Before this blog becomes the least visited site on the Internet, here’s an update, finally. Rejoice, folks.
So, it happens that I have THREE more laser diodes. And it appears that, by some weird force of the Universe, I have lost my 200mW Maglite Laser. Yeah, that one which could light matches, pop balloons and cut tape. It’s missing, after a frantic twenty minute search in my home today.
Maybe I give up too easily.
Over the December holidays, while I was happily overseas missing Geminids, a few packages arrived.
First, a BLU-RAY LASER DIODE. It’s still embedded in the optical assembly of the Blu-ray drive. From a PS3! To make a wonderful kickass Blue Laser when I finally come to it.
And I have 2 remaining Sony 16x DVD Laser Diodes, just like the one used for the 200mW Maglite Laser. These little things are known to produce 250mW, and over 300mW with proper cooling.
So I decided to get working on another. Because the current regulation circuit of the Mini Maglite limited the current to produce only 200mW, I had to come up with my own current regulation driver circuit to allow higher current. And this time, because I don’t know what’s the ideal current required, I’ll need the current to be adjustable.
The driver circuit is supposed to regulate voltage and current. One of the best things to have in a laser diode driver is variable voltage and current supply.
Voltage Regulation
The voltage source that this circuit is designed to regulate is one supplied by an alkaline/lithium battery. An AA/AAA/AAAA battery supplies approximately 1.5 Volts DC. This is very useful and very stable for the most part. When a battery is left unused for a while, the first burst of energy dispelled from the battery can spike up to 10 times the average power of the battery! Therefore, for a 1.5V battery, this would add up to approximately 15V. This burst is very small and very short that in most situations would not even kill the laser diode, but there are times when the burst packs some power along with it, supplying well over a watt of energy to the diode. This can spell instant death for most diodes!
To regulate the voltage we can either use a voltage regulator and set it up in voltage regulation mode and limit the supplied voltage (this would still miss some of this spike and still pass it on to the diode) or we can use a capacitor. Capacitors work by charging up when there is a change in voltage. Direct Current voltage turns a capacitor into an open-circuit (a cut wire), and thus any spike or change in line regulation would work first on charging up this capacitor. Capacitors have 2 readings on them that correspond to maximum voltage and capacitance. A capacitor will work to regulate the line up to the maximum power that it can soak up as fast as it could.
Current Regulation
The current supplied by the battery is rather stable, but in most cases, is too much to drive a laser diode. For instance, a DVD-burner laser diode would need about 200-250mA of power at about 2.5-3 volts (for any long life span to actually be expected of the diode). Laser diodes are, unfortunately, a very light load when wired directly to a battery, and an alkaline battery would easily put out about 500mA or more, and lithiums put out 2 or 3 times that much! This too is an instant death situation for our beloved laser diode. Using a potentiometer, the current supply can be controlled.
The chip that I use for current regulation is the LM317. The chip can be used as a voltage regulator and as a current regulator.
Come in the driver circuit.
Items used to the build the driver:
1. Small circuit board
2. LM317
3. 100 Ohm Potentiometer
4. 47uF 35V Capacitor
5. Silicon Diode 1N4001
6. 4.7 Ohm Resistor
The schematic for the driver is as follows:
Or a nicer ‘photo’ schematic:
I’ll do my own nicer version another time.
I spent a quite a while this afternoon figuring things out, and finally get the circuit together.
Reason why I took so long? My bad soldering skills.
With the driver completed, I turned the potentiometer to the maximum resistance.
I soldered some wiring to the laser diode. This is where the problem comes in. Because, as I mentioned, My Soldering Sucks, I think I might have applied too much heat to the laser diode, even if it’s coming from its connecting leads behind. I doubt so, however, but it’s a possibility.
I hooked everything up to 4 AA batteries.
I placed a multimeter before the circuit to read and verify the current going into the diode.
And adjusted the potentiometer slowly, and watch as the current on the multimeter increases.
However, even as I reach 600mA, which is more than enough to fry the diode, the laser diode didn’t even light up once. Perhaps it did, but for a split second at most, or maybe I blinked. Or perhaps, the heat applied when soldering the wiring to the laser diode’s connecting leads killed it.
Didn’t really have the time to determine the problem, but at least, the driver worked! Current is adjustable up to 600mA!
And I have another of the same laser diode ready. But I actually planned to have that under Liquid Nitrogen at NUS, but it seems unlikely because I’ll be needing a new laser diode for this project, and my research attachment to NUS is ending pretty soon.
Also, a Blu-ray laser diode! Finally, I can’t believe it, but I just ordered a 300mW Phazor red laser diode. Ugh.
…
In other news, there was bowling tournament yesterday. Singapore Polytechnic Open Championships. With other Polys, JCs and Universities. AC nearly made a clean sweep of all the prizes! But I won’t blog because I didn’t win anything. Hmph. Congrats to all prize winners!
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