DIY Homemade laser diode driver

hmm. you know xgeek, it does say vout for a reason. the adj line is only to sense the resistors. alhtough, i thought the same thing. was wondering...
hangon. your using between 3 and 13 ohms?? this is the LM317? DDL's circuit says to use a 100 ohm trimmer not 10.

BlueFusion said:

hmm. you know xgeek, it does say vout for a reason. the adj line is only to sense the resistors. alhtough, i thought the same thing. was wondering...
hangon. your using between 3 and 13 ohms?? this is the LM317? DDL's circuit says to use a 100 ohm trimmer not 10.

Click to expand...

Bluefusion please don't be sarcastic I am just asking a question. I know what vout does but was unsure if the load is also split across the adjust.

I can use a 10 ohm rather than a 100. The output current is set as follows 1.25 / your resistance. So 1.25 / 10 ohms = 0.125 mA with the pot wound open and reducing the resistance of the pot will increase the current. The 3 ohm resister I am using is to limit the max current to 0.416 mA if I close the pot all the way and the pot resistance goes to 1 ohms (a short).

xgeek said:

... was unsure if the load is also split across the adjust.

Click to expand...

The Adj pin sinks negligible current (~ 50 microamps), so for calculation purposes, you can assume all the current goes to the load.

Paul

Slow down guys...

First of all... at the spot where you have that resistor, you don't need all that much "rating" because all that pin is doing is regulating the current through the inside of the LM317. The voltage between the Vout and Adj is a figure always fixed at 1.25V (or damn near it). The rating on these resistors only becomes a problem when you go into 1A range or so... 0.5W should be more than enough, trust me.

You can use a 10-ohm trim pot to get a more accurate reading on the current. But here is the thing now... most pots will be very finicky and inaccurate to some degree. The lowest you would be able to go to is around a half an ohm resistance on that 18-turn (check the part's spec sheet for a better result), and most stop at 1-ohm. Most will also top out a bit higher (from experience) than the rating.

As about the power rating... here are the variables and the formulas:
P=power
V=voltage
R=resistance
I=current

V = I * R
P = I * V = R * I^2 (that's current squared) = V^2 (voltage squared) / R

Using these... a full current load through your resistor between Vout and Adj would net you 0.5W

GL;
DDL

I got some 3 watt 25 ohm rheostats from Radio Shack. They are an overkill, but I didn't care since these are being used with my lab laser I built. So if you want something quick and easy to work with, and are not concerned about the size, I would recommend these. They go as low as .3 of an ohm. The rheostat works beautifully in this circuit and I have no other resistors connected.

I got some 200uF 16V caps from a DVD Writer board. Will these work? Or is the voltage too small/ capacitance to big?
Thanks

You will be fine with those.

hey daedal i was wondering if you can post a pic of the finished pc board and i was also wondering in the schematic is U1 a switch?

toked323

u1 is a LM317 regulator

thanks dude have you made this circuit if you have please post a few picts for me

nope i haven't made it yet, but will plan to in the next week. good luck

thanks for all your help greatly appreciated

that's what we are here for and to have fun selling, making and using lasers ;D

yea i just bought a 50mw greenie from DX do you know where i can get cheap goggles?

try wicked lasers, their goggles are about$40, but that is about as cheap as you can get em.

Things is right, and the lasershades are winners for red or green protection. I have a pair for red protection and I love them.

http://www.wickedlasers.com/lasers/Red_650nm_LaserShades-49-11.html