets start with the pinout of the standard LM317 To-220 package



Now in the picture you posted the resistors are between pin 1 and 2 the adj pin which has the 1.25 ref and the output pin or pin 2. The laser Diode is in parallel with the combination and gets LD+ from pin 1. Now to use the LM317 as a voltage regulator you need to put a resistor between Vout and adj and another between adj and ground creating a voltage divider for the internal comparator to send out the correct voltage. As in this example from the data sheet below



For this image Vout or pin 2 = 1.25 (1+r2/r1) the input voltage does not matter any voltage drop is dissipated as heat. Yes I know it says LM117 read the data sheet they are the same functionality just with different load regulation tolerances and they use the same data sheet.



Now for an adjustable current source or the picture you posted.
Lets look at the data sheet further and find the application notes section. You will find this picture showing how to use the LM317 as a current source



This may look very familiar because it is what you posted. Look the Adjustable resistor is between adj and vout. That is where the 1.25V reference is. Using this reverence and then using the Adj pin as the output you have a current source.

Good?

chipdouglas said:

what does anything in your post have to do with what i'm talking about? My first post only adresses what the OP wants info on. Have you even taken a look at any of my posts or do you just pick and choose specific words to argue against?



midas i am sure you are wrong in this. the lm317 is the voltage regulator in this schematic. it enables you to use varying voltage above your minimum rated all the way up the the maximum voltage that the lm317 can handle. i think the max is like 14 or 18vdc. look in the pic... where it says "ideal voltage 7.2", now why do you think it says that? it is because you can go higer because of the LM317. and why do you keep saying "LM417"? is this a typo? the lm317 by itself is not a "proper driver"

and my post count has nothing to do with my electronics knowledge.... religion and physics are major topics here but i am no scholar in those fields LoL. i know about the ddl driver because i have made only one back in 2008 when i first joined here. from information i learned here. i had no previous electronics knowledge.
michael.

Click to expand...

To respond to you new info from the edit

The lm317 is a proper driver the reason it says 7.2 ideal is because it is a linear driver and it has to dissipate any extra voltage by means of heat. The LM317 can handle ~40V over the output voltage. But the difference is heat so thermal dissipation or PD the PD is ~PD=((Vin-Vout) * I) so if your Vin is huge then your PD will also be huge and it will get hot fast.

So to once again summarize the LM 317 is a dual driver that is a proper current source as shown in your posted picture.

And to answer your question I said LM417 because you did and because you did not tell me it was a typo before I posted I said it next time I will try to figure out what I meant to type.