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Old 08-19-2007, 04:21 PM #1
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Default Pulsed Mode Driver circuit for SONY DVD 16x Laser

Hi guys,
like many of you I ordered a SLD1236VL laser diode from Senkat, but sadly I noticed
that no one asked how to power it in pulsed mode.
Now.... If I buy a 250mW laser... I want 250mW of power, not just 80mW (or maybe something
more overdriving it... But shortening its life of course). So I started designing a small
driver circuit, my goal would be to keep it simple and small enough to fit a maglite
or something similar.
But I need some help, the datasheet is quite _seraphic_ and doesn't disclose all the
infos I need to build a perfect calibrated driver circuit.
For example, how much is the max current in pulsed-mode? The diode resistance?
The pulse length and duty cycle?

If you take a look at the datasheet you'll notice that in the last page there's a small
diagram, showing the laser temperature in function of current. From that diagram
we can infer that pulse width is 40ns and the maximum current at room temperature
is something near to 270mA (tough the laser has been built to work correctly at
75 celsius degrees, that means almost 380mA ).

What we know for sure is:
Operating voltage: 2.5V
Pulse width: 40nS

What we know with a minor degree of precision is ;p :
Max current at 25 degrees: 270mA
Max current at 75 degrees: 380mA

What we don't know is:
Laser load resistance: ???
Pulse duty cycle: ???

I'm quite sure that everyone in this forum is much more an expert than me, so
what I wanna ask is: what is a "common" laser resistance in dvd-diodes? And in
general... What is the duty cycle used while writing?
I hope someone will be able to answer because I really don't want to hook
my oscilloscope to a DVD-burner to take measures ;ppppp.

Thanx a lot in advance to everyone!


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Old 08-19-2007, 04:30 PM #2
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

I am eager to see the rsults of all the input you will receive from this post ! GREATLY looking forward to it, actually - I know everyone on here is SUPER smart - well, excelt ME of course ! LOL !! When it comes to electronics, some of th knowledge held by folks on herre is second to none - if any group of people can come up with a good pulsed driver, it will be the folks on this forum ! Start submitting your ideas and info, folks - I have a full cup of coffee right now, and am waiting eagerly to see the results :-)

G !
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Old 08-19-2007, 04:37 PM #3
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

Yeah, that looks interesting, sorry I can't help with any details tho. :'(
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Old 08-19-2007, 06:17 PM #4
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

I already asked about this here:

http://www.laserpointerforums.com/fo...1183788027/210

The biggest problem as noted is we don't have a full spec sheet for the diode.
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Old 08-19-2007, 07:00 PM #5
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

OK, noob question(s) alert:

Why is pulsed better (or not!)?
Do the 250mw 16x Diodes not operate at 250mw if simply connected to a battery?
Do you see the pulses, or are they really quick?
How does that affect burning/popping? *


Thanks,

Dan :-)
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Old 08-19-2007, 07:30 PM #6
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

Quote:
Originally Posted by danielbriggs
Do the 250mw 16x Diodes not operate at 250mw if simply connected to a battery?
Well, in CW (continuous mode -> aka with a simple battery) the diode is going to fry in a matter of milliseconds, but if you put a resistor you'll be able to get at most 80mW. That is the maximum power in CW mode. So yep, pulsed mode is better than CW, because in pulsed-mode the diode can operate at its full power. And like a CPU (more or less), you can achieve even higher rates with enough cooling.

Quote:
Originally Posted by danielbriggs
Do you see the pulses, or are they really quick?
How does that affect burning/popping?
1. In general you'll see the pulses only if you sweep the laser VERY rapidly over a wall, in that case you won't see a straight line but a line of dots... Anyway this depends strictly on the pulse duration. With a frequency sufficiently high (say for example 100kHz) it's not possible to distinquish between a laser operating in CW mode or not.
2. More power, more popping ;p and 250mW is better than 80 ;p

ps
Don't attach the laser directly to the battery!
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Old 08-19-2007, 07:46 PM #7
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

OK, let me get this straight:

Pulsed LD are better because:
I get 250mw of power as opposed to 80mw of power
It's not going to burn out as readily
There will be no visual difference

Disadvantages:
Make the pulsed circuit and cram it into a Maglite!

Ultimatley I want:
A MiniMaglite AA torch with a Sony SenKat 16x Diode
This will be encased in a little bit of an aluminium heatsink I will make on a lathe or CNC - Or is one not needed?
This will be squashed inside a 5mw Aixiz module with all the gubbings removed, so I've got a 250mw diode with a nice lens in a fancy brass case.

