Hello,
This is my first post on the forum. I've built a laser before but now I'm on summer break from school so I have time for a more in-depth project.
I've ordered a SF-AW210 Blu-Ray diode which is a few days away so I've just been working on the driver using a test load in the mean time. My driver is basically the one from the "It Can Be Done" page, except with 25 ohm pot, three 10 ohm resistors in parallel, and a 47 uF capacitor. And I am simply using a 9V battery as my power source.
For my test load I'm using the 6 1N4001 diodes as is needed to represent the blu-ray diode. I couldn't find any 1 ohm resistors so to measure the current I've used two methods:
1) three 10 ohm resistors in parallel in place of the 1 ohm to give me a 3.3 ohm eq resistance (you may be noticing a pattern here, I have a crapload of 10 ohm's)
2) removed all diodes and just completed the circuit through my DMM set to measure current.
Now here, when I started taking measurements, is where I noticed things didnt seem to be adding up correctly. With my three 10 ohm resistors (parallel -> Req = 3.3 ohm) in series with my 25 ohm pot across the constant voltage reference of the LM317 I calculated beforehand that my current range should be something like this:
Min ~ 1.25/(25 + 3.3) = 44mA
Max ~ 1.25/(0.2 + 3.3) = 350mA (give or take)
This was the goal from the beginning, getting a nice range where I could easily get to about 200 - 250mA. But, when I started taking measurements at my load I found that while my Min current was behaving beautifully, giving me right around 40 - 45mA, there was something wrong with my max current. It was increasing as I turned my pot down, but not as fast as it should have been. The max current I was getting with my pot all the way down was about 145mA which I knew was nowhere near as much as it should have been.
So what I did was went back to my driver and started taking measurements there. First I checked to make sure that the resistances were correct. It swept from about 3.5 ohms to about 29 ohms so I knew that the problem wasn't in the resistors of the pot, they were functioning perfectly.
So then I rehooked up the power and started measuring the voltage across the constant reference pins. I started with my pot turned up and the voltage across there seemed good, about 1.19-1.22V. BUT THEN, as I started decreasing the resistance between the pins the voltage started decreasing with it!!!! With the pot turned all the way down I was getting only about .5V or less across the pins that were supposed to remain at a constant 1.25V. Thus, comes my max current of about 140mA (.5/3.5 = 142mA).
I'm just wondering has anybody encountered this before? I have no idea what's going on. Just to test it and be sure, I replaced the resistors with a really large one just to see if the voltage would stay at 1.25V or change. When I did this the voltage across the pins shot up with it, I believe all the way up to 4.5 or 5V. So clearly something isn't working properly with the LM317, the "constant" voltage seems to be changing with the resistance rather than staying fixed.
Does anybody have any advice on this? Should I just get a new LM317 and go from there or is it something else I'm doing? And does anyone have any additional pointers for building a laser from a SF-AW210 blu-ray diode?
Thanks
Here's a picture of my circuit on my protoboard if you'd like to see. Sorry it's kind of tough to see some things (also note that not everything in the picture is exactly how I described it above. I took this before it was finished):
Link
This is my first post on the forum. I've built a laser before but now I'm on summer break from school so I have time for a more in-depth project.
I've ordered a SF-AW210 Blu-Ray diode which is a few days away so I've just been working on the driver using a test load in the mean time. My driver is basically the one from the "It Can Be Done" page, except with 25 ohm pot, three 10 ohm resistors in parallel, and a 47 uF capacitor. And I am simply using a 9V battery as my power source.
For my test load I'm using the 6 1N4001 diodes as is needed to represent the blu-ray diode. I couldn't find any 1 ohm resistors so to measure the current I've used two methods:
1) three 10 ohm resistors in parallel in place of the 1 ohm to give me a 3.3 ohm eq resistance (you may be noticing a pattern here, I have a crapload of 10 ohm's)
2) removed all diodes and just completed the circuit through my DMM set to measure current.
Now here, when I started taking measurements, is where I noticed things didnt seem to be adding up correctly. With my three 10 ohm resistors (parallel -> Req = 3.3 ohm) in series with my 25 ohm pot across the constant voltage reference of the LM317 I calculated beforehand that my current range should be something like this:
Min ~ 1.25/(25 + 3.3) = 44mA
Max ~ 1.25/(0.2 + 3.3) = 350mA (give or take)
This was the goal from the beginning, getting a nice range where I could easily get to about 200 - 250mA. But, when I started taking measurements at my load I found that while my Min current was behaving beautifully, giving me right around 40 - 45mA, there was something wrong with my max current. It was increasing as I turned my pot down, but not as fast as it should have been. The max current I was getting with my pot all the way down was about 145mA which I knew was nowhere near as much as it should have been.
So what I did was went back to my driver and started taking measurements there. First I checked to make sure that the resistances were correct. It swept from about 3.5 ohms to about 29 ohms so I knew that the problem wasn't in the resistors of the pot, they were functioning perfectly.
So then I rehooked up the power and started measuring the voltage across the constant reference pins. I started with my pot turned up and the voltage across there seemed good, about 1.19-1.22V. BUT THEN, as I started decreasing the resistance between the pins the voltage started decreasing with it!!!! With the pot turned all the way down I was getting only about .5V or less across the pins that were supposed to remain at a constant 1.25V. Thus, comes my max current of about 140mA (.5/3.5 = 142mA).
I'm just wondering has anybody encountered this before? I have no idea what's going on. Just to test it and be sure, I replaced the resistors with a really large one just to see if the voltage would stay at 1.25V or change. When I did this the voltage across the pins shot up with it, I believe all the way up to 4.5 or 5V. So clearly something isn't working properly with the LM317, the "constant" voltage seems to be changing with the resistance rather than staying fixed.
Does anybody have any advice on this? Should I just get a new LM317 and go from there or is it something else I'm doing? And does anyone have any additional pointers for building a laser from a SF-AW210 blu-ray diode?
Thanks
Here's a picture of my circuit on my protoboard if you'd like to see. Sorry it's kind of tough to see some things (also note that not everything in the picture is exactly how I described it above. I took this before it was finished):
Link
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