Help please, external power for greenie

For complicated reasons I need to drive a 5mw green through an opto isolator. I have 12v and 6 volts avaiable. The opto is a 4N25, I also have LM317's to make regulators.

I managed to fry my first greenie when I got it totaly wrong :-[ My electronics expertise is not up to getting this up and running, can anyone help me with a circuit please?

Regards rog8811

How did U want to Power your 4n25 LED to Start the laser?
I'm pshycic so...
Simple answer: PIN 1 is the LED pos. Use 5v from your (or CPU logic maybee )goes through 470 ohm series resistor to pin 1, grnd to pin 2.(opto is on now)

Now pins 4&5 can drive the base of a POWER NPN transisor to switch power to the
LM317 current regulator.

5v to 470 ohm to pin 4, pin 5 to base of the npn, emiter to ground, collector to ground of your laser driver! driver POS to power source.

Simple as brain surgery right?

CaPEESH? ;D ;D

Power into the 4N25 diode I have done with the transistor on the circuit board that drives the whole thing ( I cannot use this directly to the LM317 as it is a 12v circuit that tends to sit above ground...I killed  my greenie when I tried using a pot to get it to come closer to ground  ).
It looks like I need to get myself a NPN then   I was trying to do it straight from the opto transistor...... As I said, i am at the limits of my knowledge here.

Thanks for the info laserrod

Regards rog8811

@ laserrod I have drawn out the circuit that you described, could you please confirm this is what you meant.

Man your good!  That is exactly what I wrote for you to do!
Great schematic!

Refinements:
I goofed ;D, so swap pin 4 and 5. It's backwards as U drew it. So col is 5 and emit is 4.
5 is Pos, 4 is Neg.
The 1st schem is better because the 317 is a true current limiter.(floating because it is not grounded). 2nd one looks wrong.

The 470 resistors should be increased because pin 1 & 2 current limit is .02 amp and pin 4 & 5. maybee .01 amp or so. Your not using 5v like I asummed.
I think it's best to find what the highest resistor that works is; and then go a little lower for insurance. Use less power, the better, RIGHT!

Don't blow you laser. First; test with  3 series diodes as Dummy load (laser)and make sure the NPN voltage drops to about .7 volts across collector (it's full on and saturated) & grnd and measure current equal or more to target LOAD.

And of course make sure your Opto LED grd is Isolated from Opto transistor grd. :
The whole idea here is to give that wonderfull 5,000 volts of isolation between switching circuit and the driven LASER circuit.


Cheers [smiley=beer.gif]

Don't blow you laser. First; test with 3 series diodes as Dummy load (laser)and make sure the NPN voltage drops to about .7 volts across collector (it's full on and saturated) & grnd and measure current equal or more to target LOAD.

Click to expand...

I can use my dead greenie possibly as it still draws 300ma?

Modified circuit follows.....

Built, up and running.
Thankyou for the help Laserrod!

Regards rog8811

Way to go man!
Glad to help!

Cheers [smiley=beer.gif]

UPDATE.... I have put up a movie on the XY from one speaker thread in multimedia, as you can see the greenie draws lines, I want it to flash more.

Question, would a capacitor across the laser module give the effect I want? If so any ideas of what kind of value?