DDL driver HELP needed

[chido]

paulham, you type [ img ] at the beginning of your url and [ /img ] at the end of it. Remove spaces.
Like this:
[ img ]http://img352.imageshack.us/my.php?image=imgp1949640x480ke9.jpg[/img] remove the spaces at the beginning.

 

[geek]

Rather than start a new thread I thought I would add to this one, as the title pretty much says it. I've put together the DDL driver, and everything seems to be correct. I have a 1 turn 20 ohm pot, and a 5.1 ohm resistor in series, and I'm using 6 alkaline AAA cells to power it right now. The problem is my diode is barely lasing. I measured the current with the LD in the circuit and I see 65mV over a .9 ohm resistor (measured how it is described in the circuit posted on page 1). I'm not sure where the problem is. Does the LD draw less current if it is toasted? Is it a battery issue? I see a 2.99 volt drop from the diode and 1.25 reference voltage for the LM317. Any help would be appreciated.

 

[chido]

What LD are you using?

 

[geek]

I bought a pair on ebay. The data sheet doesn't have a brand or anything. Says the threshold current is 65mA, with max CW at 150mW and max Pulsed 300mW. It is REALLY dim right now, I would expect it to be at 65mA, but I'm still a bit worried that I messed something up.

 

[chido]

I know this might sound stupid, but have you decreased the pot's resistance, because at your pot's maximum resistance, (20 ohms) that's close to the current you're supposed to get.

 

[geek]

Yeah, I get a range from 14.5mA to 65mA when I turn the pot. I just replaced the LD with 4 rectifier diodes and I see exactly the same results. Measured the resistor again just to make sure and it is 5.4 ohms.

 

[jayrob]

Rather than start a new thread I thought I would add to this one, as the title pretty much says it. I've put together the DDL driver, and everything seems to be correct. I have a 1 turn 20 ohm pot, and a 5.1 ohm resistor in series, and I'm using 6 alkaline AAA cells to power it right now. The problem is my diode is barely lasing. I measured the current with the LD in the circuit and I see 65mV over a .9 ohm resistor (measured how it is described in the circuit posted on page 1). I'm not sure where the problem is. Does the LD draw less current if it is toasted? Is it a battery issue? I see a 2.99 volt drop from the diode and 1.25 reference voltage for the LM317. Any help would be appreciated.

Yeah, I get a range from 14.5mA to 65mA when I turn the pot. I just replaced the LD with 4 rectifier diodes and I see exactly the same results. Measured the resistor again just to make sure and it is 5.4 ohms.

Something is not adding up there. If you have a 5.1 ohm resistor, and a 20 ohm pot, the max resistance using the LM317 based (DDL) driver, would be 25.1 ohms - about 50mA's. The least resistance would be 5.1 ohms - about 245mA's. So, that should be the range of the driver. From 50mA's to 245mA's. As long as the supply voltage is over 6 volts. (the LM317 drops out using 2 X 3.0 volt batteries) 6 AAA in series should be plenty. (obviously not parallel)
Jay

 

[geek]

As I turn the pot my resistance goes from 5.7 to 23.0 ohms. I know there is something wrong, but I'm not sure what it is. I measured the voltage drop across a 1 ohm resistor in series with the LD to get the mA reading to the diode. I have 6 AAA batteries in series running the thing, and I read 8.9 volts. Am I measuring the current wrong?

 

[jayrob]

As I turn the pot my resistance goes from 5.7 to 23.0 ohms. I know there is something wrong, but I'm not sure what it is. I measured the voltage drop across a 1 ohm resistor in series with the LD to get the mA reading to the diode. I have 6 AAA batteries in series running the thing, and I read 8.9 volts. Am I measuring the current wrong?

That part sounds all good, but how are you measuring the current? 5.7 ohms should give you around 220mA's. And 23 ohms should give you around 55mA's...
Jay

P.S. geek, I know you have one of my heatsinks, so just making sure you are not trying to drive an open can with only 245mA. You will want more current for the open can diodes. At least 350mA's. We like 420mA's though!

 

[geek]

That part sounds all good, but how are you measuring the current? 5.7 ohms should give you around 220mA's. And 23 ohms should give you around 55mA's...
Jay

P.S. geek, I know you have one of my heatsinks, so just making sure you are not trying to drive an open can with only 245mA. You will want more current for the open can diodes. At least 350mA's. We like 420mA's though!

So I was measuring the current by placing a 1ohm resistor in series with the LD. Just now though I placed put the multimeter in between the power supply and the LM317 and I get the readings I dreaded. A max of about 220mA. I must have had something messed up with the previous measurements. Damn. At least I know the circuit works. Now I just have to find out how the diode died.

Oh, and no open can. A closed can from ebay. A pair of them actually, so hopefully I can make the other one work.

 

[geek]

Well it seems I am fairly incompetent or I bought some bad diodes. I just tried out the second one, with a working DDL circuit starting at about 70mA up to ~220mA. I have what amounts to a nice red LED. I had on an anti-static wristband, used anti-static tweezers, and didn't solder anything for the second go round. Just turned on the circuit and touched the wires to the LD after it had been pressed into the housing. Any suggestions on what I've done wrong?

 

[chido]

Did you short out the capacitor before connecting the LD?

 

[geek]

Did you short out the capacitor before connecting the LD?

For the first one yes. For the second one the circuit was connected and "running" I guess before I connected it to the LD, so there should not have been any voltage spikes correct? As the capacitor was connected to the circuit and not directly to the LD?

 

[chido]

WRONG, oh shit man, I can't believe you did that. If you don't have the LD connected to the capacitor and you turn the circuit on, the capacitor charges with the same voltage as you batteries, which in your case is about 9v, so when you connected your LD you dumped 9 beautiful volts into it.

EDIT: Hey, don't feel bad, at least now your diode is resting peacefully at LD HEAVEN. ;D

 

[geek]

Well that explains the second one. The first one was connected to the LD first, then hooked up to the batteries. Apparently I managed to screw that one up in some other way. I'll have plenty of time to think about it while waiting for some more diodes to get here. I'm rather disappointed in myself.

I wish they came to a more dramatic demise. Like a nice impressive flash or something.

 

[chido]

How did you connect the first one to the circuit? Did you solder it?