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Laser driver with feedback

W

woop

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Hi all.
i have been looking around this site a bit, and it seems most people are using constant current sources or bought drivers.
anyone successfully made a driver with optical feedback?
I was looking at some of the drivers on sams laser FAQ and it seems the diodes i encountered from dvd drives are not compatible with most of the circuits. would the "SG-LD2" be suitable for driving DVD burner lasers?
from memory, the last diodes i killed where common cathode i think (is that usual for dvd drives?)
schematic: repairfaq.ece.drexel.edu/sam/sgld2sch.gif
 





W

woop

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ok so i have decided to experiment a bit.
i cut down that schematic in the last post to the bare minimum for running off a battery
and i have made some pcb's to test it out.
if anyone knows anything about drivers of this kind please give me some hints.

also does anyone know specs for input current, output power and voltage for DVD lasers (16x or 18x recorders)
 
A

a_pyro_is

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Woop, welcome to the forum.
Please understand that while no one here will be upset with you for asking a question, the info you're asking for is already on the forum. The search button is your friend (make sure to look further back than 1 week)

Most of the DVD reds are built without an internal photodiode, so I don't think you can easily make that circuit work. But there is a much easier way to drive a laser diode. Just use a very common constant-current source.
 
rog8811

rog8811

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I seem to recal that a lot of the LD's that have been used, though they have a sense diode pin, there is no connection inside the can...I realise this is not always the case but worth checking...and welcome to the forum.

Regards rog8811
 
W

woop

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that "This post was made in the last..." feature is really annoying :-[
still even further back from a week, no one seems to be using home made feedback circuits.

I seem to recall that a lot of the LD's that have been used, though they have a sense diode pin, there is no connection inside the can...I realize this is not always the case but worth checking...and welcome to the forum.
Click to expand...
really?? in my (limited) experience, dvd writers do tend to have a 3rd pin which is connected to a photo diode. although i have only looked at one writer and a few readers.
if this is the case i wonder why. maybe they have some other form of feedback for the laser power level, because you would think that this would be necessary to write dvd's.

i was thinking that using a feedback circuit would be the way to go, i mean all the consumer applications use a feedback loop and it seems like a far superior way of driving a LD than simple current limiting. especially if the current is adjusted while the LD is turned on, due to warm up and the risk of blowing the LD on next use without optical feedback.
anyway, i have made the boards for this driver so i might as well use them.

to get decent power out of a LD. should i set it to a particular current and hope it works or connect a meter to the photo diode and increase current until the light output stops increasing?

and with the dvd writer specifications. there seems to be a lot of conflicting advice on these forums.
what is the best general current for a 18x dvd writer diode?

and one last thing. these open can diodes. would they fit in an Axiz laser housing and do they have feedback? specifically the ones from pioneer 112D drives

thanks
 
A

a_pyro_is

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I can't speak about the 112D diode as I haven't seen one. The open can diode I do have has three pins, but there is no PD connected to the third.

Yes, you must have some sort of means to measure the optical output in order to write to a disk, but in almost all I've seen, there are either one or two discrete photo diodes.
 
C

chimo

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woop, welcome to the forum. I have used about 200mA for a drive current for the 16x group buy LDs, although that is overdriving it somewhat. Good luck on your mods!

Paul

woop said:
that "This post was made in the last..." feature is really annoying  :-[
still even further back from a week, no one seems to be using home made feedback circuits.

I seem to recall that a lot of the LD's that have been used, though they have a sense diode pin, there is no connection inside the can...I realize this is not always the case but worth checking...and welcome to the forum.
Click to expand...
really?? in my (limited) experience, dvd writers do tend to have a 3rd pin which is connected to a photo diode. although i have only looked at one writer and a few readers.
if this is the case i wonder why. maybe they have some other form of feedback for the laser power level, because you would think that this would be necessary to write dvd's.

i was thinking that using a feedback circuit would be the way to go, i mean all the consumer applications use a feedback loop and it seems like a far superior way of driving a LD than simple current limiting. especially if the current is adjusted while the LD is turned on, due to warm up and the risk of blowing the LD on next use without optical feedback.
anyway, i have made the boards for this driver so i might as well use them.

to get decent power out of a LD. should i set it to a particular current and hope it works or connect a meter to the photo diode and increase current until the light output stops increasing?

and with the dvd writer specifications. there seems to be a lot of conflicting advice on these forums.
what is the best general current for a 18x dvd writer diode?

and one last thing. these open can diodes. would they fit in an Axiz laser housing and do they have feedback? specifically the ones from pioneer 112D drives

thanks
Click to expand...
 
Z

Zarniwoop

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Aug 16, 2007
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The open-can LD from that drive does fit in an Aixiz module - that's what I'm using now. But it is harder than most to get it out of its heatsink intact.

Now that I look closely inside, I can see that the extra pin indeed has no connection.
I assume in the actual drive they do the power moitoring externally.

There's something to be said for the simplicity and parts-availability of an LM317-type circuit, but if you get a feedback circuit working, I'm sure a bunch of us would be interested in seeing it.

Look at the Threads of Interest at the top of the Experiments and Modifications section.
In there you can find measured current vs. output power curves for various diodes including open-can types.
 
Gazoo

Gazoo

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Speaking of open can diodes, I finally got the guts to run mine up to 600ma's of current...this measured 308mw's on my LPM-1.. ;D This diode came out of a 112D and I can tell you I know it is very durable electrically. I ran it for about 5 minutes with a TEC, but the cube my diode is in started to get warm and the output dropped to 285mw's. I could add a fan to the heatsink of the TEC and I am sure that the cube would then stay cool. I really need to redo the whole thing anyway. :p
 

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MarioMaster

MarioMaster

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yea gazoo those are very low powered tecs, i think you could have some fun with a larger one that could keep the diode at a lower temperature even when running at 600ma

i would really like to buy some as i only have the high powered kind and can't be run off of the psu inside my lab laser i made without the transformer overheating :(
 
W

woop

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thanks for the replies. I will use a current limiting circuit first and if i can be bothered rigging up an external photodiode i will try the feedback type driver.

so is a TEC just a pelter cooled laser?
i read that someone was running a 112D laser with 400mA and getting good results without a TEC. i wonder how much current one could take with just the Axiz case as a sink.
I also read that the 112D lasers where some of the easiest to extract? how are they attached? I am thinking of getting one from here:
www.centrecom.com.au/catalog/default.php?cPath=49&page=1&sort=3a
(I am in Australia)

**EDIT** Fixed link {SenKat}
 
W

woop

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Re: Laser driver with feedback laser diode

WOW 400mW from the 112D laser!!! :eek:
it doesn't look as fragile as i thought, its not fully open, like the sides look like they would protect it a bit.
yeah i think i would be happy with 150-200mW
my aixiz case has a plastic lens though. i hope it doesn't melt or anything.

i think maybe i should attach a thermistor to the diode while i am testing it
 
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