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Task Force 242998 flashlight --> burning laser

Greyfox

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While shopping at Lowe's Hardware for potential parts and tools for my projects, I came across this flashlight for only $18US. It's a single cell AA flashlight based around a boost converter to drive a 1W LED. The boost converter itself is self-contained, and on a separate and enclosed board away from the LED chip. This made it almost too easy to pull and test. Since 1W is fairly close to the expected power in to an LD, I figured it was as good a match as I was apt to find.

Initial test: I hooked up a spare IR LD to see what it could push, and measured about 250mA across it. Slightly high, but within a viable range to work with.
On my next test, I ran a generic 16X DVD burner LD to it and through a 2.2ohm resistor. Current was approx. 185mA, and it was able to light a match with ease. Right now, I'm wishing I had a good laser power meter to see exactly what it was producing. Oh well, I found a good, safe spot to go for, so on to the build!


1 16x DVD burner LD (GB diodes are perfect!)
1 Aixiz 12mmx30mm housing
1 3/8" flat washer
1 2.2ohm resistor
1 uF capacitor
1 918-type diode

Beyond the obvious basics, I had a few tasks at hand:
I had to cut the outer diameter of the washer back enough to fit inside the housing. I cut it small enough for it to rotate easily, but not so small that it was falling free.
The Aixiz housing (rear portion) was cut short by a few mm for it to act as a proper spacer and hold everything in place after assembly. I also cut notches in the side for the wires to emerge without being crimped against the driver housing.

The 1W LED board was removed from the assembly. The wires were left as long as possible for ease of connection and further testing.

Here's the simple circuit wiring:


+-------+
| Y| (+)
| +--/\/\/--+----+----+
| Boost | 2.2ohm _|_ | |
| Conv. | /_\ === L D
| | | | |
| +---------+----+----+
| K| (-)
+-------+


Very simplistic, and yes, there is a chance of LD blowout. With further work, someone could probably fit a small regulator in the housing, but the LM317 wouldn't regulate properly after this boost circuit.

I realize this isn't exactly a how-to, but I hope it has provided a bit of insight and another choice for those unable or unwilling to acquire the other options.
 

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Hemlock_Mike

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Fox --

You're doing good here ! Your next step may be to reduce the series resistor a little and watch the LD current. Good work and understanding of the circuit.

Mike
 

Gazoo

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Very nice, although I would bet the driver is already polarity protected and there is already a capacitor on the output. But we don't know for sure without being able to see it.

The only change I would have made is to use a 10uf 16V capacitor across the diode. This is what I fit in that particular Aixiz housing and solder it directly across the diode.

Also it looks as though the GB diodes are holding up with 250ma's of current. I am curious to know how well the regulator in that flashlight works. I would be very interested in knowing how much current it puts out at 1 volt. :p

I really like that flashlight and as I recall it received good reviews on CPF. It looks really easy to mod and I thank you for sharing this.
 

Hemlock_Mike

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What Gazoo says - Always have a capacitor directly soldered at the base of the LD. Never remove it.
Now if you are daring, start increasing the current toward 250 mA. :) I'd stop there as that's about the best you can do but make sure you watch the heat. I presume you have an Aixiz module for simple mass heatsink. Don't increase unless you have this heat disapation.
Mike
 

Greyfox

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Hemlock Mike said:
Fox --

You're doing good here ! Your next step may be to reduce the series resistor a little and watch the LD current. Good work and understanding of the circuit.

Mike
Actually, I ended up removing it. The diode I used was a former closed-can that I opened to solder on a new anode. It handles the 270-280mA very happily. If it dies a few hours sooner, so be it.


Hemlock Mike said:
What Gazoo says - Always have a capacitor directly soldered at the base of the LD. Never remove it.
Now if you are daring, start increasing the current toward 250 mA. :) I'd stop there as that's about the best you can do but make sure you watch the heat. I presume you have an Aixiz module for simple mass heatsink. Don't increase unless you have this heat disapation.
Mike
Yes, the majority of an Aixiz module is still present. I had to cut it back for it to fit and keep pressure on the circuit, but this also turns that metal frame into a heatsink as well. With what I had seen from the output, I don't think heat will be too much of a problem so long as I use it intermittently and turn it off when it starts warming up.
 

Greyfox

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Gazoo said:
Very nice, although I would bet the driver is already polarity protected and there is already a capacitor on the output. But we don't know for sure without being able to see it.

The only change I would have made is to use a 10uf 16V capacitor across the diode. This is what I fit in that particular Aixiz housing and solder it directly across the diode.

Also it looks as though the GB diodes are holding up with 250ma's of current. I am curious to know how well the regulator in that flashlight works. I would be very interested in knowing how much current it puts out at 1 volt. :p

I really like that flashlight and as I recall it received good reviews on CPF. It looks really easy to mod and I thank you for sharing this.
It may be, and I intend to snag another. The circuit itself is soldered into the base (see the pic above), and I didn't want to risk toasting the chip(s) inside on the first shot. Once I've had a chance to trace the paths, I'll acquire a few good dummy loads and test it out. Expect to see a power curve in the future.

Edit:

I actually ran a few tests on it under extreme conditions, and forgot to mention them. Under a shorted load (ammeter only) it managed to shove just over an amp through the circuit, and under no load (voltmeter only) managed to reach as high as 7.4V.
 

Gazoo

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I would love to see the power curve whenever you get around to it. That flashlight is available it my Lowes, and I bet most Lowes if not all stock it.
 




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