LM317 Drivers

Today I made two LM317 drivers, aka DDL drivers.

The larger one was my first build, used a LM317T, 2 10-ohm resistors, 200ohm pot, 1 1N4001 diode, and a 25mF capacitor, tops out at 108mA for a blu-ray.

Second one is my slim style build, as i gained some experience with building them, I could make it smaller and thinner.  ;D

The driver utilizes a LM317T, 1 1ohm resistor, 1 1N4001 diode, and a 10mF capacitor, with a 200 ohm pot, tops out at 330mA, which is decent for a LOC.







My question is if i just did not use a resistor could i strike at least 420mA for a LOC?

I would appreciate comments and assistance.  

Congrats!

If you don't mind the laser not being adjustable, you can just replace the pot and put a 3-ohm resistor in it's place for 420mA. You don't need any other resistors.

Great, Thanks for the information bud

Thanks for the comment pseudolobster

Jimmymcjimthejim said:

If you don't mind the laser not being adjustable, you can just replace the pot and put a 3-ohm resistor in it's place for 420mA. You don't need any other resistors.

Click to expand...

If you do only use one resistor, make sure it's rated for 1W... At 420mA your resistor will be passing more than half a watt, so it's a good idea to use beefy resistors at that point. I've been using 6x 0.1W surface mount resistors in parallel in my prototype lobsterdrives and they heat up pretty good at 420mA.

XCreedX said:

My question is if i just did not use a resistor could i strike at least 420mA for a LOC?

I would appreciate comments and assistance.

Click to expand...

Good job!

Yes you could, you do not have to have the series resistor in the circuit. But you must be aware of the possibility of turning it up way too high.

Since you should always set current with a test load, you should not have a problem. Also, you must remember to discharge the cap after setting the current, and before you connect your LD.

For up to 200mA's, your ok with a 1/4 watt pot. But for over that, and up to 400mA's, you should have a 1/2 watt pot.

The Ohms law on this is voltage X current = watts.

1.25 volts (at the LM317 sense pin) multiplied by .400 (mA's) = .5 (watts)

Here is a nice 100 ohm, 4 turn, 1/2 watt pot that I found. It is perfect for a DDL driver that would be adjustable between 12.5mA's to 400mA's. (It will go higher, but the recommendation from ohms law is to keep under 400mA's)

Here's the post that shows the pot used in a DDL driver. There is a link to the pot from Digikey in this post:
http://laserpointerforums.com/f51/pioneer-8x-blu-ray-bdr-203-a-36790-5.html#post500740

jayrob said:

you must remember to discharge the cap after setting the current, and before you connect your LD.

Click to expand...

So important, I think I'll quote him again.

jayrob said:

you must remember to discharge the cap after setting the current, and before you connect your LD

Click to expand...

You could, of course, put a small (470[ch937] or so) 603 or 805 package smd resistor across the cap, so that it is drained for you.

Nvm i got it, I used a 3/4 watt rated 1.5ohm resistor and i get 415-420 mA. Thanks for the help