DIY Homemade laser diode driver

Ok this is the first DDL driver that I am building but in the second post by DDL that has the picture of the circuit in a breadboard the LM317T looks like the pins are reversed to me I understand the pin out is like this from right to left
1.IN
2.OUT
3.ADJUST
but in the picture it looks like the + from the battery is going to the adjust pin and it looks like you just put the LM317T in backwards. Please clarify what the right pin out is and if the picture is correct.

Also in Rog's picture that he posted on the first page he connects the 3 and 2 pins on the pot but in DDL's picture he connects the 1 and 2 pins can you do either?

On a pot you have 3 pins what is how do you know which one is 1, 2, and 3 and how do you measure the ohms on a pot what pins do you use?

Sorry for all the noob questions but I want to get this right and not fry anything lol

Any help is appreciated

Justin

If I use LDD for LD 2W.
How do I calculate how?
If, I use the flex drive Yes or no?
Thanks. Takira

How many Ma should the battery be giving out?

So I've read way to many posts here to try to figure out my problem... still no luck. So I thought I would just see if anyone knows what's going on here:

I built the circuit from daedal's original post, except that I used a 47uF 10v capacitor, a 25k 3watt rheostat as later suggested, and a 10 ohm resistor instead of a 4 ohm one. I eventually want to power a blu-ray diode, and so I am using a 9v battery since the blu-ray diodes need a few more volts. My test load is a red LED, and when I power it up and change the potentiometer, the current changes from 8mA to 13mA... not exactly high powered.

Here's what I was thinking the current should be:
MAX:
1.25v (coming out of the LM317) / 10 ohms = 125mA
MIN:
1.25v / (10+25) = 36mA

The battery is fine - I've tested with fresh batteries as well as a 9v wall adapter
The potentiometer works as well. I tested the resistance with my DMM and it measures 0 ohms on one side and 24.8 on the other.

Attached is a picture. The wire isn't soldered to the LED right now because I was testing the current.


Any ideas of what's going on?

Thanks!
-awlego

Well an LED will never draw more than 15mA (for the type you are using). To test the driver you need a real test load made of 7 (or 6, I can't remember) 1N4001 diodes and a 1 ohm resistor (I suggest you test a few resistors because the tolerance on those can modify the resistance, and so modify your readings) connected in series. You measure the current by setting your DMM to mV and placing your probes on each extremity of the resistor.

Hope this helps.

Thanks. I'll try it tomorrow and see.

So I made the test load with a 1ohm resistor (it actually measured 1.1, but it was the best I had) and the 6 1N4001 diodes. I measure the mV across the resistor and get nothing... and I measure the volts across the diodes and get 7v. This makes me think that my LM317 isn't working correctly, shouldn't it use 3v by itself.

Any ideas?

First, 1.1 ohm probably means that your MM wires have a 0.1 resistence. Touch both wires and read on the screen. 0.1 right? ;P

Secondly, what you just said is imposible. If voltage is falling on the diodes some voltage should fall on the resistor too. Are you sure you're using the MM properly?

Thirdly, using a test load on this driver is useless, your MM on current mode will work even better than a test load to measure it. Just put the MM in current mode as the load of the driver

You need a load to measure amps. You need to connect the DMM in series because it measure the current that goes through a circuit element. A DDM doesn't have enough resistance, so all you're doing is shorting the circuit. Not a good idea.

Hmm... I'll take measurements again.

Also, I redid the whole circuit on a project board to make the connections more stable, but now the potentiometer doesn't do anything :/ I'm thinking I hooked the LM317 wrong. I've found multiple pinout's... which one is correct?

I attached one. The other is the one at the beginning of this thread.

Thanks.

Datasheet catalog for integrated circuits, diodes, triacs, and other semiconductors, view is a good source of data sheet.


Look at the chip if you can find the company logo, else search the full name of the IC.

Note that you have a 25k pot, that's 25000 ohm.

Bluefan said:

Note that you have a 25k pot, that's 25000 ohm.

Click to expand...

Oh ya, I forgot, when the pot's value is high, sometimes the minimum resistance is not zero, but more like 50.

No, my pot is most definitely 25 ohm. I tested it with the DMM.

And thanks for the data sheet link. I'll take a look.

Alright. I figured it out. I was hooking the test load in backwards. Hahaha.
Now my voltage drop is 4.5 across the diodes and I measure from 38mV to 65mV across the resistor, with the mV changing smoothly as I turn the pot

The low value makes sense, as with a 10 ohm fixed resistor and a 25 ohm pot, my max resistance would be 35 ohms, and 1.25v/35 = 35.7mA

However, my high value should be 125mA... (1.25v/10 = 125mA)
I measured the 10 ohm and the pot with the DMM, and both have the correct resistances. (I checked the pot at it's low and high resistances and both were correct)

Any ideas what might be up now?

Thanks in advance!
-awlego

Try wiring two 10 ohms resistors in parallel, according to my calculus, you should get 5 ohms :

1/Re = 1/R + 1/R
1/Re = 1/10 + 1/10
1/Re = 2/10
1/Re = 1/5
Re = 5