Is it right? Laser Driver

Afew questions first flease.

1. What is your power source? (if its a battry, than the first diode is redundent,(not needed))
2. Whats the part number for the pot?

If its a battery, this would me my layout.

if not, than i would keep your first diode in place, and add another cap to the front end directly before the LM317.

1. It's a 9V battery.

2. I think this is what I have, 100ohm TrimPot

http://jaycar.co.nz/productView.asp?ID=RT4640&w=100ohm+potentiometer&form=KEYWORD

Hi Dylan, Here is the recommended variable LM317 circuit schematic from the Data Sheet.

It is usually a good idea to include the C1 cap even if you are working off a battery as this will help to stabilize the circuit. Also watch the polarity of the electrolytic caps as I noticed that the one in your drawing was reverse polarity.  Good luck on your project.

John

NOTE: Pins 2 and 3 in the above schematic are reversed from normal convention. See my last post and link to ON Data Sheet.

Ok, it looks to me from your diagram, that you may have the pot, contented to the wrong pin on the lm317, it needs to be connected to the adj pin on the lm317, to the middle pin on the pot.

Than a ground ran over to the left pin on the pot.

Than a resistor ran from the output on the lm317, through a diode, to the right pin on the pot.

That should get you started, than look to my diagram if you are getting some movement on the output voltage, you may need to place caps to stable the output voltage.

Hi Guys, I didn't like the way the pin out was labeled in my ST Data Sheet so I looked up an ON Data sheet that clarifies things. Here is a link to the ON LM317T data sheet:

http://datasheet.octopart.com/LM317TG-ON-Semiconductor-datasheet-613672.pdf

Unlike the 7805 series the adjust is on the first pin on the left, the output is on the middle pin and the input voltage must go to the far right pin.

John

Looks good john, i was not far off.

Hi Lupe, I have noticed that you are doing a great job trying to help people with their questions. Keep up the good work.

John

That's a big help so the right pin connected to the resistor is the side with the "knob/screw"?

Also thx Johnd

If you look, pin 3 has a "CW" over it.

So that leads me to think the to out side pins are fixed at 100ohm's, and the center "#2" pin is the one that sweeps on the pot.

And CW=Clockwise, means all the way clockwise, will give you pin 3 to pin 2 connection. (Very low resistance.)

Thats the way my pots are anyways.

Right side will be pin 1

Center will be pin 2

Left will be pin 3.