* Stuff that in the Maglite *

Then under that I've made a swanky pulsed driver circuit that puts a clean supply at the right voltage and the right power

* Stuff the circuit in the Maglite *

Then I clip in a CR123A 3.6v lithium battery - Is this enough - DDL was talking about needing 6v for a driver circuit

* Stuff the juice in the Maglite *

Get a Niteize IQ tail switch upgrade so I can do different ammounts of power

* Screw that on *

Done!
Does that sound reasonable?

Also - Just realised - Does the Niteize IQ tail switch upgrade Fast strobe pulse the laser right - or will I still need your special pulsed laser circuit.

Apart from making it green, is there anything else that can be improved or changed to make the best DVD burner mini Maglite?

Thanks,

Dan :-)
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Old 08-19-2007, 07:49 PM #8
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

Quote:
Originally Posted by ponzo
ps
Don't attach the laser directly to the battery!
Apart from not getting the full power - why? All the guides say to do so?
Are the videos with DVD-RW mods 250mw diodes that are running at 80mw because of continuous, THAT powerful @ 80mw?
So if I do it "properly" with the same 250mw but in pulsed - will I get a laser 3x the power?
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Old 08-19-2007, 07:59 PM #9
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

Dan,
It might help you to understand better if you study the sld1236vl data sheet. It doesn't have complete specs.

http://www.sony.net/Products/SC-HP/c.../sld1236vl.pdf

Yes, we all overdrive the diodes with CW current as opposed to PW current.

The Nite ize is more like a strobe, you will see it pulse. Maybe every second or so, I don't remember off hand.
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Old 08-19-2007, 08:26 PM #10
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

I am also a little underimpressed with the data tha is available from Sony on these LDs.

The pulse width is relational to the speed of the DVD burner. Since these are used to burn "pits" in a DVD I would assume that the duty cycle would be no more than 50%. If it is 50%, that's a 12.5MHz square wave.

The question that needs to be answered is if these can be driven for a longer pulse than 40ns at 250mW or will the heat buildup be too great? You could probably get more info by looking up DVD LD driver chips. Good luck!

Paul
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Old 08-19-2007, 11:57 PM #11
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

In pulse mode, the diode PEAks at about 250 mW - You will need a Joule meter to measure this. THe Average output will be around 80 mW. Fine for experimenting but not POPBANGSMOKE....
We here add heatsinking and push the little suckers to the max CW output. True, mine might last only 1000 hours of intermittent use vs 10,000 continuous use but HEY -- I'll just put in a new diode in a few years !!!

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Old 08-20-2007, 12:47 AM #12
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

Thanx a lot for your comments, I'm really eager to see this cool LD and make some tests to find the better way to reach the highest power!
Now let's just hope that my neighbor won't steal again the envelope from my mailbox! :P
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Old 08-20-2007, 01:47 AM #13
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

Ponzo - I CAN tell you that what the data sheet says, and what truely happens are two different things ! Since the data sheet says max CW output at 80mw, they are only running a small fraction of the current through them that we are - hence we get higher CW power ratings out of them. I was running a 12 DVD burner diode by Sony at 1240ma, and getting over 160mw of power out of it ! And that is average - filtered output - filtered meaning I had it hooked up to a voltage, and current regulating source. I have NO doubts that you, or someone can come up with a pulsed driver circuit for these diodes, and only then will we see the true potential and longevity of these babies !

Oh - and hooking them straight up tp a voltage source - like two AA batts will have disastrous side effects ! You have to run these guys with some regulation or they will toast VERY quick ! I do NOT agree with the demo on instructables (No offense intended to the author) since two AA batts will not give you a very good lifetime out of the diodes - great for MY business of selling diodes htough - since folks will blow through a few an hour I am sure !
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Old 08-20-2007, 02:25 AM #14
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

I hope you meant 240ma and not 1240ma... ;D
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Old 08-20-2007, 03:21 AM #15
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

Here is a circuit to maybe get someone started:

pulse driver

http://www.repairfaq.org/sam/laserdps.htm#dpspld

Obviously intended to run from mains voltage and for very high current diodes, but should be workable for our small diodes.

Jon
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Old 08-20-2007, 12:10 PM #16
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

I just talked a little bit with Daedal and he told me that he's overdriving his LD to get full 250mW in CW mode, of course using a reasonably big heatsink and some thermal paste. Now, I bought just two diodes (one for me and another for a friend) so my tests will be limited coz I won't have many chances to fail ;p. But if Daedal is able to overdrive it so much in CW mode, I think I can do the same in pulse-mode, reaching a good compromise between power and thermal dissipation inside a maglite. Of course I'll let you know as soon as the LDs will arrive and I hope that some of you, with a Laser-meter, will be able to take some accurate measurements .
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