Need some help on my LM317 driver

[Kleskas]

Hello, I've been reading this forum for a while now and I finally made myself to try making one of easier current regulators with LM317.

So I started yesterday, gathered all the info of what components I need. I bought all the stuff and started soldering today. I just finished all the work. It's all messy and takes a lot of space, but I just want to get it working for the first time

Here are the pics:
http://imageshack.us/a/img541/6928/img2674m.jpg
http://imageshack.us/a/img812/3197/img2673re.jpg
http://imageshack.us/a/img202/7150/img2676dj.jpg

Here are schema I painted to make ir more clear to understand:
http://img577.imageshack.us/img577/5360/img2676schema.jpg

I've done this like it's explained here Laser driver - It can be done

I connected power supply, turned on the switch, the LED indicator is working and everything seems to work. 100 ohm Pot was set to around 50% (50 ohm). But I measured the output Voltage and it was ~9V. Input Voltage was ~11V from power supply.

Shouldn't it be around 3-4 Volts at the output? I haven't tried to connect my Red Laser Diode yet, since I am not sure if it's working correctly.

Any ideas about my driver? Is i soldered in the correct way?

 

[Cyparagon]

You NEED to put a load on it. It's a constant current driver so you need to monitor the current. Pay no attention to the voltage - it will settle where it needs to.

 

[Kleskas]

Ok, I tried connecting my LD to the driver. I turned on and LD lit up. But it's so low, you can only notice that it's working when looking directly to it in front, there is not even a visible dot on my hand. The voltage dropped to ~2.4V when it's turned on.

Any ideas what's going on?

 

[Things]

Sounds like your diode is dead, 2.4V drop sounds about right. Put an ammeter in series with the LM317 and your diode and check the current.

 

[Tw15t3r]

Erm, you do know that to set the current for the driver, you either use a "test load" or set it to minimum current right?

Also, you have to connect your diode before you turn on the driver. And before you connect the diode, make sure the capacitors are discharged by shorting them out.

Hope you didn't blow your diode. If you're measuring a low current flowing through it, adjust the variable resistor / potentiometer and ramp the current up and see what happens.

 

[Kleskas]

The current was set at minimum since Pot was at 100 ohm at the start, later I moved it all the way to 0, the difference was very low at the LD (little red dot inside was a bit more visible), tho the LED indicator lit up pretty bright at 0 ohm.

I can't measure Amps going through the circuit, I must be measuring it at the wrong place. What points should I be measuring to get the readings?

I was aware of connecting the LD before turning the driver on and every time I reconnected it I discharged my caps.

It's an old LD from some random broken CD Player, possible that it's not working correctly. Gonna try getting another LD from CD-Rom.

 

[Tw15t3r]

If you're using a CD player diode, it lases IR, and not 650nm red light. The dim red you see is because it's on the edge of the red, so please don't look into it anymore (you might damage your vision). It's not very high power either, since it's only a player. If you took it from a CD burner, then all the more, do not look into it.

No one really uses CD diodes since it's not visually appealing, and has limited potential in terms of power. Get a diode from a DVD burner if you want to do a red pointer.

 

[Kleskas]

Now it's getting more clear to me, thanks for explanation. Hopefully that didn't damage my eye in any way. And yeah, I believe it's from old simple home CD reader/player, a friend gave me that some time ago.

I have another LD from old Samsung CD-Rom, but it has 10 pins, no idea which one is what. I believe it's not a red LD as well, since it has so many pins to connect or I might be wrong.

Anyway, tomorrow I'm going to dis-assembly some old home theater DVD Player, maybe I'll find some usable LD there.

 

[Cyparagon]

Test load isn't necessary. It's built to run in the correct operating range of the diode. Any potentiometer setting is fine.

Either you set the current too low so it is dim, or forgetting to discharge the cap before connecting your diode killed it.

 

[Tw15t3r]

Now it's getting more clear to me, thanks for explanation. Hopefully that didn't damage my eye in any way. And yeah, I believe it's from old simple home CD reader/player, a friend gave me that some time ago.

I have another LD from old Samsung CD-Rom, but it has 10 pins, no idea which one is what. I believe it's not a red LD as well, since it has so many pins to connect or I might be wrong.

Anyway, tomorrow I'm going to dis-assembly some old home theater DVD Player, maybe I'll find some usable LD there.

Do note that if it's just a player, you won't get very high powers out of it either, since the laser only needs to read a DVD, and that requires low power. A burner on the other hand needs to cause a chemical change in a DVD's dye to effectively "etch" on data, and hence is significantly more powerful. Regardless, it will be visible at the very least.

 

[Kleskas]

I connected another LD from old DVD-Rom and I noticed some strange behavior. When I set Pot to around 25ohm LD is working almost at full power for as long as I keep it on, but when I try to move Pot more to 0 ohm LD gets more brighter but after 5 seconds it dims to almost not visible beam.

What could cause this?

Power supply is 9V from converted 230V and can provide 600mA current so it can't be a power problem I think.

 

[Tw15t3r]

Not sure what's the problem, but it sounds like you've reached the limit of the diode. Find the max setting that allows you to get the brightest dot and leave it there. Or it could be temperature issue? I'm just wildly guessing here.
Does the LD get brighter after you turn the current back down? Or do you have to switch it off first, let it rest, and try again? If you have to let it rest, it likely is a temperature issue.

 

[Things]

Laser diodes will fail if you try overpower them, simple as that. a DVD-ROM diode won't be anything more than a couple of mW output, I probably wouldn't go over 25-50mA of current max.

 

[Kleskas]

It's not temperature problem I guess, I turned Pot till laser started to dim, then turned it back and the laser got back instantly to the brightest beam again. That must be overpower problems then, it just can't handle more.

Thanks for advice.

I should order some more powerful LD before I put it in a host.